ALBERT

Description: A different approach to fitting taper equations has been developed, which eliminates the necessity of using several functions to predict diameter inside bark at different parts of the stem. The variable form taper function is easy to develop and saves computing time. For the data used in this study, it predicted tree profile as a function of height, diameter at breast height, and height from the ground with less bias than many of the taper-estimating systems found in the literature.

Description: Biomass and nutrient contents of regenerating woody plants and litter fall were measured after a northern mixed conifer–hardwood forest was harvested by conventional and whole-tree methods. Before harvest, the central Ontario study site was occupied by a 95-year-old pine (Pinusresinosa, P. strobus) and aspen (Populustremuloides, P. grandidentata) stand growing on gently rolling, gravel-free outwash sands. Four years after harvest, aspen abundance increased 100-fold in both harvested areas, with higher densities after whole-tree harvest (WTH) (4.1 stems/m2) than after conventional harvest (CH) (2.7 stems/m2). No self-thinning of aspen occurred between 2 and 4 years after harvest. Total aboveground woody biomass accumulated at 2.0 t•ha−1•year−1 in the WTH area and 1.5 t•ha−1•year−1 in the CH area; the preharvest rate was 2.0 t•ha−1•year−1. Peak autumn litter production occurred earlier in the harvested areas than in an adjacent uncut area. Cycling of N and K in litter fall returned to preharvest rates after 4 years. Cycling of Ca in litter fall was lower after WTH than after CH. Vegetation uptake of N and K (litter fall plus woody biomass) in the harvested areas in year 4 exceeded the preharvest value. Increased N accumulation in woody biomass (3.0 kg•ha−1•year−1 before harvest, 10.6 kg•ha−1•year−1 after WTH) would place a relatively greater demand on forest floor N pools in the WTH than in the CH area owing to lack of N input in logging slash. Although WTH did not reduce initial rates of biomass production, Populus spp. had lower concentrations of N, Ca, and Mg in the WTH area than in the CH area. There may be a danger that WTH on less fertile sites in the region will produce dense, unproductive aspen stands with low rates of self-thinning.

Description: Firebreaks were tested in the Northern Territory of Australia for their performance in halting the spread of 113 experimental grass fires burning in blocks which ranged from 1 to 4 ha in size. The widths of firebreak tested ranged from 1.5 to 15 m. The most intense of the fires burnt with a rate of spread of 1.9 m s−1 and had a fireline intensity of 17 MW m−1. The fastest fire stopped by a firebreak burnt with a forward rate of spread of 2.2 m s−1 and had a fireline intensity of 8 MW m−1. A logistic response function was fitted to the data on firebreak breach; this resulted in an equation for predicting the probability of firebreak breach. The probability of firebreak breach was found to increase with increasing fireline intensity and the presence of trees within 20 m of the firebreak and to decrease with increasing firebreak width. A published relationship between fireline intensity and flame length provided a sensible approximation to the width of firebreak that could be breached, via flame contact, by a fire of a given fireline intensity. Practical implications of the results are discussed.

Description: A framework for analysis of even-aged plant monocultures was developed and used to examine hypotheses on the process of competition, using data obtained from three independently established red pine (Pinusresinosa Ait.) stand-density experiments. Growth rate and relative production rate (a measure of tree vigour) were computed for the individual trees in stands of differing density at points in time when these stands had the same mean stem volume. Competition is shown to be both asymmetric (small trees lose vigour more rapidly than large trees as density increases) and two-sided (not only do larger trees affect smaller trees, but to some degree small trees also cause growth reduction in larger neighbours). Increasing density results in increased size inequality as smaller trees lose vigour and become suppressed. The asymmetric, two-sided competition process in red pine stands is considered ecologically inherent for a species adapted to existence in even-aged monocultures.

Description: The growth of individual trees from four thinning treatments in a 64-year-old Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) stand was analyzed to determine desirable residual stand structures after thinning. Dominant and codominant trees had the highest individual tree stem volume growth rates over the previous 5 years, and accounted for most stand volume growth in thinned and unthinned stands. Two measures of growing space, crown projection area and sapwood basal area (a surrogate for leaf area), were used to measure how efficiently individual trees used their growing space. Crown classes were useful in characterizing growing space efficiency (volume growth per unit of growing space) only in the unthinned treatment. In thinned treatments, tall trees with medium-sized crowns were most efficient, while in the unthinned treatment, tall trees with relatively large crowns were most efficient. A large crown in an unthinned stand was comparable in size to a medium-sized crown in a thinned stand. Results suggest growing space is not limiting individual tree growth in thinned stands and that thinning to a particular stand structure is more appropriate than thinning to a particular level of stand density.

Description: Effects of short-term flooding on stomatal conductance, net photosynthesis, and water status of sweet gum (Liquidambarstyraciflua L.) seedlings were studied under controlled environment conditions. Flooding for 9 days induced partial stomatal closure, resulting in significant declines in transpiration and net photosynthesis. The response to flooding was rapid with an average daily stomatal conductance declining from a preflood level of 0.43 cm•s−1 to 0.26 cm•s−1 by 24 h after flooding began (40% reduction). The average preflooding daily net photosynthesis was reduced from 13.7 to 10.2 mg CO2•dm−2•h−1 (25% reduction) during the same period and the average daily stomatal conductance and net photosynthesis for the 9th day of flooding were reduced by 70 and 77%, respectively, compared with preflood levels. The leaf xylem pressure potential measurements, however, indicated that water deficits did not develop as a result of flooding. Partial stomatal reopening 3 days after termination of flooding was noted with an average daily stomatal conductance approaching 63% of the preflood levels and an average daily net photosynthesis reaching 46% of its preflood levels. Maintenance of positive net photosynthesis throughout flooding, and partial stomatal and photosynthetic recovery following drainage may account for the tolerance of sweet gum seedlings to short-term flooding.

Description: Relationships among forest soil carbon, nitrogen, and sulfur, vegetation type, and atmospheric deposition of wet sulfate were tested using 169 forested plots across Minnesota, Wisconsin, and Michigan. Plots were geographically stratified into five zones, with wet sulfate deposition increasing from 156 (zone 1) to 380 (zone 5) equiv.•ha−1 • year−1. Total S concentrations, adjusted for N levels, indicated higher concentrations in eastern than in western zones in both the upper mineral soil (ca. 0.0152 and 0.0133% S, respectively) and forest floor (ca. 0.124 and 0.113% S, respectively). This illustrates that forest soil S levels reflect geographic gradients in atmospheric sulfate deposition. Total C and N concentrations and C:N and C:S ratios were affected by vegetation type. Jack pine and red pine mineral soil had lower concentrations of C and N compared with balsam fir, maple, and aspen. Forest floor C and N showed no clear pattern.

Description: Patterns of height increment and ramification in Betulapubescens Ehrh. of sprout and seed origin were studied at Kannus (63°53′ N) during the first few growing seasons, 1982–1985, employing trees of various ages (0–15 years). Sprouts developed very much more rapidly than seedlings during the first three seasons, as a consequence of the free growth pattern and associated pronounced growth flushes. Their annual height increment declined somewhat after a few years, however, whereas that of trees of seed origin remained constant or increased slightly. The mode of height growth in birches over 10 years of age appeared to approach the short-duration growth model. Branches of sprouts also grew more than those of seedlings, in the first few growing seasons, with distinct differences in branching pattern visible between the two tree forms, and also between sprouts originating from buds located above and below ground. Young sprouts used practically all buds to form branches and short shoots, giving them a bush-like appearance. In contrast, most axillary buds on seedlings remained dormant and the individuals adopted an arboreal mode of growth at an early stage. The less branched appearance of older trees of seed origin was also due in part to the death of a higher proportion of buds and branches.

Description: Previous reconstructions of the late Quaternary biogeographical history of lodgepole pine (Pinuscontorta Dougl.) have been based upon inferences from the modern geographical distribution of morphological and genetic variation. These studies have led to the widely accepted conclusion that relict populations of the Rocky Mountain subspecies of lodgepole pine (ssp. latifolia Engelm.) persisted in glacial refugia located in northwestern Canada. New fossil pollen evidence of the late Pleistocene and Holocene distribution of lodgepole pine in the western interior of Canada contradicts this view. Pinuscontorta ssp. latifolia migrated northward into Canada from refugia located south of the continental glacial limits and did not reach its northern range limits in the southern Yukon until the late Holocene.

Description: A procedure is presented for estimating the coefficients of allometric models for predicting tree component biomass. The resulting equations force the sum of the component estimates to be equal to the estimate of total biomass. An illustration of the procedure is given using published biomass data and the relationship of this procedure to previously published procedures is discussed.

Description: The most common method for determining tree profile models is by fitting an analytical function to a set of sample trees. In situations where the forester has relatively little a priori knowledge about the nature of profiles, choosing the analytical form of the parametric model is a critical problem without a satisfactory solution. An alternative is to use a nonparametric approach in which the model of the profile is explicitly specified by a tabulation of diameters at discrete heights. In this paper, it is shown how the model can be determined from the sample trees by means of a classical nonparametric probability density function estimation technique. Field tests and a measure of goodness of fit are used to express how well the models match the actual stem profiles. Using the Moroccan cedar (Cedrusatlantica Manetti) tree as an example, it is shown how the new nonparametric model can be compared with any classical parametric model. The results achieved demonstrate the advantages in using a nonparametric representation of stem profiles, which, moreover, is well suited to computer calculation constraints.

Description: An epidemiological survey was carried out in a rubber tree (Heveabrasiliensis Willd. ex A. Juss) plantation to study and describe the epidemics of the root-rotting fungi Rigidoporuslignosus (Klotzsch) Imazeki and Phellinusnoxius (Corner) G. Cunn. Infection and mortality of the trees were systematically recorded half-yearly for 6 years. During the first year, the outbreak resulted in a considerable enlargement of the initial disease centers and the appearance of new ones. Pathogen activity was found to decrease 6 years after planting. This was attributed to the increase in defense reactions with the age of the tree and to disruption of trophic connections between forest inocula and decaying taproots of rubber trees. The type of root disease is discussed, mainly in terms of the kinetics of the creation of disease centers.

Description: Seventy-five eastern Cottonwood (Populusdeltoides Bartr.) clones, selected from tests representing the top one-third of clones tested throughout the Lower Mississippi River Valley, were analyzed for alpha cellulose content, specific gravity, and volume after three growing seasons. All traits were found to differ significantly among clones. Mean clonal alpha cellulose content ranged from 48.2 to 55.8% of oven-dry, extractive-free wood with an average of 51.1%. Specific gravity averaged 0.33, with clones ranging from 0.27 to 0.39. Specific gravity was highly inherited, while alpha cellulose content was found to be moderately heritable. Negative genetic correlations between volume and both wood properties indicate that using a selection index to simultaneously improve all three traits is currently not possible. Two other selection methods were discussed. These selections showed substantial gain differentials in volume, but either a small loss or improvement in specific gravity and alpha cellulose content. This indicates that at age 3 years only volume should be considered in a selection program.

Description: Two young plantations of Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) were examined for the presence of a symptomless endophytic fungus, Meriaparkeri Sherwood-Pike (Hemiphacideaceae). This fungus occurred in the needles of nearly every tree examined, with infection frequencies increasing with the age of the needle. Previous reports have asserted that M. parkeri is a mutualist that produces insecticidal toxins. The maternal parentage of the trees and age of the needles were highly significant predictors of infection frequencies. A detailed examination of two families of trees revealed that infection frequencies differed between sites and were positively correlated with the height of the host. Mutualism and microhabitat effects are discussed.

Description: Forest soil respiration insitu was used as a comparative measure of the metabolic activity of substrate in eastern Ontario jack pine (Pinusbanksiana Lamb.) ecosystems that had been exposed to various burning treatments, including wildfire. The five burning treatments consisted of a 1920 wildfire, experimental understorey burning (nonlethal to the overstorey) of this age-class in 1962 and 1963, a 1964 wildfire, and experimental burning of this age-class in 1977. Seasonal respiration trends were similar on all treatments. Carbon dioxide evolution increased in the spring (4000 mg•m−2•d−1) in response to ambient warming (5000 mg•m−2•d−1 in August) and decreased in late fall as seasonal temperatures declined (4000 mg•m−2•d−1 in November). Precipitation and autumnal litter fall apparently acted as secondary modifiers of this general trend by affecting substrate moisture content and nutrient quality, respectively. Highest metabolic activities were measured on the 1963 understorey burning treatment followed in decreasing order by the 1920 wildfire, the 1964 wildfire, the 1962 experimental understorey burn, and the 1977 burn of the 1964 age-class. Multiple comparisons of overall seasonal respiration means revealed lower rates (P 

Description: Productivities of 5 black cottonwood clones from each of 10 source populations (50 clones in total) were compared at one plantation site in western Washington. The source populations are located west of the Cascade Mountains, between central Oregon and southern British Columbia. Most source stands represented populations in major river valleys. Individual clones were selected for superior form and growth rate. Spacing was 1.2 × 1.2 m (6944 stems•ha−1) and trees were harvested after 4 years. Considerable variation in mortality, height, and productivity were found among clones within individual stands and among stands. Southwestern clones were generally more productive. Heights of individual clones averaged between 8.5 and 11.8 m at 4 years. Average dry weight production of black cottonwood clones was 12.5 Mg•ha−1•year−1 and varied between 5.2 and 23.1 Mg•ha−1•year−1 for individual clones. Three new Populustrichocarpa × P. deltoides hybrids planted in the trial were generally more productive than black cottonwood or the 'Robusta' hybrid, with average heights varying from 11.5 to 12.2 m and dry weight production ranging from 15.6 to 27.8 Mg•ha−1•year−1 for an average of 23.6 Mg•ha−1•year−1. The high yields in this experiment are attributed to favorable climate (1940 degree-days•year−1)3, cultural treatments (irrigation, N fertilization) and genetic constitution of certain clones. The data promise substantial gains in short-rotation productivity from combining clonal selection with interspecific hybridization.

Description: Precipitation and throughfall quantity and chemistry were measured in several Pinuscontorta ssp. latifolia ecosystems in southeastern Wyoming. Bulk deposition (open collector) was somewhat enriched chemically in comparison with wetfall (shielded collector), suggestive of dry deposition. With the exception of low S concentrations, atmospheric chemistry was comparable to other continental locations in North America. Concentrations of most solutes were much higher in canopy throughfall than rainfall. Canopy evaporation accounted for a 27% increase of dissolved solids in throughfall, the remaining differences being attributed to canopy leaching and washing of dryfall. Throughfall was most enriched in K+, Mg2+, and organic anions, indicating the importance of canopy leaching. Very high spatial variation was observed within the forests, precluding the detection of annual or site differences in throughfall chemistry. Our estimates of dry deposition to the lodgepole pine ecosystem were lower than for more polluted regions of eastern North America. Except for SO42−, wetfall supplied larger amounts of the major elements than dry deposition. Canopy leaching was a major flux pathway in these ecosystems, particularly for K+, Mg2+, and SO42−.

Description: A laboratory experiment was performed to determine the effect of slope on the downhill spread rate of forest fire. Results with beds of pine needles showed that the spread rate decreased to 64% of the level rate as slope was raised to 22°, then gradually increased back to the level rate at 45°. Some theory about how the flame radiates to the unburned fuel was advanced to account for this phenomenon.

Description: Mechanical stress generated by growing wood cells causes heart checks in the ends of timber, while lumber end-splits and warps. It is not possible to prevent these growth stresses but they can be minimized. Trees generate relatively high stress in order to bend stems and branches into positions more favorable for the tree, as is known from reaction wood, whose growth stresses are extremely high. One controls the stresses by giving trees no reason to reorient themselves, that is, by providing stable growth conditions. To this end, trees should have sufficient, uniform light, and where light is scarce, as in understories, one-sided light changes have to be avoided. In particular, the spatial distribution of trees in the stand should be uniform; multistoried forests are preferable to single-storied, even-aged plantations. The stands should be thinned slightly, frequently, and uniformly, rather than haphazardly and severely after long periods. In areas with strong prevailing wind, close spacing may minimize the stresses, whereas on steep slopes wide spacing appears to be preferable.

Description: Four indices of site quality were compared with volume growth of pure, ideal ponderosa pine (Pinusponderosa Laws.) stands in western Montana. Indices based on quantifying the biophysical factors or physiological processes that control productivity (available water index and a relative index of seasonal photosynthesis from computer simulations) worked as well as those based on tree or stand measurements (site index and leaf area index). The following correlations of mean annual stem volume increment were found: with leaf area index, R2 = 0.93; with available water index, R2 = 0.95; with site index, R2 = 0.98; with gross photosynthesis R2 = 0.96. The available water and photosynthesis indices were also highly correlated to site index (R2 〉 0.95). However, the tree-dependent site quality indices varied by stand density. Leaf area index and volume growth increased with stand density while site index decreased. Simulations indicated that depletion of soil water effectively halted transpiration and photosynthesis by midsummer and illustrated that even with adequate water, cold spring and fall temperatures ultimately defined the length of the growing season and hence site quality. We conclude that an ecosystem process model can provide an index to site quality independent of tree or stand measurements.

Description: One-year-old Pinussylvestris (L.) seedlings were wounded at the stem base by stripping off stem bark pieces of approximately 10 mm in length and covering about 50% of the stem circumference. The seedlings were thereafter planted out in the field or in a climate chamber. The field experiment was repeated on four different planting dates. Wounded and control seedlings were successively harvested for gas chromatographic determination of changes in resin acid concentrations of the bark surrounding the wounded area. Independent of planting date, wounded seedlings were found to have higher concentrations of total resin acids than corresponding controls. The most important quantitative changes in resin acids were observed for isopimaric, levopimaric + palustric, dehydroabietie, abietic, and neoabietic acid. In wounded seedlings the concentration of dehydroabietic acid showed the most significant increase, both in the field and in climate chamber experiments. This increase was rapid and appeared within 1 week in the field and within 3 days in the climate chamber. The other resin acids identified showed a somewhat similar variation pattern, but the differences were not as distinct as for dehydroabietic acid. These wound-induced rapid changes in resin acid concentrations could be important for resistance to pathogens.

Description: Measurements were made of the transfer of N,P,K, Ca, Mg, Mn, and B to the atmosphere during low-intensity (350–600 kWm−1) prescribed burns in three Australian subalpine eucalypt forests dominated by overstoreys of either Eucalyptuspauciflora (Sieb. ex Spreng), Eucalyptusdives (Schau.), or Eucalyptusdelegatensis (R. T. Baker). Elemental transfer was calculated as the difference between the quantity of an element in the fuel (litter plus understorey) before burning and that present in the postfire residues which were recovered quantitatively using small aluminium trays. Complete recovery of fine ash is essential for accurate budgeting for elements other than N. The mass ranges of elements transferred to the atmosphere (kilograms per hectare) were as follows: N, 74–109; P, 1.96–3.04; K, 12.1–21.0; Ca, 18.7–29.7; Mg, 4.5–9.7; Mn, 1.6–4.3; B, 0.08–0.12. These transfers represented, as a percentage of the element initially present in the fuel, the following: N, 54–75; P, 37–50, K, 43–66; Ca, 31–34; Mg, 25–49; Mn, 25–43; B, 35–54. The percentage loss of elements was positively linearly correlated with the percentage loss in fuel weight. High concentrations of P and cations occur in fine ash, especially grey (mineral) ash. In comparison with unburnt litter, concentrations of Ca, Mg, and P were increased by 10- to 50-fold, 10- to 35-fold, and 10-fold in fine (

Description: An alternative approach to goal programming is described. The approach incorporates both cardinal weighting and ordinal ranking of deviation variables, and does not require apriori specification of goal target levels. Ordinal rankings are used to describe feasible and optimal policy spaces. Cardinal weightings are then adjusted through an interactive procedure until the decision makers are satisfied with the weightings and with the resulting compromise solution. The procedure is demonstrated using a hypothetical reforestation budget allocation problem.

Description: The variability of wood specific gravity and yield of 23 white spruce provenances from the Great Lakes – St. Lawrence forest region was studied 20 years after planting at Harrington Forest Farm, Québec. The results indicate no relationship between wood specific gravity of provenances and their respective growth performance. The southwestern section of this region showed a small decrease in wood specific gravity, but it was compensated for by a strong increase in volume growth, resulting in an important gain in dry weight productivity. The variability of white spruce wood specific gravity was split into three sources: 11% was attributed to provenance differences, 8% to provenance and repetition interaction, and the remainder to differences among trees of the same provenance and to experimental error. In a breeding program, a first selection should be made at the provenance level on the basis of volume productivity and a second selection on the basis of wood specific gravity values within the selected provenances, to maximize the overall genetic and economic gain.

Description: A soda lime technique was used to measure CO2 evolution at the soil surface in four mature forest types (aspen (Populustremuloides Michx.), paper birch (Betulapapyrifera Marsh.), black spruce (Piceamariana (Mill.) B.S.P.), and white spruce (Piceaglauca (Moeneh) Voss)) in interior Alaska. Surface temperature, 15-cm depth temperature, and soil moisture were measured concurrently with CO2 evolution. Accumulated CO2 evolution ranged from 1315 to 1654 g CO2•m−2 for the period May 1 – September 30 in 1981 and 1982 in the four stands. Data were used to develop three-dimensional response surfaces and test mathematical models of respiration in relation to substrate temperature and moisture. GRESP, a biologically based model, provided a fairly accurate simulation of the seasonal course of respiration as a function of substrate temperature and moisture. In an attempt to better define the observed response surface trends, a best-fit equation model, BRESP, was formulated. BRESP includes the moisture portion of the GRESP equation, and an altered temperature equation which more adequately defines the upper and lower thresholds of respiration in relation to substrate temperature. GRESP and BRESP each produced similar r2 values; however, higher order polynomial equations gave a better-fit model. The weakest area of all models for simulating seasonal trends was during the periods of peak respiration in June.

Description: Canopy leaching or retention of all major ions was determined for three deciduous forests in eastern Tennessee that are currently receiving wet and dry acidic deposition. For all three canopies, the retention of atmospherically deposited cations (H+ and [Formula: see text]) exceeded retention of deposited anions [Formula: see text] on a charge-equivalent basis. Charge balance was maintained by ion exchange between the deposited cations and K+, Ca2+, and Mg2+ on the canopy surfaces. It was found that 40–60% of the leaching of K+, Ca2+, and Mg2+ from these canopies results from this exchange process, with the remainder attributable to coleaching with plant-derived anions. Because the cation exchange can be largely attributed to retention of deposited H+, we interpret it as a measure of the acidic deposition effect on foliar cation leaching. Dry deposition was found to be an important input for most of the major cations and anions. The data indicate that organic anions may be important counter ions to cation leaching, especially in the absence of acidic deposition, and that acid–base reactions in the canopy can obscure the true H+-exchange reactions between the deposition and the canopy.

Description: To compare litter decomposition and nitrogen (N) dynamics in 16-year-old black locust and pine-hardwood forest stands, weight loss, N concentration, and litter quality of the dominant species in each stand were monitored for 863 days, using litterbags. The species studied were Robiniapseudo-acacia L. (leaflets and rachises), Liriodendrontulipifera L., and Rubus spp. (leaves and stems) in the black locust stand and Kalmialatifolia L., Pinusrigida Mill., and L. tulipifera in the pine-hardwood stand. Between-stand comparison of L. tulipifera leaf litter indicated a significant stand effect on weight loss during the first 8 months but no significant stand effects on N concentration and net immobilization. Initial lignin content was highly correlated to percent weight remaining and net N immobilization after 331 and 863 days. All litter types exhibited an absolute increase in "lignin" that appeared to originate from the more soluble litter fraction. Robiniapseudo-acacia leaflets, P. rigida, K. latifolia, and Rubus stems decomposed slowly, but only the latter two species were in the net N immobilization phase at day 863. Rubus leaf litter decomposed rapidly, releasing 70% of its original N by day 331. The role of Rubus and other understory species in influencing organic matter and N accretion in these early successional systems is discussed. Robiniapseudo-acacia leaflets contained 81% of their original N at day 863. This retention of N, coupled with its greater potential to form recalcitrant material during decomposition, suggests a mechanism to explain the long-term effects of Robiniapseudo-acacia on N storage in the forest floor and soil.

Description: The role of three common fungal isolates from the heartwood of mature coastal western red cedar (Thujaplicata Donn) in the detoxification of thujaplicins was investigated. A Sporothrix species, Kirschsteiniellathujina (Peck) Pomerleau & Etheridge, and a Phialophora species are shown to form a succession of fungi, in that order, which invade red cedar heartwood from within and cause discolouration of the heartwood from light straw to red and various shades of brown. Thujin, a recently described lactone compound in red cedar heartwood extractives, is shown to be present in discoloured wood only. It is formed by the oxidative dimerization and isomerization of thujaplicins by the Sporothrix isolate. The other two fungi may play a minor role in thujaplicin degradation. Thujin is shown to lack toxicity to Poriarivulosa (B. & C.) Cooke, the common decay fungus of coastal western red cedar.

Description: Studies on nonsymbiotic dinitrogen fixation (C2H2) in soil were conducted in 20 different forest stands in central Sweden. The stands were between 40 and 120 years old and included both coniferous and deciduous types. The relationships between nitrogenase activity and site productivity, stand composition, and soil properties were examined. Based on three samplings during the growing season, a considerable difference in activity was found to occur between the stands. The highest yearly mean activity for a stand was 200 times the lowest value. The activity was positively and significantly correlated to site productivity. The effect of stand composition on the activity in the forest floor was studied on five sites. The activity was similar under spruce (Piceaabies (L.) Karst.) and pine (Pinussylvestris L.), higher under spruce than beech (Fagussylvatica L.), and much higher under birch (Betulapendula Roth) than spruce when compared two by two on identical parent material. The activity under birch was mainly concentrated in the birch leaf litter. Evaluating the influence of soil properties by regression analysis revealed a strong positive correlation between activity and pH. The soil acidity alone explained 85% of the variation in yearly mean activity among the 15 coniferous stands. The conversion factor between C2H2 reduction and 15N2 fixation was determined for five soils and ranged from 1.6 to 5.6. The N2 fixation down to a depth of 6 cm during the growing season was estimated to 0.4–1.4 kg ha−1 in these soils.

Description: A greenhouse study was conducted to determine the influence of soil water potential and endomycorrhizal fungi on root growth of yellow-poplar (Liriodendrontulipifera L.) and sweet gum (Liquidambarstyraciflua L.) seedlings grown at three soil bulk densities. Silt loam soil was compacted in PVC pots to bulk densities of 1.25 (low), 1.40 (medium), or 1.55 (high) Mg • m−3, and equilibrated at −10 kPa soil water potential. Newly germinated seedlings were transplanted into the pots, inoculated with fungal chlamydospores of Glomusmacrocarpum or Glomusfasciculaturn, or distilled water (control), and grown for 3 months at −10 or −300 kPa soil water potential. Total porosity, air-filled porosity, water content, and mechanical resistance of the soil were determined for samples compacted to the same bulk densities and equilibrated at the same soil water potentials as were used in the greenhouse study. Root growth was reduced by the high mechanical resistance caused by bulk densities of 1.40 and 1.55 Mg • m−3 at −300 kPa water potential. At both water potentials, total length of lateral roots and fibrosity of the root system of both tree species decreased significantly when bulk density increased from 1.40 to 1.55 Mg • m−3. Air-filled porosity less than 0.12 m3 • m−3 limited root growth when water potential was −10 kPa, and mechanical resistance greater than 3438 kPa restricted growth at −300 kPa. At −10 kPa, root length and fibrosity were greatest for inoculated sweet gum seedlings at each bulk density. At −300 kPa, sweet gum seedlings inoculated with G. fasciculatum had the greatest root length and fibrosity at the low and medium bulk densities. Mycorrhizal effects on root length of yellow-poplar were variable, and fibrosity was not significantly affected by mycorrhizal treatment.

Description: Asymbiotic nitrogen fixation in litter was assayed by acetylene reduction across a range of 25 forested sites in the Willamette Valley and Oregon Cascade and Coast ranges and periodically over a year at two Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) plantations in the Willamette Valley. Laboratory experiments showed that optimal conditions for N fixation by Douglas-fir litter were 200% moisture content and 22 °C. Annual fixation was 1.08 ± 0.13 kg/ha at one Willamette Valley plantation, 0.39 ± 0.06 kg/ha at the other. Fixation rates at the other 23 sites, which were sampled less frequently, ranged from 0 to 5 g N ha−1 day−1 and exceeded trace levels at only six sites, indicating annual totals much less than those at the Willamette Valley plantations. At four coastal and valley sites sampled by litter layer, older L layer Douglas-fir litter fixed the most N per gram dry weight. Percent N, percent C, and the C:N ratio of that litter layer did not differ significantly among sites or correlate with N-fixation rates. Forest-floor litter in most Northwest forests fixes no more than trace amounts of N, at most ~1 kg N ha−1 year−1. These amounts are smaller than N input from precipitation.

Description: The effects of a systematic thinning (alternate row) on water stress and growth in a 19-year-old Douglas-fir plantation (Pseudotsugamenziesii var. menziesii Franco) was studied during 5 years in northeastern France. Thinning has an important effect on water balance. The increase of the soil water reserve led to a lower duration and level of water stress in the thinned plot, especially during the first 3 years after thinning. This study revealed a rapid evolution of the water balance, since the evapotranspiration ratio of the two plots (control and thinned) had increased from 0.83 during the 1st year to 1.03 during the 5th year after thinning. Together with microclimate influences, thinning increased tree growth substantially (more than 100%); this growth increase resulted from a higher growth rate and longer growth periods (from 26 to 49 days).

Description: A number of nondestructive techniques for analyzing the timing, frequency, and magnitude of natural disturbances in forest stands are discussed in this paper. Intensive age determination of trees is desirable for reconstructing forest disturbance history, but age distribution alone is not always a sufficient basis for a disturbance chronology. Frequently all-aged forests have undergone severe past disturbance which cannot be readily identified from the distribution of trees among age-classes. Radial growth patterns provide more direct evidence of past canopy tree deaths. In cases where a large sample of tree ages and growth records is not feasible, structural attributes of forests can provide valuable supplementary evidence. Evidence of the effects of disturbance history and age structure on diameter distributions is examined, and principles for valid interpretation proposed. Crown area distributions and diameter distributions of nonsuppressed trees potentially appear to be more reliable structural indicators of past canopy disturbance than simple size distributions. For regional studies of disturbance frequency, random dispersal of medium to large plots across large landscape units is recommended as a sample design.

Description: A four state-descriptor dynamic programming model was used to seek economically optimal thinning regimes for high and low thinning in loblolly pine (Pinustaeda L.). Given the assumptions of the study, low thinning generated higher present values than high thinning. Growth equations were estimated from data generated by a stochastic growth simulator. Reasons for the occurrence of slightly suboptimal solutions are discussed. The paper reviews situations in which the principle of optimality might be violated when thinning problems are being solved with forward recursion dynamic programming.

Description: We used data on 2356 trees from 43 prescribed fires in Idaho, Montana, Oregon, and Washington states to model postfire tree mortality. Data were combined for seven species of conifers to develop binary logistic regression models for predicting the probability of mortality. Probability of mortality increased with percentage of the crown killed, and decreased as bark thickness increased. Models are presented with and without species as a categorical variable. The models predicted well for trees burned in both slash fires and fires in natural fuels. The models are applicable for assessing fire-caused mortality both of individual trees and in mixed conifer stands of the Pacific Northwest.

Description: The 17-year response of understory vegetation to forest thinning experiments was examined in two study sites on the central Oregon coast to determine the role of overstory species composition and stand density on forest succession. At 6 months, no significant difference in shrub, herb, and moss species composition or abundance was detected between the two study sites. Seventeen years after treatment, however, the Piceasitchensis (Bong.) Carr. site had much less vegetation cover and diversity than the Tsugaheterophylla (Raf.) Sarg. site. Overall response of most vascular species to thinning was insignificant because of their high variability in the medium and heavy treatments. Carpet-forming mosses were consistent in increasing their percent ground cover following thinning in the Picea site, and were the only species group to increase cover relative to initial conditions. Tsuga saplings were significantly more abundant under Picea canopies than under Tsuga canopies, probably because of the increased openness of Picea canopies. The increased abundance of saplings at both sites, particularly following heavy thinning, led to a two-layered overstory canopy and relatively less shrub and herb cover and diversity. Except for ferns, most plants that persisted had animal-dispersed seed. Thinning had little effect on the loss of understory species relative to the controls. Increases in diversity with thinning occurred primarily as the result of increased invasion by shade-tolerant species. Regardless of thinning treatment, only one-third or less of the original plant cover was maintained on study plots at stand age 30 years. Early thinnings without subsequent treatments are unlikely to maintain stable herb and shrub populations in forest types where the understory would otherwise be eliminated during the intermediate stages of stand development.

Description: Analysis of energy partitioning between defensive investments and growth in woody plants indicates that increasing a tree's life-span should require increased energy investment in protective measures such as thick bark and defensive chemicals. Increased investment in such defenses, however, logically must slow down the growth rate, thereby raising the mortality rate for juveniles in competition for height growth. Early reproduction should also reduce the growth rate. It is hypothesized that rapid growth can substitute for these defenses, but the consequence is rapid decline upon reaching maturity. These predictions are tested with data compiled from the literature for 159 species of North American trees. Data analysis supports predictions. Longevity of angiosperms, but not of gymnosperms was correlated with increased investment in defenses as measured by volumetric heat content of the wood. Wood density was not as good a measure. Longevity of gymnosperms was predicted by resistance to wood decay. For both taxa there was a negative correlation between growth rate and longevity, supporting the hypothesis of growth trade-offs. Age of sexual maturity was closely predicted by longevity in angiosperms. There was no such relationship for conifers as a whole, though there was for pines. The lack of relationship for all conifers might be explained by (i) variation in reproductive opportunities for young trees of different species, or (ii) variation in growth rates of young trees in certain adverse habitats occupied by conifers.

Description: Tree-ring analyses of hickory (Carya spp.) from the long-term ecological research site, Coweeta Hydrologic Research Laboratory, revealed that concentrations (micrograms per gram) of lead, aluminum, and zinc are increasing, that concentrations of copper, cadmium, nickel, and manganese have remained generally constant since the 1880's, and that hickory annual radial growth increments are declining. Lead, aluminum, and zinc burdens (microgram per growth interval), unlike their respective concentrations, have remained generally constant during the 1900's. The interpretation of growth and burden data indicates that hickory trees at Coweeta are in a mature phase of their life cycle and that annual growth does not seem to be reduced by pollutants.

Description: Thinning stands of lodgepole pine (Pinuscontorta Douglas var. latifolia Engelmann) is thought to increase vigor and thereby reduce susceptibility to mountain pine beetle (Dendroctonusponderosae Hopkins). Partial cut stands of lodgepole in the Kootenai and Lolo National forests, Montana, U.S.A., provided opportunity (i) to determine growth response of 76- to 102-year-old lodgepole pines following thinning and (ii) to test the hypothesis that vigor of residual trees infested and uninfested by beetles does not differ. Lodgepole pine stands receiving different partial cutting prescriptions were sampled. Characteristics measured for trees within the sample were diameter at breast height, grams of stem wood per square metre of foliage, periodic growth ratio, and leaf area. Trees in most treatments showed decreased growth the 1st year following thinning. The 1st year was followed by increased growth during the next 4 years. Of the tree characteristics measured, only dbh was significantly different on both forests between live trees and trees killed by the mountain pine beetle; the latter were larger (P 

Description: Four forest floor manipulation treatments were applied to an eastern Ontario jack pine (Pinusbanksiana Lamb.) ecosystem. These included a one-time complete removal of the forest floor to mineral soil; annual removal of the total forest floor to mineral soil; one-time removal of the forest floor, ashing of the material, and broadcast spreading of the ash onto exposed mineral soil; and an untreated control. Eight years after treatment radial tree growth on the treated plots showed a 30% reduction compared with the untreated plot. Annual removal of the forest floor caused most severe nitrogen depletion in jack pine foliage, forest floor, and mineral soil. Effects of one-time removal and burning treatments were less severe, but significant. Any interference with the normal buildup of the forest floor during stand development should be avoided if site quality is to be maintained for tree growth.

Description: The environmental parameters associated with grey mould, Botrytiscinerea Fr.: Nocca & Balbis, on container-grown Douglas-fir, Pseudotsugamenziesii (Mirb.) Franco, were studied in a plastic-covered greenhouse and a fibreglass-covered greenhouse near Victoria, British Columbia. Disease losses and numbers of B. cinerea spores were much higher in the fibreglass-covered house, where seedlings were taller and more succulent because the fibreglass reduced light intensities. From July to October the length of time when the combination of temperature and relative humidity that favours B. cinerea spore germination and infection was 14.5 times greater in the fibreglass-covered than in the plastic-covered house. Conditions beneath the seedling canopy that enhance the disease were more prevalent in July and August than in the autumn when the disease becomes evident, suggesting that earlier application of preventive fungicides may benefit disease control. Grey mould inoculum originated from outside the greenhouses, but once the disease was established on the seedlings, numbers of spores within the houses exceeded those outside. Airborne spore numbers both outside and within the greenhouses were highest during the day. Numbers of spores within the houses peaked when the irrigation system was on; this is ascribed to the mechanical effect of the irrigation water on spore dispersal rather than to changes in greenhouse environmental parameters.

Description: Growth and development of native species of trees in response to long-term increases in atmospheric CO2 concentration were studied. Seedlings of two competing perennials, Pinustaeda L. and Liquidambarstyraciflua L., were obtained from germinated seeds and grown through one complete growing season at 350, 500, and 650 μL•L−1 CO2. The plants were grown in CO2 controlled greenhouses under natural photoperiods and light regimes, with temperature controlled to simulate mean local climate. Stem length and basal stem diameter increased with increasing CO2 in both species. Liquidambarstyraciflua maintained size dominance in all concentrations. The dry weights of stems, roots, and leaves increased in both species. In P. taeda, however, the seedlings reached maximum size at 500 μL•L−1 while L. styraciflua continued to increase up to 650 μL•L−1. Liquidambarstyraciflua produced significantly more branches and leaves at the higher CO2 concentrations than at 350 μL L−1. Differences in plant shape and responses in growth rate of these two naturally competing tree species suggest that continuing atmospheric CO2 enrichment could affect future interactions between the species and might produce changes in community composition.

Description: Using a large data base of permanent research plots in coastal Douglas-fir, a growth projection strategy is developed. The emphasis is on stratifying growth influences into potential and modifier functions for components of diameter and height growth within a stand table. Growth periods are defined as equal increments of top height through time. The model developed is an individual-tree, distance-independent, stand-projection model.

Description: Morphological and phenological variation among five black cottonwood (Populustrichocarpa Torr. & Gray) clones from each of 10 natural populations were studied at one plantation site in western Washington. Source populations are located in major river valleys, west of the Cascade Mountains, between central Oregon (latitude 44°44′ N) and southern British Columbia (latitude 49°05′ N). Populations and individual clones were selected for superior form and growth rate. Tested at a spacing of 1.2 × 1.2 m, the 50 clones displayed a large range of variation in 15 leaf, branch, and phenology characters studied. Clones and populations differed significantly in 14 and 10 characters, respectively. Population means for seven characters and a character association (principal component) varied clinally with source latitude, longitude, and (or) elevation. The most consistent genetic cline follows a geographic gradient from southwest to northeast: southwestern clones develop smaller leaves on more erect branches, and continue growth later in the fall. Variation patterns seem to reflect regional climatic gradients, annual disturbance in riparian environments, and the life history characteristics of the species. The results point to the great potential of clonal selection for black cottonwood improvement.

Description: An enzyme-linked immunosorbent assay was developed for the quantitative detection of the sap-staining fungus Ophiostoma sp. C28 in artificially inoculated wood. The fungus can be detected in wood samples as small as 1 mg dry weight and at concentrations much lower than those at which staining becomes visible.

Description: Terminal bud growth in 2nd-year seedlings and subsequent elongation of the overwintering bud in the 3rd year were studied in California red fir (Abiesmagnifica A. Murr.) and two elevational sources of white fir (A. concolor (Gord. and Glend.) Lindl.). During each growing season the seedlings were either watered or left unwatered to provide 2nd and 3rd year treatments of wet–wet, dry–wet, wet–dry, and dry–dry seasons. Harvests were done biweekly during the second growing season and once at the end of the third growing season. Rate and duration of primordium production were negatively related and there were no differences among seed sources for the number of primordia produced in the 2nd year. Watering more than doubled the number of primordia, mainly through increasing the rate of production. Internode number and length were negatively related on a genetic and environmental basis. Changes in internode length tended to compensate for environmentally induced changes in internode number which resulted in a year to year stability in height growth. Height growth was more buffered against changes in internode number in red fir than in white fir. Watering induced a summer shoot in 80% of low-elevation white fir seedlings and 40% of red fir and high-elevation white fir seedlings. Summer shoots doubled the height increment for the current season and increased the number of needle primordia in the winter bud by 26%. The larger buds were the result of a prolonged period of primordium production.

Description: The leaf and root tissue water relations of Quercusalba L., Quercusmacrocarpa Michx., and Quercusstellata Wang. seedlings before and after drought were examined to evaluate the occurrence and comparative extent of osmotic adjustment in seedlings of these species. Drought resulted in active osmotic adjustment in leaves of all three species, with decreases in osmotic potential at full tissue hydration and at the turgor loss point from 0.25 to 0.60 MPa. Active osmotic adjustment in Q. stellata, and increased root tissue elasticity in Q. macrocarpa and Q. alba, resulted in turgor loss of roots occurring at a water potential 0.36 to 0.66 MPa lower in drought-stressed than in well-watered seedlings. Species differed in tissue water relations only before drought, with Q. stellata exhibiting lower osmotic potentials than Q. alba and Q. macrocarpa. Estimates of the osmotic potential at full saturation were generally lower in leaves than in roots, but the osmotic potential at turgor loss was similar. Roots exhibited turgor loss at lower values of relative water content and experienced a more gradual decrease in water potential per unit water content during dehydration than did leaves. This response indicates greater relative tissue capacitance in roots than in leaves in these species.

Description: The objective of this paper is to explain the distributions, assumptions, interpretations, and relationships of the two compatible, stochastic models of fire history: the negative exponential and the Weibull. For each model the "fire interval" and "time-sinee-fire" distributions are given. Both models apply to homogenous stationary stochastic processes. The negative exponential states that the instantaneous fire hazard rate is constant for all stand ages. The Weibull states that the instantaneous fire hazard rate increases with stand age when the shape parameter is 〉 1 (the negative exponential is a special ease of the Weibull when shape = 1). An empirical method is given for separating from an observed fire history distribution, the pre- and post-fire suppression distributions. Four relationships are derived from the models and defined per study region (per stand): (i) the fire cycle (average fire interval), (ii) the annual percent burned area (fire frequency), (iii) the average age of the vegetation (average prospective life-time), and (iv) the renewal rate.

Description: Published data and newly presented evidence demonstrate that the proportion of N or P lost from plant material during combustion under a wide range of conditions increases linearly with percentage loss of fuel weight during combustion. For N the correlation is strong, and the slope (β) of the regression line approaches unity for combustions under field or simulated-field conditions, but reduces to 0.78 for materials combusted in a muffle furnace. Almost all of the losses of N are due to volatilization. The relationship for P is less well defined, and β is lower (0.56 for field studies; about 0.2 for simulated-field or laboratory combustions). Calcium is not volatilized at the temperatures generated in most vegetation fires, thus increases in the ratio of Ca to other elements during combustion (i.e., higher ratios in burnt residue) indicate nonparticulate transfer of elements to the atmosphere. Increased ratios for Ca to N, P, K, Mg, Mn, and B were demonstrated for several components of eucalypt litter fuels, especially where the degree of combustion was high. The positive relationship between increase in Ca:element ratio and percentage element loss in nonparticulate form during combustion, is of Mitscherlich form so that initial increases in the ratio represent proportionally most element loss. Partitioning of the transfer of elements from the litter and understory to the atmosphere measured during low-intensity fires in three eucalypt forest communities demonstrated a low particulate contribution (and thus a high nonparticulate transfer) for N, K, P, and B. Particulate contributions to elemental transfers are less where combustion is more complete, resulting in formation and transport of fine grey ash which has a high Ca:element ratio. Of particular ecological importance is the significant transfer of P by nonparticulate mechanisms, because such P is likely to be permanently lost from burnt sites and natural rates of P replacement are usually very slow. Fine grey or white ash is highly nutrient enriched (e.g., up to 50-fold for P compared with concentrations in unburnt fuel), and hence its transport from the site in the smoke column, or subsequently by either wind or water, can result in substantial export of nutrients.

Description: The quality of data collected in surveys of forest health depends on a subjective interpretation of tree condition. Many factors influence classification, including the observer's experience, the observer's bias, the weather at the time of the classification, and the appearance of the tree. The effects of some of these factors can be quantified and attempts made to reduce their impact. It may be possible to account for others during the analysis and interpretation stages of the inventory process.

Description: The problem of determining the effects of forest fire on stand yields is often neglected in forest yield analyses. Using previous theoretical results, "fire-adjusted, volume–rotation curves" can be developed which provide a graphical technique for determining optimal rotation age and long-run yield when the risk of fire is present. For white spruce of the northern interior of British Columbia it is shown that even modest rates of fire can result in very large reductions in long-run yield. Similar results are established for the effects of fire on land expectation value, which is dissipated very quickly under the risk of fire.

Description: Current annual stem growth rates per hectare of unthinned young stands of balsam fir (Abiesbalsamea (L.) Mill.) were 2–3 times greater than in adjacent stands thinned 4–6 years earlier, largely because unthinned stands contained 2.5–4.0 times more foliar weight per hectare. Stem growth rates per tree in thinned stands were 3–8 times greater than those in unthinned stands because of the reduced competition and the lower ratio of heterotrophic to autotrophic tissues (S/F). However, the foliar efficiencies, as measured by annual stem growth per unit of foliar weight (E), of thinned plots were not significantly greater than those of unthinned plots, in spite of the reduced competition and lower S/F ratio. The lack of response of foliar efficiency to thinning is discussed in relation to published information about photosynthetic rates and stem respiration rates. In all stands, the E values of dominant trees were equal to, or less than, those of subordinate trees, in spite of their superior competitive position and lower S/F ratio. The lack of correlation between competitive position and foliar efficiency is also discussed.

Description: Xylem sap extraction of branches as a new field problem-solving technique in forestry, environmental pollution, and botany is described. The influence of extraction pressure, crown aspect, height into the crown, tree age, time of year and day, and soil chemistry on the ion concentrations in xylem sap are discussed. Xylem sap extraction with a pressure chamber provides a good indication of the nutrient status of a species if the trees are of similar age, and if they are sampled at the same aspect, crown height, time of day, time of year, and on the same soils. Pseudotsugamenziesii (Mirb.) Franco (Douglas-fir), growing on nutrient-poor acid soils and moderately fertile alkaline soils showed significant differences in growth rate and ion concentrations in the xylem sap and soil. Trees on the faster growth site (

Description: Red spruce, Picearubens Sarg., from 30 provenances was tested over a 23-year period at six locations in the Maritimes Region of Canada. Twenty-eight of the provenances were from the Maritimes Region and two were from West Virginia. Hybrid index was used to distinguish pure red spruce from red–black spruce derivatives. Trees from three of the Maritimes provenances were considered to be of hybrid origin. These three provenances produced the fastest-growing trees in the tests. The genetic variation pattern, at the provenance level, in pure red spruce of Maritimes origin is not well defined. Use of seed from provenances identified as superior for reforestation would result in about 10% greater height and diameter growth than would be obtained from average seed. The use of seed of poor provenances could result in a corresponding loss of growth. Height at ages 10, 15, and 23 years and diameter at age 23 years were all strongly correlated, suggesting that superior provenances of red spruce can be identified at age 10. The Maritimes Region can be considered as a single breeding zone for tree improvement efforts with red spruce.

Description: The factors influencing leaf litter decomposition and nutrient release patterns were investigated for 3.6 years in two mixed conifer forests in the southern Sierra Nevada of California. The giant sequoia–fir forest was dominated by giant sequoia (Sequoiadendrongiganteum (Lindl.) Buchh.), white fir (Abiesconcolor Lindl. & Gord.), and sugar pine (Pinuslambertiana Dougl.). The fir–pine forest was dominated by white fir, sugar pine, and incense cedar (Calocedrusdecurrens (Torr.) Florin). Initial concentrations of nutrients and percent lignin, cellulose, and acid detergent fiber vary considerably in freshly abscised leaf litter of the studied species. Giant sequoia had the highest concentration of lignin (20.3%) and the lowest concentration of nitrogen (0.52%), while incense cedar had the lowest concentration of lignin (9.6%) and second lowest concentration of nitrogen (0.63%). Long-term (3.6 years) foliage decomposition rates were best correlated with initial lignin/N (r2 = 0.94, p 

Description: Litterfall was measured for 4 years and leaf litter decomposition rates were studied for 3.6 years in two mixed conifer forests (giant sequoia–fir and fir–pine) in the southern Sierra Nevada of California. The giant sequoia–fir forest (GS site) was dominated by giant sequoia (Sequoiadendrongiganteum (Lindl.) Buchh.), white fir (Abiesconcolor Lindl. & Gord.), and sugar pine (Pinuslambertiana Dougl.). The fir–pine forest (FP site) was dominated by white fir, sugar pine, and incense cedar (Calocedrusdecurrens (Torr.) Florin). Litterfall, including large woody debris

Description: In a previous study a nitrogen mineralization model was developed by combining the potentially mineralizable nitrogen (No) with functions representing the effect of temperature and soil moisture on the mineralization rate constant (k). The model performed well in predicting the amount of net nitrogen mineralized during a growing season when soil was incubated in plastic bags placed in incubators or buried in the field. In the present study a similar model was used to estimate net nitrogen mineralized in situ from Wood Mountain loam an Orthic Brown soil at Swift Current, Saskatchewan under (a) summerfallow, (b) cropped-dryland and (c) cropped-irrigated conditions. Model output showed good agreement to field measurements especially for the first 45–60 d, but thereafter tended to underestimate the measured data particularly under cropped-dryland conditions. During a growing season the cropped-irrigated system predicted 69 kg ha−1 net nitrogen mineralized, but 81 kg ha−1 was measured; the corresponding values for summerfallow were 64 and 86 kg ha−1, and for cropped-dryland 36 and 52 kg ha−1, respectively. The model is not dynamic since it does not allow for No to be replenished continuously by nitrogen derived from decomposition of fresh residues and rhizosphere microbial biomass. Net nitrogen mineralized from this source might explain at least part of the underestimate predicted by the model. Other sources of possible discrepancy could be imprecision in measuring the mineralization of nitrogen and in estimating the parameters in the model. Nonetheless, it was established that one of the main shortcomings of the model was that it underestimated the amount of nitrogen mineralized whenever the soil became very dry and was then rewetted by rainfall. This was probably because the latter process resulted in large flushes in mineral nitrogen in situ while in the laboratory estimate of No and k, this effect is not adequately simulated. Key words: Q10, No, N mineralization, rate constant, temperature function

Description: A survey of the DTPA-extractable Cu levels of approximately 1000 fields representing a large number of soil types in Saskatchewan suggested that, under current cropping systems, Cu deficiencies appear to be concentrated in the Grey Soil Zone. They are especially probable in seven soil associations, which include light Transition of Grey and Brownish-Grey Podzolic soils. Soil criteria for detecting Cu deficiencies in cereal crops cannot be fully documented using conventional calibration tests and techniques. However, data from 21 field trials and a growth chamber study indicated that the critical level of DTPA-extractable Cu in these soils is approximately 0.4 mg∙kg−1 for cereals. Large spatial variability of DTPA-extractable Cu levels has been found to occur in a level field, thus suggesting that the Cu status of a field may not be adequately described by assessing the Cu levels of composite field samples. Key words: DTPA-extractable Cu, soil survey, critical level, spatial variability

Description: The thermal stability and acidic characteristics of Al interlayered montmorillonite were affected by citric acid which was present during its formation. Perturbation to the formation of Al interlayers by citric acid resulted in more gradual loss of their structural water in the 430 °C to 520 °C region at initial citric acid/Al molar ratios of 0.1 and 0.5. The data clearly reveal that, besides hydroxy-Al polymers, hydroxy-Al-citrate complexes adsorbed on the surfaces of montmorillonite very substantially contribute to the total and third buffer range titratable acidity of the clay. Key words: Hydroxy-Al-citrate interlayers, smectite, organic acid, DTA, third buffer range, organic carbon

Description: To investigate the content of amorphous forms of Fe, Al and Si in podzolic soils, the B horizons from 54 Humo-Ferric Podzols and 24 Eluviated Dystric Brunisols were sampled in northern Ontario. Dithionite-citrate-bicarbonate (DCB) Fed and Ald, acid NH4-oxalate Feo, Alo and Sio, Na-pyrophosphate Fep, Alp and Cp and NaOH-tetraborate Fet and Alt were determined on all samples. Feo/Fed ratios averaged 0.87 and suggested that most of the extractable Fe was amorphous. Inorganically bound Fe and Al in pyrophosphate extracts were estimated by addition of NH4OH to the extracts. The amount of inorganically bound Fe, expressed as a percentage of that extracted by DCB, was calculated at 79 ± 23%, whereas the corresponding value for Al was 61 ± 20%. (Alo-Alp)/Sio atomic ratios, plus linear correlation analysis of (Alo-Alp) against Sio, suggested the presence of amorphous aluminosilicates with Al/Si ratios approaching 3. (Feorg + Alorg)/Cp ratios averaged 0.10, a figure near the value suggested by other authors for the maximum amount of Fe and Al bound to organic matter. (Cp/(Fep + Alp) atomic ratios did not appear to be useful in differentiating Podzolic from Brunisolic soils. Key words: Podzolic soils, chemical criteria, extractants

Description: Subsoil moisture accumulation due to cultivation and particularly summerfallowing is considered as an important causative agent of dryland salinity. However, few studies have been conducted to quantify the magnitude of this accumulation. The amount of additional moisture that had accumulated under cultivated land as compared to adjacent native prairie was determined at two sites in Southern Alberta. In comparison to noncultivated sites, a total of 74.0 cm of additional moisture was found under the cultivated area of a Dark Brown Chernozem and 36.2 cm under a Brown Chernozem to a depth of 6 m. Only relatively insignificant changes in salt content were found. Key words: Dryland salinity, soil moisture, soluble salts

Description: Repeated freezing and thawing of glacial till cores of clay loam texture results in the formation of granic and metafragmic microfabrics. These units of fabric are best developed near the surface of cores kept at moisture levels between field capacity and saturation. Well-sorted lacustrine sediments with fewer voids tend to form banded fabrics. Many of the morphological features such as vesicles, metavughs and desiccation cracks commonly attributed to freeze-thaw processes are evident in all materials tested. Discrete units of fabric observed in this study are very similar to units of fabric observed in the Ah horizons of Black Chernozemic and Cryosolic soils. Results of this investigation strongly support earlier research which suggests that frost processes are major contributors to their microstructural development. Key words: Granic, freeze-thaw, microfabrics

Description: Response of spring wheat (Triticum aestivum) to varied amounts of broadcast and band-applied phosphorus (P) was examined at soil temperatures of 10, 15, 20 and 25 °C. The research emphasized the response of shoot yields with time and the root proliferation in the band-applied P. A non-destructive technique to measure growth with time was developed. This method allowed interpretation of plant responses even though the temperature treatments markedly changed the rate of physiological development. The relative plant-shoot response to P application did not change with time or developmental stage in this experiment. There was a marked effect of temperature on plant response to band-applied P. Band application was more efficient than broadcast P at 10 °C soil temperature, but less efficient at 25 °C soil temperature. Root proliferation in the fertilizer band was significantly different from the control soil-zone only at 10 °C and was not diminished by concurrent application of broadcast P. The efficiency of band application was confirmed with 32P labelling of the banded P. Banded P accounted for more of the total plant P at lower soil temperatures than at higher soil temperatures, regardless of concurrent application of broadcast P. Temperature had little effect on yield response to broadcast P at the final sampling or throughout the growth period. Tissue P concentrations decreased with increases in temperature and with time. Key words: Temperature, root proliferation, band, broadcast, phosphorus

Description: Although corn (Zea mays L.) stalks contribute to the total quantity of organic material in soil, their direct influence on soil structural stabilization may be small. In a laboratory study 14C-labelled corn stalks were placed on the surface of, or buried at, a 5-cm depth in a sandy loam soil. The soils were incubated at 25 °C for 119 d to determine the extent of organic carbon redistribution. Approximately 70% of the buried stalk carbon and 90% of the surface stalk carbon remained in the soil after incubation. Most of the residual carbon was identifiable as stalk tissue. Less than 5% of the added carbon was intermixed with the soil. Both the lack of C redistribution in the soil and the high loss of the mineralized 14C as CO2 stress the importance of the initial distribution of added organic materials in soils. The results imply that corn stover is a poor source of soil C and that it would be best used as a surface protectant against raindrop impact. Key words: Carbon mineralization, carbon redistribution, corn stalks, soil structure

Description: Wheat (Triticum aestivum L.) was grown in rotation with maize (Zea mays L.) and soybeans (Glycine max L.) as first crops at the National Irrigation Research Station, Nanga, Zambia. Two nodulating soybean cultivars used in the first season of the rotation were compared for their ability to support symbiotic N2 fixation by Bradyrhizobium japonicum using a nonnodulating cultivar as a reference crop and the 15N isotope dilution technique. All first crops received two levels of P (0 or 30 kg P ha−1). The legumes received a blanket application of 20 kg N ha−1, whereas maize received two rates of N (20 and 60 kg N ha−1). There were no benefits of residual P from the first crops to the succeeding wheat. However, the yields of wheat grown on plots where fixing legumes had been grown the previous season were significantly higher than those where maize had preceded. The superior wheat yield in the soybean-wheat rotation over the maize-wheat rotation was attributed to residual N from biological N2 fixation by the preceding legume crop. The benefits were greater when the lower yielding soybean cultivar preceded wheat in the rotation presumably due to its lower soil N demand. Key words: 15N isotope dilution, B. japonicum, N fixation, residual P, residual N, crop rotation

Description: A good statistical relationship was obtained between the exchangeable-sodium ratio and the sodium adsorption ratio (SAR) in Brown Solonetzic and associated soils in southern Alberta. Reliable estimates of the exchangeable-sodium status of these sulfate-rich soils may be anticipated when SAR values are less than 20. Prediction of the exchangeable-sodium status of soils on the basis of SAR values is preferable for both Solonetzic soil and irrigation suitability classification. A saturation extract SAR value of five in the B horizon generally corresponds to an exchangeable calcium to sodium ratio of 10. Saturation extract SAR values of five and 12 are recommended as revised soil chemical criteria for Brown Solonetzic soil and irrigation suitability classification, respectively. Key words: Solonetzic soils, exchangeable cations, sodium adsorption ratio, selectivity coefficient, irrigation suitability

Description: Field and growth chamber experiments were conducted to evaluate the short-term effects of selected crops on macro-aggregation of a Kamouraska clay soil. Under field conditions, the growth of barley (Hordeum vulgare L.) and alfalfa (Medicago sativa L.) for up to 2 yr resulted in increased macro-aggregate size and stability compared to a fallow control and to initial conditions. Under these two crops, the proportion of water-stable aggregates of the 2- to 6-mm fraction increased from 25% in May 1986 to 40% in September 1987 at the expense of the 0.25- to 1.0-mm fraction which decreased from 37% to 19% over the same period. Macro-aggregation after 2 yr was not different in corn (Zea mays L.) and fallow control. Seasonal variations in aggregate stability were significant but small and less important than the effects of cropping treatments. Results of the growth chamber experiment agreed with those obtained under field conditions suggesting that controlled environment experiments can be used to model cropping effects on the aggregation of this soil. Key words: Aggregation, soil structure, clay soil, corn, barley, alfalfa

Description: Mean and dominant tree heights were determined on 28 sample plots within 18 jack pine (Pinusbanksiana Lamb.) plantations varying in age from 6 to 16 years. An average dominant tree was removed from each plot for stem analysis. The height versus age data were used to determine 2-, 3- and 4-year growth intercepts in each sample tree. Growth intercepts were positively correlated with foliar concentrations of nitrogen, phosphorus, and potassium, total nitrogen concentration in the main rooting layer of the mineral soil, as well as soil physical parameters associated with good drainage. Depth of forest floor and Ae horizon, clay content, bulk density, and drainage class were negatively correlated with growth. Close correlations were also revealed for site occupancy by ericaceous ground cover species and growth intercepts. The numerous site variables included in this study were reduced to five factors with significance to jack pine growth: (i) ericaceous cover – forest floor, (ii) drainage, (iii) extractable P, (iv) exchangeable K, and (v) Ae horizon development.

Description: A factorial experiment was used to examine the effects of soil temperature, brush competition, and fertility on the postplanting growth and development of white spruce (Piceaglauca (Moench) Voss) and white pine (Pinusstrobus L.) on a clear-cut forest site at the Petawawa National Forestry Institute. Environmental monitoring was used to confirm that soil temperature treatments were effective and that the brush competition treatments caused significant (α = 0.0001) differences in photosynthetically active radiation at tree level. On the basis of foliar analysis, both fertilization and brush control improved nutrient availability to the planted trees. Owing to adequate, well-distributed precipitation, soil moisture tension was not greater than 0.6 bars (1 bar = 100 kPa) in any treatment during the growing season. Growth response by both species was dominantly controlled by the soil temperature factor. Fertility produced secondary benefits to white pine, and brush control had secondary benefits to white spruce. Examination of a developmental sequence of height growth, leaf length growth, basal area growth, and terminal bud mass indicated that soil temperature treatments were beneficial throughout the growing season, that brush control was important only in late season, and that fertilization had slight negative effects in early season but a positive effect by late season. Developmental features also indicated that soil temperature effects were manifested by reduced shoot and needle extension in the trees, competition effects by reduced availability of light, nutrients, and moisture, and fertilizer effects by increased foliar element concentrations.

Description: Logging residue decomposition rates were determined in four conifer forest ecosystems in the State of Washington, U.S.A. (coastal western hemlock, Puget lowland Douglas-fir, high-elevation Pacific silver fir, and eastern Cascade ponderosa pine), by examining wood density changes in a series of south-facing harvest areas with residues of different ages. Decomposition rates were determined for two diameter classes (1–2 and 8–12 cm) and two vertical locations (on and 〉20 cm above the soil surface). Pacific silver fir and ponderosa pine ecosystems had the lowest k values (0.005 and 0.010 year−1, respectively) followed by Douglas-fir (range, 0.004–0.037 year−1) and western hemlock (range, 0.010–0.030 year−1). Small-diameter residues decomposed at rates significantly slower than large-diameter residues in Douglas-fir and western hemlock ecosystems; this relationship was also implied in the other ecosystems. In all four ecosystems, dry season moisture contents were lower in smaller-diameter residues. Moisture levels associated with small-diameter residues were too low for significant decomposition to occur during the dry summer period and probably contributed to the slow annual decay rates. Residues located above the soil surface decomposed significantly slower than residues on the soil surface only in the Douglas-fir ecosystem. Dry season residue moisture, rather than initial lignin concentration, appeared to be the dominant factor determining residue decomposition rates on exposed harvested areas.

Description: The importance of microrelief in relation to mass loss was studied in a Minnesota ombrotrophic forested peatland. Litter and paper strips placed in hummocks for 1 yr lost significantly more mass (two and three times, respectively) than similar material placed in hollows. Less favorable environmental conditions for decomposition, especially lower temperature, reduced decomposition in the hollows. Key words: Peatlands, ombrotrophic, decomposition, Histosols

Description: The objective of this study was to evaluate different available P extracting methods in relation with soil properties, oat yield and plant P uptake. Six chemical extractants (Bray-1, Bray-2, new Mehlich, North Carolina DA-4, DA-10, and Olsen) and two anion exchange resins (F− and HCO3−) were compared on 42 acid soils. The DA-4, DA-10, new Mehlich, and HCO3− resin methods showed the best correlation with oat yield and plant P uptake. The Bray-1, Bray-2 methods were significantly less correlated than the other methods. The HCO3− resin was better than F− resin to predict plant P uptake and yield. Available P levels as determined by these eight methods were classified poor, medium and rich by the Cate and Nelson procedure. Oxalate extractable Al, pH (NaF), pH (H2O), exchangeable (Ca + Mg), forms of P, maximum P fixation capacity and soil texture have great influence on the plant P uptake. Soil organic matter content and oxalate-extractable Fe had significantly less important an effect. The Bray-1 and Bray-2 methods were the most affected by soil properties especially oxalate-extractable Al. The P-HCl/P-DAF ratio proposed by Mehlich to identify forms of soil P indicated that seven soils contain predominantly Ca-P and 21 soils with predominantly Al-P and Fe-P. This ratio was related with oxalate extractable Al (r = − 0.32*), pH NaF (r = − 0.59**), pH H2O (r = 0.52**) and exchangeable Ca + Mg (r = 0.55**). The maximum P fixation capacity (M) ranged from 150 to 4200 μg P/g soil and was closely related with oxalate-extractable Al (r = 0.81**), pH NaF (r = 0.74**), pH H2O (r = − 0.36*) and Mehlich ratio (r = − 0.33*). The maximum P buffering capacity (Mb) of soils was also measured and showed the best correlation with oxalate-extractable Al (r = 0.84**) and pH NaF (r = 0.53**). Key words: Soil testing, available P, anion exchange resins, P fixation, oxalate-Al, forms of P

Description: Three field experiments were undertaken over a 2-yr period to compare the response of winter wheat to fall-applied large urea granules containing a nitrification inhibitor (dicyandiamide, DCD) with that of commercial urea granules (prills) applied as a top dressing in the spring. The objective was to determine the effectiveness of large urea granules coupled with DCD in conserving N when applied at planting or one month after planting. Granules of 1, 2 and 3 g urea as well as 2 g urea + DCD were compared with commercial urea prills at an application rate of 80 kg N ha−1. Large urea granules, as compared with fall-incorporated commercial urea prills, were effective in conserving N over the winter period especially when applied 1 mo after planting and resulted in yields and apparent N recovery similar to those with top dressed commercial prills applied in the spring. Incorporation of DCD into 2-g granules (50 or 100 g kg−1 urea) further increased the conservation of N fertilizer as reflected by higher yields and greater apparent fertilizer N recovery. Uptake of 15N from 2-g urea granules decreased with distance from the granule. However, plants furthest from spaced large granules were able apparently to obtain sufficient N to reach the yield potential dictated by the weather and soil conditions. Yield and N recovery data indicated that N conservation increased with increasing granule size. Crop response and fertilizer N availability decreased as depth of placement exceeded 10 cm. Placement between the 5 and 10 cm depths appeared to maximize fertilizer N availability. It was concluded that a combination of large urea granules and a nitrification inhibitor (such as DCD) can effectively conserve fall-applied N and result in yield responses and N uptake by winter wheat similar to that with commercial urea prills applied as a top dressing in the spring. Key words: Time of application, yield, 15N recovery, apparent fertilizer N recovery

Description: Numerous techniques for measuring near-surface soil moisture with a neutron probe have been reported. Placing the neutron probe horizontally on the ground surface within a hydrogenous shield has been discussed theoretically, but field adaptations have not. Such a shield was designed and used, yielding measurements of near-surface soil moisture quickly and accurately. Key words: Neutron probe, soil surface moisture, calibration

Description: The relationships among the spatial variations of soil water content, soil texture, soil solution electrical conductivity, and bulk soil electrical conductivity were examined for a field characterized by net drainage and low concentrations of dissolved electrolytes. Bulk soil electrical conductivity was measured over various depths at 52 locations within a 1.8-ha field using noncontacting electromagnetic inductive meters. Soil water content (0–0.5 m depth) was measured at the same locations using the time domain reflectometry method. Measurements of soil texture and soil solution conductivity were obtained from core samples from 37 of the sampling locations. Soil water content at the site ranged from 0.06 to 0.36 m3 m−3. Clay content ranged from 2.5 to 44% percent and bulk soil electrical conductivity ranged from 0.0 to 0.21 S m−1. Significant correlation existed among almost all of the measured variables. Regression analysis indicated soil solution conductivity had no effect on measured bulk soil electrical conductivity for soil water contents less than 0.25 m3 m−3. Bulk soil electrical conductivity explained 96% of the spatial variation of soil water content independent of a wide range of soil texture. Autocorrelations of soil water content were similar to autocorrelations for bulk soil electrical conductivity. Under conditions similar to those in the study area, it should be possible to infer spatial variations in soil water content quickly by measuring bulk electrical conductivity using noncontacting electromagnetic inductive meters. Key words: Spatial variability, soil water, electrical conductivity, soil texture

Description: Mean annual rates of calcium carbonate removal from soils in a subarctic climate estimated from data on two chronosequences of calcareous storm ridges, appeared to be relatively constant through time. Concentrations of dissolved calcium carbonate in the soil solution in the study sites calculated from the rates of weathering of CaCO3 and of water drainage are in the range expected for equilibrium with calcite. The same conclusion could be drawn from published studies elsewhere. Over a wide range of conditions, the dissolution rate of calcite appears to be high enough to maintain equilibrium concentrations in water percolating calcareous soils and rocks. Consequently, the rate of calcium carbonate weathering can be predicted from (1) the solubility of CaCO3 and (2) the water drainage rate. Key words: Calcium carbonate weathering, soil chronosequence, subarctic soils

Description: A micropenetrometer with a diameter similar in magnitude to that of a root is capable of measuring variations in tip resistance over distances as small as 0.1 mm. Measurements at this scale offer the potential of characterizing zones of high resistance to penetration and the frequency of occurrence of zones of low resistance which could be exploited by a growing root. Spectral analysis provides a new approach to characterizing soil structure and has been applied to the micropenetrometer tip resistance profiles obtained from beds of aggregates. Nine different aggregate size ranges were considered; the aggregate diameters varied from less than 0.36 mm to 6.4–12.8 mm. The analyses indicate that larger aggregates are more resistant to penetration. In addition, comparison of variance spectra among several of the aggregate sizes reveals information on the structural make up of soil aggregates, namely that larger aggregates are made up of smaller "component" aggregates which offer higher resistance when they occur in large aggregates than when they occur individually in loose packing. The use of spectral analysis also appears to provide information on the spatial separation of zones of low resistance which correlate with aggregate size if the aggregate diameters are larger than 1.6 mm. Key words: Soil strength, soil resistance to penetration, micropenetrometer, aggregate size

Description: Information on rates of change of the structure of different soils under different cropping systems is vital to research in soil conservation. Much data on soil structure cannot be used to provide information on rates of change because of an inability to relate measurements at a given time to cropping history. A conceptual model is presented which facilitates quantification of cropping history in relation to soil structure. The model relates structural form, structural stability, stabilizing materials, biological factors and forces which may be exerted on the soil. Soil and crop management practices influence the nature and magnitude of forces involved, biological factors, and the level of stabilizing materials. The model is applied, for illustrative purposes, to five different cropping treatments involving the production of corn and bromegrass grown for different lengths of time over a 15–yr period. Functions to describe the accumulation or loss of stabilizing material under the two different cropping systems are assumed and functions describing the relations between calculated levels of stabilizing materials and structural stability, and between structural stability and structural form are then presented. The model provides a framework for expressing the impact of soil and crop management practices on soil structure and includes variables which could be used for assessing the "quality" of soil under current conditions. It also provides a method for characterizing the susceptibility of soils to structural change arising from soil and crop management practices. Extensive research is required to evaluate the model, however potential applications justify the effort which will be required. Key words: Tensile strength, wet aggregate stability, compaction index, corn, bromegrass, soil conservation

Description: The response of grain corn (Zea mays L.) to applied K was studied for 10 yr on three southern Ontario soils. On a Conestogo L, the most profitable rate of K application was 2.5 times higher than expected and the critical concentration of NH4OAc-K, above which no response occurred to either applied K or increasing NH4OAc-K concentrations, was higher (2 ×) than expected, based on 1 M NH4OAc-extractable K and interpretation by the Ontario Ministry of Agriculture and Food soil test. All soils fixed substantial quantities of applied K, but the amount fixed by the Conestogo L was not greater than that fixed by the other two soils. When no K was applied, corn removed less nonexchangeable K (NEK) from the Conestogo L than from the other two soils. A greenhouse experiment was conducted to determine if either the availability of NH4OAc-K or NEK to alfalfa (Medicago sativa L. 'Banner') was lower on highly responsive soils than on less responsive soils. By the end of the experiment, soils on which crops were very responsive to applied K (Guelph L, Conestogo L, and Teeswater SiL) had supplied less K to alfalfa than had soils (Brookston L and Fox SL) on which response to applied K in field trials was similar to that predicted by the soil test. Total K uptake was related to NEK uptake suggesting that differences in the K-supplying capacities of the soils were associated with the availability of NEK to alfalfa. It was concluded that the responses to higher rates of applied K than expected in field trials were due to lower uptake of NEK. The clay mineralogy of the soils was dominated by illite with lesser amounts of vermiculite. No appreciable differences in mineralogy were found between the two groups of soils and NEK uptake was not significantly related to the amount of clay nor to the illite content of the coarse clay and fine clay fractions. Key words: NH4OAc-K, nonexchangeable K, illite, vermiculite, alfalfa, corn

Description: The effects of humus on plant metabolism are conditioned by the release of the hormone-like activities contained in HEf bound to HSp. HEf and HSp are both humic fractions that can be separated from each other by acidification with acetic acid or other organic acids. HEf is composed of small molecules and shows hormone-like activities; HSp possesses higher molecular weight and works as a support for HEf. The molecular sizes of the separated HEf and HSp are both low enough to permit root absorption. The dispersion and solubilization of humic molecules are essential to the release of cytokinin-like activity from HSp, but are only preliminary to the release of auxin- and gibberellin-like activities. These can be released by a partial acidification of the humic extracts that do not result in complete depolycondensation. The process appears to regulate the delivery of the hormone-like substances and is influenced by their particular arrangement in the humic aggregate. Key words: Humus fractions, biological effect, nitrate uptake, hormone-like activity

Description: Soil-erodibility indices were investigated in two regions of Ontario to evaluate their seasonal variation and differences between soil types. Shear strength and water-stable aggregates 〉0.5 mm were strongly negatively correlated with gravimetric soil water content for a Guelph sandy loam soil in southwestern Ontario. Similar variation of shear strength was estimated in three other southwestern Ontario surface soils as a result of seasonal changes in moisture content. Shear strength and aggregate stability increased as four eastern Ontario soils, ranging in texture from loamy sand to clay, dried and warmed following spring thaw. Laboratory incubation at constant temperature and water content showed that shear strength increased in two fine-textured soils with increasing degree days but changed very little in two coarse-textured soils. At the point-of-thaw in the field, all of the eastern Ontario soils exhibited very high values of the indices 1/shear strength and 1/aggregate stability, averaging approximately 15 times those of early July. During spring fallow and seed-bed to 10% canopy periods, the mean values of these indices were 3.7 and 1.4 times, respectively, those in early July. For winter-thaw conditions in the three southwestern Ontario soils, the index 1/shear strength averaged 17 times greater than in the summer. Spring values of this index averaged approximately twice those of summer. Results suggest that Ontario soils are much more susceptible to erosion under thaw and spring conditions than later during the growing season. Soil water content and soil warming may affect the re-establishment of resistance to erosion in soils rendered erodible by freezing, thawing, and saturation. Key words: Erodibility, shear strength, aggregate stability

Description: The rapid increase in anhydrous ammonia use in Western Canada has created concerns about possible detrimental soil effects, particularly solubilization of organic matter. Anhydrous ammonia was injected at rates of 0.206, 0.416 and 0.834 g NH3-N into undisturbed soils taken in 20-cm-diameter cylinders. Both field capacity (FC) and permanent wilting point (PWP) moisture contents were used. Samples were taken at 0–2.5, 2.5–5.0, 5.0–7.5 and 7.5–10.0 cm from the injection point, 1 day after injection. For the 0.416 g NH3-N rate samples were also obtained 35 days after injection. Soluble organic carbon (SOC) was measured in a 1:15 soil:water extract. The SOC was closely related to the NH4+-N concentration (r2 = 0.79 to 0.99; P 

Description: In the early 1980s, an internal Agriculture Canada review, carried out as a result of a request from the Province of Saskatchewan, indicated a need to determine whether there were any sites in the Province that posed a possible B toxicity problem. The soil and irrigation water quality (SAR, pH, EC, B concentration) and the B content of alfalfa (Medicago sativa L.) were assessed at 29 irrigation projects in Saskatchewan. Langmuir and Freundlich B adsorption equations were determined for another 13 soils that allowed assessment of the effect of soil zone and texture on these relationships. It was found that, except for a few locations where crops sensitive to B may experience some problems, water quality with respect to B was acceptable for most projects. The survey showed that salinity posed more of a threat to production under irrigation than did B toxicity. Boron toxicity was closely associated with salinity problems. Freundlich equations described the data for the 13 soils best; K values ranged between 0.24 and 2.04. These values were not affected by soil zone; coarse-textured soils had K values less than 0.5 and fine-textured soils values greater than 1.5. Data presented in our study can be used to determine where the irrigation practice of individual irrigation projects in Saskatchewan is appropriate for maintaining proper salt balance in the soils so as not to impede plant growth. Key words: Boron toxicity, alfalfa, SAR, Freundlich isotherm

Description: A kinetic process was investigated by which H+ ions interact with soil surfaces giving rise to a positive electric charge distribution. A two-step process took place in the range of time examined. A first rapid step was always followed by a relatively slower step, and a first-order kinetic equation was applied to describe this second step of the process. The values of specific rate, calculated at different initial H+ ion activities and two different amounts of soil, indicated that a diffusion-controlled mechanism was governing the rate of the slower step and consequently the overall rate of the process. Protonation and deprotonation specific rates were also calculated in the presence of varying concentrations of supporting electrolytes. It was found that the specific rate was dependent on either the structure of the electric double layer formed on soil surfaces in the presence of electrolyte, or on the particular surface electric charge distribution of the examined soil. Key words: Protonation kinetics, specific rate, diffusion phenomena, permanent charge, pH-dependent charge, diffuse double layer

Description: An undisturbed site under forest cover near Breton, Alberta, was chosen to study the dynamics of a Gray Luvisol. Soil moisture and temperature were monitored at selected depths over a 2-yr study period. Canopy drip collectors and gravity lysimeters were used to study soil solution transport and the process of lessivage. The order of cation concentration for canopy drip, LFH and Ae lysimeter samples was K+ 〉 Ca++ 〉 Na+ 〉 Mg++. The lysimeter samples from the Bt showed Na+ 〉 Ca++ 〉 K+ 〉 Mg++. Lysimeter studies further indicated that micaceous clays were being illuviated into the upper Bt horizon. Water movement into the Ae horizon was found to be regulated by the LFH horizon; ice lensing in winter appeared to enhance the formation of the platy structure. The major processes in this soil are the translocation of Fe, Al and organic constituents both in solution and in colloidal form; the concentration of these elements was a function of the rate of water movement. The concentration of other cations was independent of the rate of water movement. Key words: Genesis, pedogenesis, Gray Luvisol, dynamic pedology, clay migration, lessivage, illuviation

Description: Horizontal Ksat was estimated as one of eight classes according to guidelines based on soil morphology and then measured by a piezometer method in soils of the Ottawa area that differed widely in texture and structure. The Ksat class estimated by two observers was either the same as, or one class different from the measured class for 14 and 16 of 18 layers tested (average 83%). Measured horizontal Ksat exceeded vertical Ksat by a factor of 9 in some sandy layers with strata of relatively coarse material. Measured vertical Ksat exceeded horizontal Ksat by a factor of more than 3 in some layers having numerous more-or-less vertical earthworm channels. Horizontal Ksat of the layers measured ranged from 0.3 to 14 m∙day−1 and vertical Ksat values for those layers ranged from 0.1 to 27 m∙day−1. Guidelines for estimating horizontal Ksat were revised on the basis of results from this study to give more emphasis to stratification. The results support the view that adequate estimates of vertical and horizontal Ksat can be made rapidly from the observation of soil morphology if specific guidelines are followed. The guidelines are based on relationships between soil morphology and measured Ksat values. Key words: Horizontal Ksat, vertical Ksat, soil morphology

Description: This study describes a number of different preparation techniques for recording solid state 13C NMR spectra of whole mineral soils. Removal of paramagnetic Fe3+ improves the quality of 13C NMR spectra of whole soils and of particle size fractions. The C:Fe ratio appears to be an important indicator for obtaining satisfactory 13C NMR spectra of whole soils and fractions separated from them. If the C:Fe ratio is 〉〉 1, the quality of the spectrum will be good; if the ratio is 〉 1, a reasonable spectrum will be obtained, but if the ratio is

Description: Crop yields and heights and soil chemical properties on and immediately adjacent to an oil pipeline right-of-way (ROW) were monitored over a 10-yr period. Effects of soil mixing on chemical properties were still apparent despite good crop management. With the exception of alfalfa, field crop yields on the ROW were reduced by an average of 28% 10 yr after installation. Key words: Soil mixing, degradation, crop heights

Description: Aggregates (1–2 mm) from a soil under continuous corn management were subjected to a mild shaking treatment and ultrasonic energy levels ranging from 100 to 1500 J mL−1 water to determine the degree of aggregate disruption and dispersion. More clay- and fewer sand-size particles were recovered with greater amounts of applied energy indicating greater aggregate disruption and dispersion with higher energy levels. Most of the breakdown of sand-size aggregates occurred between energy levels of 300 and 500 J mL−1. Ultrasonic energy levels of 500 J mL−1 or greater were more effective than using 20% hydrogen peroxide plus 16 h of shaking in dispersing sand-size microaggregates. Surface area measurements of the clay indicated no severe fragmentation or alteration of primary particles had occurred. With increased applied ultrasonic energy and more complete dispersion, the amount of organic C recovered increased in the clay- and decreased in the sand-size fractions. At complete dispersion, there was no evidence of redistribution of organic matter by ultrasonification and the sand-, silt- and clay-size fractions contained 5, 30 and 60% of the soil organic C. Results of this study suggest that ultrasonic dispersion techniques can be used as a physical method to separate microaggregates from soil and thereby study the nature of organic matter within them. Key words: Ultrasonic dispersion methodology, aggregates, organic matter distribution, particle size fractions

Description: Soil ammonium and nitrate in the top 15 cm of soil were monitored after application of ammonium nitrate and ammonium sulfate to plots at 14 PF (previously fertilized) and 12 NF (never fertilized) lowbush blueberry (Vaccinium angustifolium Ait.) stands representing a range of soil types and management histories. Overall, nitrate values in unfertilized and ammonium sulfate plots were higher at PF than at NF sites, suggesting greater nitrification at PF sites. In laboratory incubation studies, nitrification proceeded immediately in soil from a PF site, but only after a 4-wk lag in that from an adjacent NF site. Nitrification rates were low compared to that in a garden soil (pH 6.6). N-Serve inhibited nitrification in both soils. In ammonium nitrate plots, "excess" N values (N values in fertilized plots minus values in unfertilized plots) were higher for PF than for NF sites, suggesting greater immobilization, plant uptake or loss of N at NF sites. There was no evidence, in laboratory studies, of immobilization of added N by soil from either type of site. Rhizome N concentration increased significantly in response to fertilization at an NF site, but not at a PF site. Key words: Blueberry (lowbush), fertilizer and soil nitrogen

Description: The effects of rhizobium inoculation, vesicular-arbuscular mycorrhizal (VAM) fungi and seed-applied captan on field bean growth and N2 fixation were studied under greenhouse conditions. 15N isotope dilution methods were used to measure N2 fixation in a soil containing indigenous Rhizobium phaseoli. Inoculation of rhizobia onto host plants increased N2 fixation by 50 – 82 mg N per plant compared with uninoculated controls. The incidence of nodulation was also increased by R. phaseoli inoculation. Addition of VAM to the soils increased bean dry matter production by 9 – 54% over plants not receiving VAM, and increased the N2 fixed by rhizobially-inoculated plants by 4 – 27 mg N per plant. VAM addition resulted in greater uptake of soil N by the plants. Inoculation of captan-treated field beans with inoculum derived from a captan-tolerant strain of R. phaseoli did not result in improved N2 fixation rates compared with inoculation with the nontolerant parent strain. Seed-applied captan reduced the proportion of nodules formed by both strains of added rhizobia, but did not result in decreased amounts of N2 fixed by the root systems. Captan did not reduce the effectiveness of VAM. Key words: Rhizobium phaseoli, captan, VA mycorrhizae, N2 fixation, 15N

Description: Molybdenum, Co and B concentrations in, and uptake by, corn and bromegrass were measured over a period of several years from three field experiments in which sewage sludge was applied and compared with ammonium nitrate as a source of N. There was little effect of sludge on B and Co concentrations in the crops grown. Slight increases in uptake were apparently due to yield increases due to sludge. A lime-treated sludge increased Mo concentration in plant tissues after several years of sludge application. The increase in plant Mo concentration was highest in the eighth and last year of the experiments, although lime-sludge application had ceased 1–3 yr previously. The soil-sludge interactions contributing to increased Mo uptake are discussed. Key words: Molybdenum, cobalt, boron, sewage sludge, corn (Zea mays L.), bromegrass (Bromus inermiss Leyss).

Description: The Versatile Soil Moisture Budget (VSMB) and the Soil-Plant-Air-Water (SPAW) model were compared and tested against soil-water content data from a long-term experiment in which wheat was grown on fallow land in the semi-arid zone of Saskatchewan. Both models were driven by daily air temperatures and precipitation data. At the expense of requiring more detailed soil and crop information, the SPAW model simulated the water balance and its components in greater detail than the VSMB. Predictions of soil-water contents throughout the growing season with either model corresponded very well with the measured data. The overall mean absolute difference in total soil-water content to a depth of 120 cm was 1.5 cm for the VSMB and 1.2 cm for the SPAW model. Predictions of water distribution in the profile were also satisfactory. A choice between the two models, to be used under semi-arid growing conditions, will depend on the availability of input data and the required level of output. Key words: Soil-water movement, modelling, evapotranspiration

Description: Available water-holding capacity (AWC) maps of Alberta, Saskatchewan and Manitoba were derived from Soil Landscape maps (1:1 million scale) by substituting AWC classes for soil textural classes. The maps provide information required for the geographical interpretation of soil water and crop modelling analyses. Key words: Available water-holding capacity, maps, texture

Description: A previous study showed that large differences in K uptake by alfalfa (Medicago sativa L.) grown in the greenhouse occurred on soils which had similar ammonium-acetate-extractable K (NH4OAc-K) concentrations at seeding. Differences in total K uptake appeared to be closely related to the uptake of nonexchangeable K (NEK). The objective of this study was to determine what fractions or forms of NEK in the soils were responsible for the large differences in total K uptake noted in the greenhouse experiment. The total amount of NEK extracted in seven sequential extractions with boiling 1 M HNO3 (Mactotal) varied widely among soils and was significantly related to the total amount of K (r = 0.69; P 

Description: In a field experiment in which heavy applications of liquid dairy manure were added annually for 6 yr to a vermiculite-containing corn-cropped sandy clay loam soil (Mountain series), fixation potential and X-ray diffraction analyses were done to determine if fixation of added K+ and NH4+ had occurred and clay mineralogical changes could be detected. Of the 850 kg K+ and the 460 kg NH4+ added per hectare each year, approximately 28% of the K+ and 24% of the NH4+ remained fixed. This caused a marked increase in the 1.0-nm peak at the expense of the 1.4-nm peak due to collapse of vermiculite layers to form pedogenic mica. Thus, changes in soil management, specifically in fertilizer practices, can result in significant changes in clay mineralogy within a short period of time. Such changes are agronomically important and should be taken into account in the interpretation of clay mineralogical data. Key words: Potassium and ammonium fixation, vermiculite to pedogenic mica transformation, liquid manure application

Description: Distilled water leaching of new alundum/ceramic plate lysimeters removed considerable amounts of Ca, Mg, Na, K, SO4, Cl and Zn. After washing with 3 L of distilled water, levels were still of sufficient magnitude to interfere with the analysis of solutions with low solute concentration. Washing the plates with 2 L of 1 N HCl extracted considerable amounts of Ca, Mg, Na and K, and higher amounts of Fe, Zn, Al and Mn, but further distilled water washing resulted in rapid equilibration with a spike solution. Rinsing new lysimeters with progressively more acidic solutions indicated residual zinc contamination when the solution pH was below 6.0. There was virtually no iron or manganese contamination from the lysimeters at a solution pH between 3.0 and 5.0. Aluminum was leached from the plates at solution pH of between 3.5 and 4.0; however, the high Al concentration in the soil solution at these pHs may mask this interference. Although Al poses a considerable contamination problem at solution pHs of 3.0, soil solutions at this pH level are unlikely except in unusual situations (e.g. soils developed on acid mine tailings). The pumping of 2 L of 1 N HCl followed by large volumes of distilled water through the lysimeters is recommended for most field studies. Prior testing of the plates is required if low solute concentrations are expected or if elements other than those mentioned here are of interest. Key words: Lysimeters, ceramic samplers, soil water collection, alundum lysimeters, soil solution

Description: Drying rates of frozen aggregates varied from 2 mg cm−2 h−1 to zero, mainly in response to decreasing water content. Temperature, windspeed and dryness of the air controlled the maximum rate of drying. The variation in drying rate with water content was explained by the balance between ice and water in the pores. Key words: Frozen soils, evaporation, environmental factors

Description: Field studies were conducted to evaluate the effect of the rate and timing of N application and the amount of seed-placed P on grain yield and protein content of winter wheat grown on zero-tilled and conventionally tilled land in Manitoba. Yield increased with increasing amounts of fall-applied N and P. Yield, as affected by time of N application, decreased in the order: spring, freezeup, seeding, and applied on snow in winter. Split application of N resulted in yields comparable to that obtained with N applied at seeding. Protein concentration in grain decreased when small amounts of N led to large increases in dry matter but increased when sufficient quantities of N fertilizer were added to meet the requirements for both yield and protein. The amount of fertilizer N recovered in the grain did not differ with time of application in 1979–1980. However, in 1980–1981, N recovery was consistently higher with spring applications of N than with applications at any other time. Differences between the two seasons reflected the higher moisture availability for crop growth in 1980–1981 as compared to 1979–1980. Key words: Winter wheat, zero tillage, nitrogen, phosphorus, protein

Description: The surface horizon from a Humo-Ferric Podzol was amended with both CaCO3, and P to investigate the changes in the ionic composition of the soil solution and the charge characteristics of the horizon. Addition of CaCO3 increased the concentrations of Ca and [Formula: see text] and decreased the total concentrations of Mg, Na, K, Al, Zn, Mn, Si and [Formula: see text] in the soil solutions. In addition, the pH of the soil solutions, the content of negatively charged sites on the soil surfaces, the relative proportion of Mn2+ and Zn2+ of sulfate ion pairs were raised. In contrast, the concentrations of exchangeable Zn and Mn, the amount of positively charged sites and the proportion of metals linked with the "modelled" fulvate ligands were reduced. The addition of increasing rates of P reduced the total concentrations of Mg, K, Al, Si, and the concentrations of [Formula: see text] and [Formula: see text] in solution but did not affect the pH or the CEC of the soils appreciably. The concentrations of Si, phosphate-P, [Formula: see text] and of the sulfate ion pairs in solution were increased by increasing P additions to the soil. Key words: Liming, phosphorus fertilization, soil solution, GEOCHEM, ion speciation