ALBERT

Notizen: Abstract. England and Wales have 155 314 1 × 1 km squares, of which 140049 have more than 50% soil cover. The total soil organic carbon content, based on the dominant soil series and dominant land cover type, is estimated to be 2773 × 106 t C. Scotland has 84929 1 × 1 km squares, of which 82 420 have a nominated dominant soil series. The total soil organic carbon content is estimated to be 19011 × 106 t C, 6.85 times the total organic carbon content of the soil of England and Wales. The total organic carbon content of the soil of Great Britain is estimated to be 21 784 × 106 t C, of which 87% is in Scottish soils and 75% is in Scottish peats.A map of the mean soil organic carbon content of 10 × 10 km squares of the National Grid using classes of equal range illustrates the narrow range of organic carbon contents of the soils of England and Wales and the dominance of organic carbon in Scottish soils. A map using the same data, but with classes of unequal ranges increasing in size with increasing carbon content, is better for showing detailed differences within England and Wales.

Notizen: Abstract. Land cover data from the June agricultural census of England and Wales have historically been published annually at the parish level. This level of spatial resolution masks heterogeneity of land use within parishes, limiting the value of the data for detailed spatial analyses. However, variation in land characteristics across parishes can be used to model variation in land cover, thereby allowing the spatial basis of the census data to be transformed. This procedure, referred to as areal interpolation, is illustrated using two land classification systems based on soils for a study area in northern England. The results indicate that the spatially transformed data offer a better description of the distribution of land covers than that provided by the raw census data. They also demonstrate the extra value that can be obtained by combining extant data sources within a GIS framework. Potential roles for areal interpolation in environmental modelling and policy formulation are discussed briefly.

Notizen: Abstract. The disposal of water treatment sludge produced when turbid water is treated with flocculants (alum and polyDADMAC) and filtered for clarification is becoming increasingly expensive in South Australia. The physical and chemical properties of the sludge suggest that it might be used as a plant growth medium, and a glasshouse experiment compared the growth and elemental composition of broad beans in both alum and polyDADMAC sludge applied at different rates.Dry matter production differed significantly between treatments. Poly + Fertilizer (F) and Poly 4%+ F produced the most dry matter. The Alum + F treatment produced significantly less dry matter than the Poly + F treatment but it was not significantly different from the control. The difference in plant growth between the pure poly and pure alum treatments resulted from increased availability of the fertilizer phosphorus in the poly sludge and the supply of some potassium and nitrogen by the poly sludge. Fertilizer was required for optimum plant growth. Greater rates of fertilizer may be required if alum sludge is to be used as a growth medium, than if poly sludge is used.There was no evidence that aluminium toxicity would be a problem if water treatment sludges are used as growth media. The physical properties of the sludges (i.e. water holding capacity, drainage characteristics and structural stability) are probably more important than their inherent nutrient levels, although poly sludge does supply some nitrogen and does not fix phosphorus to the same extent as alum sludge.

Notizen: Abstract. Soil productivity, the intrinsic ability of land to yield useful products, can be affected by soil erosion. While much research has been carried out on the processes, there is as yet little information on the impact of soil erosion on in situ productivity of agricultural land in the British Isles.This paper reports the results of a de-surfacing experiment on deep sandy soils in East Anglia. Grain yields of fertilized barley planted immediately after de-surfacing were at least 15 and 45% less on 15 and 25 cm de-surfaced plots than on non-desurfaced soils. There was strong evidence pointing to an acceleration of soil erosion itself on the de-surfaced plots. Both the amount of water stored in the topsoil and water use by the crop decreased with increasing severity of simulated erosion. We observed a drop in organic matter and readily available nitrogen with erosion. Nitrogen mineralization and leaching losses were also affected by simulated soil erosion.The experiment showed that sudden severe erosion may induce substantial barley production losses on deep sandy soils. The size and effect of de-surfacing depends on a number of factors such as soil depth, subsoil type, precipitation and crop type.

Notizen: Abstract. The objective of the present study was to investigate the potential of undersown catch crops to counteract soil degradation after autumn ploughing. Italian ryegrass (Lolium multiflorum Lam.) and white clover (Trifolium repens L.) were undersown in spring wheat on a loam soil in southern Norway, allowed to grow as cover crops after grain harvest and ploughed in to 20 cm depth as green manure in late October. Ryegrass prevented a collapse of the ridged plough furrow profile during winter, which occurred on grain monoculture and white-clover plots. Also, it tended to improve the water stability of aggregates, aggregate size distribution, bulk density, and pore volume in soil sampled in May. The preservation of the plough furrow profile was mainly attributed to enmeshment by an extensive system of fine roots and less to rhizosphere and microbial effects on aggregate stability. The results showed that ryegrass catch crops may give rapid structure improvements that are likely to contribute appreciably to easier seedbed preparation and less soil degradation in arable farming systems, even if the soil is ploughed in autumn.

Notizen: Abstract. Drainage hydrographs from mole-drained plots having different tillage treatments (tractor tined, gantry tined, tractor ploughed and gantry ploughed) were measured for different rain events over a growing season. In the autumn just after tillage, a large rainfall produced peaky drain flows on the tined plots but a rather flat response from the ploughed plots. In the winter, the drain response to a small rain event showed less differences in peak flows between the treatments. The recession time constant of the hydrographs was used as an index of the structural macropore development in the soil above the water table. Hydrographs from the gantry plots recessed more quickly than those on the tractor plots and those on the tined plots recessed more quickly than those on the ploughed plots. Lack of soil compaction on the gantry plots and continuous vertical fissuring created by the non-inverting tillage tines resulted in the gantry tined treatment having the fastest drainage response. In the ploughed plots compaction and smearing of the soil at the base of the plough layer restricted the rate of downward movemenl of water. The work indicates that soil management practices can play an important role in the drainage and leaching of aggregated soils.

Notizen: Abstract. Trafficked and non-trafficked (12 m gantry) crop production systems, which had been maintained on an Evesham series 60% clay soil since 1986, were used again in 1993 during the cultivation and sowing of winter wheat. After a one year set-aside break, mouldboard ploughing, tine cultivation and rotary digging were compared. Measurements were made of tillage energy, soil tilth, cone penetration resistance, biological activity and crop performance, and on specific plots, soil density, seedbed tilth and water release characteristics.Despite the one year's set-aside break, the effect of the previously applied traffic treatments remained and resulted in a smaller specific plough resistance and tillage energy on the non-trafficked soil. Tine cultivator draught however was greater on the non-trafficked compared with the trafficked plots. The specific energy required for rotary digging on non-trafficked soil was similar to that required during the ploughing of similar plots.A measure of indefinite biotic activity indicated that this was apparently greater on the non-traffficked soil, while soil density was decreased by up to 18% in these conditions compared with the trafficked land. Average cone resistance over the depth range 0 to 0.5 m was 1.51 MPa on the trafficked, compared with 1.24 MPa on the non-trafficked soil. Cone resistance also tended to be greater after tine cultivation compared with that after ploughing. Water release curves were interpreted as showing more macropores within the topsoil of the non-trafficked compared with the trafficked plots. Tine cultivation on trafficked soil had more smaller pores than mouldboard plough cultivation. Winter wheat yield was increased by 25% (from 8 to 10 t/ha) on non-trafficked compared with trafficked soil.

Notizen: Abstract. In field and laboratory experiments the conditioner‘Agri-SC’has shown improvements in the structure of loamy sand soils in east Shropshire, UK. It resulted in statistically significant decreases in soil bulk density values and increases in soil porosity and aggregate stability. Further experiments are in progress on both loamy sand and silt loam soils.

Notizen: Abstract. Data from 143 nitrogen (N) response trials on winter cereals carried out at sites across England during the period 1981–1988 were reviewed. Linear regression models for the relationship between optimum N requirements and soil mineral nitrogen (SMN) were evaluated. Multiple regression analyses and F tests were used to determine whether separate regression lines for different combinations of soil group and N Index, substituting for cropping history, were justified, and whether the additional terms used to account for SMN in the 30–60 cm and 60–90 cm depth bands significantly improved the regression model used to fit the data.The results indicated that optimum N requirement can be predicted from SMN 0–30 cm and 30–60 cm data. However, although the slope of the regression line does not change for different combinations of soil group and N Index, the intercept does. If no allowance is made for differences between sites which alter this intercept, the amount of variation in optimum N requirement accounted for by the regression models is considerably reduced. Factors which should be considered are mineralization of previous crop residues, organic manures and indigenous organic N, and the depth to which SMN is accessible by plant roots.

Notizen: Abstract. A laboratory study was designed to provide data on the decomposition of rape, sunflower and soyabean residues put in bags buried in soil. The residue bags were removed at intervals during 1 year, analysed for remaining total mass, organic and water-soluble C, water-soluble sugars, as well as for volatile acids and phenolic compounds. The decomposition dynamics of total mass, total organic and water-soluble organic C, and water-soluble sugars were reproduced satisfactorily by a double-exponential model of the first-order type.Generally, no large differences in the rate and magnitude of decomposition among the residues were observed; the greatest losses of both total mass and chemical components occurred in the first month of the study, during which the volatile acids and phenolic compounds disappeared almost completely. Of the three residues, soyabean showed the lowest loss of organic carbon, losing 66% of the original content over the course of the year compared with 73 and 75% for sunflower and rape, respectively.

Notizen: Book Review in this ArticleSoil Microbiology By R.L. Tate.

Notizen: Abstract. Because of the observed variability in soil available P (Olsen) contents, phosphorus budgets were used to predict changes in the soil P status of an intensively managed 6 ha grassland catchment in Northern Ireland. The P accumulation rate of approximately 24 kg/ha/y suggested an increase of soil available P (Olsen) of 1.0 mg P/kg/y. Soluble reactive phosphorus concentrations in drainflow measured on a daily basis for a two year period (January 1981 — December 1982) were compared with the two year period January 1990 — December 1991. The median concentration had increased by 10.0 μg P/1 in 1990/91 compared with 1981/82. This difference was only apparent in mean concentrations for the two time periods, after data associated with high flow events, which were more frequent in 1981/82, were excluded from the comparison. This rate of increase of 1.1 μg P/1/y, which was interpreted as reflecting an increase in soluble reactive phosphorus concentration in soil solution, is comparable to the increase in background soluble reactive phosphorus of 1.5 ± 0.54 μg P/1/y which was reported recently over a 17 year period from diffuse sources in the much larger (4400 km2) Northern Ireland catchment of Lough Neagh.

Notizen: Abstract. A long-term field experiment was initiated in June 1988 in a silty clay loam soil to investigate the potential of Lantana camara, an obnoxious weed, for improving structural properties and productivity of soil in rice-wheat cropping. Lantana was incorporated into the soil 10–15 days before puddling at 10, 20 and 30 t/ha (fresh weight).At the end of the sixth cropping season, Lantana additions increased the organic carbon (OC) of the 0–15 cm soil layer by 11–24%, and of water-stable aggregates (WSA, 0.50–8.0 mm diameter) by 10–21%; OC of WSA 〈0.50 mm diameter remained unaffected. About 17–25% of the applied OC was retained in the soil. The OC increase resulted in a decrease in bulk density of the plough layer (0–15 cm) by 7%, a decrease in aggregates of 2–8 mm diameter and of clods by 4% and 6%, respectively. There was an increase in water-stable aggregates and aggregate porosity, and a decrease in clod-breaking strength from 420 to 216 kPa. Soil cracking at the surface changed from wide, deep cracks in hexagonal pattern to a close-spaced network of fine cracks. Lantana additions increased 〈5mm wide cracks at the expense of 10–20 mm wide cracks; 5–10 mm wide cracks remained unchanged. Total volume of cracks decreased by 36% and surface area of cracks by 55% compared with the control plots.

Notizen: Abstract. Five soils from the South of England were incubated with additions of magnesium fertilizers; two also received magnesian limestone. After two years, the recovery of the added magnesium by 0.5 h extraction with 1 m ammonium nitrate was 75–89% for kieserite granules, 64–84% for calcined magnesite powder (〈 1 mm), but only 20–41% for calcined magnesite granules (1–3 mm) and 26–32% for ground magnesian limestone. These were all much greater than the Mg dissolved by extracting the fertilizers directly in 1 m ammonium nitrate.In calcareous soils, recovery of Mg was less from the calcined magnesite but most of this reduction was due to its particle size rather than to soil pH.The four magnesium sources are evaluated as fertilizers for agriculture. Kieserite is the most reliable means of raising low soil Mg status.

Notizen: Abstract. A qualitative model was used to assess the risk of S deficiency in cereals in Britain. A risk index was generated for each of 6301 soil data points by considering the inputs of S from atmospheric deposition, the content of soil organic matter, and factors influencing the potential leaching of sulphate, i.e. soil type, texture, pH and annual rainfall. The results show that currently 11% of the British land area is at high risk of S deficiency, and a further 22% at medium risk. The high risk areas are in south-east Scotland, the Scottish Borders, East Anglia, the Welsh Borders and south-west England. These agree well with the distribution of reported incidences of S deficiency in cereals. If the UK target for reduction in SO2 emissions by the year 2003 is met, the model predicts that the high and medium risk areas will increase to 23 and 27%, respectively. Thus, agricultural use of S-containing fertilizers is likely to increase in importance in the near future.

Notizen: Abstract. The effects of different sizes, amounts, and positions of rock fragments on soil properties and erosion were studied in experimental plots (10 treatments including bare soils and soils under natural vegetation, with 3 replicates each) installed on a hillslope.Over five events, the largest amounts of runoff were from bare soils containing abundant rock fragments, either partially embedded on the surface or incorporated in the upper part of the soil. Stoneless soils gave smaller amounts, and the smallest runoffs were measured on soils under natural vegetation. Generally, large rock fragments (cobbles) caused greater runoff than smaller fragments (coarse gravel). However, soils with appreciable amounts of coarse gravel on the surface generated considerable runoff under rainfalls of low intensity and long duration, but smaller amounts at greater rainfall intensities.Sediment loss was greater from soils with cobbles than from soils containing coarse gravel; vegetation greatly decreased sediment loss from both.In a 12-month period, the organic matter content of the soils decreased by 15.5 to 23.0%, decreasing soil aggregate stability. The organic matter content was greater in the collected sediments than in the soil.

Notizen: Abstract. The effects of rock fragments on soil temperature, soil moisture conservation, night time water vapour absorption and wheat biomass production were investigated. Under conditions of moderate water stress, water conservation was generally greater in the stony soils. Under conditions of pronounced drought the opposite occurred, with stony soils conserving less water than soils free of stones, though soils with large cobbles on the surface conserved the most water.Stony soils were generally warmer during daytime and cooler at night than soils free of rock fragments. In the warmest month (July) the diurnal amplitude reached 14.3 °C in the control soil and 24.1 °C in the stony soils. Night time absorption of water vapour in the upper 15–20 cm was less for the stony soil (17.8% cobble cover), than for the stone-free soil. Cobbles on the soil surface increased biomass production by increasing moisture conservation. After removing all the stones from the surface of 16 plots, total dry matter yield of rainfed wheat was on average 20% less than from plots with stones on the surface.

Notizen: Abstract. Economic land evaluation is a method for predicting the micro-economic value of implementing a given land-use system on a given land area. This is a more useful prediction of land performance than a purely physical evaluation, since many land-use decisions are made on the basis of economic value. Measures of economic suitability include the gross margin, net present value, internal rate of return, benefit:cost ratio, and utility functions based on these. The economic value of the in-situ resource quality of a land area may be inferred directly from land characteristics or from Land Qualities which, when less than optimum, result in decreased yields or increased costs. The economic value of geographic land characteristics may be determined by spatial analysis. Single or multi-criteria economic optimization and risk analysis can extend the economic land evaluation from a natural resource or management unit to a production or planning unit. Computerized tools may be used to assist in economic land evaluation.

Notizen: Abstract. A coarse urban compost, low in organic matter but mature, was tested for agricultural use. The response of Tewera ryegrass to this compost (applied at 12 and 48 t/ha) was evaluated in a field trial over two years. For a satisfactory yield the larger dose was necessary. This dose also gave greater values for the apparent recovery of N in both years. However, the N concentration in ryegrass was always below the sufficiency ranges proposed for N. The values of the potentially mineralizable N of the compost showed that the applied N at the greater rate of compost application was not sufficient to cover crop removal of N. In contrast, concentrations of P, S, K, Mn and Zn were within their corresponding sufficiency ranges. The dose of 48 t/ha did not increase Cu, Ni, Pb and Cd concentrations in the ryegrass.

Notizen: Abstract. The relationships between vegetation and acid properties of soils from a mangrove swamp in southeastern Nigeria were examined. Field moist soils were moderately acidic with pH ranging from 5.3 to 6.8. Air dry pH ranged from 2.9 to 4.9 indicating strong acidity; the values increased with profile depth and were related to decreasing fibrous root content. Less acidic conditions (air dry pH 4.3–4.9) were associated with the less fibrous soils under Avicennia africana and Pandanus candelabrum; more acidic conditions (air dry pH 2.9–3.8) occurred in the more fibrous Rhizophora spp. and Nypa fruticans soils. Species occurrences and levels of aluminium and sulphate in the profiles were related, suggesting that hydrogen ions, aluminium and sulphate were the main contributors to exchangeable acidity. Unless crops are known to tolerate very acidic conditions, the fibrous Rhizophora and Nypa soils should not be drained for cultivation.

Notizen: Book Reviewed in this article:Flame Spectrometry in Environmental Chemical Analysis: a practical guide By Malcolm S. Cresser.Soil compaction i n crop production Edited by B.D. Soane and C. van Ouerkerk.

Notizen: Abstract. The production of CO2 in the field and the contribution of carbon from crops to the soil were evaluated for the double crop wheat-soyabean rotation on a typical soil of the Rolling Pampa to assess the effects of two tillage systems, mouldboard ploughing and shallow discing, on the soil carbon balance. Microbial biomass and respiration under controlled conditions were also determined.No differences in soil microbial biomass contents were detected between tillage systems after two years, but the biological activity of incubated soils and the mineralized fraction of organic carbon were greater (P= 0.05) at the 0–5 cm depth in disc tillage. This suggested an increase in the labile fraction of organic matter in that layer, though the total carbon content of the soil did not vary significantly.Soil moisture was not a limiting factor at any time of the year and production of CO2 in the field was regulated by temperature (r 〉 0.89, P= 0.01). There were no differences between tillage systems in the emission of CO2 to the atmosphere, which was estimated at 11.6 t C/ha/yr. The contribution in dry matter from the crops ranged from 15.3 to 17.0 t/ha/yr, and the carbon input was approximately 7.0 t/ha/yr. Consequently, the soil lost carbon with the wheat—soyabean rotation but tillage systems did not affect carbon inputs and losses from the agrosystem.

Notizen: Abstract. Erosion was surveyed in Strath Earn, Scotland, following severe weather conditions during the first 18 days of January, 1993. A rapid field mapping system was devised to record the nature of erosion. A total of 208 fields was surveyed and 76 exhibited erosion. Most fields with erosional features were either ploughed or in autumn cereals. The most common form of erosion was ephemeral gullies along topographic hollows. This erosion was primarily associated with ploughed land whereas sheetwash and rill erosion occurred more on autumn sown land. Land use change and climatic variability, especially increasing rainfall over the last 20 years, account for the incidence of erosion. Individual erosion events rarely cause major problems for farmers, but the increasing frequency of erosion events raises important questions for sustainable land use in the arable areas of Scotland.

Notizen: Abstract. A forage model (FORYLD) was used to estimate average potential (constraint-free) yields (By) and yields under rainfed conditions (Bya) of alfalfa and wheatgrasses for the prairie region of Western Canada. Yield estimates were determined using 30-year climatic means (monthly values) and assumed available water-holding capacities (AWC) of soils ranging from 50 to 280 mm as inputs to the model. Calculations were made for 252 areas or zones known as Agroecological Resource Areas (ARAs) for the region. Estimates of By for alfalfa ranged from over 17.5 t/ha, in areas where three cuts of alfalfa were feasible if the crop were fully irrigated, to less than 10 t/ha in some northern ARAs where restricted length of the growing season limited potential to only one cut. For wheatgrasses By ranged from 15 to 17.5 t/ha in most areas where two cuts are possible. Estimates of Bya for alfalfa, based on the predominant AWC for soils in each ARA, ranged from less than 2 t/ha in the driest portion of the prairie region to more than 8 t/ha in the more humid areas. Yields of wheatgrasses were very similar to those of alfalfa in the driest zones but slightly more in some of the more humid regions. Effects of varying soil AWC on yield estimates are presented for the major soil groups of the prairies.

Notizen: Abstract. A 15-year field experiment investigated crop residue management practices, with crop residue removal, burning and incorporation as the main treatments and nitrogen levels as subtreatments. The effects of crop residue management practices on rice and wheat yield were measured for 11 years. Surface soil samples were taken to study nitrogen and phosphorus immobilization/adsorption and their release under laboratory conditions. The field experiment indicated that residue burning and residue removal resulted in greater grain yields of rice (5.57 and 5.53 t/ha, respectively) and wheat (4.12 and 4.02 t/ha, respectively) than residue incorporation (4.51 t/ha rice and 3.72 t/ha wheat). Laboratory experiments indicated that by the addition of crop residues nitrogen and phosphorus were converted to unavailable forms through immobilization and adsorption, respectively.Crop residue management practices were discontinued after 13 years and wheat and maize crops were grown in sequence. There were significantly greater yields of wheat (3.57 t/ha in 1992–93 and 3.6 t/ha in 1993–94) and of maize (2.1 t/ha in 1993) in plots where the residues had previously been incorporated than where the residues were previously either removed or burned. This is attributed to release of nitrogen and phosphorus from the incorporated residues.

Notizen: Abstract. Statistical techniques are used to test and re-interpret archival data from soil surveys of the tidal floodplain of the River Gambia. Key soil attributes include salinity, ripeness and the acid sulphate hazard. Soil taxonomic units derived by cluster analysis of all the validated data do not correspond with the intuitively-defined soil series of the original surveys. However they do correspond with practical soil mapping units, and distinguish areas of quite different geotechnical behaviour, kinds and degrees of salinity and acid sulphate hazard.

Notizen: Abstract. The effects of silt-laden Yellow River irrigation water on the properties of reclaimed dune sands were investigated at the Shapotou Research Station in Ningxia Autonomous Region, China. The practice resulted in distinct and rapid improvements in the physical and chemical properties of reclaimed desert soils. Irrigation led to the development of sandy loam topsoils, with up to 39 cm accumulating over 25 years of treatment. These topsoils had improved structure, greater soil organic matter contents and smaller bulk densities than buried desert sands. Geochemical analyses suggested river silt and sheep manure were making distinctive contributions to the improved soil fertility, with older topsoils having progressively greater concentrations of Ca, Mg, K, P, S, Fe, Mn and Zn. Soil Cr concentrations are increasing and it seems appropriate that changes in heavy metal concentrations in irrigated soils are monitored.

Notizen: Abstract. Changes in soil physical and chemical properties associated with different land uses including natural savannah were compared in Nigeria. The study was conducted on large unreplicated sites. There was a significant coarsening of texture, depletion of organic matter and nutrients and increase in bulk density under Eucalyptus camaldulensis and Mangifera indica (mango) plantations, and also under arable and fallow conditions compared with under natural vegetation. The soil conditions were slightly better under Mangifera than under Eucalyptus, and in the fallow land than the arable land and tree plantations, but the differences were mostly non-significant. The land uses studied were less efficient than the natural savannah in protecting the soil from loss of organic matter and nutrients by offtake or surface washing. The options open to Nigerian smallholder fanners are discussed in relation to sustaining soil fertility and productivity.

Notizen: Abstract. The agricultural implications of differences in soil physical properties along an Alfisol catena were evaluated. The properties studied were steady infiltration rate, saturated hydraulic conductivity (Ks), available water capacity, bulk density, field air capacity and soil texture. The catena consisted of Rhodustalfs, Haplustalfs and Tropaqualfs. A significant increase in clay content downslope was the major factor influencing the changes in associated soil physical properties. Steady state infiltration rate decreased significantly downslope. The Rhodustalfs occurring at the crest showed a steady infiltration rate of 1.91 cm/h which is optimum for surface irrigation. This decreased to 0.68 cm/h in the Haplustalfs and to 0.29 cm/h in the Tropaqualfs at the bottom of the catena; the last showing suitability for rice cultivation. Ks decreased downslope showing poor soil drainage and aeration in lower horizons of the Haplustalfs and Tropaqualfs. Available water increased downslope from 97 mm/m in the Rhodustalfs to 106 mm/m in the Haplustalfs and 122 mm/m in the Tropaqualfs. These results indicate the importance of the catena approach for soil characterization when planning agricultural projects.

Notizen: Abstract. Extraction and adsorption techniques were used to study the behaviour of Al, Fe, Mn, Co, Ni, Cu and Zn in soils from around Lake Nasser in the Eastern Desert of Egypt, to assess the potential of such areas for agricultural development and the risks of pollution of the lake. Soil metal contents were very variable, either because of particle size sorting by flowing water or through changes in redox resulting from flooding by lake water. Metal availability was low. Extraction using EDTA and oxalate suggested that mobility of copper was controlled by carbonate, whereas Co, Ni and Zn were controlled by Fe and Mn oxides. Adsorption studies confirmed the strong ability of these soils to remove Cu and Zn from solution, and suggested that Cu and Zn concentrations in solution were controlled by carbonate. Some trace metal fertilizers will probably be required for certain crops, but pollution of the lake by leaching of metals from soil is unlikely. The main process by which metals could be lost from the soil to lake water is a lowering of soil redox potential as a result of flooding by lake water.

Notizen: Abstract. The effect of humic acids on transformation of phosphorus fertilizer was studied in an alkaline soil. Soil P was fractionated following 4 and 15 days incubation after humic acids were applied with phosphorus fertilizer to the soil. The availability of phosphate in the soil and total phosphorus in plants were determined at earing stage and at maturity in a pot experiment, and wheat yield was examined in a field trial. Addition of humic acids to soil with P fertilizer significantly increased the amount of water soluble phosphate, strongly retarded the formation of occluded phosphate and increased P uptake and yield by 25%.

Notizen: Abstract. The decline in topsoil (0–0.1 m) pH (CaCl2) over 11 years (1979–90) was measured in a rotation, tillage, stubble and nitrogen fertilizer experiment on a Chromic Luvisol at Wagga Wagga in S.E. Australia. The rotations consisted of annual wheat cropping (WW) with and without nitrogen fertilizer (100 kg N/ha/year), alternating lupin-wheat (LW) and subterranean clover-wheat (CW). The initial mean pH at the site was 4.9 and the experiment was preceded by subterranean clover-based pasture for most of the previous 19 years. An initial rapid decline in soil pH under all treatments over the first 8–9 years was followed by a 2–3 year period when no further decline was detected. The annual rate of pH decline over the first 8–9 years varied from 0.06 for WW to 0.09 units for WW with added N fertilizer. Apparent steady-state for WW after 11 years was approximately 0.5 pH units higher than for WW with added N fertilizer. There was no difference between CW and LW in the rate of decline or in the apparent steady-state reached. Six years’ stubble burning in a LW rotation promoted a slightly higher pH than where stubble was retained. However, there was no significant effect of tillage in either LW or CW rotations. By 1990 the addition of N fertilizer to WW had increased the concentration of exchangeable aluminium by 100% and of manganese by 24%. The inclusion of a legume in the rotation increased the concentration of aluminium but did not affect manganese. However, burning stubble in the LW rotation slightly decreased manganese concentrations.

Notizen: Book Reviewed in this article:Estimating fertilizer requirements: a quantitative approach By J. D. Colwell.Soil Science: methods and application By David I. Rowell.

Notizen: Book reviews in this article: Soil science and sustainable land management in the tropics Edited by J.K. Syers & D.L. Rimmer. Long term experiments in agriculture and ecological sciences Edited by R.A. Leigh & A.E. Johnston.

Notizen: Abstract. The erosion susceptibility of the Erosion Research Farm at Kabete Campus was mapped using a qualitative parametric method. A grid soil survey of the 4 ha farm was combined with a map of slope gradients, slope segments being delineated by breaks in slope. Rainfall erosivity and soil erodibility were also measured. Areas with the greatest erosion susceptibility according to this method were those occupying convex slope positions and slopes of more than 30%. Field observations and soil loss measurements generally supported the erosion susceptibility rating map produced by this method. The soil and erosion susceptibility maps were useful for planning erosion control measures and for selecting suitable sites for runoff plot experiments.

Notizen: Abstract. The Agricultural Catchments Research Unit model (ACRU) includes a decision support system (DSS) for estimating the water content of soil at field capacity (θfc) and wilting point (θwp) when these characteristics are not directly measurable. Three methods of estimation are proposed: (a) based on silt and clay content and bulk density, (b) based on clay content only, and (c) based on soil series. These three pedotransfer functions are compared with respect to both the estimation of θfc and θwp and the propagation of errors when the actual evapotranspiration of a wheat crop (E) is predicted over the growing season by the ACRU model.The standard error of estimation was between 0.066 and 0.082 m3/m3 for θfc, between 0.056 and 0.069 m3/m3 for θwp and between 29.9 and 34.8 mm of water for E. The method based on silt and clay contents and bulk density predicted θfc and θwp for non-swelling soils most precisely. The method based on soil series was better than other methods for swelling soils. It also performed better for estimating available water capacity and consequently for predicting E from a conceptual soil water model. The propagated error of estimating θfc and θwp using the DSS reached 15–18% of the simulated E. The error in the prediction of E can reach 26–30% when spatial variation in soil properties is also estimated.

Notizen: Abstract. Finely ground calcium carbonate was applied at six rates (0–7.0 t/ha) to samples from four depths of an acid tropical soil (Oxisol). The mixtures were kept moist and maintained at 18 °C for a period of 30 days. There was a significant increase (〉 28%) in soil pH at all the sampling depths. Extractable P also increased significantly (〉 90%). Significant positive correlations between pH, extractable P and liming rate were obtained (r 〉 0.9, P= 0.01). The effect of time was significant only on the 10th day after liming, when soil pH had stabilized. Exchangeable Al was completely eliminated on the 5th day after liming, when most of the soil samples had pH values 〉 5.0. The results clearly indicate that liming, as a management practice, could be used to alleviate or prevent acidification of Oxisols like the soil studied.

Notizen: Abstract. The efficiency with which fertilizer nitrogen (N) is used in agricultural systems might be improved if the amounts applied at each top dressing were adjusted to avoid the accumulation of mineral-N in the soil profile to levels in excess of the growth requirements of the crop. Such tactical application of fertilizer would be feasible if soil mineral-N could be determined rapidly in the field with sufficient accuracy. This paper describes a rapid field test for both the ammonium and nitrate components of soil mineral-N based on reading paper test strips with a reflectometer, recalibrated for use with KC1 solution. The new test is volumetric and also accounts for the effects of fluctuations in soil water content by means of a standard dilution procedure to provide an absolute measure of soil mineral-N in about one hour. Measurements of ammonium and nitrate in a clay loam soil sampled from grazed pasture were compared with those made by conventional laboratory based methods; they generally differed by less than 5%. The proportion of mineral-N as ammonium averaged about 50% overall and typically exceeded 70% in spring. Ammonium and nitrate were not well correlated. The use of a filter-press to expel soil solution increased the sensitivity of the test five-fold to enable application in studies of soil N transformations in unfertilized and semi-natural environments.

Notizen: Comparisons of nitrate concentrations in soil core extracts and ceramic suction cup isolates were made on a coarse sand and a sandy loam to evaluate the methods for estimating nitrate concentrations percolating through the root zone. On the coarse sand the comparisons were made at 80 cm on three dates during the winter of 1988/89. For each date, 103 soil samples and 101 or 102 suction cup isolates were taken. On the sandy loam the comparisons were made at 25 and 80 cm on two dates in March 1990. For each date and depth, 57 soil samples and 55–57 suction cup isolates were taken. On the coarse sand the mean nitrate concentrations were the same for the two methods. On the sandy loam the results obtained using the two methods differed significantly in only one of the four comparisons. However, the results indicated that the suction cup isolates differed slightly from the volume-averaged concentrations obtained from the soil samples. The type of frequency distribution, normal or lognormal, seemed to be influenced both by the mean nitrate concentration and by the soil structure, and thus by the pattern of percolation. The size of sample required to estimate the mean nitrate concentration with a probability of 95% and a precision of 10% varied from 7 to 106.

Notizen: The diffusivity of oxygen in soil was measured by periodically changing the gas above a soil core from nitrogen to air and vice versa. The concentration wave was measured as a function of depth with an oxygen electrode. For different Fourier components in the signal, phase shifts were calculated. The diffusivity follows from the increase of the phase shift with depth. Phase shifts are more suitable than signal amplitudes for the derivation of diffusivity. They are also easier to measure and do not require electrode calibration.For a clay soil with an air–filled porosity of about 0.05 m3 m−3 a local diffusivity of 0.9 × 10−9 m2 s−1 was measured. This is several orders of magnitude smaller than macroscopic values for entire core samples of the same soil type. This low value can be explained by the presence of locally water–saturated clay.

Notizen: Proto-imogolite sols can be considered as highly dispersed forms of proto-imogolite allophane, the most widespread type of allophane in volcanic and non-volcanic soils world-wide. The solubility characteristics of such sols define the conditions of precipitation of allophanes in soils, and the maximum concentrations of aluminium released during acidic episodes from soils, such as podzols, that contain allophane. Direct measurement of Al, Si and pH values in equilibrium with proto-imogolite sols, approached from higher and lower pH, indicated a solubility equation: 〈displayedItem type="mathematics" xml:id="mu1" numbered="no"〉〈mediaResource alt="image" href="urn:x-wiley:13510754:EJSS179:EJSS_179_mu1"/〉where log*Kso lay in the range 7.14 to 7.23 after equilibration for 4–24 weeks at 22 + 2°C in 17 of the 20 systems studied. The mean value of log *KSO at 298 K was calculated as 7.02. This value indicates that proto-imogolite will be more stable than amorphous aluminium hydroxides at H4SiO4 concentrations above 5 × 10−6m, but less stable than bayerite below 10−3m H4SiO4, and than gibbsite below 10−2m. Proto-imogolite is more stable than micro-crystalline gibbsite in 10−4m H4SiO4, a typical minimum concentration in soil solutions and streams in landscapes where podzols are present. The rapid formation of proto-imogolite effectively prevents the formation of gibbsite seeds in soil, except in highly leached and warm environments, i.e. in older landscapes in the tropics.Although the presence of 10−4m silicic acid has been found to eliminate the acute toxicity to fish exhibited by solutions containing 6–7 μm Al at pH 4.96, little or no proto-imogolite would form under these conditions. Silicic acid would, however, prevent the precipitation of aluminium hydroxides, and could inhibit the formation of the A113 polycation. These polymeric species are a likely cause of the increased toxicity exhibited by partially neutralized aluminium solutions.

Notizen: The mobility of polycyclic aromatic hydrocarbons (PAH) in soils can be influenced by the presence of dissolved organic matter. Partition coefficients of selected polycyclic aromatic hydrocarbons, ranging from 3-ring to 6-ring compounds, to water-soluble soil organic matter (WSSOM) were determined. Partition coefficients were determined for WSSOM obtained from two soils under agricultural use and forest and for commercially available humic acid (Aldrich), taking advantage of a reversed phase (C18) separation method. The WSSOM was characterised with regard to charge and hydrophilic/hydrophobic properties with a dissolved organic matter (DOM) fractionation method. No sorption to WSSOM was found for the tri- and tetracyclic PAH, whereas the penta- and hexacyclic PAH showed a significant binding to both types of WSSOM and to Aldrich humic acid. The affinity of penta- and hexacyclic PAH to WSSOM was considerably lower compared to the affinity to Aldrich humic acid. This is suggested to be due to the lower amount of hydrophobic fractions, c. 30%, in the natural WSSOM as compared to Aldrich humic acid. Effective partition coefficients (Koceff) for the sorption of PAH to bulk soil calculated from KDOC and DOM in the naturally occurring concentration range were only 60–70% of the Koc values in pure water. The impact of DOM on pollutant transport is further influenced by non-equilibrium behaviour of PAH in soils and by sorption of DOM to the solid-soil matrix. Several scenarios are described in which the effect of DOM on pollutant transport may become important.

Notizen: The first part of this paper deals with the sorption of Na, Cs, Sr, Ni, Cu and Pb on two humic fractions derived from a soil. The sorption data for individual elements were obtained using the continuous-flow stirred-cell (CFSC) technique, in which the metal sorptive solution is pumped through a cell containing a known mass of the humic acid retained by a filter and the solution emerging from the cell was analysed by either atomic absorption spectrometry (Cu, Ni and Pb) or by the combined use of radioisotope dilution and gamma-ray spectroscopy (Na, Cs and Sr). Sorption isotherms were determined at two flow rates. It was found that, in general, the sorption isotherms for all the metals studied could be described by the Langmuir equation and parameters derived from the fitted line provided information on the metal-humate binding strengths and the maximum amount of metal sorbed per unit mass of humic acid. Caesium showed anomalous behaviour at certain flow rates in both its sorption and desorption behaviour.In the second part of the paper we discuss the sequential sorption and desorption of one metal by another on the same humic fraction, using Na, Cs, Zn and Cd. The aim was to elucidate the nature of the binding process when several metals were competing simultaneously for the functional groups on the humic acids. In addition, at the end of the experiment, the humic material was isolated and analysed by gamma-ray spectroscopy to determine the metals still bound in this fraction. Some tentative conclusions concerning the nature of the metal-humate complexes are made on the basis of these data.

Notizen: Books reviewed in this article:Anderson, S.H. & Hopmans, J. (eds) Tomography of Soil–Water–Root ProcessesBurman, R. & Pochop, L.O. Evaporation, Evapotranspiration and Climatic DataFoster, S. & Smout, T.C. (eds) The History of Soils and Field Systems.Jayawardane, N.S. & Stewart, B.A. (eds) Subsoil Management TechniquesLal, R. (ed.) Soil Erosion Research MethodsMcDonald, P. (ed.) The Literature of Soil Science.Thomas, D. & Middleton, N. Desertification: Exploding the Myth.Ure, A.M. & Davidson, C.M. Chemical Speciation in the Environment.Wolt, J.D. Soil Solution Chemistry: Applications to Environmental Science and Agriculture.

Notizen: The sorption of zinc (Zn) by two acid tropical soils, Mazowe clay loam (kaolinitic, coarse, Rhodic Kandiustalf) and Bulawayo clay loam (coarse, kaolinitic, Lithic Rodustalf), was studied over a wide range of Zn solution concentrations. Samples of the two soils used in the experiments were collected at both uncleared, uncultivated (virgin) sites and cultivated sites. The two virgin soils showed similar abilities to bind Zn. Mazowe soil (40 g organic matter kg−1) presented the highest affinity for Zn. Yet, Bulawayo soil (23.5 g organic matter kg−1) sorbed almost the same amount. Bulawayo soil had higher pH and Fe and Mn-oxide content than Mazowe soil. Once cultivated, the two soils behaved quite differently. After 50 years, Mazowe soil had lost 60% of its organic matter and effective cation exchange capacity (ECEC). In this soil, Zn sorption capacity had also been decreased by 60%. Clearing and 10 years under cultivation had affected neither the organic matter content nor the ECEC of Bulawayo soil. For this soil, Zn sorption was even higher in the cultivated soil, presumably due to an increase in the amount of Fe and Mn oxide from subsoiling. Zinc sorption was dependent upon pH, with retention dramatically increasing in the pH range 6–7. Sorption occurred at pH values below the point of zero charge (PZC), indicating that the sorption reaction can proceed even in the presence of electrostatic repulsion between the positively charged soil surface and the cation. In the two soils, the reversibility of the sorption reaction was very low. More than 90% of the sorbed Zn was apparently strongly bonded.

Notizen: The effects on productivity, botanical and chemical composition of cutting species-rich hay meadows in Somerset on four different dates between late May and early September in two consecutive years, were measured. Plots that had received 200 kg N ha−1 year−1 with low levels of P and K for the previous 5 years were compared with plots that had previously received no fertilizer.Previous fertilizer treatment increased metabolizable energy (ME) production only with cutting in May. Dry-matter (DM) yield increased significantly with date of cutting until August, whereas ME value declined correspondingly. There was no difference in either yield or quality of herbage cut between August and September. ME output per hectare increased very significantly between May and July, but showed no further change between cutting dates.Botanical diversity was reduced by cutting in May after 1 year and by cutting in either May or September after 2 years, and was greatest with cutting in August. The dominance of Holcus lanatus on previously fertilized plots increased after cutting in either May or September. The contribution to vegetation cover of species that regenerate primarily by seed, including annuals, was greatly influenced by cutting date in preceding years, whereas species that regenerate vegetatively were not affected.

Notizen: Sixteen landraces and twelve natural populations of Ladino white clover, and six large-leaved control varieties, were assessed in Lodi (southern Lombardy, Italy) under a mowing regime for persistence, defined as ratio between clover dry matter (DM) yield over the last two years and clover DM yield over the five-year crop cycle. Clover content in the sward was on average 35·2% in the fourth year and only 5·5% in the fifth year. Natural populations showed greater persistence and larger variation for this feature than landraces. Six natural populations were more persistent and higher yielding in the long-term than the Italian variety Espanso and one of these populations performed better than the best of the control varieties, namely Lune de Mai and Olwen, at P 〈 005. Persistence of the ecotypes was positively associated with stolon density and DM yield assessed in the third year, and to intemode length, whilst it was inversely related to seed yield and its components, especially the production of seed heads, so that hardly any ecotype could combine good persistence with high seed yield. This study discusses the potential use of these genetic resources in white clover breeding and suggests stolon density as a low-cost, approximate indicator of long-term yield.

Notizen: Measurements of rates of growth and senescence of leaf lamina per tiller and of changes in tiller population densities were made in three experiments designed to investigate the influence of sward slate on leaf turnover and net production under continuous stocking.In each experiment initially uniform swards were fenced to provide four plots on which animal numbers were adjusted twice weekly to give a series of swards maintained as nearly as possible in a steady state with respect to sward surface height (range 1.1–6.4 cm) and herbage mass (range 440–2690 kg OM ha−1). Two experiments were carried out in July–September on vegetative swards and one in May–June on a reproductive sward. Measurements were begun 3–7 weeks after treatments were started and were repeated weekly during 3–4 week measurement periods.In all three experiments the rate of lamina growth per tiller increased linearly with an increase in sward surface height and herbage mass. In the two experiments conducted in July–August this relationship was partially offset by a linear increase in the rate of senescence per tiller but net production per tiller also increased linearly in relation to sward height and mass. In the experiment conducted in May–June the rates of growth and senescence per tiller increased in parallel so that net production per tiller showed no relationship with sward condition.Tiller population densities in the July–August experiments were highest in swards maintained between 2 and 3 cm surface height and declined in swards maintained above and below this height. In the experiment in May–June tiller numbers were similar in all treatments prior to the summer solstice but diverged in a manner similar to the other experiments later in the year.The rate of lamina growth per unit area increased in a manner consistent with an asymptotic relationship and the rate of senescence increased linearly with increasing sward height and mass in all three experiments. Net production per unit area was reduced on swards below about 2.5 cm in height but was insensitive to variation in sward surface height between 2.5 and 6.0 cm (approximately 1000–2500 kg OM ha−1 herbage mass).The effectiveness of adjustments in tiller numbers and production per tiller and of changes in the balance between growth and senescence as mechanisms of sward homeostatis, together with their implications in the scope for manipulating herbage production by grazing management are discussed briefly.

Notizen: There was a three-fold variation in epicuticular wax content between populations of white clover and a five-fold variation between populations of red clover. The mean for all populations of red clovers was twice that of white. There was also a two- to three-fold variation within each population.The epicuticular wax content of white and red clovers grown in the field showed an increase with age. Thin layer chromatography showed no qualitative differences in the epicuticular waxes extracted either between populations or with sampling date.The higher levels of epicuticular wax found in some clovers were considered to be of possible significance as a source of antifoaming compounds in bloat-inducing pastures.

Notizen: Differences in ease of digestion of bundle sheath cell walls of leaf blades of Panicum spp. are shown to be associated with differences in bundle sheath cell wall structure, including the presence or absence of a suberized lamella. These structural differences are correlated with photo-synthetic type (viz. C3, intermediate C3/C4, and the C4 types, PCK, NADP-ME and NAD-ME), as are mesophyll: bundle sheath area ratios.

Notizen: The construction of a transducer and the use of a recording system to measure jaw movements of grazing sheep is described, The time spent grazing, ruminating and idling may be measured by this equipment and the data produced automatically processed using a microprocessor which determines each minute whether the animal is grazing, ruminating or idling and also summarizes these data to give total times. The accuracy of this technique in relation to manual observation is discussed.

Notizen: The effect of two heights of cutting (5 and 8 cm) on the dry matter harvested and persistency of a range of different grass species and varieties were monitored over a 3-year period (1976 to 1978). Dry matter harvested was measured in the second and third harvest year and persistence of sown grass was assessed at the end of the first and third harvest year. The grasses were managed under a frequent cutting system, i.e. simulated grazing. Results showed that at the low cutting height tetraploid hybrid ryegrasses and diploid Italian ryegrasses in the third harvest year gave lower annual dry matter harvests of sown grass and were less persistent than at the high cutting height, whilst, in contrast, perennial ryegrasses gave higher annual harvests of sown grass but persistency was unaffected. In general at the low cutting height varieties of cocksfoot, meadow fescue and tall fescue gave comparatively higher annual harvests of sown grass in the second harvest year but lower yields of sown grass in the third harvest year. A notable exception was Cambria cocksfoot which in the second harvest year gave higher yields of sown grass and was more persistent at the low cutting height.However, at 5 cm cutting height, the proportions of weed grasses (mainly Poa spp.) in swards sown to tetraploid hybrid ryegrasses and diploid Italian ryegrasses were generally greater, particularly in mid-season.

Notizen: Laminae of Lolium perenne and Phleum pratense were tested mechanically and the results analysed using engineering composite theory and fracture mechanics. As the lamina dries the fibres double in stiffness. The intervening cells show a sevenfold increase in stiffness below 20% water content (based on dry weight). Work to fracture across the veins is almost independent of water content, but below 50% water content the mode of fracture changes. It is predicted that total fibre content will not affect hay shatter; total protein content may affect it by altering the water-binding properties.

Notizen: Grass silages made from first-harvest perennial ryegrass in mid-May and early-June and termed high-D and low-D respectively had mean DOMD values of 694 and 633 g kg−1 and were offered ad libitum to twelve Ayrshire cows in a 16-week feeding experiment using a cyclic changeover design. The silages were supplemented with a concentrate containing 363g CP per kg DM at daily rates of 1.5, 3.0 and 4.5 kg per cow. The average daily intakes of silage DM were 12.6 and 11.1 kg per cow on the high- and low-D silage treatments respectively, and were not significantly different on the three concentrate treatments. The mean daily milk yields were 171, 18.6 and 21.0 kg per cow on the low-D silage treatments, and 19.6, 21.2 and 22.8 kg per cow on the high-D silage treatments at the 1.5, 3.0 and 4.5 kg rates of concentrate feeding respectively. Fat and lactose concentrations in the milk were not affected significantly by treatment, whereas the CP and SNF concentrations increased progressively and significantly as the rate of supplementary feeding increased. It is concluded that a high-protein concentrate supplement allows silage to make the maximum contribution in the diet, and gives a high response in terms of milk yield and composition.

Notizen: Grass which had grown without interruption from late April was cut as for hay in early July in each of 2 years. Fifteen dates of removal of the cut herbage were compared ranging, at 1-d intervals, from the day of cutting to 14 d after cutting. Sward regrowth was studied.A delay of 5 d in removing cut herbage reduced herbage dry matter harvested during the remainder of the growing season by 9% and a delay of 10 d reduced yield by 16%. Delaying the removal of cut herbage reduced the density of grass tillers considerably in the short term, but the effect had worn off in 8 to 12 weeks. The presence of cut herbage reduced the rate of extension of leaf blades considerably. Delaying the removal of cut herbage reduced the area per leaf blade and the weight per unit area and these effects persisted for several weeks. Grass growing under cut herbage had a less negative leaf water potential and a rather cooler but much darker environment in which to grow than uncovered grass.

Notizen: Book reviews in this article: Milk from Grass Edited by C. Thomas and J. W. O. Young Nitrogen Fixation in Legumes Edited by J. M. Vincent Herbage Intake Handbook Edited by J. D. Leaver Man's Proper Study By Richard J. Colyer Introduction to Sheep Fanning By R. G. Johnston

Notizen: Information about the grazing behaviour and the return of dung to pasture by lactating dairy cows was collected from stocking rate experiments in northern Victoria. Grazing behaviour was observed for 24-h periods in mid-summer in two years. Grazing time increased as herbage allowance decreased to about 32 kg DM cow−1 d−1 but as herbage allowance decreased further grazing time also decreased. A herbage allowance of 32 kg DM cow−1 d−1 corresponded to a stocking rate of about 5.5 cows ha−1. This effect of herbage allowance on grazing time may have been confounded by herbage mass, however. Rumination time of the cows increased by 003 h for each kg increase in herbage allowance while resting time was not affected by treatment.The effects of stocking rate on some of the characteristics of faecal output were measured for a 3-d period in mid-summer. The number of pats deposited per cow daily declined by 0.66 for each unit increase in stocking rate. The fresh weight of dung also declined as stocking rate increased by 0.16 kg per unit of stocking rate. While the values for the amounts of dung deposited on the pasture by the cows at the lower stocking rates are similar to many of those reported in the literature, this study has quantified the way in which stocking rate may influence this in one instance. Furthermore, provided that some measure of herbage intake is made when measurements of dung excretion are performed, it is suggested that estimates of in vivo digestibility can be obtained.

Notizen: Two red clover (Trifolium pratense) cultivars, Red Head (tetraploid) and Kuhn (diploid), were sown at a seed rate of 13 kg ha−1 either alone or in mixture with Italian ryegrass (Lolium multiflorum) cv. RvP sown at seed rates of 10, 15, 20 or 30 kg ha−1. RvP was also sown alone at a seed rate of 30 kg ha−1 and received nil or 300 kg ha−1 fertilizer a−1 fertilizer N. All plots were established using the barley cultivar Midas sown at a seed rate of 100 kg ha−1 as a nurse crop.Neither clover cultivar nor ryegrass seed rate significantly influenced either dry matter harvested or botanical composition over the 3 harvest years. On average over all years the grass-clover mixtures produced 75% of the yield of the N-fertilized RvP, 125% of the clover monocultures and 225% of the unfertilized RvP. The red clover contribution to the total dry matter harvested of the mixtures averaged 45–60%. The dry matter concentrations of the mixtures were considerably higher than those of the pure clover stands. In the third year yields were markedly reduced in comparison with those in the first and second years.It was concluded that Italian ryegrass can be a suitable companion grass for red clover. Its superior yielding capacity over other grasses such as perennial ryegrass or timothy under a conservation management can be coupled to advantage with red clover to give a sward which Is essentially stable, at least over a 2- to 3-year cropping period, although giving slightly reduced yields in the third year. Italian ryegrass-red clover mixtures, without the use of fertilizer N, can produce high DM yields of good quality herbage.

Notizen: Red clover cv. Hungaropoly was slot-seeded into a perennial ryegrass-dominant sward in April 1979. Glyphosate and paraquat were applied separately as bandsprays each at two doses and at two band widths. Control plots were either slot-seeded without a herbicide bandspray or received ±150 kg N ha−1 a−1. Red clover establishment was assessed and amounts of dry matter (DM) and total N accumulated were measured at two harvests in 1979 and three harvests in 1980. Bandspraying increased seedling vigour and development and resulted in the eventual replacement of 1 t grass DM ha−1 by an equivalent amount of red clover. Of the treatment variables investigated, bandspray width had the greatest influence on red clover establishment and productivity. The slot-seeded area, meaned for all treatments, produced a total of 6.40 and 13.16 t DM ha−1 in 1979 and 1980. This was estimated to be equivalent to the all-grass sward receiving 112 kg N ha−1 a−1 during the second year of the experiment or 238 kg N ha−1 over the 2 years when measured in terms of N yield. Slot-seeding overcomes several of the problems associated with conventional establishment of red clover.

Notizen: Two experiments were conducted to determine the effect of pre-harvest treatment by formic acid spray on the moisture concentration (MC) of perennial ryegrass (Lolium perenne) in vegetative growth. In Experiment 1 aqueous solutions containing 0.080, 0.148 and 0.259 kg formic acid per litre were applied to a perennial ryegrass sward (fresh matter yield 21.0 t ha−1) at a constant volume of 41.2 litres t−1to give active ingredient application rates of 3.5, 6.0 and 11.5 kg t−1 respectively. In Experiment 2 similar solutions were applied to a perennial ryegrass sward (fresh matter yield of 6.9 t ha−1) at 35.2, 19.0 and 10.9 litres t−1 respectively to give a constant formic acid application of 2.8 kg t−1. The changes in MC and chemical composition after treatment with acid were compared with those in untreated plotsIn both experiments treatment with acid significantly reduced the MC (P 〈 0.001) within 5 h of treatment from 4.4 to 3.0 kg per kg of dry matter (DM) in Experiment 1 and from 3.0 to 2.6 kg per kg DM in Experiment 2. There was no effect of level of acid applied in Experiment 1 or of the volume of water applied with the low level of acid in Experiment 2 on the changes in MC of acid-treated plots. There was however a significant (P 〈 0.00l) difference between the MC of plots treated with acid and those untreated which was maintained in Experiment I for up to 9 d even during rainfall.There were no differences between the chemical compositions of samples from acid-treated plots in either Experiment I or 2 or between untreated and acid-treated plots in Experiment 2. However there were significant differences between untreated and acid-treated plots in Experiment 1 for the content of nitrogen (N), water-soluble carbohydrate (WSC) and digestible organic matter (DOM). There were changes in the content of N, WSC and DOM with time in both experiments. In Experiment I there was an interaction between sampling time and treatment for both N and WSC but not for DOM. Compared with untreated plots, treatment with acid at all levels accelerated the loss of WSC and delayed the fall in N content. There were no such interactions in Experiment 2.

Notizen: The main object of the experiment was to assess the effect of the relative proportion of non-protein nitrogen (NPN) to total nitrogen in silage on digestion in the sheep. Four unwilted perennial ryegrass silages were made with the addition of formic acid at 0, 2·2, 4·2 and 5·2 litres t-1 to provide foods with NPN proportions reducing from 0·26 to 0·20 of the total N. The digestion of the silages was studied in a 4 × 4 Latin Square experiment with sheep cannulated in the rumen, proximal duodenum and terminal ileum.Results for organic matter (OM), cellulose and N showed no major difference between silages in their digestion in the rumen, small intestine and caecum and colon, though small differences (P 〈0·25) in rumen fermentation pattern and in the proportion of digestible OM disappearing in the small intestine were observed. Concentrations of ammonia N in the rumen and rates of rumen bacterial protein synthesis did not differ significantly between silages and there were no treatment effects on the passage of individual amino acids to the small intestine. The results indicate that the proportions of NPN to total N in the silages examined had little influence on the efficiency of silage N utilization in the rumen or on the passage of undegraded dietary protein to the small intestine.

Notizen: Two experiments were carried out to determine whether the differences in intake and feeding value previously shown between two grass cultivars when offered to ruminants as chopped artificially dehydrated (dried) material could also be demonstrated when the grasses were offered in other forms. Two cultivars of tetraploid Italian ryegrass (Lolium multiflorum), Sabalan and Tetila, were established in the same field in 1975. In 1976 they were grazed and conserved (two cuts of primary growth) as dried material or as silage.The composition of the herbage selected at pasture and conserved showed higher concentrations of normal detergent fibre and acid detergent fibre in the dry matter for Tetila than for Sabalan, but differences between cultivars in digestibility were small. In both grazing and winter feeding trials differences in voluntary intake between the two cultivars were not significant, but at pasture young beef cattle spent less time grazing and tended to spend more time ruminating on Tetila than Sabalan. There was no measure of animal performance at pasture but liveweight gain was 15% higher for Sabalan than Tetila when both were offered to young beef cattle as the sole feed of dried grass or of silage. The voluntary intakes of the three forms of feed were very similar, which in part reflected a similarity in digestibility. However, gains were lower for calves given silage than those given dried grass. This may have been due to a lower efficiency in the utilization of the nitrogeneous components of silage for tissue growth than those of dried grass.

Notizen: Four grass silages, all made in mid-July from second-harvest perennial ryegrass swards, were compared in a 16-week feeding experiment with twelve Ayrshire cows. Two silages were unwilted and two wilted. All the silages received formic acid (‘Add-F’) at the rate of 3 litres t-1 either with formalin at the rate of 1 litre t-1 or without formalin. The unwilted and wilted silages had mean dry matter (DM) concentrations of 200 and 243 g kg-1, and in vitro D-values of 0·293 and 0·272 respectively. The silages were offered ad libitum plus 6 kg concentrates per cow per day. The daily intakes of unwilted and wilted silage DM were 10·2 and 9·2 kg per cow respectively on the formic acid treatment, and 10·2 and 9·2 kg on the formic acid + formalin treatment. The mean daily milk yield on the unwilted silage treatments was 19·2 kg per cow which was significantly higher than the yield of 17·2 kg per cow on the wilted silage treatments. The formalin had no significant effect on milk yield. The four silage treatments had small and non-significant effects on milk composition. It is concluded that the unwilted silages, which had excellent fermentation characteristics, were superior to the wilted silages as a feed for dairy cows.

Notizen: Book review in this article Forage Evaluation: Concepts and Techniques Edited by J. L. Wheeler and R. D. Mochrie Improved Feeding of Cattle and Sheep By P. N. Wilson and T. D. A. Brigstocke Nitrogen Cycling in West African Ecosystems Edited by T. Rosswall Land Evaluation By S. G. McRae and C. P. Burnham

Notizen: Three field experiments showed that perennial ryegrass can be successfully slot-seeded into an existing Festuca-Agrostis sward. Ryegrass survival was satisfactory in all cases but was improved on a low fertility site by the application of fertilizer N, P and K in the slot at sowing.The effect of varying inter-row spacing from 37·2 to 15 cm was measured in a 3-year experiment. In year one, involving seven cuts, slot-seeding increased total herbage dry matter harvested by a mean value of 17%; inter-row distances of 22·2-30 cm gave the optimal combination of ryegrass + old sward herbage. Differences in yield between inter-row spacings declined in the subsequent two years, as the rows of ryegrass thickened. Ryegrass digestibility (measured only in year two, from six cuts) was higher than that of the old sward; total metabolizable energy harvested from 15-cm rows was 20% higher than that from unsown controls. Increasing N input from 200 to 400 kg ha-1, starting in year two, only produced a significant increase in total herbage harvested in year three but proved effective in increasing the ryegrass contribution from the wider spaced rows.

Notizen: In three separate feeding experiments using a total of thirty individually-housed Ayrshire cows three silages made from perennial ryegrass were given ad libitum together with supplements of four different hays in the long form. The in vitro D-values of the silages ranged from 0·298 to 0·283, and the hays from 0·280 to 0·200. The daily intake of hay DM varied from 0·2 to 4·2 kg per cow and was given either without or with a daily maximum of 2·2 kg concentrate DM containing 379–527 g CP per kg DM. On average, 1 kg hay DM decreased silage intake by 0·24 kg DM with a range of 0·21–1·20 kg. The hay supplements had only small and non-significant effects on total DM intake, milk yield and milk composition, but increased the daily intake of drinking water. In three behavioural studies, the eating and ruminating times expressed as min per kg DM did not differ significantly between the various supplement treatments. It is concluded that hay has only a marginal value as a supplement for grass silage, although the hay could serve as a useful ‘buffer’ feed if the amount of silage was limited.

Notizen: Two areas of an early-heading perennial ryegrass cv. Cropper were harvested by either a precision-chop or a flail harvester at around 50% ear emergence (15 May 1978) and 14d later (29 May). Formic acid (85%) was applied at the rate of 2·2 litres t-1. Mature crossbred wethers were used in a 2 × 2 factorial design to determine the effect of stage of maturity and method of harvesting (chop length) on the in vivo digestibilities of formic acid-treated grass in experiment 1 and formic acid silage in experiment 2. Apparent digestibility coefficients were determined at a fixed level of feeding for both grass and silage and at ad libitum access to feed for silage only.There were no significant differences in the concentrations of crude protein (CP), ether extract (EE), acid-detergent fibre (ADF) or acid-detergent lignin (ADL) in grass or silages of differing chop lengths but the later cut forages had significantly higher ADF and ADL concentrations and lower CP concentrations than the early-cut forages. The ADF and ADL concentrations were also higher in the silages than in the corresponding grasses.In general, the fermentation characteristics of precision-chopped silage were better than for the corresponding flail-cut silage but date of harvest was a more important determinant of quality and the late, flail-cut silage had the highest butyrate and ammonia N concentrations and the highest pH (411) of any treatment. There was a significantly higher intake of precision-chopped as compared with flail-cut silage with both the early-and the late-cut silage but there were no significant differences attributable to stage of maturity (i.e. date of harvest) or significant interaction between chop length and maturity. The slightly increased intake of early harvested, precision-chopped silage as compared with late precision-chopped silage was not significant.Dry matter digestibility (DMD) of the grass decreased at a rate of 0004 units d-1 post 50% ear emergence. The results of experiment 2 indicated a decrease of 0·207 units d-1 in silage fed at a similar level. The late-cut silage (DMD 0·292, mean of both harvesting treatments) thus had a significantly lower digestibility than the corresponding grass (mean DMD 0·247). Chop length had a variable influence on the DMD of both grass and silage fed at a fixed level but treatment differences were non-significant. However, a trend towards higher digestibility of flail-cut as compared with precision-chopped silage was apparent and this became statistically significant when the animals were allowed ad libitum access to feed. This may be a response to the generally lower intake of flail-cut silage.

Notizen: Book review in this article Weed and Pasture Management in South Africa Edited by N. M. Tainton Collecting and testing tropical forage plants Edited by R. J. Clements and D. G. Cameron Herbage Intake by Grazing Dairy Cows By J. A. C. Meijs

Notizen: Two experiments were carried out to evaluate propionic acid-treated hay as a feed for sheep in which eighteen ewes (experiment 1) and eighteen ewe lambs (experiment 2) were fed ad libitum on hay only. At feeding, the propionic acid-treated hays had higher D-values and water-soluble carbohydrate concentrations, but a lower dry matter concentration, than the untreated hays. The voluntary feed intake and liveweight gain of the sheep fed on two acid-treated hays and on an untreated hay in experiment 1 were similar. In the second experiment an acid-treated moist hay was eaten in greater amounts by the sheep and liveweight gains were greater than on the corresponding untreated hay, but were not significantly different from those of sheep fed on field-cured hay.

Notizen: Six varieties of white clover, each grown with perennial ryegrass, four intervals between cuts and two levels of applied nitrogen in all combinations, were compared in a field experiment during the first 27 months after sowing. Information about yields, crop fractions, heights and ryegrass tillers has been presented in an earlier paper (Wilman and Asiegbu, 1982). The present paper is concerned with the more detailed studies of white clover, which help to explain the yield results and contribute to the understanding of the response of this species to management when grown in competition with grass.Increasing the interval between harvests increased the length of clover stolon per unit area of ground and increased stolon diameter, petiole length, weight per leaf and number of leaves harvested as a proportion of the number present in the sward while only slightly reducing the rate of leaf emergence, helping to explain the positive effect of increasing the interval on clover yield noted in the earlier paper. During regrowth, successive leaves had longer petioles and the length of individual petioles increased beyond the stage at which the leaflets were fully opened. Weight per leaf in clover increased considerably from April to June and declined to below the April value by October. It was shown that weight per leaf can be greatly increased by increasing the interval between harvests without reducing the number of leaves harvested per unit area per year. The stolon length measurements provided some support for the view that medium large-leaved varieties of white clover can with advantage be defoliated rather less frequently than small-leaved varieties. Stolon length was less adversely affected by applied N in the medium large- than in the small-leaved varieties. The small-leaved varieties had thinner stolons than the medium large-leaved varieties but about twice the stolon length when no N was applied, and a relatively high proportion of leaves which escaped defoliation. The application of N reduced stolon diameter, increased petiole length and had little or no effect on weight per clover leaf.

Notizen: Data from twenty-two comparisons carried out at ADAS Experimental Husbandary Farms are used to compare untreated and formic acid-treated silages. Additive treatment led to an improved fermentation in some crops, particularly those of low DM concentration (〈262 g kg-1). Where this occurred there were associated benefits in silage digestibility (+0·234 units), intake (+16%) and the growth rate of young cattle (+0·28 kg d-1). Where the fermentation of the untreated silage was good, both digestibility and animal performance associated with treated and untreated silages were similar. It is suggested that the justification for using formic acid in a commercial situation is thus restricted to occasions where the untreated crop would be liable to develop a clostridial fermentation. These may be when crops contain less than 35 g water-soluble carbohydrate kg-1.

Notizen: The change in structure of continuously grazed versus infrequently cut swards of perennial ryegrass (Lolium perenne L), cv. S23, was investigated during their first full harvest year. Measurements were made from early May until late September. The intensity of stocking by sheep in the grazed sward was adjusted in an attempt to maintain a high level of radiation interception and the cut sward was harvested at approximately monthly intervals.The herbage mass, lamina area index and radiation interception of the cut sward varied in a cyclic pattern between harvests but in the grazed sward these parameters showed considerably less variation, although they all increased early in the season and then declined later. The proportion of dead material above ground increased throughout the season in both sward types but was more marked in the grazed sward.There were major differences between the grazed and cut swards in the number of tillers per unit ground area; the difference became more marked throughout the season and by September the tiller densities in the grazed and cut swards were 3·204 m-2 and 6·203 m-2 respectively. Divergence in tiller density was associated with differences in specific stem weight and leaf area per tiller.Rates of appearance and death of leaves on tillers in the grazed sward were determined. During May, leaf appearance exceeded leaf death but this was reversed in June. During the rest of the season as a new leaf appeared on a tiller so the oldest leaf died.

Notizen: A rising-plate meter was used in a double sampling technique to measure the herbage mass of rotationally grazed perennial ryegrass-white clover swards over a period of 2 years. The meter was calibrated by developing a linear regression between meter reading and herbage dry matter mass as measured by cutting 0·2-m2 quadrats to ground level.There was a strong relationship between meter reading and herbage mass, and correlation coefficients were consistently 0·2 or above. The calibration regression was normally constant for extended periods, especially over the winter and spring. The relationship was more variable over the summer but appeared to follow a pattern that was to some extent repeatable between years. The slope of the regression (kg DM ha-1 cm-1) was 312 and 267 in the two winters and reached values of 800 and 452 in the two summers. The calibration relationship was adequately described by a linear model over the winter and spring but there was a tendency for a curved relationship in mid-to late summer.The standard pooled regression found with winter ryegrass-clover swards was not applicable to the more erect prairie grass, and the standard regression overestimated slightly the yield of heavily grazed swards. There was no evidence of a difference in relationship between irrigated and non-irrigated swards over the summer.The individual meter readings could be used to develop a useful diagrammatic picture of the changes that occurred in sward structure as the pastures were subjected to different managements and this could be used to illustrate problem areas in pasture management.The meter was useful in overcoming the problem of variability of herbage mass within paddocks and could give precise estimates of herbage mass, especially when it was possible to use a pooled regression encompassing a large number of calibration cuts. In these cases the meter could be used to detect differences of about 8%.

Notizen: A novel hybrid stubble turnip, Appin, bred by the Scottish Plant Breeding Station (Brassica campestris ssp. rapifera cv. Tigra ×B. campestris ssp. nipposinica cv. Mizuna) was compared in small-plot cutting trials with stubble turnip (B. campestris ssp. rapifera cv. Ponda), forage rape (B. napus ssp. biennis cv. Canard) and fodder radish (Raphinus sativus cv. Neris) for 3 years, 1975–77, samples being taken from October to December or January each year to cover the likely period of utilization by grazing lambs. Except for the first year, Appin proved to yield less DM than Ponda, and be inferior in digestibility and metabolizable energy (ME) content, though N contents were on occasion higher. Canard had the highest overall ME content. In dry conditions in autumn 1977, Ponda proved the more reliable crop, suffering less depression in yield than other species. Anti-metabolite contents were determined in freeze-dried samples taken in winter 1976-77 and showed Canard to have the most brassica anaemia factor (S-methyl cysteine sulphoxide): contents of thiocyanate were generally similar between crops.As the degree of utilization of such forages when grazed can outweigh differences in recorded above-ground DM yields from cutting trials, it was considered that claims of better root anchorage and hence better utilization for Appin warranted evaluation in a grazing trial.

Notizen: Two grass silages made from perennial ryegrass, and with D-values of 0·216 and 0·255, were offered ad libitum to 18 Ayrshire cows in two feeding experiments. On the control treatment the silages were supplemented with soybean meal only, and on the other two treatments with equal weights of DM from either barley or dried molassed sugar-beet pulp plus the same weight of soya as on the control treatment. The daily intakes of silage DM were not significantly different on the barley and beet-pulp treatments, and, on average, the intake of silage DM was reduced by 0·24 and 0·20 kg by feeding 1 kg barley and beet pulp DM respectively.The daily milk yields were not significantly different on the barley and beet-pulp treatments with mean values of 19·2 and 19·2 kg per cow respectively compared with 17·2 kg on the control treatment. On the barley and beet-pulp treatments the fat, SNF, CP and lactose concentrations in the milk and the live weights of the cows were not significantly different. It is concluded that the barley and beet pulp had similar feeding values and replacement rates when used as supplements with grass silage, and that the two feeds were interchangeable on an equal DM basis.

Notizen: An experiment examining the relationship of daily herbage disappearance (DHD) and daily herbage allowance (DHA) is described. Cows with calves were grazed at three stocking rates on Kleingrass and Coastal Bermudagrass pastures. DHD and DHA were monitored at 14-d intervals. A significant positive linear relationship was noted between DHD and DHA (P〈inlineGraphic alt="leqslant R: less-than-or-eq, slant" extraInfo="nonStandardEntity" href="urn:x-wiley:01425242:GFS9:les" location="les.gif"/〉0·25). Equations derived for Coastal Bermudagrass and Kleingrass were not significantly different and resulted in a combined equation Ŷ= 0·275X + 0·209 with an r2 vaiue of 0·27. As DHA exceeded 6–9 kg DM per 100 kg live weight, efficiency of defoliation by the cows and calves declined.

Notizen: The effects of five herbicides on seed yield and viability of perennial ryegrass cv. S24 were tested at two sites. Benzoylprop-ethyl, chlorfenpropmethyl, difenzoquat, ethofumesate and flam-prop-isopropyl were safe to use at doses recommended for use in other crops. When applied at three times the recommended dose, only difenzoquat reduced the yield and germination of seed and benzoylprop-ethyl reduced seed germination. The recommended doses of difenzoquat and ethofumesate were safe when applied on cv. Barlenna at different growth stages. Difenzoquat reduced seed yield only after three times the recommended dose was applied to tillered plants. Ethofumesate, even at three times the recommended dose, did not affect seed yield but plant numbers were reduced by early treatment. The results suggest that the herbicides tested may be safe to use in perennial ryegrass seed crops at the recommended doses but more work is needed on the safety of difenzoquat in relation to crop growth stage.

Notizen: We followed in situ the evolution of nitrogen recently incorporated into a soil under maize culture for 4 years. Each year, a different pair of plots treated by removal or return of maize crop residues received a single pulse of 15N-labelled fertilizer. Unlabelled fertilizer was otherwise supplied. In parallel, plots supplied with unlabelled fertilizer received a single pulse of 15N-labelled maize crop residues.Varying weather affected total and fertilizer-derived N in the crop and residual inorganic N in the topsoil, but it did not affect fertilizer-N immobilization and remineralization. There was no consistent effect of crop residue return on total soil N, immobilization of fertilizer N, or the decay kinetics of recently immobilized N.Recently incorporated organic N from crop residues and microbial immobilization of inorganic N displayed similar mid-term decay kinetics. Crop residue N and immobilized N enter a labile compartment with an average residence time of a few months. A proportion, estimated at 28%, enters a more stable compartment from which the mineralization was imperceptible in 4 years. Particle-size fractions 〉50 um, which receive most of the crop residue N, retained it for only a short time. The mid-term stabilization of N was mainly in soil fractions 〈50 um.

Notizen: Two complementary approaches to modelling soil anoxia and denitrification are compared. The first postulates a structurally and biologically heterogeneous soil matrix (physical aggregates) and Michaelis—Menten kinetics; the second a random distribution of cylindrical air-filled pores, a uniform metabolic activity and zero-order reaction kinetics. Simple functional approximations to both models are developed, allowing their differences to be explored. At water contents corresponding to aggregate saturation the anoxic fractions and denitrification rates predicted by the aggregate model exceed those predicted by the simple-structure model. In drier soils the predictions of the latter model typically exceed those of the former by between one and three orders of magnitude, the discrepancy lessening as the oxygen reaction potential and the mean radius of the aggregates increase. The aggregate model is much more sensitive to air-filled porosity, and shows a decreased denitrification efficiency when nitrate concentrations are low. It is likely to predict sharper rainfall-induced denitrification events, and a smaller background activity, than the distri-buted-pore treatment. Whichever of these or other process-based treatments of denitrification is adopted, simple approximations like those presented here greatly facilitate inclusion in larger-volume systems models.

Notizen: A model of anaerobiosis based on gas diffusion and microbial respiration is proposed for soil aggregates. Unlike previous models, it accounts for the dependency of O2 consumption on O2 and CO2 concentrations and, consequently, on chemical reactions of CO2 in soil solution. The model is tested with experimental data of respiration and O2 distribution within spherical remoulded aggregates of different sizes saturated with water. Most of the model parameters were estimated experimentally.Fick's law could describe O2 diffusion inside the saturated aggregates. The model agreed well with O2 profiles measured soon after saturation. Later, the model underestimated anaerobiosis, probably because of changes in radial distribution of microbial activity inside the aggregates. Respiration as a function of O2 concentration was satisfactorily described by the model. Nevertheless, each size of aggregate was analysed separately because of an apparent relation between size and maximal aerobic respiration. This seems to be associated with a non-homogeneous distribution of aerobic respiration. The model represents an improvement on those currently used to estimate anaerobiosis inside aggregates.

Notizen: Accurate estimates of total nitrous oxide (N2O) losses from grasslands derived from flux-chamber measurements are hampered by the large spatial and temporal variability of N2O fluxes from these sites. In this study, four methods for the calculation of mean N2O fluxes (n= 6) on total N2O losses are compared, namely the arithmetic mean, the geometric mean, the lognormal mean and the mean derived from Finney's method. Mean fluxes were calculated from weekly flux measurements on grassland at four contrasting sites in the Netherlands with three management treatments each. Total losses were calculated by interpolation of the mean fluxes and integration over time. Spatial variation of N2O fluxes was large. The geometric mean was generally much smaller, up to a factor of 7, than the arithmetic mean. The lognormal mean was much larger, up to a factor of 11, than the arithmetic mean, possibly because this estimator is biased for small sample size. Arithmetic means and Finney's method were generally in reasonable agreement. The order in estimated N2O loss increased in the order geometric mean〈arithmetic mean≤Finney's mean〈lognormal mean. Because of the small sample size (n = 6), the uncertainty about the precise frequency distribution, the sensitivity of estimators based on logtransformed data, and the problems associated with negative fluxes, the arithmetic mean was preferred as the most appropriate estimator. Evidently, the choice of an estimator of the mean can have great effects on the estimation of total N2O losses.

Notizen: Intensively managed grasslands are potentially a large source of nitrous oxide (N2O) in the Netherlands because of the large nitrogen (N) input and the fairly wet soil conditions. To quantify the effects of soil type, N-fertilizer application and grazing on total N2O losses from grassland, fluxes of N2O were measured weekly from unfertilized and mown, N fertilized and mown, and N fertilized and predominantly grazed grassland on a sand soil, a clay soil, and two peat soils during the growing season of 1992.Total N2O losses from unfertilized grassland were 2.5–13.5 times more from the peat soils than from the sand and clay soils. Application of calcium ammonium nitrate fertilizer significantly increased N2O flux on all sites, especially when the soil was wet. The percentage of fertilizer N applied lost to the atmosphere as N2O during the season ranged from 0.5 on the sand soil to 3.9 on one of the peat soils. Total N2O losses were 1.5–2.5 times more from grazed grassland than from mown grassland, probably because of the extra N input from urine and dung. From 1.0 to 7.7% of the calculated total amount of N excreted in urine and dung was emitted as N2O on grazed grassland. The large N2O losses measured from the peat soils, combined with the large proportion of grassland on peat in the Netherlands, mean that these grasslands contribute significantly to the total emission from the country.

Notizen: Solutions labelled with 15N were applied as (15NH4)2SO4 or K15NO3 to isolated microplots in the floor of mountain beech forest (Nothofagus solandri var. cliffortioides) and incubated for 135 days under field conditions of moisture and temperature. Solid state 15N CPMAS NMR spectra of the forest litter layer showed that more than 80% of the total signal intensity was attributable to the secondary amide-peptide peak. The degree of 15N enrichment or form of N did not alter the relative intensity of signals attributable to 15N in peptides, nucleic acids and aliphatic amine groups (amino sugars and free NH2 on amino acids). Combinations of 13C and 15N-NMR spectra, edited by a process that exploited differences in proton spin properties between distinct categories of organic matter, indicated incorporation of 15N in humified organic matter rather than partly degraded plant material. This application demonstrated that solid state 15N CPMAS NMR has potential for use in studies of N immobilization under field conditions and with materials containing little N and small 15N enrichment.

Notizen: The limit to the precision with which moisture-release data may be related to soil structure is examined. Thin sections in two orthogonal planes were prepared from cores for which moisture release data and saturated conductivity measurements were also collected. Structural parameters are inferred indirectly through estimation of the mass fractal dimension from the moisture-release curve, and directly through measurement of the scaling properties of the pore space and solid matrix from the thin sections using image analysis. Theoretical results are presented which show that, in the absence of additional information, the interpretation of the moisture-release curve is ambiguous for several reasons. A power-law exponent is a consequence of either a fractal pore volume; a fractal solid volume; a fractal pore wall; or a non-fractal, self-similar pore wall, and one cannot infer from the measurement which is the case. Experimental results are presented which confirm that direct measurement of the fractal dimension of the solid matrix is a good predictor of the Brooks–Corey exponent for the soils studied here. Therefore, although a specific structural parameter characterizes the moisture-release curve, the latter cannot be used as a detailed measure of soil structure.

Notizen: In order to understand better the mechanisms of structural crust formation on coarse-textured soils, mixtures of 92.5% sand and 7.5% Ca2+-kaolinite are exposed to simulated rainfall in experiments- involving a range of sand particle sizes, drop diameters and drop kinetic energies. For each combination of these variables, clay illuviation is measured and the changes in surface structure are observed on thin sections. The intensity of clay illuviation is inversely proportional to sand particle size and is shown to be determined by both rainfall and drop kinetic energy. A washed-out layer forms at the surface of all samples exposed to drop impact. The lower boundary of this layer is generally marked by a relative concentration of clay micro-aggregates in the form of a band. These micro-aggregates are probably fragments derived from grain coatings initially present in the washed-out layer. They accumulate at a depth that increases, on average, with drop kinetic energy and with the particle size of the sand fraction. Based on similarities with natural crusts, it is proposed that clay-band formation in structural crusts formed on coarse-textured soils may be initiated by the displacement of micro-aggregates or other small particles from the washed-out layer, followed by their accumulation due to mechanical straining. The experiments also point to the potential importance of the particle size of the sand fraction on the morphology of structural crusts.

Notizen: A filter–paper technique that can be used to measure the matric potential of field soil is described in detail. When a calibrated batch of filter papers is used, the precision is limited by the variability between individual papers and the limitation of weighing to the nearest mg. The absolute accuracy is also limited by the instruments used for calibration. There was reasonable agreement between batches of the same type of paper, suggesting that our generalized calibration curves can be used for Whatman No. 42 filter papers where accuracy is not paramount.For potentials ≥−2.5 MPa, papers need to be equilibrated with the soil for 6 d. To achieve the same accuracy at lower potentials longer equilibration periods are required. Results suggest that the technique should be effective down to at least −100 MPa if soils are allowed to equilibrate fully with the papers. Coefficients of determination (r2) for the calibration lines were all ≥0.92. A regression of log(-matric potential) measured by the filter paper technique against measurements made using tensiometers and a psychrometer over a range of potentials between −1 kPa and −10 MPa gave an r2 value of 0.995.

Notizen: A model of P-sorption kinetics was developed, that accounts for the dependency of reaction rate on concentration, sorbed P content, sorption maximum and time. The sorption phenomena predicted by the model agree with available observations in the literature. The model was tested with batch experiments for 17 acid top– and subsoils. The experiments revealed a significant correlation between the sorption maximum, Fm, and the sum of amorphous iron and aluminium in soils. Plotting the dimensionless P–sorption ratio, F(c, t)/Fm, which may be interpreted as the fractional saturation of the sorption capacity of a soil, against the natural logarithm of the exposure variable, I, gave S–shaped curves. Different parts of the S–shaped curve can be experimentally assessed, depending on the initial fractional saturation of the P–sorption capacity of soils. Apart from this dependency, one set of parameter values sufficed to describe the sorption kinetics of 10 different sandy top– and subsoils. For non–sandy soils, the parameter values differed and depended on the initial P content. The model enables extrapolation to long times, which is necessary for applications to field conditions.

Notizen: Previous work has shown that rice plants growing in reduced soil are able to solubilize P by inducing an acidification in the rhizosphere through H+ produced in Fe2+ oxidation by root–released O2, and by the direct release of H+ from the roots to balance excess intake of cations over anions. In this paper, equations for the diffusion and interaction of P and acid in soil are developed to predict the resultant increase in P uptake by the roots. Good agreement was obtained between the profiles of P and pH in the rhizosphere measured in the previous experiments, and those predicted using the equations with independently measured parameter values. The equations showed that solubilization accounted for over 80% of the P taken up. Measurements of the solubilization parameters in a range of reduced rice soils showed that H+ addition increased the quantity of P that could be desorbed per unit weight of soil and the concentration of P in solution, in all the soils tested. The quantity of P solubilized per unit H+ added at a given solution P concentration varied about 50–fold between soils, with a median of 11.9 mmol P per mol H+. The native soil solution P concentration varied 50–fold (median = 0.91 UM) and the soil pP buffer power (the quantity of P desorbed per unit decrease in –log of the P concentration in solution) varied 100–fold (median = 0.36 mmol kg−1 pP−1); the soil pH buffer power varied 7–fold (median = 0.075 mmol kg−1 pH−1). Calculations indicated that, in most of the soils tested, rice plants would depend upon solubilization for the bulk of their P.