ALBERT

Description: Environment and management effects on the N supply to crops are not well understood. We assessed the influence of tillage system (conventional tillage or no-till), N fertilizer (0 or 60 kg N ha-1) and year on N sources and supply of a Dark Brown Chernozem loam soil, and N utilization by spring wheat (Triticum aestivum L.) in 2 yr. The main N source was mineralized N; only 14–23% of wheat N was derived from fertilizer, and non-exchangeable ammonium made no measurable contribution. Soil NO3 and exchangeable NH4 content at sowing and net N mineralization during the growing season (Nmin) were influenced more by year than by N addition and tillage. Nmin was 90–100 kg N ha-1 in 1999, a moist growing season but only 21–39 kg N ha-1 in 2000, a drier year. In both years, soil inorganic N to 60 cm at sowing averaged about 60 kg N ha-1 of which half was N mineralized since the previous harvest. Year accounted for 65–81% of the variation in N uptake. Fertilization increased N uptake and wheat yields, especially in 2000, but fertilization and tillage had no effect on post-heading N uptake and N translocation. Nitrogen use efficiency (NUE) and N recovery were lower with N applied and not affected by tillage. Our study indicated that available N was affected more by environment than management. In dry conditions, when Nmin is low, N application may be more effective in increasing yield and N uptake than in wet years, an observation that may merit further attention. Key words: Available N, N mineralization, N recovery, N use efficiency, non-exchangeable ammonium, tillage

Description: Light fraction of organic matter is a source of nutrients for plants and a substrate for microbes, while total organic matter is critical for optimum physical conditions and retention of nutrients and other chemicals in soil. The objective of this study was to evaluate the effects of cultivation and grassland type on light fraction and total C and N in a Dark Brown Chernozemic soil. Three paired-sets of soil samples, in five replications, were collected from three cultivated field areas under annual crops [mostly wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.)] and from three adjacent grassland areas. The three sets were a 30-yr-old bromegrass (Bromus inermis Leyss.)/alfalfa (Medicago sativa L.) dominated stand cut annually for hay (Lm) and cultivated area 1 (Ct1), an unbroken native grass stand having no vegetation removed (Ng) and cultivated area 2 (Ct2) and a bromegrass/crested wheatgrass (A gropyron cristatum L. Gaertn.) dominated stand on a land reverted to grassland 60 yr ago having no vegetation removed (Og) and cultivated area 3 (Ct3). Soil samples from the 0- to 5-cm, 5- to 10-cm, 10- to 15-cm, 15- to 20-cm and 20- to 30-cm depths were taken using a 4-cm-diameter coring tube sampler. Total organic C (TOC), total N (TN), light fraction organic C (LFOC) and light fraction N (LFN) in soil were determined and the equivalent mass technique was used to calculate their masses in different soil layers. Total mass (for all soil layers) was less in the cultivated areas compared to the grassland areas by 31 to 43% for TOC, by 84 to 85% for LFOC, by 15 to 34% for TN and by 82 to 84% for LFN. The effect of cultivation was much greater in the surface 5-cm depth compared to deeper soil layers. The proportions of LFOC in TOC and LFN in TN as well as the TOC:TN ratios were lower in the cultivated areas than in the grassland areas, whereas the LFOC:LFN ratios were similar in cultivated and grassland areas. The light fractions of C and N were thus more responsive to change from grassland to cultivation of annual crops compared to the total C and N. Within the grassland areas, the mass of TOC and TN in most of the soil layers was greater in the Lm compared to both Ng and Og areas, while the LFOC and LFN did not show the effect of grassland type. The differences in the mass of both total and light fraction C and N in the cultivated areas were small and generally not significant. The findings suggest that including legume in grassland stands can sequester more organic C and N into the soil even when used for hay production. Key words: Cultivated land, light fraction C and N, native grassland, total organic C and N

Description: Light fraction of soil organic C (LFOC) represents a major portion of labile soil organic C (SOC) and is a key attribute of soil quality. Soil respiration (Cmin) is an important index depicting the potential activity of the labile SOC. Six field experiments, varying in duration (8 to 25 yr), in location (Brown, Dark Brown and Black Chernozemic soil zones of Saskatchewan) and soil texture, were conducted to evaluate the impact of tillage and crop rotations on crop production and soil quality. We sampled the 0-7.5-cm depth of soil in these experiments to determine the treatment effects on LFOC, the proportion of LFOC in the SOC (LFOC/SOC) and Cmin. Increasing the frequency of summer fallow in cropping systems decreased the LFOC in all soil zones; it also decreased the proportion of LFOC in SOC and Cmin. Tillage had little impact on LFOC in the Brown and Dark Brown Chernozemic soil zones, although it significantly decreased LFOC in the Black Chernozemic soil zone. Thus, crop rotation had a greater impact on LFOC than tillage. Tillage did not influence Cmin in any soil zone. Because adoption of no-till management increased SOC in all soil zones, we concluded that LFOC was not a sensitive indicator of the impact of tillage on this soil quality attribute for these Chernozemic soils in Saskatchewan. We also found that LFOC/SOC is directly proportional to sand content. This relationship may assist us in partitioning SOC pools with differing turnover times when modeling SOC dynamics. Key words: Soil organic C, light fraction organic C, tillage, crop rotations, texture, mineralizable C

Description: Producers and scientists are seeking more accurate methods for estimating the N-supplying power of soil at the field level. This has become more urgent as new management technologies, such as precision farming, gain popularity on the Canadian Prairies. We characterized the N status of the soil on an 18-ha site on which a new long-term alternative farming experiment was being initiated at Scott, Saskatchewan, by taking 160 cores in a systematic manner in June 1994. In these cores we determined: i) total soil N; and ii) the N-supplying power of the soil by determining mineralizable N by aerobic incubation at optimum temperature and moisture, and by extracting NH4–N with 2 M KCl at 100°C. Because the field had been fertilized shortly before sampling, residual fertilizer N severely affected the quality of determinations of N supplying power at the 0- to 7.5-cm depth. Consequently, we limited our investigation to the 7.5- to 15-cm depth. We also determined pH, bulk density, and particle size distribution. Using geostatistics, simple correlations, and multiple regression analyses, we demonstrated a close association between the biological and chemical measures of N-supplying power of the soil. Semivariograms revealed that the spatial structure of the variance of both variables was similar, with about 70% of the variance resulting from unidentified processes, and the rest explained by spatial structure. Field maps prepared with block-kriged estimates, revealed that these two measures of N-supplying power were similarly distributed throughout the landscape, and followed closely the spatial distribution of total soil N throughout most of the field. However, we identified two areas of the field where the two estimators of N-supplying power had a weak association with total soil N. Multiple regression and cluster analysis indicated that this disparity was a function of differences in soil pH, bulk density, and geometric mean diameter of soil particles, suggesting that soil erosion-transport processes may have altered the nature of organic N in areas of the field. The relationship between N mineralized during a 24-wk incubation and NH4–N extracted with hot KCl was not affected by these differences, suggesting that the biological and chemical procedures tested were accessing similar pools of soil N. We concluded that hot KCl NH4–N should prove useful for quantifying the N supplying power of soils. Key words: Geostatistics, estimation, kriging, spatial variability, mineralizable N

Description: Information is required on the usefulness and limitations of simulation models for estimating nitrate-nitrogen (NO3-N) and water status of soil in different agroecological zones of western Canada. Therefore, four simulation models (CERES, EPIC, NLEAP and NTRM) were used to predict distribution of NO3-N and water in the soil profile from long-term spring wheat (Triticum aestivum L.) rotations for the 1990 growing season at Melfort and Scott, Saskatchewan. The models estimated NO3-N and water levels in the crop rooting zone (0–1.5 m) of the soil profiles generally well. However, EPIC underestimated NO3-N levels in the top 0.3 m for fallow (F) rotations at Melfort, whereas NLEAP overestimated amounts in the same depth increment of Melfort soil for the majority of rotations. In addition, CERES and NTRM markedly overestimated NO3-N levels in the Melfort soil solum (0–0.6 m) for the unfertilized continuous wheat (W) rotation. Soil water content was overestimated in the top 0.3-m layer of Melfort soil for the two W rotations by CERES and EPIC and for all rotations by NTRM. As well, EPIC markedly overestimated water content in the crop rooting zone for both rotations at Scott. There were differences among models in accurately simulating NO3-N and water status of the soil profile, but these differences were not great. Overall, these models should be effective in estimating soil NO3-N and water content for wheat cropping systems, thereby aiding agronomic decisions and environmental impact assessments. Key words: Crop Estimation through Resource and Environment Synthesis (CERES), Erosion/Productivity Impact Calculator (EPIC), nitrogen, Nitrogen Leaching and Economic Analysis Package (NLEAP), Nitrogen, Tillage, and Residue Management (NTRM), Triticum aestivum L.

Description: Growing season rainfall affects fertilizer N recovery, particularly in semi-arid environments. However, the influence of rainfall distribution during the growing season is not well-understood. We conducted a 7-yr study (from 1997 to 2006) to assess this effect, and that of no-till (NT) vs. conventional tillage (CT), on fertilizer N recovery by spring wheat (Triticum aestivum L.) fertilized with 15N-labelled urea at 40 kg N ha–1 and grown on stubble on a Dark Brown Chernozem soil in Saskatchewan, Canada. Two of the seven experimental years had growing season rainfall close to normal, one was above normal and four were below normal. Tillage treatment did not affect 15N recovery by wheat; however, 15N recovery in the top 15 cm of soil averaged 47% under NT vs. 39% under CT (P = 0.02). Total N and 15N uptakes were most affected by "year" due to variation in growing season rainfall distribution. Excluding an ultra-low value of 3.8% (or 1.5 kg N ha–1) in 2002, due to extreme drought, 15N recovery by wheat averaged 47.5% (range 30–57%), and percent N derived from fertilizer was 12–20%. Rainfall in May correlated significantly with 15N and total N uptake (r = 0.605 and 0.699, respectively). The recovery of 15N in wheat head correlated negatively with June rainfall (r = –0.624), probably because more moisture increased soil N mineralization, which diluted the 15N pool. During grain filling, soil N uptake was 12–30 kg ha–1, compared with negligible amounts (〈 7%) of 15N; however, about 15 kg ha–1 of 15N were remobilized vs. 34–74 kg ha–1 of soil N. It is concluded that, in this semi-arid region, fertilizer N uptake is influenced more by rainfall in May than other months of the growth period.Key words: 15N-labelled urea, fertilizer N recovery, N uptake, rainfall, remobilized N, tillage

Description: Cutforth, H. W., Angadi, S. V., McConkey, B. G., Miller, P. R., Ulrich, D., Gulden, R., Volkmar, K. M., Entz, M. H. and Brandt, S. A. 2013. Comparing rooting characteristics and soil water withdrawal patterns of wheat with alternative oilseed and pulse crops grown in the semiarid Canadian prairie. Can. J. Soil Sci. 93: 147–160. To improve sustainability and increase economic returns, producers in the semiarid Canadian prairie are diversifying their cropping systems to include alternative crops such as pulses and oilseeds in rotation with wheat. Producers must adopt crops and cropping systems that use water most efficiently. We compared the root systems and water withdrawal patterns for three pulse crops (leguminous grain crops) [chickpea (Cicer arietinum L.), pea (Pisum sativum L.) and lentil (Lens culinaris Medik. L.)] and three oilseed crops [canola (Brassica napus L. and Brassica rapa L.) and mustard (Brassica juncea L.)] with one cereal crop [wheat (Triticum aestivum L.)] under well-watered, rain-fed, imposed drought water regimes during 1996–1998. Wheat withdrew the most water, whereas pulses withdrew the least amount of water from the soil profile. Pulses withdrew substantially less water than oilseeds and wheat below about the 80-cm depth, whereas oilseeds withdrew less water than wheat from the upper regions of the soil profile, thus increasing soil water available to the following crops. Therefore, producers can increase the overall efficiency of a crop rotation by growing deeper rooting crops, such as wheat and canola, following pulses, and by growing crops, such as wheat, that will use the increased soil water reserves following canola.

Description: The influence of five crop rotations and the rotation phases (i.e., rotation-yr) on some soil organic matter characteristics was investigated in a long-term (23 yr) study carried out on an Orthic Dark Brown Chernozemic soil at Scott, Saskatchewan. The cropping systems included different cropping frequencies and crop types (cereals, oilseeds, and legume-hay). Soil samples were taken from the 0- to 7.5- and 7.5- to 15-cm depths in mid-September 1988, 2 wk after harvest of the grain crops (i.e., 2 mo after hay harvest and plowdown). Most effects of rotations, and rotation phases, on soil biological characteristics assessed, were significant primarily in the top 7.5-cm soil depth. Increasing the cropping frequency did not increase soil organic matter. Excessive preseeding tillage of stubble plots may have masked any potential advantage provided by frequent cropping. Including alfalfa (Medicago sativa L.) hay crops in rotation with grain crops decreased soil organic matter in the fallow and grain crop rotation phases of rotations. This was likely due to increased moisture stress depressing associated cereal production in this semiarid environment. As expected, rotation phase did not influence soil organic C, but alfalfa under-seeded into barley (Hordeum vulgare L.) increased soil organic nitrogen. We believe this was due to crop residue inputs from the seedling alfalfa. Microbial biomass C and N, C mineralization, the specific respiratory activity (ratio of CO2-C respired/microbial biomass C) and hydrolyzable amino acids were also greater in the rotation phases in which barley was underseeded with alfalfa. Carbon mineralization and specific respiratory activity were directly related to estimated crop residue-C returned to soil, but not residue-N. However, both were increased by including alfalfa in the rotation. Carbon mineralization and specific respiratory activity were more sensitive indexes of soil organic matter quality than biomass C and N per se. Hydrolyzable amino acids and amino sugars responded to the treatments in a manner similar to total soil organic N. Relative molar distribution of amino acids was unaffected by crop rotation or rotation phase. Potentially mineralizable N in this soil was low compared to other Canadian prairie soils, even though the total soil organic N of the Scott soil was relatively high. We concluded that (i) all soil biochemical characteristics studied are useful for assessing soil quality changes; (ii) when studying soil changes, thin (0- to 7.5-cm) soil slices are more likely to reveal treatment effects than thicker slices; (iii) all rotation phases should be analyzed whenever forage legumes are constituents of crop rotations. Key words: C mineralization; microbial biomass, amino acids, N mineralization, specific respiratory activity

Description: The size distribution and stability of aggregates are important characteristics influencing tilth, erosion, water infiltration and nutrient dynamics in soil. We need to understand how soil management influences agregation so that we may make suitable modifications to farming practices to enhance soil stability. Two long-term crop-rotation experiments in southern Saskatchewan were used to examine the effects of management on aggregation. In 1991, soil was collected three times during the summer from the top 5 cm of soil as part of a 25-yr experiment at Swift Current (Orthic Brown Chernozemic soil) and twice as part of a 27-yr experiment at Scott (Orthic Dark Brown Chernozemic soil). The two medium-textured soils were dry-sieved by rotary sieve and then wet-sieved after (i) slow wetting and (ii) fast wetting of the 1–2-mm size fractions. The wind-erodible fraction (

Description: We examined 1990-1996 crop and soil N data for no-tillage (NT), minimum tillage (MT) and conventional tillage (CT) systems from four long-term tillage studies in semiarid regions of Saskatchewan for evidence that the N status was affected by tillage system. On a silt loam and clay soil in the Brown soil zone, spring what (Triticum aestivum L.) grain yield and protein concentration were lower for NT compared with tilled (CT or MT) systems for a fallow-wheat (F-WM) rotation. Grain protein concentration for continuous wheat (Cont W) was also lower for NT than for MT. For a sandy loam soil in the Brown soil zone, durum (Triticum durum L.) grain protein concentration was similar for MT and NT for both Cont W and F-W, but NT had higher grain yield than MT (P 〈 0.05 for F-W only). For a loam soil in the Dark Brown soil zone, wheat grain yield for NT was increased by about 7% for fallow-oilseed-wheat (F-O-W) and wheat-oilseed-wheat (W-O-W) rotations. The higher grain yields for NT reduced grain protein concentration by dilution effect as indicated by similar grain N yield. However, at this site, about 23 kg ha-1 more fertilizer N was required for NT than for CT. Elimination of tillage increased total organic N in the upper 7.5 cm of soil and N in surface residues. Our results suggest that a contributing factor to decreased availability of soil N in medium- and fine-textured soils under NT was a slower rate of net N mineralization from organic matter. Soil nitrates to 2.4 m depth did not indicate that nitrate leaching was affected by tillage system. Current fertilizer N recommendations developed for tilled systems may be inadequate for optimum production of wheat with acceptable grain protein under NT is semiarid regions of Saskatchewan. Key words: Tillage intensity, N availability, soil N fractions, N mineralization, crop residue decomposition, grain protein