Acidity generated by N fertilizers depends on factors such as the composition of the fertilizer, climatic and soil conditions, and the crops grown. Our objective was to quantify the acidifying effects of urea and anhydrous NH3 when used as fertilizers for cereal production in Saskatchewan, Canada. The fertilizers were injected annually (at 10‐cm depth) into a medium‐textured, moderately acid (pH ≈5.5) Typic Haploboroll, at rates of 0, 45, 90, and 180 kg N ha−1 for 9 yr. Soil acidity increased as N application rate increased, with anhydrous NH3 causing greater acidification than urea. Although pH values as low as 4.3 were recorded in soil treated with anhydrous NH3, KCl‐exchangeable acidity remained low. The major effect of acidification was a depletion of exchangeable Ca and Mg. The solubility of Mn (but not Al) increased substantially as pH decreased, with solution concentrations of almost 30 mg Mn L−1 being recorded 6 d after injection of NH3. Acidity generated by anhydrous NH3 compared well with values predicted assuming that all of the applied NH3 was oxidized to NO3− (with the production of 1 mol H+ mol−1 of N) and that these protons were partly neutralized by OH− released when NO3− was taken up and assimilated by plants. Acidification due to export of bases in grain was insignificant because wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.) remove only a slight excess of cations over anions. Urea failed to realize its full acidification potential because of an apparent loss of urea‐N from the soil by NH3 volatilization.
Integration of green manuring as fallow replacement in dryland cereal production requires selection of well‐adapted legumes. The objectives of this study were to (i) analyze vegetative growth of annual legumes and (ii) assess the relative merits of each legume as shortterm green manure crop. Inoculated black lentil (Lens culinaris Medikus), Tangier flatpea (Lathyrus tingitanus L.), chickling vetch (Lathyrus sativus L.), and feedpea (Pisum sativum L.) were tested on an Orthic Brown Chernozem soil (Aridic Haploborolls) at Swift Current, SK, Canada, from 1984 to 1990. Legume species and years differed significantly in dry matter (DM) production of shoots, roots, and nodules; DM partitioning; growth habit; relative growth rate; and weediness. Total legume DM ranged from 601 to 3961 kg ha−1, with 6‐ yr means of 1669 kg ha−1 for black lentil, 1486 for Tangier flatpea, 2230 for chickling vetch, and 3008 for feedpea. Nodulation was most abundant with chickling vetch and least with Tangier flatpea; nodule DM ranged from 2 to 329 kg ha−1. Coefficients of determination between nodule and legume DM were r2 = 0.93*** for chickling vetch and r2 = 0.78*** for feedpea, indicating their ability to benefit from symbiosis with Rhizobium. Nodulation was greatly influenced by soil mineral N and soil water. Average DM allocation to roots as a percentage of total legume biomass averaged =7% for chickling vetch and feedpea and 12% for black lentil and Tangier flatpea. Feedpea canopy height was double to triple that of black lentil. The degree of decumbency (stem length/canopy height) was 1.09 for black lentil, 1.19 for chickling vetch, 1.21 for feedpea, and 1.29 for Tangier flatpea. Growth rate analysis identified chickling vetch as an early‐developing legume. Feedpea and chickling vetch were definitely more suited to green manuring in semiarid climates than black lentil and Tangier flatpea. Feedpea has good growth habits and greatest DM production. Chickling
Data on plant water use and soil water depletion by green manure legumes are needed to develop sustainable cropping systems in a semiarid environment. The objectives of this study were to determine: (i) seasonal water use by legumes, (ii) their water use efficiency (WUE), and (iii) residual soil water contents after legume growth compared with summerfallow and continuous spring wheat (Triticum aestivum L.). Black lentil (Lens culinaris Medikus), Tangier flatpea (Lathyrus tingitanus L.), chickling vetch (Lathyrus sativus L.), and feed pea (Pisum sativum L.), were seeded into wheat stubble with snow trap strips on an Orthic Brown Chernozem soil (Aridic Haploborolls) at Swift Current, SK, from 1984 to 1990. Legume water use exceeded that of fallow at 4 to 6 wk after seeding. When legumes were tilled into the soil at full bloom, differences in water content between cropped treatments and fallow were largest and most consistent in the top 0.6 m, suggesting that the legumes extracted water primarily from this depth. In an extreme drought year, substantial water depletion occurred below 0.6 m. Water use efficiency of legumes was 11 to 29 kg ha−1 mm−1, similar to that of spring wheat. Feed pea and chickling vetch used water more efficiently than the other legumes or N‐fertilized wheat. Significant differences in WUE across years were related to differences in DM production. Soil water contents above the 0.6‐m depth in late fall following green manuring were 62 to 82% that of fallow and increased over winter to 79 to 103% of fallow. Subsoil water was, on average, recharged after wheat to only 68% but following green manure to 81% of fallow. Partial fallow replacement with legumes would reduce the risk of erosion and nutrient leaching and minimize the hazard of salinization and eutrophication of downstream ecosystems.
' ql{ winkleman, G' E' 1996' Nitrogen bclefits from four green-manure legumes in dryland cropping systems. can. i. punt Partial replacement of fallow with legume green manures has the p"ll"ti""i to improve i.ia ptJu"tt-"r.14 agricultural sustainability in the northern Great Plains' This is possible if N gains by annual legumes and enhan.eirrrent of soil N aiailability are optimized. The objectives of the study were to (i) determine the N distributionln different vegetative components of four annual legumes; (ii) estimate their ability to accumulate N through fixation; and (iii) compare the N uptate of ihe cereal crop that follows tegume green manure with that of cereal grown on fallow or of cereal ieceiving N fertilizer. Blac k lentii-(Lens culinaris Medik.), Tangier flatpea (Lathyrus tingitanus L'), chickling vetch (Lathyrus sativus L)l and feedpea (Pisum satiwm L.) were grown in rotation with spring wheat (Triticum aestivum L.). Nitrogen concentration in iegume nodulei was several times greater than in any other plant part' However, N concentration in legume shoots was, on average, 27o/o greiter than in legume rJots. Total legume N content (% x mass) ranged from 4l to 126 kg hrl in years of low weedinJss. fn tt ose yeari, Uetow-"grounA Galculations and Statistical AnalysesSoil bulk densities determined at the same experimental site in a previous study (Dyck et al. 1977) were used together with depth increments to convert nutrient concentrations to nutrienfcontents. Plant and grain N yields were calculated as the product of nutrient concentrations and crop yields' The difference in plant N uptake between each legume at firll bloom and the N taken up by spring wheat from the continuous-wheat control treaunent when sampled the same day as the legumes was used to estimate total N fxed by the green--atture crop. For the wheat refefence crop, it was issumed, on the baiis of earlier experiments at the same site, that the below-ground N uptake was 20Yo of the total plant uptake and that the recovery of fertilizerN was 50% of the amonnt applied Campbell and Paul 1978 CANADIAN JOURNAL OF PLANT SCIENCE
O. T. 1996. Soit microbial and biochemical properties after ten years of fertilization with urea and anhydrous ammonia. Can. J. Soil Sci. 76: 7-l4.The influence of nitrogen (N) fertilizers, eipecially anhydrous ammonia, on soil quility has been qr:estioned frequently by pro_ponents of organic farming uoO to* input sustainabie agriculture. A 10-yr experiment wis conducted on an Orthic Dark Brown Chernozemic loam, at Scott, Saskatchewan, to examine ih. influ.n.. of uiea and anhydrous ammonia, at rates of N up to I 80 kg ha-l' on yields of cer-eals and oilseeds. In the 10th yr, we sampled soil from the 0-to 7.5-and 7.5-to l5-cm depths of each treatment 3 d before and 6 and 26 d after fertilization to'aisess the impact of applied N on microbial populations and soil biochemical properties. The^long-term residual effects ofN fertilization on ioil properiies were evident prioitothe 1Oth annual N application. The short-term effects were most pronounced 6 d after the 1gth N application. Generally, effects were greater in the7.5-to 15-cm depth, where N was.placed. the s'oit, which was already acidic (pH ='5.2 in 0.01 M CaCl2), decreased in pH in proportion to N_rate and more so for anhydrous ammonia than urea. Geneially, fungal and bacterial populations (plate counts) were positively related to N rate and were greater in soil treated with anhydrouj imm6nia than in urea-treated soil. In contrast, the actinomycete population was inversely related to N rate and was less for anhydrous ammonia than for urea. Nitrifier counts were increased by low rates of N (added substrate) but were similar to the check at high N rates (high acidity). There were no significant effects of N treatment on denitrifiers or yeasts. In contrast to the plate coun-t results, *i.t6bial biomass decreased with increasing rates of N and was lower for anhydrous ammonia than for ur.u. fio*.u.., the authenticity of this response is questionable because the fumigation-incubation method of biomass determination is compromised under acid conditioni. Carbon mineralization was unaffected but N mineralization and nitrification tended to decrease at the 1 80 kg N ha-l rate of anhydrous ammonia. Significant nitriflication occurred at pH < 5.0 suggesting possible adaptation of nitrifiers in this acid soil. Wet aggregate stability (WAS) was ulgffecled by N treatments. We conItua"ittrut, if producers in the Dark Brown soil zone apply fertilizirs at rates less than 90 kg N hr', deterioration of soil quality should be minimal.
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