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crop residues under conventional and zero tillage. Can. J. Soil Sci. 84: [403][404][405][406][407][408][409][410]. Field experiments were conducted to determine decomposition patterns of red clover (Trifolium pratense), field pea (Pisum sativum), canola (Brassica rapa) and wheat (Triticum aestivum) residues under zero and conventional tillage. Crop residue amounts produced in 2 trial years ranged from 1.6 t ha -1 for monoculture wheat to 6.05 t ha -1 for peas, and tillage had no effect. The extent of dry matter (DM) decomposition was usually less under zero than under conventional tillage, e.g., 31 to 41% of canola DM decomposed under zero tillage while 41 to 50% decomposed under conventional tillage in 12 mo. Corresponding percentages for other residues under zero and conventional tillage, respectively, were: 65 and 75% for clover, 43 and 45 to 55% for pea, and 27 and 40% for wheat. The rate and extent of DM decomposition were positively correlated with N and P concentrations, and negatively correlated with C/N, C/P, lignin/P and lignin/K ratios. These decomposition patterns have implications for nutrient release and soil cover. Rapid decomposition is not necessarily desirable because the nutrients released are subject to losses in soil. , le canola (Brassica rapa) et le blé (Triticum aestivum) quand le sol est travaillé de la manière usuelle ou n'est pas travaillé. La quantité de déchets de culture produite lors des deux années de l'essai variait de 1,6 t par hectare pour la monoculture du blé à 6,05 t par hectare pour le pois, et le travail du sol n'a aucune incidence sur ce paramètre. En général, la matière sèche (MS) se décompose moins quand le sol n'est pas travaillé, à savoir décomposition de 31 à 41 % de la MS du canola avec le nontravail du sol contre 41 à 50 % avec des labours, au bout de douze mois. Les pourcentages correspondants pour les autres cultures avec le non-travail et le travail ordinaire du sol sont les suivants : 65 % et 75 % pour le trèfle; 43 % et 45 à 55 % pour le pois; 27% et 40 % pour le blé. La rapidité et l'importance de la décomposition de la MS présentent une corrélation positive avec la concentration de N et de P et une corrélation négative avec les ratios C/N, C/P, lignine/P et lignine/K. Ces modes de décomposition ont des implications sur la libération des éléments nutritifs et sur la couverture végétale. On ne souhaite pas nécessairement une décomposition rapide, car alors, les éléments nutritifs dans le sol pourraient subir des pertes.

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

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The effects of tillage and preceding legume crops on N flux in the soil–plant system require quantification for developing sustainable cropping systems. We measured changes in soil and plant N under the influence of tillage [no till (NT) vs. conventional tillage (CT)] and previous crops [spring wheat (Triticum aestivum L.), red clover (Trifolium pratense L.) green manure, and field pea (Pisum sativum L.)]. The study was conducted from 1994 through 1996 on a well‐drained sandy loam soil (coarse‐loamy, mixed, frigid, Typic Cryoboralf) near Fort Vermilion, Alberta (58°23′N, 116°2′W). Nitrogen uptake by wheat was increased by NT and legume crops. At seeding, CT soil had 28 kg ha−1 more NO3–N to 100‐cm depth than NT soil. Apparent net N mineralization in the growing season was 71 and 22 kg N ha−1, respectively, for the NT and CT systems. Previous crop effect on net N mineralization (kg N ha−1) was red clover (56) > field pea (51) > wheat (34). Approximately 18 kg N ha−1 was net‐mineralized from red clover residues compared with insignificant amounts from pea and wheat residues. Microbial biomass turnover's contribution to net N mineralization (28 to 40 kg N ha−1) was increased by NT and previous legume crop. Soluble organic N decreased by 7 kg ha−1 between seeding and maturity for all experimental treatments. The results indicate that N fertilizer recommendations should allow for greater mineralization of organic N under NT than CT and following a legume green manure.