PRODUCTIVITY OF 4 ANNUAL LEGUMES AS GREEN MANURE IN DRYLAND CROPPING SYSTEMS

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 short-term 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 almost-equal-to 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 vetch also seems promising for marginal soils.