Yield and green-manure benefits of interseeded legumes in a high desert environment

Relay intercropping legumes into vegetable crops provides cover and green-manure benefits to subsequent crops, but has not been adequately researched in high desert regions. This study evaluated the dry matter, N yield, effect on a subsequent forage sorghum [Sorghum bicolor (L.) Moench] crop, and estimated fertilizer-replacement value (FRV) of several legumes interseeded into sweet corn (Zea mays L.). The study took place under furrow irrigation in north-central New Mexico (study site elevation, 1737 m) on a Fruitland sandy loam (coarse-loamy, mixed, calcareous, mesic Typic Torriorthent). Five legumes (hairy vetch, Vicia villoso Roth; barrel medic, Medicago truncatula Gaertn.; alfalfa, Medicago sativa L.; black lentil, Lens culinaris Medik.; and red clover, Trifolium pratense L.) were interseeded into sweet corn at last cultivation or blister stage in 1993 and 1994. Corn ears and stover were harvested in August. The following spring, plots were plowed and seeded to forage sorghum. Estimated FRV for the legumes were calculated from regression equations for sorghum dry matter yield as a function of N fertilizer rate. Herbage N yields in the fall were greatest for hairy vetch and barrel medic and averaged across interseeding dates, ranged from 55 to 64 kg ha-1 in 1993 and 100 to 108 kg ha-1 in 1994. Whole-plant N yields (herbage + roots + crowns) in May were greatest for hairy vetch, 205 kg ha-1 in 1994 and 172 kg ha-1 in 1995. Seasonal dry matter yield and N uptake of sorghum were greatest following hairy vetch in 1994, and hairy vetch and alfalfa in 1995. Based on seasonal sorghum yield, hairy vetch and alfalfa had the highest FRV, ranging from 78 to 140 kg ha-1 N