LENTIL GREEN MANURE AS FALLOW REPLACEMENT IN THE SEMIARID NORTHERN GREAT-PLAINS

Green manures (GM) may offset inorganic N needs and improve soil quali ty, Study objectives were to determine effects of green manure on soil -N fertility, water use, soil quality, and yield of spring wheat (Trit icum aestivum L.), On two treatments, lentil (Lens culinaris Medikus c v. Indianhead) was green manured in a green manure-spring wheat rotati on. Lentil was killed by disking (GMMF) or chemicals (GMCF). Additiona l treatments were annually cropped wheat (AW) in a mechanical fallow ( MF) or chemical fallow (CF) sequence. No inorganic N was used on GMMF and GMCF. Experiments were started in 1991 on a Williams loam (fine-lo amy, mixed Typic Argiboroll) near Culbertson, MT. Green-manure treatme nts used 56 mm more water than fallow treatments when lentil was grown to lower-pod set. When lentil was killed at full bloom, there were no differences in water use among GM and fallow treatments, There were n o differences among treatments in soil water at wheat planting, Wheat yield was 25% less on GM than on MF and CF, Soil NO3-N (0-0.6 m) was 3 5% less on GM than MF and CF rotations. There were no differences in s oil quality indicators of bulk density, organic C, pH, electrical cond uctivity, and deep NO3-N (0.6-1.8 m) among treatments after two cycles of GM, Potentially mineralizable N was 66% greater on GM treatments t han on fallow treatments, Short-term results (5 yr) show that availabl e N limited wheat production more than did soil water on the GM treatm ents, Soil improvement using green manures may require many additional cropping cycles.