Nonharvested Forage Legumes: Nitrogen and Dry Matter Yields and Effects on a Subsequent Corn Crop

Abstract

In government cropland diversion programs, forage legumes are grown for one or more years without harvesting, except during emergency feed shortages. Our objectives were to determine herbage and root dry matter (DM) and N yields of nonharvested and conventionally harvested (3 cuts/yr) 1- to 3-yr-old stands of alfalfa (Medicago sativa L.), red clover (Trifolium pratense L.), and birdsfoot trefoil (Lotus comiculatus L.), and the grain and stover DM yields and N uptake of subsequent corn (Zea mays L.) crops. Nonharvested legumes were not cut and herbage residue was accumulated in place until plowdown. Soil NO3− was measured in the spring following fall plowing of the 1- to 3-yr-old legume stands. The soil was a Tallula silt loam (coarse-silty, mixed, mesic Typic Hapludoll). Averaged for all species and years, nonharvesting resulted in 285% and 244% more legume DM and N for plowdown than a three-harvest schedule. This was attributed to greater herbage DM and N accumulation in nonharvested legumes. Root-plus-crown DM and N yields were similar for the two harvesting regimes. Nonharvested alfalfa and birdsfoot trefoil accumulated 280% more DM than red clover, but similar amounts of N. Average spring soil NO3− in the top 1 ft of soil was 34% larger after plowdown of 1 yr of nonharvested legumes than after plowdown of legumes which were harvested; however, soil N03− in spring did not correlate with legume N plowed down the previous fall. Whole-plant corn yields were 13% greater following 3 yr of legume nonharvesting than following harvesting, but were not affected by legume species. Whole-corn plant N uptake was 18, 35, and 51% greater, respectively, following 1, 2, and 3 yr of nonharvesting than after conventional harvesting of legumes. Corn plant N uptake in the first year after legume plowdown was most related to the amount of herbage N incorporated, and less to legume species differences. We conclude that the greatest positive effect on yield of a subsequent corn crop from non-harvested legume plowdown is from legume stands older than 2-yr and in the first year after plowdown. Birdsfoot trefoil and alfalfa should be selected to supply N and DM for plowdown in nonharvested legume production systems.