Nitrogen from Forage Legumes: Harvest and Tillage Effects1

Abstract

AbstractIncreasing interest in forage legumes as green manures in crop rotations has emphasized the need for information on harvest and tillage management of modern cultivars. Our objectives were to: 1) determine the effects of four seeding year harvest managements on sweetclover [Melilotus officinalis (L.) Lam.], red clover (Trifolium pratense L.), and alfalfa (Medicago sativa L.) herbage and root dry matter (DM) and N yields, and on DM yield and N recovery by a subsequent sudangrass [Sorghum bicolor (L.) Moench] crop, and 2) determine the effect of moldboard or chisel plowing on DM yield and N uptake by sudangrass grown following incorporation of alfalfa residues. Two separate experiments were conducted on a fine‐silty over sandy‐skeletal, mixed, mesic Typic Hapludolls. With a hay harvest management (three or four harvests), legumes had similar total season herbage N yields (261 kg ha−1), and root DM (1.4 Mg ha−1) and N yields (30 kg ha−1), and total plant N yields (325 kg ha−1). Unharvested sweetclover had greater fall whole plant N yields (348 kg ha−1) than alfalfa (195 kg ha−1) and greater root DM (5.1 Mg ha−1) and N yields (175 kg ha−1) than alfalfa or red clover (average root DM and N yields of 1.9 Mg ha−1 and 48 kg ha−1, respectively). Nitrogen incorporation (272 kg ha−1) was greater when legume herbage was accumulated in situ than when herbage was removed and only fall regrowth and/or crowns and roots incorporated (86 kg ha−1). Legume species selection within harvest management had little effect on sudangrass DM yield or N uptake. Tillage method had no consistent effect on sudangrass, DM yield, or N uptake. Since fallowing resulted in sudangrass yields similar to those from the best legume treatments, it might be considered as an alternative to legume production for diverted cropland on some soils.