SUITABILITY OF SUNN HEMP AS AN ALTERNATIVE LATE-SUMMER LEGUME COVER CROP

The tropical legume 'Tropic Sun' sunn hemp (Crotalaria juncea L.) may have potential as an alternative legume cover crop or as forage for ca ttle in southern temperate regions. This study determined dry-matter p roduction, chemical composition, and N release from sunn hemp residue under conventional and no-tillage systems as might be used in corn (Ze a mays L.) production. Sum hemp was sown in mid-August and mowed in ea rly December on a Norfolk sandy loam (fine-loamy, siliceous, thermic T ypic Kandiudult) and a Lucedale fine sandy loam (fine-loamy, siliceous , thermic Rhodic Paleudult) in Alabama (1991-1992). Mesh bags were use d to determine residue decomposition and N release. Average dry-matter production was 5.9 Mg ha(-1) 9 to 12 wk after planting. At mowing, re sidue N content averaged 126 kg ha(-1). Residue overwintered on the so il surface until early April. During the first 4 wk following mowing, N release from residue was 50%. In April, N remaining in overwintered residue was only 38% of that after mowing in December (45 kg N ha(-1)) . Nitrogen release from residue during the subsequent corn growing sea son was 13% in no-tillage and 43% in conventional tillage. Sunn hemp p roduced sufficient dry matter to cover and protect the soil from erosi on and provided sufficient N to benefit a succeeding summer crop. In a ddition, forage quality of leaves was suitable to provide late summer and fall grazing. Sunn hemp has potential to be managed as an alternat ive to winter legume cover crops in warm temperate regions.