Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/2/1997
Publication Date: N/A
Interpretive Summary: Winter legume cover crops like hairy vetch and crimson clover can provide nitrogen to following crops and can also improve soil productivity. Their use is restricted, however, because winter legume cover crops accumulate most of their biomass and nitrogen during the spring, which can delay timely plantings of most summer cash crops. We investigated the possibility that a tropical legume, Tropic Sun sunn hemp, could be planted immediately following harvest of corn to be used as an alternative to winter legume cover crops. Average dry-matter production was 2.63 tons/acre just 9-12 wk after planting. This residue contained 120 lb/acre nitrogen. Seventy-five lbs of this nitrogen was released to the soil during the winter and from 13 to 43% of the remaining 45 lbs was released during the following corn growing season, dependent on corn tillage system. Sun hemp residue provided >96% soil surface coverage during the winter to protect the soil from erosion. In addition, forage quality of leaves was suitable to provide late summer-fall grazing. Sun hemp offers an alternative to winter legume cover crops with potential for reducing soil erosion, adding nitrogen to the soil, and as a forage for dairy cattle in southern temperate regions.
Technical Abstract: The tropical legume sunn hemp (Crotalaria juncea L.) may have potential as an alternative legume cover crop for reducing soil erosion, adding N to the soil, or as forage in southern temperate regions. The objective of this study was to determine dry-matter production and soil coverage, chemical composition, and N release from sunn hemp residue under conventional tillage and no-tillage systems as might be used in a corn (Zea mays L.) production system. Tropic Sun sunn hemp was sown in mid August and mowed in early December 1991 and 1992 on a Norfolk sandy loam (fine, loamy, siliceous, thermic, Typic Kandiudults) in east-central Alabama and in 1992 on a Lucedale fine sandy loam (fine, loamy, silieceous, thermic Rhodic Paleudults) in southwestern Alabama. Mesh bags were used to determine residue decomposition and N release. Average dry-matter production was 5.9 Mg/ha 9-12 wk after planting. At mowing in early December, residue N content averaged 126 kg/ha. Residue was left on soil surface (over-wintered) until early April. During the first 4 wk following mowing, N release from residue was 50%. In the spring (16 wks after sunn hemp was mowed), N remaining in over-wintered residue was only 38% of that after fall mowing (45 kg/N ha). Nitrogen release from over-wintered residue during the subsequent corn growing season was 13% in no-tillage and 43% in conventional tillage. Sunn hemp residue provided >96% soil surface coverage after fall mowing. An average of 71% of the soil surface remained covered the following spring when corn would be planted. Sunn hemp produced sufficient dry-matter to cover the soil and provided sufficient N to benefit a succeeding summer crop. In addition, forage quality of leaves was suitable to provide late summer-fall grazing.