Sunn‐Hemp Utilized as a Legume Cover Crop for Corn Production

The benefits of winter legumes as cover crops for corn ( Zea mays L.) are diminished by the earliness of corn planting in relation to biomass and N production by the legumes. Tropical legumes may offer an alternative to winter legumes because they produce adequate biomass before corn planting. We determined the suitability of ‘Tropic Sunn’ sunn‐hemp ( Crotalaria juncea L.) as a cover crop for corn on a Compass loamy sand (coarse‐loamy, siliceous, subactive, thermic Plinthic Paleudults) in central Alabama using a split‐plot treatment structure in a randomized complete block design with four replications from 1991 to 1993. Main plots were winter fallow and sunn‐hemp planted in mid‐August, and subplots were N (0, 56, 112, and 168 kg N ha −1 ) applied to corn 3 weeks after planting (WAP). Sunn‐hemp biomass production approximately 14 WAP (first frost) averaged 7.6 Mg ha −1 with an N content of 144 kg ha −1 in the first 2 yr of the study. Corn grain yield following sunn‐hemp averaged 6.9 Mg ha −1 whereas yield following winter fallow averaged 5.7 Mg ha −1 . Grain N averaged 16.3 kg ha −1 greater for corn following sunn‐hemp than fallow plots. Before first frost, sunn‐hemp produced excellent biomass to serve as a winter cover crop in corn production while producing N equivalent to 58 kg ha −1 of N fertilizer during the 3‐yr period, based on corn yield and N response. Sunn‐hemp has potential to be utilized as an alternative to winter legumes for ground cover and as an N source for a subsequent corn crop in the Southeast.