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.