Submitted to: Agronomy Journal
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/17/2004
Publication Date: 2/1/2005
Citation: Balkcom, K.S., Reeves, D.W. 2005. Sunn hemp utilized as a legume cover crop for corn production. Agronomy Journal. 97:26-31. Interpretive Summary: The benefits of winter legumes (plants capable of producing nitrogen) as cover crops for corn are reduced by the earliness of corn planting which limits typical winter legume growth and nitrogen production. Tropical legumes may offer an alternative to winter legumes because they grow quickly prior to corn planting. Scientists at the J. Phil Campbell Sr. Natural Resource Conservation Center and the National Soil Dynamics Laboratory compared 'Tropic Sunn' sunn hemp to plots with no cover crop for corn at the Alabama Agricultural Experiment Station's E.V. Smith Research Center from 1991-1993. Nitrogen rates (0, 56, 112, and 168 kg N ha-1) were applied three wk after planting corn to all plots. Sunn hemp plants grew quickly, averaging 7.6 Mg ha-1 (3.4 tons ac-1), 98 days after planting for the first two years of the study. Corn grain yields following sunn hemp averaged 6.7 Mg ha-1 (107 bu ac-1) while yields following no cover crop averaged 5.6 Mg ha-1 (89 bu ac-1). Sunn hemp shows potential to be used as an alternative to winter legumes in the Southeast because it provides a large amount of ground cover and N, which can benefit a subsequent corn crop.
Technical Abstract: 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 nitrogen (N) production by the legumes. Tropical legumes may offer an alternative to winter legumes because they produce adequate biomass prior to 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 design with four replications from 1991-1993. Main plots were winter fallow and sunn hemp planted in mid-August, and sub-plots were N (0, 56, 112, and 168 kg N ha-1) applied to corn 3 wk 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 6.7 Mg ha-1 while yield following winter fallow averaged 5.6 Mg ha-1. Grain N averaged 15.6 kg ha-1 greater for corn following sunn hemp than fallow plots. Prior to first frost, sunn hemp produced excellent biomass to serve as a winter cover crop in corn production while producing N equivalent to 57 kg ha-1 of N fertilizer over 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.