Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/17/2007
Publication Date: 10/15/2007
Citation: Schomberg, H.H., Martini, N.L., Diaz-Perez, J.C., Phatak, S.C., Balkcom, K.S., Bhardwaj, H.L. 2007. Potential for using Sunn Hemp (Crotalaria juncea L.) as a source of Biomass and N for the Piedmont and coastal plain regions of the southeastern USA. Agronomy Journal. 99:1448-1457. Interpretive Summary: Because of the mild winter conditions in the southern USA, many vegetable producers grow crops in both summer and winter. Cover crops grown during periods when no cash crop is grown help maintain soil organic matter and can provide nitrogen by fixing nitrogen from the air into plant tissue and soil. Agricultural Research Service scientists from the J. Phil Campbell, Sr. Natural Resource Center in Watkinsville, GA and the Soil Dynamics Laboratory in Auburn, Al, along with scientists from the University of Georgia and Virginia State University evaluated how to best manage sunn hemp (Crotalaria juncea L.), a tropical legume as a cover crop/green manure in the South. The researchers evaluated planting and harvest date effects on sunn hemp biomass and N production at a Piedmont and Coastal Plain location in Georgia. In general, maximum biomass was produced from May and June plantings, depending on the harvest date. Averaged across locations and planting dates, sunn hemp produced 2.1, 3.9, and 4.9 tons/acre biomass and 110 to 180 lb nitrogen/acre after 60, 90, and 120 days, respectively. The researchers developed equations to predict sunn hemp biomass and N accumulation using days after planting and data from the two Georgia locations. This equation did a good job of predicting sunn hemp biomass production for three previous studies in Alabama and one in Virginia. This equation can help producers determine the optimum planting and harvesting times for sunn hemp in the South. The information from this research could promote the adoption of sunn hemp as a cover crop/green manure on the more than 4 million acres of vegetables and 7 million acres of corn grown in the South. Many vegetable and row crop producers will use this information along with NRCS and Extension personnel in the region.
Technical Abstract: Sunn hemp (Crotalaria juncea L.), a tropical legume, could be a good cover/green manure crop for vegetable producers in the Southeast USA because of its rapid growth and N2 fixing ability. Limited information is available about planting date effects on biomass and N production when sunn hemp is grown in temperate to semi-tropical climates. We determined biomass and N content of sunn hemp at 30, 60, 90, and 120 days after planting (DAP) for four planting dates (mid-April to mid-July) at a Piedmont and a Coastal Plain location in Georgia. Averaged across locations and planting dates sunn hemp produced 4.8, 8.8, and 11.0 Mg ha-1 biomass and 125, 205, and 201 kg N ha-1 at 60, 90, and 120 DAP, respectively. In general, maximum biomass at a given DAP was produced from May and June plantings. Equations to predict sunn hemp biomass and N accumulation based on DAP, cumulative degree days (CDD), and cumulative solar radiation (CSR) produced relatively accurate predictions for independent data from Alabama and Virginia. Surprisingly, DAP was the best predictor of biomass and N. Our results suggest sunn hemp may fit well into short-rotation sustainable vegetable production systems in the Southeast and that by using the equations we developed producers may easily estimate the potential return when using sunn hemp as a cover/green manure crop.