Potential for Using Sunn Hemp as a Source of Biomass and Nitrogen for the Piedmont and Coastal Plain Regions of the Southeastern USA

Abstract

The tropical legume sunn hemp (Crotalaria juncea L.) could be a valuable green manure/cover crop for vegetable producers in the southeastern USA because of its rapid growth and large N2 fixing ability. Planting and termination date effects on biomass and N accumulation are relatively unknown for the region, but would help producers manage sunn hemp between summer and winter cash crops. We determined sunn hemp biomass and N content 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. Maximum biomass at a given DAP was produced from May and June plantings in the Piedmont and from April and May plantings in the Coastal Plains. Maximum biomass and N ranged from 8.9 to 13.0 Mg ha−1 and 135 to 285 kg ha−1, respectively. An equation for estimating sunn hemp biomass as a linear function of cumulative degree days (CDD) and cumulative solar radiation (CSR) was verified with independent data from Alabama, Florida, and Virginia. A similar equation for estimating N content as a quadratic function of CSR was not as accurate but still might be useful. Sunn hemp can fit well into short‐rotation sustainable vegetable production systems in the Southeast, and these equations can be used by producers to make reliable estimates of sunn hemp biomass production.