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Cover Crops

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

^a USDA-ARS, J. Phil Campbell, Senior, Natural Resource Conservation Center, Watkinsville, GA 30677
^b Dep. of Horticulture, Univ. of Georgia, UGA-Tifton Campus, Tifton, GA 31793
^c USDA-ARS, National Soil Dynamics Lab., Auburn, AL 36832
^d New Crops Program, Virginia State Univ., Petersburg, VA 23806

^* Corresponding author (harry.schomberg{at}ars.usda.gov)

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.

Abbreviations: CDD, cumulative degree days • CSR, cumulative solar radiation • DAP, days after planting • EVS, E.V. Smith Research Center, Alabama • MNV, Monroeville Research Site, Alabama • UFL, Citra Research Center, University of Florida • VSU, Randolph Research Farm, Virginia