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International Journal of Agronomy
Volume 2011, Article ID 237510, 8 pages
Research Article

Planting Date and Seeding Rate Effects on Sunn Hemp Biomass and Nitrogen Production for a Winter Cover Crop

1USDA-ARS, National Soil Dynamics Laboratory, 411 S. Donahue Drive, Auburn, AL 36832-3439, USA
2Department of Agronomy and Soils, Auburn University, 201 Funchess Hall, Auburn, AL 36849-5412, USA

Received 2 May 2011; Accepted 5 July 2011

Academic Editor: Rodomiro Ortiz

Copyright © 2011 Kipling S. Balkcom et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Sunn hemp (Crotalaria juncea L.) is a tropical legume that produces plant biomass and nitrogen (N) quickly. Our objectives were to assess the growth of a new sunn hemp cultivar breed to produce seed in a temperate climate and determine the residual N effect on a rye (Secale cereale L.) cover crop in east-central Alabama from 2007 to 2009. Plant populations, plant height, stem diameter, biomass production, and N content were determined for two sunn hemp planting dates, following corn (Zea mays L.) and wheat (Triticum aestivum L.) harvest, across different seeding rates (17, 34, 50, and 67 kg/ha). Rye biomass was measured the following spring. Sunn hemp biomass production was inconsistent across planting dates, but did relate to growing degree accumulation. Nitrogen concentrations were inversely related to biomass production, and subsequent N contents corresponded to biomass levels. Neither planting date nor seeding rate affected rye biomass production, but rye biomass averaged over both planting dates following wheat/sunn hemp averaged 43% and 33% greater than rye following fallow. Rye biomass following corn/sunn hemp was equivalent to fallow plots. Early planting dates are recommended for sunn hemp with seeding rates between 17 and 34 kg/ha to maximize biomass and N production.