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Title: Effect of Sunn Hemp (Crotalaria juncea L.) Cutting Date and Planting Density on Weed Suppression in Georgia, USA

Author
item Morris, John - Brad
item Cho, A - University Of Florida
item Chase, C - University Of Florida
item Treadwell, D - University Of Florida
item Koenig, R - University Of Florida
item Morales-payan, J - University Of Puerto Rico
item Murphy, T - University Of Georgia
item Antonious, G - Kentucky State University

Submitted to: Journal of Environmental Science and Health
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/26/2015
Publication Date: 6/16/2015
Citation: Morris, J.B., Cho, A.H., Chase, C.A., Treadwell, D.D., Koenig, R.L., Morales-Payan, J.P., Murphy, T., Antonious, G. 2015. Effect of Sunn Hemp (Crotalaria juncea L.) Cutting Date and Planting Density on Weed Suppression in Georgia, USA. Journal of Environmental Science and Health. 50(9):614-621.

Interpretive Summary: Sunn hemp is a legume used for fiber, cover cropping, and as a green manure crop for soil improvement. Sunn hemp was evaluated for weed control in Georgia. Three sunn hemp seeding rates including a seed production, intermediate seeding, and a cover crop rate were used. Weed counts were recorded at 4, 8, and 12 weeks after planting. All three seeding rates reduced weedy grasses and yellow nutsedges were smaller than the sunn hemp free weedy fallow. Lower sunn hemp seeding rates reduced weed populations in this study and can be recommended to growers.

Technical Abstract: A field study was conducted in 2008 and 2009 at the USDA, ARS, Plant Genetic Resources Conservation Unit in Griffin, GA to investigate weed suppression by sunn hemp (Crotalaria juncea L). The objectives were to: 1) evaluate the effects of apical meristem removal (AMR) at three dates [5, 6, and 7 wks after planting (WAP) on May 14, 2008 and May 21, 2009] and 2) assess the impact of seeding rates (11, 28, and 45 kg ha-1) on weed biomass reduction. Weed species were identified at 4, 8, and 12 wks after sunn hemp planting. Sunn hemp cutting date had no significant effect on weed suppression in 2008 but significant differences for grass weeds at 4, 8, and 12 WAP and for yellow nutsedge at 8 and 12 WAP did occur when compared to the control in 2009. In comparison to the sunn hemp-free control plot in 2009, all three seeding rates had reduced grass weed dry weights at 4, 8, and 12 WAP. The total mass of yellow nutsedge when grown with sunn hemp was reduced compared to the total mass of yellow nutsedge grown in the weedy check for all seeding rates at 8 and 12 WAP. Lower grass weed biomass was observed by 12 WAP for cutting dates and seeding rates during 2008 and 2009. Sunn hemp cutting date and seeding rate reduced branch numbers in both years. The reduction in sunn hemp seeding rates revealed a decrease in weed populations.