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ARS Home » Southeast Area » Griffin, Georgia » Plant Genetic Resources Conservation Unit » Research » Publications at this Location » Publication #268701

Title: Apical Dominance and Planting Density Effects on Weed Suppression by Sunn Hemp (Crotalaria juncea L.)

item Cho, Alyssa - University Of Florida
item Chase, Carlene - University Of Florida
item Treadwell, Danielle - University Of Florida
item Koenig, Rosalie - University Of Florida
item Morris, John - Brad
item Morales-payan, J - University Of Puerto Rico

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/9/2014
Publication Date: 2/26/2015
Citation: Cho, A., Chase, C.A., Treadwell, D.D., Koenig, R.L., Morris, J.B., Morales-Payan, J.P. 2015. Apical Dominance and Planting Density Effects on Weed Suppression by Sunn Hemp (Crotalaria juncea L.). HortScience. 50(2):263-267.

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 seeding rate and cutting on weed reduction in Florida. Three sunn hemp seeding rates including a seed production, intermediate seeding, and a cover crop rate were used. The main stems were cut at 3, 4, and 5 weeks after planting. The increase in seeding rate caused a decrease in light penetration, increase in leaf areas for the sunn hemp plants, and reduced weed weights. Cutting did not effect sunn hemp shoots, light penetration, leaf areas, and no effect on weed reduction. This may help growers manage their sunn hemp crop production in Florida.

Technical Abstract: A field study was conducted in 2008 and 2009 in Citra, Florida to evaluate the effects of seeding rate and removal of apical dominance of sunn hemp (Crotalaria juncea L.) on weed suppression and seed production of sunn hemp. Three seeding rates of sunn hemp were used; a representative seed production rate of 11 kg/ha, an intermediate seeding rate of 28 kg/ha, and a cover crop seeding rate of 45 kg/ha. Cutting the main stem at 3, 4, or 5 weeks after planting to break apical dominance was compared to an uncut treatment. Cutting had no significant effect on shoot biomass, photosynthetically active radiation (PAR) penetrating the canopy, and nondestructive leaf area index (LAI). As a result, cutting also had no effect on weed density and biomass in 2008 and very little effect in 2009. Increase in seeding rate resulted in linear decrease in PAR and increase in LAI in both years. Seeding rate had a greater effect on suppression of weed biomass than suppression of weed density. There was a linear decline in sunn hemp branching with increased seeding rate in 2009 and, averaged across years, flower number decreased linearly with increased seeding rate. Cutting to break apical dominance induced branching but had no effect on flower number. No seed pod production occurred and we postulate that lack of seed production may be due to the absence of effective pollinators in fall when short-day varieties of sunn hemp flower in Florida.