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

Abstract

Additional index words. sunn hemp, Crotalaria juncea, cover crop, cultural weed management Abstract. A field study was conducted in 2008 and 2009 in Citra, FL, to evaluate the effects of seeding rate and removal of apical dominance of sunn hemp (Crotalaria juncea L.) on weed suppression and seed production by sunn hemp. Three seeding rates of sunn hemp were used: a representative seed production rate of 11 kg · ha L1 , an intermediate seeding rate of 28 kg · ha L1 , and a cover crop seeding rate of 45 kg · ha L1 . Cutting the main stem at 3, 4, or 5 weeks after planting to break apical dominance was compared with 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 on 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 the lack of seed production may be the result of the absence of effective pollinators in fall when short-day varieties of sunn hemp flower in Florida.

Herbage Accumulation, Nutritive Value, and Regrowth Potential of Sunn Hemp at Different Harvest Regimens and Maturity

“…Previous research suggests that sunn hemp accumulates a large amount of biomass and has regrowth potential after initial harvest due to axillary buds breaking dormancy, forming primary and secondary branches (Abdul-baki et al, 2001;Schomberg et al, 2007;Cho et al, 2015). Previous research suggests that sunn hemp accumulates a large amount of biomass and has regrowth potential after initial harvest due to axillary buds breaking dormancy, forming primary and secondary branches (Abdul-baki et al, 2001;Schomberg et al, 2007;Cho et al, 2015).…”

Effect of sunn hemp (Crotalaria junceaL.) cutting date and planting density on weed suppression in Georgia, USA

“…In this study, similar weed biomass amounts were measured regardless of sunn hemp cutting date during both years. Generally, weed populations were much lower in Georgia than what was found in Florida [3] because the fields utilized in this experiment had been exposed to years of continuous crop production of other legume, vegetable, and grass species.…”

“…Cutting sunn hemp after 5 WAP does not produce results that would benefit growers, however, weed reduction by the sunn hemp cover crop in this study confirms the interference by sunn hemp for greater establishment of weed biomass. [3] Conclusions These results suggest that sunn hemp is a good summer and fallow crop in either agronomic or vegetable crop rotations in Georgia. Even though only year 2 treatments provided significant weed suppression by sunn hemp when .…”

“…[28] Sunn hemp can sequester carbon, serve as a pollen and nectar source for bees, be used as a fiber, paper pulp, fuel, seed crop, and as a mulch. [3] Since sunn hemp is a subtropical species and does not tolerate freezes, it can be grown as a warm season cover crop. It can be used in Georgia and other southern areas in the United States in which farmers have fallow periods after their crops.…”

“…Cover crops such as sunn hemp (Crotalaria juncea L.) establish and accumulate biomass rapidly, providing important benefits to the cropping system such as weed reduction and provides needed nitrogen to subsequent crops. [3] Corn grown in sunn hemp straw resulted in reduced weed biomass and greater corn ear yields. [4] Non-crop intervals (fallow) often occur between two vegetative crops grown in one year.…”