Competition of Sicklepod with Soybeans

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Abstract
The competitive effects of sicklepod(Cassia obtusifoliaL.) on soybeans(Glycine maxL. ‘Bragg’) were studied on Malbis sandy loam soil and Chesterfield sandy loam soil during 1968 to 1970. Weed density was a linear function of soybean yield for the densities studied (0 to 15 weeds/m2). The regression coefficient of weed density (weeds per square meter) on bean yield (kilograms per hectare) was −92 and −101 for the two soils, respectively. When the data were combined across both soils and years, the regression coefficient was −95. Densities of 7.7 weeds/m2reduced soybean yield 19 to 32% and 34 to 35% on the two soils, respectively. The weight of weeds at harvest was also inversely correlated to soybean yield. Sicklepod was more competitive when grown 15 to 30 cm from the drill than in the drill. Soybean yields were reduced in some instances when sicklepod was allowed to compete for as little as 4 weeks. If weeds were removed at 2 to 4 weeks after soybean emergence, no further weed removal was needed for maximum yield of soybeans.