Tolerance of Soybean Cultivars to Weed Competition and Herbicides

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Abstract
The competitiveness of 10 soybean [Glycine max(L.) Merr.] cultivars to weeds, their tolerance to twice normal rates of commonly used soybean herbicides, and the soil residual properties of these herbicides were studied during 4 years at Lincoln, Nebraska. Three soybean cultivars showing the least percentage yield loss from weeds were ‘Harosoy 63′, ‘Amsoy’, and ‘Corsoy’; whereas cultivars showing the greatest yield loss were ‘Hawkeye 63′, ‘Shelby’, and ‘Lindarin 63′. The two herbicide treatments causing the greatest average soybean yield loss were 3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea (linuron) at 4.5 kg/ha and α,α,α-trifluro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) at 2.2 kg/ha. Cultivar selection was important in reducing soybean yield loss from herbicides as linuron at 4.5 kg/ha reduced yields 5% for ‘Harosoy 63’ to as much as 31% for ‘Ford’. ‘Neal’ oat(Avena salivaL.) yields showed 4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline (nitralin) to be the most persistent herbicide in soil in this study followed by trifluralin. Plowing the soil eliminated the phytotoxicity of nitralin and trifluralin to subsequently planted oats.