The Technical and Economic Effects of Johnsongrass (Sorghum halepense) Control in Soybeans (Glycine max)

Publisher Website
Google Scholar
Abstract
The effect of johnsongrass [Sorghum halepense(L.) Pers.] on soybean [Glycine max(L.) Merr.] yields, grades, and net returns were determined by regression analysis of data from 252 field research plots from 1971 through 1976. Johnsongrass control from 0 to 100% was achieved by various combinations of summer fallow, dalapon (2,2-dichloropropionic acid) as a preplanting application at 8.3 kg/ha, or trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) at 0.8 to 1.7 kg/ha incorporated into the soil before planting. Repeated usage of trifluralin at 1.7 kg/ha, either with or without use of summer fallow, provided the most effective and most profitable soybean production. Foreign material in soybean seed samples was about 0.8% with 100% johnsongrass control and nearly 6% with no control. At least 70% johnsongrass control was required to avoid deductions from gross harvested weights caused by seed moisture levels exceeding 13%. Levels of johnsongrass control in excess of 60% tended to increase soybean test weights. With 100% johnsongrass control, about 1.2% damaged soybean seed occurred; whereas, without johnsongrass control, about 1.7% seed damage occurred. The level of johnsongrass control had little effect on the level of split soybean seed at harvest. Failure to control johnsongrass resulted in predicted soybean grades of 4.1; whereas, nearly 100% johnsongrass control was necessary to provide U.S. No. 1 grade soybeans. Soybean yields were increased 4.8 to 6.2% for each 10% increase in johnsongrass control when plots were not fallowed or after fallowing, respectively. Net returns in soybean production were nearly twice as great with 100% johnsongrass control as when johnsongrass was not controlled.