Influence of Cultural Practices on Weed Management in Soybean

Abstract

Weed management in soybean [Glycine max (L.) Merr.j is influenced by cultural practices including planting date, fertilizer and herbicide application, and cultivation. Field studies were conducted in 1990, 1991, and 1992 to examine the interactions of planting date, deep-banded fertilizer, banded and broadcast herbicide applications, rotary hoeing, and cultivation on weed management in soybean. Soybean was planted in early May, with or without deep-banded fertilizer, and planted in late May without fertilizer. Nineteen weed management treatments were included in the study, ranging from mechanical control only to broadcast herbicides followed by rotary hoeing and cultivation. Weed density, soybean population, and soybean yield were measured. Gross margin over weed control cost was calculated for each weed management system. Applying deep-banded fertilizer at planting did not influence weed densities, soybean population, or soybean yield. Rotary hoeing 4 to 6 d after planting reduced soybean populations 9 to 15%, while rotary hoeing 12 to 21 d after planting did not reduce soybean populations. Rotary hoeing did not reduce weed densities or improve soybean yield when herbicides were broadcast or band-applied. In the absence of herbicides, timely rotary hoeing followed by two cultivations reduced weed density and increased soybean yield to within 75% of the hand-weeded control. Cultivating broadcast preemergence and postemergence herbicide applications increased soybean yield and gross margin in eight of 10 instances. Soybean yield and gross margin over weed control costs was greatest where postemergence herbicides were broadcast and soybean cultivated once, followed by banded postemergence herbicide application and soybean cultivated twice. Soybean yield was greater when planted in early May than late May in 89% of the weed management treatments in 1991 and 78% of the weed management treatments in 1992. Therefore, planting early, broadcasting or banding postemergence herbicides, and cultivating resulted in more consistent weed control and higher gross margins than other weed management strategies.