Influence of cultural practices on weed management in soybean

Weed management in soybean [Glycine max (L.) Merr.] is influenced by cultur al practices including planting date, fertilizer and herbicide application, and cultivation. Field studies were conducted in 1990, 1991, and 1992 to e xamine the interactions of planting date, deep-banded fertilizer, banded an d broadcast herbicide applications, rotary hoeing, and cultivation on weed management in soybean. Soybean was planted in early May, with or without de ep-banded fertilizer, and planted in late May without fertilizer. Nineteen weed management treatments were included in the study, ranging from mechani cal control only to broadcast herbicides followed by rotary hoeing and cult ivation. Weed density, soybean population, and soybean yield were measured. Gross margin over weed control cost was calculated for each weed managemen t system. Applying deep-banded fertilizer at planting did not influence wee d densities, soybean population, or soybean yield. Rotary hoeing 4 to 6 d a fter planting reduced soybean populations 9 to 15%, while rotary hoeing 12 to 21 d after planting did not reduce soybean populations. Rotary hoeing di d not reduce weed densities or improve soybean yield when herbicides were b roadcast or band-applied. In the absence of herbicides, timely rotary hoein g followed by two cultivations reduced weed density and increased soybean y ield to within 75% of the hand-weeded control. Cultivating broadcast preeme rgence 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 broadc ast and soybean cultivated once, followed by banded postemergence herbicide application and soybean cultivated twice. Soybean yield was greater when p lanted 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, plant ing early, broadcasting or banding postemergence herbicides, and cultivatin g resulted in more consistent weed control and higher gross margins than ot her weed management strategies.