Control of Weeds in an Oat (Avena sativa)—Soybean (Glycine max) Ecofarming Rotation

Soybeans [Glycine max(L.) Merr.] and oats (Avena sativaL.) were grown in a rotation using reduced or no-tillage crop production systems at Lincoln, Nebraska, over a 4-yr period. Oat stubble was treated after harvest with 3.4 kg/ha of metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one] to reduce the growth of late summer weeds. The following spring soybeans were planted directly into the undisturbed stubble or into a seedbed prepared by tandem discing. Three seedbed preparations, two soybean cultivars, and six preemergence weed control treatments were compared. Glyphosate [N-(phosphonomethyl)glycine] applied at 0.8 kg/ha or tandem discing were equally effective in producing a weed-free seedbed. Herbicides applied preemergence on soybeans were still necessary for the reduced tillage or no-tillage production systems if weeds were to be adequately controlled in soybeans without cultivation. Differences in seed-yield occurred between cultivars only when late summer rains benefited the later maturing ‘Williams' soybeans over earlier maturing ‘Wells'. With adequate weed control, soybeans and oats can be grown in a no-tillage, crop rotation, production system in eastern Nebraska to produce high yields with a minimum of labor and soil exposure.