Submitted to: Weed Technology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/1/2009
Publication Date: 1/23/2010
Citation: Anderson, R.L. 2010. A 2-Year Small Grain Interval Reduces Need for Herbicides in No-Till Soybean. Weed Technology. 23:398-403. Interpretive Summary: Producers who use rotations comprised of one or two crops, such as corn-soybean, often experience an increase in pest problems across time. Weeds especially increase in density with such rotations if herbicide resistance or ineffective control occurs. We showed that adding a two-year interval of small grain crops can reduce the number of weeds that emerge in the following corn or soybean crops. But, this benefit only occurred in no-till. Tilling the soil increased the density of weed seedlings five-fold in both corn and soybean. Crop yield was reduced 25 to 50% in the tilled system because of increased weed interference. No-till practices not only reduced density of weeds, but also delayed the initial seedling emergence, thus accruing a second benefit for managing weeds. Designing rotations to include cool-season crops in a no-till system may eliminate the need for herbicides in soybean to manage weeds.
Technical Abstract: This study measured weed interference in soybean and corn as affected by residue management tactics following a sequence of oat and winter wheat. Residue management tactics compared were conventional tillage, no-till, and no-till plus cover crops. Treatments were split into weed-free and weed-infested conditions; prominent weeds were green and yellow foxtail, and common lambsquarters. Grain yield of soybean did not differ between weed-free and weed-infested conditions with no-till, whereas weeds reduced yield 25% in the tilled system. Corn responded inconsistently to treatments, with almost 50% yield loss in one year with all treatments. Cover crops did not improve weed management compared with no-till in either crop. Seedling emergence of the weed community differed between till and no-till; density of weed seedlings was fivefold higher with tillage whereas seedling emergence was delayed in no-till. The initial flush of seedlings occurred two to three weeks later in no-till compared with the tilled system. Designing rotations to include cool-season crops in a no-till system may eliminate the need for herbicides in soybean to manage weeds.