Submitted to: Columbia Basin Agricultural Research Annual Report
Publication Type: Experiment Station
Publication Acceptance Date: 5/1/1999
Publication Date: N/A
Interpretive Summary: Wheat residue has been investigated for its potential to negatively influence growth of the following wheat crops. This article reviews the conclusions of scientific research conducted over the past four decades, and presents results from a recently completed greenhouse experiment. As residue ages and weathers, it rapidly loses the capacity to harm the following crop. This means that the cropping system we should be most concerned about in the dryland Pacific Northwest is fall planted wheat in an annual cropping system (winter wheat not following fallow). Our greenhouse study found that seedling wheat was harmed when its roots grew through buried residue. No-till systems do not produce buried residue, and this prevents the roots of fall-planted wheat from growing through unweathered residue. According to past research, we still need to be concerned with the large amounts of unweathered residue on the soil surface near the seedlings.
Technical Abstract: Over the past four decades researchers have examined the effects of crop residue on the growth of plants. Residues have been shown to damage wheat and other crops in both laboratory and greenhouse studies. Only recent, unweathered residues produce a toxic effect. The growth impairments relate to germination, emergence, growth rates, or tillering. In a recently completed greenhouse study, wheat seedling height was reduced by 20 percent 20 days after planting when three-month-old wheat residues were placed about an inch below the seed (Stewart Wuest, unpublished data). Residue toxicity is only likely to cause problems in fall-seeded crops, because this is when we have large quantities of unweathered residues. Disease problems found in annual winter wheat cropping systems may be due to toxins as well as pathogens found in unweathered residues. These residues are often plowed under the surface where they are intercepted by the roots. No-till presents the opportunity to plant into ground with no buried residue. Fresh residues left on the surface of the soil remain a concern. Research at Pendleton has demonstrated that standing stubble can reduce light penetration into the seed row enough to reduce seedling vigor and tillering of winter wheat. Whether this results in a reduction in yield will depend on circumstances later in the growing season. In the Pacific Northwest, leaving residue near the seed row to reduce evaporation is an advantage when we plant fall crops into our light, dry soils. Our knowledge of the potential toxic effects of residue should allow us to maximize the benefits of surface residue cover produced in no-till and avoid the hazards to plant health in fall-seeded systems.