Submitted to: Pendleton Station Field Day
Publication Type: Experiment Station
Publication Acceptance Date: 5/9/1997
Publication Date: N/A
Interpretive Summary: Conservation tillage systems leave 30 percent or more of the soil surface covered with crop residue for soil erosion control. These conservation systems have not been widely adopted in the dryland wheat producing region in Oregon, Washington and Idaho because of grass weed control problems. The most troublesome weed is downy brome (Bromus tectorum), an annual grass weed. The conservation tillage weed control problem is often attributed to crop residue on the soil surface creating a more favorable seedbed for downy brome. Field experiments were conducted over three years at four different sites in northeast Oregon to determine the influence of amount of crop residue on downy brome emergence. Plots were established in winter wheat fields by hand sowing downy brome seed and distributing wheat plant residue on the soil surface. Replicated plot treatments consisted of 20, 30 and 40 percent residue cover plus a control that had no residue added. Downy brome seedling emergence observations were taken in each plot. The results showed that downy brome emergence was not significantly influenced by the amount of crop residue on the soil surface. These results indicated that increased downy brome infestations in conservation tillage systems are not caused by the crop residue. They are probably caused by conservation tillage systems placing weed seeds near the soil surface where they emerge more readily than in systems such as moldboard plowing that deeply bury weed seeds.
Technical Abstract: Grass weed control, especially downy brome (Bromus tectorum L.), is often a limiting factor for dryland wheat production in the states of Oregon, Washington and Idaho in the Pacific northwest of USA. Conservation tillage systems that leave crop residue on and near the soil surface are an effective technique to control soil erosion in this region. However, downy brome control is often more difficult with these conservation tillage systems. Field experiments were conducted over three years at four different sites in northeast Oregon to determine the influence of amount of surface crop residue on downy brome emergence. Prior to seeding winter wheat (Triticum aestivum, L) downy brome was seeded in the plots and hand raked into the top 1 cm of soil. After wheat seeding, fumigated wheat plant residue was hand distributed on the soil surface to established replicated plots with 20, 30 and 40 percent residue cover plus a control that had no residue added. Downy brome emergence observations were taken in two 340 cm2 areas of each plot. The results showed that downy brome emergence was not significantly (0.05 probability level) influenced by the amount of crop residue on the soil surface. These results indicated that if there was any difference in soil temperature or soil moisture due to crop residue of the soil surface ranging from 0 to 40 percent cover it was not sufficient to influence downy brome emergence. Increased infestations of downy brome in conservation tillage systems are probably related to higher levels of weed seed near the soil surface where they