Submitted to: Columbia Basin Agricultural Research Annual Report
Publication Type: Other
Publication Acceptance Date: March 1, 2003
Publication Date: N/A
Interpretive Summary: Scarcity of water limits winter wheat production in the dryland cereal producing regions of the Pacific Northwest. In very low-rainfall areas summer fallow, one crop using two years of soil moisture is considered economical. Tillage is the primary method for weed control in fallow areas. However, herbicides are used for weed control during the fallow period in no-till management systems. This practice is referred to as no-till chemical fallow or simply chemical fallow. Lack of adequate soil water in the seed-zone is the main reason that chemical fallow has not replaced weed control by tillage. Information is lacking about the influence of residue left from prior crops on chemical fallow seed-zone soil water content. In addition, little is known about how continuous chemical fallow impacts seed-zone soil water as the number of years in no-till increases. The autumn of 2002 was drier than normal. Seed-zone soil water content was measured, just before planting, in early October, in both chemical fallow/winter wheat and tilled fallow/winter wheat plots near Pendleton, OR. The chemical fallow/winter wheat plots had varying amounts of residue left from the previous wheat crop and seed-zone soil water increased as wheat residue increased from 6,000 to 8,000 pounds per acre. The number of years these plots had been in a chemical fallow system influenced the amount of wheat residue present. The seed-zone soil water content was slightly higher in plots that had been no-tilled for 22 years compared to water content in plots that had been no-tilled for 6 years. It was shown that during a dry fall, seed-zone soil water content in no-till chemical fallow with adequate residue cover was equivalent to water content in conventionally tilled fallow.
Technical Abstract: Lack of adequate seed-zone soil water content is one reason chemical fallow has not replaced tilled fallow in the inland Pacific Northwest winter wheat growing region. There is lack of information concerning the influence of crop residue amount and length of continuous no-till on chemical fallow seed-zone soil water content. Seed-zone soil water content was measured in early October in chemical fallow/winter wheat and tilled fallow/winter wheat plots near Pendleton, OR. The chemical fallow/winter wheat plots had varying amounts of wheat residue produced by the previous crop and length of time in no-till. In early October in a dry fall, seed-zone soil water content in no-till chemical fallow increased as wheat residue amount increased from 6,000 to 8,000 lb/acre. The seed-zone soil water content was slightly higher in plots that had been no-tilled for 22 years compared to water content in plots that had been no-tilled for 6 years. In an established no-till system with 7,200 lb/acre or more of crop residue, winter wheat stand establishment was equivalent to the conventionally tilled fallow system.