Winter Wheat – Chemical Fallow Can Replace Conventional Tillage Winter Wheat - Summer Fallow in North-Central Oregon.

Conventional tillage winter wheat-summer fallow (WW-SF), the predominant cropping system in the inland Pacific Northwest (PNW), has been shown to deplete soil organic carbon (SOC) and increase soil erosion. This research evaluates direct seeded cropping systems (DS) designed to reduce these negative impacts on soil and the environment. DS involves seeding and fertilizing in one pass under no-till. In this long-term experiment (LTE), initiated in 2003-04 crop year at OSU CBARC in Moro, Sherman County, OR,  WW-SF, is compared to DS systems that included annual winter wheat (WW-WW), annual spring wheat (SW-SW), annual spring barley (SB-SB), winter wheat-chemical fallow (WW-CF), winter wheat-winter pea rotation (WW-WP), and winter wheat-spring barley-chemical fallow rotation (WW-SB-CF). Data on grain yield, diseases, weeds, microbial biomass, soil moisture, and crop residue cover were collected. Based on the 7-yr average (2004/05 to 2010-11 crop-years) there were no significant differences in wheat grain yield among the WW-SB-CF, WW-SF, and WW-CF rotations. These yields were significantly higher than grain yields from annual crops. Yields of spring barley in SB-SB and WW-SB-CF rotations were significantly higher than wheat yields in WW-WW and SW-SW but not from wheat yield in WW-WP. Water use efficiency was highest in SB-SB and lowest in WW-WW. Root-lesion nematodes (Pratylenchus spp) populations were significantly and negatively correlated to winter wheat yields. Lowest population densities occurred in SB-SB and in certain phases of WW-CF and WW-SB-CF rotations. Population densities were particularly high in the WW-WW, SW-SW, WW-WP, and certain phases of WW-TF. Downy brome (Bromus tectorum) was the major weed particularly in WW-WW, WW-SF, and WW-CF. An economic analysis revealed that WW-CF was a promising cropping system for both farmers’ bottom line and the environment in Sherman County and perhaps in similar regions. WW-CF also manages economic risk and smoothen seasonal machinery and labor demands. If the glyphosate/diesel price ratio continues to decline the advantage of WW-CF will strengthen further. These results suggested that DS systems, particularly WW-CF, can replace WW-SF in North-Central Oregon without any detriment to grain yields. Added benefits of DS systems include increased surface crop residues (that prevent soil erosion) and SOC.