Annual Winter Wheat Increased Soil Organic Carbon Compared to the 2‐year Winter Wheat–fallow Rotation

Abstract Increasing soil organic carbon (SOC) has many benefits for crop productivity, water storage, and reduced soil crusting and erosion, but finding practical crop and soil management methods for increasing organic matter has proven very difficult in the dryland wheat ( Triticum aestivum ) region of the Pacific Northwest. This paper reports on a large, 15‐year replicated plot study where annual winter wheat could be compared to the common 2‐year winter wheat–fallow rotation to see if a difference in soil carbon could be measured. SOC was 12% greater in the surface 0–120 kg dry soil m −2 (about 0–10 cm), and 6% greater when measuring to a depth of 0–1200 kg dry soil m −2 (about 0–1 m). Expressed as soil carbon stocks, annual winter wheat was 5.30 Mg ha −1 greater at a 1200 kg dry soil m −2 depth compared to the 2‐year wheat–fallow systems. To confirm these results, a second soil sample was collected 18 months after the first. Again, SOC in the surface 0–120 kg dry soil m −2 was significantly greater in annual winter wheat compared to winter wheat–fallow rotation. In this second sample, the difference was 20%, representing 3.75 Mg ha −1 . We conclude that in rainfall zones with adequate moisture for producing annual winter wheat, it is possible to increase soil carbon stocks compared to a 2‐year wheat–fallow rotation, with substantial amounts accumulating in the top 10 cm.