Barley, corn, and wheat residue decomposition as affected by tillage and nitrogen rate in semi‐arid conditions

Abstract Summer fallow practices are of increased interest in semi‐arid irrigated areas of the western United States as a means to replenish water resources. Understanding of cereal residue decomposition in these conditions is limited, and data are needed to develop guidance. Research was conducted from 2018 to 2020 in Aberdeen, ID. Residue decomposition bag studies assessed crop type (barley [ Hordeum vulgare L.], corn [ Zea mays L.], hard red wheat [ Triticum aestivum L.; HRW], and soft white wheat [SWW]), tillage (surface and incorporated), and supplemental fertilizer‐N rates (0, 56, and 112 kg N ha −1 ) collected after application (spring, summer, and fall). Barley, corn, HRW, and SWW carbon:nitrogen (C:N) ratios were 74, 62, 105, and 87, respectively. Crop type and tillage affected residue decomposition, but fertilizer‐N had no impact. Decomposition was greatest from post‐harvest to spring for incorporated corn (37%) and least for surface barley, HRW, and SWW (21%). At the fall sampling, patterns were largely the same with minor changes from spring. Fertilizer‐N decreased C:N ratio at the spring sampling but not at the summer or fall timings. First‐order decay constants ranged from 0.00075 to 0.00300 day −1 for surface HRW and incorporated corn, respectively. This equates to a timeframe of 231–929 days for 50% of residue to decompose. Additions of fertilizer‐N to increase residue decomposition were not supported by the data but incorporation of residue by tillage and lower C:N crop types did result in more rapid decomposition. Relatively slow rates of decomposition occurred, particularly when surface applied, and these estimates can be used to improve residue management in semi‐arid regions.