Effects of Different Straw Management on Subsoil Nutrient Availability and Water Content

ABSTRACT Ditch‐buried straw return (DB) has been demonstrated to enhance nutrient supply and grain yield in rice‐wheat annual rotation systems. However, how DB affects soil nutrient stratification and the underlying mechanisms are unclear. Here, we hypothesize that DB decreases the nutrient stratification ratio by increasing nutrients in the subsoil, with the effects dependent on the duration of implementation. This was validated using a short‐term (2 years) and long‐term (15 years) DB field trials through comparing SOC and nutrients in the topsoil (0–20 cm) and subsoil (20–40 cm) after rice harvest. The results showed that DB significantly increased SOC and nutrient content in the subsoil rather than topsoil compared with rotary tillage straw return (RT), thereby reducing the stratification ratio. Moreover, these effects were influenced by the duration of implementation. We further demonstrated that the in situ rice straw layers within DB absorbed more NH 4 + and water rather than PO 4 3− and NO 3 − than RT. Theoretically, the maximum adsorption of NH 4 + , NO 3 − and PO 4 3− per gram of air‐dried rice straw under RT and DB were 6.21 versus 9.01 mg, 1.26 versus 1.02 mg and 4.83 versus 3.61 mg, respectively. Moreover, water‐saturated straw not placed horizontally is more likely to lose water. Our findings suggest that the unique straw layer of DB can retain nutrients and water in the subsoil, providing a sufficient resource supply for sustainable production of the rice‐wheat cropping systems.