Effect of straw return methods on maize straw decomposition and soil nutrients contents

By investigating the impacts of tillage and straw return methods on maize straw decomposition, a suitable approach of returning maize straw to soil was explored for straw utilization with high soil efficiency in the brown soil area of northeastern China. A two-year (2014-2015) field experiment including no-tillage with straw mulch (NTS), straw incorporation through rotary tillage (RTS) and straw incorporation through plow tillage (PTS) treatments was conducted in Shenyang, Liaoning Province. Nylon bags containing straw 2-5 cm long were buried in different depths of soil according to tillage depth of different treatments (0 cm for NTS, 15 cm for RTS and 25 cm for PTS) in the study, and the decomposition of straws and release rates of carbon (C), nitrogen (N), phosphorus (P) and potassium (K) by maize straw, along with the effects of straw return on nutrients contents of the topsoil were tested. The results showed that straw decomposition rates were high at the early phase and slowed down at the later phase under both RTS and PTS treatments, with the order of nutrients release rates in all treatments of K > P > C > N. The mean decomposition rates of straw in both years were 38.8%, 78.0% and 65.9% respectively for NTS, RTS and PTS treatments. Nutrients release rates of returned straws under NTS, RTS and PTS treatments were respectively 56.5%, 78.8% and 69.4% for C, 16.7%, 53.5% and 38.8% for N, 81.3%, 92.5% and 89.8% for P, and 92.0%, 99.4% and 98.9% for K. The tendency for straw decomposition and C and N release under NTS treatment fitted well with Logistic function, but those of RTS and PTS treatments fitted Michaelis-Menten function. Moreover, K and P nutrients release of all the three treatments changed according to the Michaelis-Menten functions. Straw return enhanced organic carbon and total nitrogen contents of the topsoil. Then total soil P content of RTS treatment was significantly higher than that of PTS (P < 0.05). However, there was no significant difference in total soil P content between RTS and NTS treatments, and in total soil K content for all the treatments. Based on comprehensive analysis from straw decomposition characteristics and fertility, straw incorporation through rotary tillage was the suitable approach for maize straw return in brown soil areas in Northeast China.