Co-application of nitrogen and straw-decomposing microbial inoculant enhanced wheat straw decomposition and rice yield in a paddy soil

Straw returning is a promising approach to improve soil fertility and to mitigate the negative effects of chemical fertilizers on soil quality. However, straw degradation is a slow and multifactorial-controlled process. Herein, a field experiment (June 2010-September 2013) was carried out to examine the effects of concurrent application of chemical nitrogen (N) and straw-decomposing microbial inoculant (SDMI) on wheat straw decomposition and rice yield in a paddy soil, Anhui Province, East China. To do so, four treatments were selected with basal N fertilization rates of 0 (CN105), 67.5 (CN24), 97.5 (CN18), and 150 (CN12) kg ha(-1). For all treatments, wheat straw and SDMI were applied at the equal rates of 6000 and 30 kg ha(-1), respectively. To assess wheat straw decomposition, straw samples were taken at tillering, elongation, heading, and maturity stages of rice growth. Results indicated that straw decomposition substantially increased two to over 15 times with rice growth. In tillering stage, N amended straws had 7.5 to almost 21% higher decomposition than CN105 due to the stimulation of soil microbes with higher N requirement. After this stage, all treatments had rather similar decomposition rates. This might attribute to SDMI application that, in turn, significantly increased soil microbial respiration (P < 0.05). Generally, N addition increased grain yield 0.4-13.6% higher than CN105. This can be due the accelerated straw decomposition caused by boosting soil microbial activity/respiration. Overall, our results suggested that CN18 was the most favorable C/N ratio for both microbial straw decomposition and rice productivity in the study paddy soil. Although we found that co-application of N and SDMI is an efficient/inexpensive approach to improve soil fertility and crop productivity through acceleration of straw degradation, full documentation of straw degradation in relation to the soil properties/agricultural management practices still requires long-term field trials.