Effects of straw return and feed addition on the environment and nitrogen use efficiency under different nitrogen application rates in the rice–crayfish system

Purpose Understanding the direction of nitrogen flow in the rice-crayfish system (RC) and optimizing the rate of nitrogen fertilizer application (ORN). Methods To this end, there were four test treatments—(i) straw with feed (SF), (ii) straw with no feed (SN), (iii) no straw with feed (NF), and (iv) no straw with no feed (NN) that was conducted to delineate the flow of the nitrogen present in the straw (straw-N) and feed (feed-N). Second, we carried out a mesocosm experiment with different rates of 15 N-labeled nitrogen fertilizer application: 0 kg N ha −1 (0 N), 75 kg N ha −1 (75 N), 150 kg N ha −1 (150 N), 225 kg N ha −1 (225 N) to explore the optimal rate under the effects of feed-N and straw-N supply. Results The results showed that at 75N, 14% and 1.86% of feed-N and 4.3% and 8.78% of straw-N is utilized by crayfish and rice, respectively. The percentage of feed-N and straw-N lost to the environment was the lowest at 75 N, i.e., 84.48% and 86.92%, respectively. Using straw return to the field and feeding as the basic management measures for RC, we observed that the rice yield was the highest under 75 N. The highest nitrogen use efficiency (NUE) was 25%, and the highest soil storing nitrogen by the fertilizer-derived was 34% under 75 N. Conclusions ORN could help in the effective utilization of feed-N and straw-N via a compensation effect, promote the absorption and transport of nitrogen, and ultimately improved NUE in RC.