| With the increasing global water crisis, water-saving cultivation in agricultural production has been regarded as a serious issue for a long term. Nonflooded mulching rice cultivation systems (NMRCS), as brand new water saving techniques, have aroused special and wide attention nationally and internationally since 1980s. Rice-wheat (R-W) rotation systems are the main cropping systems in south China. Water and nutrient (especially nitrogen) are the two critical factors that restrict the productivity and sustainability in the R-W systems. However, there are lack of the systemic studies on crop yield and fate of nitrogen in R-W systems particularly under the condition of NMRCS. The paper investigated the effects of NMRCS and N applied rate on grain yield, N uptake and fate of fertilizer N in R-W systems through different field plot experiments and one 1SN micro-plot experiment in southwest China Sichuan Province. The main results are summarized as follows:A continuous 3-year located experiment showed that nonflooded plastic film mulching (PM) led to significantly higher N uptake by rice but nonflooded wheat straw mulching (SM) caused relatively lower rice yield compared with traditional flooding under conventional N application level (150 kg hm"2 in rice season and 120 kg hm"2 in wheat season, the same below). In subsequent wheat season, however, grain yield and N uptake of wheat ranked the contrary sequence: SM > TF and PM, indicating the residual effects of SM on the growth and N utilization of wheat following rice.A continuous 2-year located experiment showed that under control (no N applied to both rice and wheat) and low N. (75 kg hm"2 in rice season and 60 kg hm"2 in wheat season) levels PM and SM treatments produced the similar effects on grain yield and N uptake of rice and wheat crops like the first experiment. While under conventional N and high N (225 kg hm"2 in rice season and 180 kg hm"2 in wheat season) levels, the differences of crop yields and N uptake among PM, SM and TF treatments obviously became smaller or were not significant, suggesting that the differences of productivity and N utilization in R-W rotation between NMRCS and traditional flooding cultivation system tended to disappear.The third located experiment further confirmed mat PM and TF could obtain similar grain yield of rice while nonflooded no mulching (NM) led to lower grain yield compared with TF, which was similar to the above two located experiments. However, SPM (wheat straw and plastic film mulching) got the same yield as TF and PM, suggesting that the negative effect of SM on rice be illuminated by measures of plastic film mulching. Grain yield of subsequent wheat followed the sequence of TF > SM and SPM > PM and NM, which was a little different with the first and second experiments. The effect of NMRCS on N uptake by rice and wheat followed the similar trend like grain yield whereas the differences between NMRCS and TF system were lower than those of yields.The results from 15N micro-plots further discovered the fate of fertilizer N in the R-W systems. In rice season, nitrogen use efficiency (NUE) was improved by various nonflooded mulching cultivation treatments (18.41-23.56%) compared with TF (15.30%). The rate of fertilizer N remained in soil (0-100cm depth), however, followed by TF (22.10%) > NM (20.90%) > PM, SPM and SM (19.57-19.91%). While the total N loss rates (55.54-62.60%) were not significantly different with NMRCS and TF cultivation system. In wheat season, NUE by wheat ranked by the sequence of TF (20.60%) > SM and SPM (17.65-18.33%) > PM and NM (15.93-15.99%). The rates of fertilizer N remained in soil (23.06-26.86%) and lost from soil-crop system (55.49-60.04%) did not showed any significant differences among all nonflooded mulching and traditional flooding cultivation treatments.In general, compared with traditional R-W system, nonflooded mulching R-W systems especially PM system can obtain the comparable or a little higher grain yield and NUE under water-saving condition. However, there is a...
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