Effects of straw mulch and nitrogen management on root growth and nitrogen utilization characteristics of hybrid rice

【Objectives】 In rice-wheat rotation, rice-rape rotation and other multi-cropping regions in China, large amounts of wheat or rape straw or other straws of rice fore-rotation crop were discarded or burned, which caused serious environmental pollution and resource waste. Hence, it has significant meaning to investigate a win-win mode between straw mulch and nitrogen (N) management. To explore the optimal straw mulch and N management mode, effects of the straw mulch and N management on root growth, N uptake and utilization and dry matter accumulation in main growth stages of hybrid rice (Fyou 498) were evaluated in this research. 【Methods】 The experiment was conducted in the experimental field of Rice Research Institute of Sichuan Agricultural University in 2013.A split-plot design was used, with the main plots under wheat straw mulch (S1), rape straw mulch (S2) and no straw mulch (S0), N management as sub-plots combined with three N management practices under N 135 kg/ha rate in this study. Three N application ratios were applied on different splits: a) 3 splits: 50% basal, 30% 7 d after transplanting (7 DAT), and 20% panicle N-fertilizer according to different leaf ages at 4th leaves emerged from the top (N1), b) 3 splits: 30% basal, 30% 7 DAT, 40% panicle N-fertilizer at 4th leaves emerged from the top (N2), c) 4 splits: 30% basal, 10% 7 DAT, 60% panicle N-fertilizer equally at 4th and 2nd leaves emerged from the top (N3), in addition, no N application (N0) was set as control. Root growth, morphological characteristics, dry matter and N accumulation, dry matter transportation in stems and sheaths, and N utilization on 20 DAT and 30 DAT and at the filling stage and ripping stage were studied. At the same time, the correlation coefficients among root growth, N uptake and utilization, and grain yield were also analyzed in this research. 【Results】 The results showed that the wheat straw mulch generally improves the dry matter accumulation and N uptake of rice, promotes the root growth and N utilization efficiency, and increases the grain yield significantly. The rape straw mulch could also increase the grain yield remarkably, but not as much as the wheat straw mulch. As for the N management practice, the N 30% basal, 30% 7 DAT and 40% panicle N management practice (N2) is the optimal N-fertilizer management practice in all straw mulch treatments. The optimal N-fertilizer management practice regulates the root growth at the main growth stage efficiently, improves dry matter transportation in stems and sheaths, promotes the N utilization efficiency, and increases the grain yield significantly. When the panicle N-fertilizer ratio increases to 60%, the root growth is poor, especially at the heading stage, the grain yield and N utilization decrease. The correlation coefficients among the root growth, N uptake and utilization and grain yield are as follows: under the straw mulch and N-fertilizer management, the root dry weight, total root volume and total root length generally have significant or extremely significant and positive correlations with the grain yield and N uptake and utilization at the main growing stage of rice (r =0.38*-0.78**). 【Conclusions】 Compared with the no straw mulch treatment, the straw mulch could promote the root growth, N utilization efficiency, dry matter and nitrogen accumulation and grain yield, especially for the treatments with the wheat straw mulch. The combination of the straw mulch and 30% basal, 30% 7 DAT and 40% panicle N management practice (N2) could regulate the root growth, promote N utilization efficiency, and increase the dry matter and N accumulation and grain yield more efficiently. Among all the treatments, the wheat straw mulch with 30% basal, 30% 7 DAT and 40% panicle N management practice (N2) is the optimal mode in this research.