Effect of methods of straw returning and planting on root growth and rice yield

This study was conducted to compare the rice root system and yield under different straw returning and planting methods. Our findings will provide the theoretical and practical basis for straw returning in different planting ways. In this study, we used a two-factor spilt-plot trail using hybrid rice cultivator F-you 498. The main plot was comprised of three different straw returning systems, i.e., no straw returning, straw mulching and straw soil-returning. The main plot was further divided into two subplots based on rice planting method, namely, the artificial transplanting and mechanical transplanting methods. The dry weight of rice root, root-shoot rate, root morphology, physiological features and yield formation under different straw returning and cultivation methods were studied. The results of our experiment are as follows: 1) Initially the root growth was restrained after straw returning, however, then the root growth was promoted. Root growth was restrained at active tillering stage and promoted from jointing stage. Better root growth was observed under straw soil-returning treatment at full heading stage and straw mulching treatment at maturing stage, respectively. The values of root diameter at each birth period, single stem and population root index, population dry weight of tillering and mature stage, root bleeding per stem of 15 days after jointing stage, 15 days after heading stage and maturing stage were higher in artificial transplanting compared to mechanical transplanting system. Mechanical transplanting system had higher root index at jointing and heading stages compared to artificial transplanting system. Different from that better root morphological index and population root dry weight were observed at heading stage in mechanical transplanting under straw soil-returning system, the root growth was comparatively better in artificial transplanting system during booting stage, and slower root aging (post-anthesis) and stronger root bleeding per stem were recorded under straw mulching system treatment. 2) Compared to no straw returning system, improved rice yield (3.50% on average) was observed in straw returning system, and straw mulching had the highest yield. The yield change rate of straw returning with artificial transplanting was 2.03%-9.81%, and that of straw returning with mechanical transplanting was -6.00%-1.30%. Straw mulching with artificial transplanting showed the highest yield-increasing rate. 3) The root dry weight at active tillering stage, root dry weight, root morphology index per stem and population root morphology index at mature stage were positively correlated with spikelets per panicle, total spikelets and yield. However, the root morphology index per stem and population root morphology index at tillering stage were negatively correlated with effective panicle number. To sum-up, in straw returning system, increased yield was observed in artificial transplanting, however, decreased yield was recorded in mechanical transplanting system. Moreover, straw mulching had higher yield than straw soil-returning. Whereas in straw mulching coupled with artificial transplanting system, early and fast root growth, slower aging and higher rate of root bleeding per stem, and higher overall yield were observed compared to other systems. Meanwhile, in straw soil-returning coupled with mechanical transplanting system, improved root growth was observed during the middle growing stage but comparatively higher and fast root aging rate and low bleeding intensity per stem were observed.