Effect of Deep Tillage on Growth and Yield of Rice Cultivars Grown under Water Deficit

Root systems play an important roles, especially under water stress conditions in rice (Oryza sativa L.). However, the contribution of root systems to growth and yield has not been clarified, because of the difficulty of investigating root systems under field conditions. In this study, we grew 12 rice cultivars belonging to different ecotypes in an upland field, to investigate the effect of tillage depth on root development, growth and yield of rice grown under water deficit. Also to identify the genotypic differences in effect. Drought stress significantly reduced plant height, panicle dry weight and total dry weight at the end of the water deficlt treatament. Water deficit imposed around the late panicle development to anthesis stage reduced grain filling. However, a sink-source imbalance increased total dry weight and the number of tillers in drought plots at harvest time. Furthermore, drought stress reduced the number of spikelets, percentage of ripened grain and 1000 kernels weight. Consequently, the grain yield was significantly reduced by both drought stress and shallow tillage. The indica upland rice cultivars showed the highest drought resistance, and the japonica upland and lowland cultivars showed reduced resistance. On the other hand, under well-irrigated conditions, deep tillage improved the growth of japonica lowland cultivars and some indica upland cultivars, but japonica upland cultivars were not affected. This result shows that the japonica upland cultivars used may have good root penetration into hard soil