Abstract
Minimizing the deterioration of grain quality caused by the high temperature stress in the ripening stage is an important agronomical issue in rice cultivation. Field trial was conducted to investigate the effects of deep-flood irrigation on the growth and quality of rice under high and normal ripening temperatures. The experiment was carried out from 2004 to 2007 using three rice cultivars (Hatsuboshi, Sasanishiki and Koshihikari). Two water management regimes were prepared : DFI (deep-flood irrigation; water level was kept in 18 cm from active tillering to maximum tiller stage) and CWI (conventional water irrigation). DFI decreased inferior tillers, resulting in a higher percentage of tillers that produce mature grains. Although DFI decreased the number of panicles, it increased the number of grains per panicle and thousand grain weight of brown rice; hence, the yield equal to that in the CWI plot. In addition, DFI markedly the decreased the occurrence of milky white grains. This effect was observed both in high and normal temperature conditions, suggesting that DFI is an effective method to overcome the deterioration effect of a high ripening temperature. The higher sensitivity of the cultivar to a high temperature, the higher the DFI effect. However, DFI should be started after production of enough tillers. Otherwise, the yield will be decreased due to a shortage of tillers. Three hundred and thirty tillers/m2 before the start of DFI may be needed to have the same level of yield as that by the conventional cultivation in addition to reducing deteriorated grains.
