Search

AbstractRecently, the occurrence of chalky grain caused by high temperature stress at the ripening stage has been a global problem for rice. We previously showed that the deep and permanent irrigation method, which is the combination of the V-furrow direct seeding and deep-flood irrigation methods, reduced chalky grain occurrence. To study the possible physiological mechanisms for reduced chalky grain occurrence by the deep and permanent irrigation method, we conducted field experiments in 2008 and 2009 to examine the effects of the deep-flood treatment on plant nitrogen (N) content, stomatal conductance and photosynthetic rate especially at the ripening stage. Results showed that in the deep-flood treatment that maintained a 20 cm water depth, leaf N content was consistently and significantly higher than the control with only a 10 cm water depth. Except two measured days, the stomatal conductance under the deep-flood treatment was significantly higher than in the control. Furthermore, stomatal conductance and photosynthetic rate in the deep-flood treatment were always significantly higher than in the control in both years. Thus, the deep-flood treatment enhanced N uptake, and consequently photosynthetic activity, resulting in the reduction of chalky grain formation, as previously reported. Accordingly, the effects of deep- flood treatment on grain quality improvement in rice may possibly be attributed to the improvement in source activity.

AbstractFormation of chalky grains which is the main cause of the degradation of rice grain quality occurs frequently when the temperature during the 20 days after heading exceeds 27ºC. In this study, we examined the grain quality, chalky grain formation, growth and yield of plants grown by the deep and permanent irrigation (DPI) method, which is a combination of the V-furrow direct seeding method and the deep-flooding irrigation method. Field experiments were conducted in 2008, 2009 and 2010. The DPI method in which the water level was maintained at about 20 cm above the soil surface, improved grain quality by decreasing the chalky grain ratio by about 5% and increasing the perfect grain ratio by about 10% as compared with the V-furrow direct seeding method in which the water level was maintained at about 10 cm above the soil surface. The DPI method decreased the number of tillers and panicles but increased the number of spikelets per panicle so that the two methods gave similar yields. DPI is a promising labor-saving method expected to reduce the formation of chalky grain due to a high temperature during ripening.