Effect Of Alternate Wetting And Drying On The Growth And Development, Grain Yield And Quality Of Rice

Rice (Oryza sativa L.) is the foremost staple food crop in China and the largest water consumer in agriculture. With the population growth, urban and industrial development and the decrease in water availability resulting from pollution and resource depletion, the increase in both quantity and quality of rice yield is necessary to meet the needs of the population growth and preferences of consumers towards the high quality, and meanwhile it is necessary to deal with the increasing scarcity of water resources. Therefore, it would have great significance to establish the water-saving techniques for high yield and good quality in promoting rice production and ensuring food security. In this study, several mid-season rice cultivars were either pot-, tank, or field-grown. Three irrigation treatments, alternate wetting and moderate soil drying (re-watered when soil water potential reached -15 to -25 kPa at 15-20 cm depth), alternate wetting and severe soil drying (re-watered when soil water potential reached -30 to -50 kPa), and conventional irrigation (control, continuously flooded), were conducted during the different growth stages or the whole growing season. The characteristics of grain yield and quality and the mechanism involved in the effects of irrigation regimes on the quantity and quality of rice yield were investigated. The main results are as follows:1. Compared with the conventional irrigation, the alternate wetting and moderate soil drying regime, conducted at either a growth stage or the whole growing season, significantly increased grain yield, whereas the alternate wetting and severe soil drying regime significantly reduced the yield. The alternate wetting and moderate soil drying regime throughout the growing season increased grain yield by 10% - 12%, while the alternate wetting and severe soil drying regime reduced grain yield by 29% - 35%.2. The alternate wetting and moderate soil drying regime conducted either during the grain filling period or the whole growing season significantly increased the rates of brown rice, milled rice and head rice, transparency and peak viscosity and breakdown value of rapid visco-analyser (RVA) profiles, and reduced chalky grains, chalkiness and hot viscosity and setback values. The results were reversed under the alternate wetting and severe soil drying regime.3. The amount of irrigation water application was 732-738 mm under the alternate wetting and moderate soil drying regime and 525-558 mm under the alternate wetting and severe soil drying regime, and was reduced by 21% - 22% and 41% - 43%, respectively, when compared with the water application (926-942 mm) under the conventional irrigation. The water productivity (grain yield per unit irrigation water, kg grain m-3) was 1.22 - 1.29 and 1.10 - 1.09, respectively, under the alternate wetting and moderate soil drying regime and under the alternate wetting and severe soil drying regime, and increased by 34% - 43% and 11% -21%, respectively, relative to under the conventional irrigation (0.90 -0.91).4. The alternate wetting and moderate soil drying regime significantly increased leaf photosynthesis, root oxidation and nitrate reductase activities, cytokinin (zeatin + zeatin riboside) contents in roots, leaves and grains, and activities of sucrose synthase, adenine diphosphoglucose pyrophosphorylase, starch synthase and starch branching enzyme in the grains, and the alternate wetting and severe soil drying regime decreased these activities or contents.5. The water-saving irrigation technique for high grain yield and good quality was proposed. A thin layer of 2-3 cm water should be kept during the recovering period after transplanting, and an alternate wetting and drying regime could be conducted at other growth stages by controlling low limits of soil water potential during the drying period, namely, soil water potential at -5 to -15 kPa at the stages of effective tillering, panicle differentiating and early grain filling (0-10 d after heading), -15 to -30 kPa at the mid season drainage stage, and -10 to -25 kPa during the mid- and late grain filling period (11-40 d after heading). Re-watering should be done by irrigation as soon as soil water potential reaches the above values. The upper-limit of the values is applied for semi-dwarf inbred cultivars or sandy soil, and the low-limit for hybrid rice or clay soil.