Effects Of Alternate Wetting And Drying Irrigation On Agronomic And Physiological Traits And Grain Quality Of Rice

Rice(Oryza sativa L.)is the foremost staple food crop in China.To achieve high yield and good quality is the two main objectives of rice production.Meanwhile,rice is the largest water consumer in agriculture,and it is important to study the water saving irrigation techniques such as alternate wetting and drying irrigation(AWD)under the situation of the increasing shortage of water resource.Although tere are many studies on AWD,these studiels are mainly focused on grain yield and little information is available on the effect of AWD on physiological traits and grain qualityof rice.In this study,two rice cultivars Yongyou 2640 and Huaidao 5 were used and grown in the cement tanks that were filled with soil in 2015 and in paddy field in 2016,and AWD(re-watered when soil water potential reached-15 kPa)were imposed from 15 days after transplanting to maturity,with flooding irrigation(FI)as control.The effects of AWD on agronomic and physiological traits and grain quality of rice were investigated.The main results are as follows:1.Grain yield and irrigation water use efficiencyCompared with FI,AWD significantly increased grain yield of rice by 13.6%-15.9%.AWD reduced the amount of irrigation water by 19%-23%.The yield increase was mainly due to the improvement in seed-setting rate and grain weight,and the number of panicles per m-2 had no significant difference between the two irrigation regimes.Spikelets per panicle were increased in AWD,but the difference was not significant between the two regimes.The AWD also significantly increased harvest index,reduced irrigation water by 19%-23%,and increased irrigation water use efficiency by 39%-48%.2.Agronomic and physiological traitsCompared with FI,AWD increased the accumulation of shoot dry matter,reduced the maximum number of tillers,and significantly increased the rate of productive tillers,the effective and efficient leaf area index(LAI)at the heading stage and LAI at maturity,non-structural carbohydrate(NSC)content in stems and sheaths at heading and its translocation to grain during maturity.The AWD improved the canopy structure of rice(the decrease in leaf base angle,and increase in light transmittance)and increased the photosynthetic rate and decreased transpiration rate of leaves.3.Root morph-physiological traitsIn the AWD regime,root dry weight,root length,root oxidation activity,root total absorbing surface area and active absorbing area,root bleeding were increased significantly,relative to those in the FI regime.The root-shoot ratio and root diameter had no obvious difference between two regimes.4.Grain fillingCompared with FI,AWD promoted the grain filling of inferior spikelets(increased average filling rate and final grain weight of inferior spikelets),increased contents of abscisic acid(ABA)and Zeatin + zeatin riboside(Z+ZR)and activities of starch synthase(StS),ADP-glucose pyrophosphorylase(AGP)and sucrose synthase(SuS)in these spikelets at early and mid grain filling stages.5.Nutrient uptake and utilizationCompared with FI,AWD significantly increased the uptake of nitrogen,phosphorus and potassium from panicle initiation to heading and increased the accumulation of N,P and K in plants at maturity.The AWD increased the internal use efficiency of nutrient(grain yield/nutrient uptake by plants)and N,P and K harvest index.6.Grain qualityUnder AWD,rice processing quality and appearance quality were improved significantly(brown rice rate,milled rice rate and head rice rate were significantly increased,and chalky rice rate and chalkiness were decreased significantly)when compared with those under FI.The AWD significantly reduced the content of arsenic(As)in grain,The contents of protein,prolimane,microelement and amino acids showed some decreases in the grain in the AWD regime,but its yield of protein and amino acids were significantly increased.