Influence Of Semi-deep Water Irrigation During Different Periods On Rice Yield And Quality

Rice-aquatic animal coculture is an ecological agricultural production mode with integrated rice cultivation and aquatic animal culture in the same paddy field based on its wetland resource,which has the advantages of lower fertilizer and pesticide application and higher economic benefits than rice monoculture.Semi-deep water irrigation is an important factor that distinguishes rice-aquatic animal coculture from rice monoculture,but the response of rice to semi-deep water irrigation is still unclear.This study set up three irrigation modes:(1)the typical high-yield irrigation model that mainly based on swallow and setting(CK);(2)semi-deep water irrigation from late tillering stage to jointing stage(SDI1);(3)semi-deep water irrigation from jointing stage to middle grain-filling stage(SDI2)using three japonica rice cultivars(Nangeng5718,Nangeng9108 and Huaidao5),three indica rice cultivars(Shenliangyou136,Huiliangyousimiao and Wanxiangyou982)and two indica-japonica rice cultivars(Yongyou2640 and Yongyou4593),with the aim to investigate the influence of semideep water irrigation on rice yield and quality and expound the genotype difference.Main results of the study were described as follows:Both irrigation modes and genotype have significant effect on rice yield.Compared with CK,two semi-deep water irrigation modes generally lowered theoretical yield and actual yield of each rice cultivar,and the higher decline amplitude was observed in SDI2 than SDI1.Analysis of yield components showed that panicles showed different response to SDI1 and SDI2 among different cultivars,while 1000-grain weight were hardly affected by irrigation modes.Yield lose under two semi-deep water irrigation modes were majorly attributed to reduced spikelets per panicle and seed-setting rate.Compared with CK,semi-deep water irrigation during different periods had significant effects on rice leaf area index and leaf area decay rate.The leaf area index of each variety was the highest under CK treatment.The leaf area index showed lower in SDI1 than SDI2 at jointing stage,and presented higher in SDI1 than SDI2 at maturity stage.The leaf area attenuation rate of CK was the lowest,followed by SDI1 treatment,and SDI2 was the highest,indicating that semi-deep water irrigation could accelerate rice leaf senescence and inhibit photosynthetic substances accumulation.Semi-deep water irrigation during different periods significantly affected rice dry matter accumulation and transportation.At each key growth stage,rice always had the highest dry matter accumulation under CK treatment,while SDI1 showed lowest dry matter accumulation at jointing stage,and SDI2 showed lowest dry matter accumulation at heading stage,30 days after heading and maturity stage.Compared with CK,semi-deep water irrigation resulted in a decrease in nitrogen accumulation at key growth stages of each rice variety.Huaidao 5 and Yongyou 4593 showed nitrogen uptake lowest under SDI1 at jointing stage,while there were no significant different between CK and SDI2 for the two varieties.Nitrogen accumulation of other varieties all ordered as:CK>SDI2>SDI1 at jointing stage,and ordered as:CK>SDI1>SDI2 at heading,30 days after heading and maturity stage.Two semi-deep water irrigation modes clearly affected rice plant type.Compared with CK,semi-deep water irrigation increased plant height,length of top three leaves,leaf basic angle and opening angle,and distance between leaf pillows,thereby weakening rice plant type.Besides,semi-deep water irrigation shortened rice panicle length and declined number of primary and secondary branches and grain density,thus reducing spikelets per panicle.Generally,rice grain quality was deteriorated by semi-deep water irrigation comparing with CK.Two semi-deep water irrigation modes both declined head rice rate and increased chalky rate and chalkiness,weakening rice milling and appearance quality.amylose content,setback presented increasing trend,while peak viscosity,cool viscosity,breakdown presented declining trend under semi-deep water irrigation when comparing with CK,while there were no significant difference among irrigation treatments.Furthermore,semi-deep water irrigation reduced appearance,viscosity,balance and taste value.Generally,rice grain quality was more affected by SDI2 than SDI1.To sum up,semi-deep water irrigation exhibited negative influence on rice yield and quality,and semi-deep water irrigation during middle and late growth period early showed larger effect than that during middle and late growth period.Indica-japonica hybrid rice showed better adaptation to semi-deep water irrigation than japonica rice and hybrid indica nce.