Study On Rice Water Status Diagnosis And Irrigation Regulation

The diagnosis of rice moisture status and field irrigation decision making is of great significance for scientific irrigation and precise management of paddy rice.This study used Ningjing4 as experimental material,through the implementation of different soil water treatment of pond experiment,the effects of soil moisture on the growth and development of rice was analyzed.The suitable soil layer for water status diagnose and regulatation was proposed based on soil moisture.The water status of rice was retrieved by using leaf scale index and canopy water spectral index.And then the diagnostic effectiveness of these index was comprehensively evaluated.The results will provide optimal means and scheme for rice water deficit diagnosis and regulation,and will provide a theoretical reference for the development of soil moisture sensors.The effects of soil water stress on dry matter and yield of rice shoot were studied on the basis of pool experiment condition.The suitable soil moisture and soil diagnostic layer was were regulated.The results showed that Soil water stress greatly affected the dry matter accumulation in rice organs and final yield.Light drought and heavy drought treatments decreased by 17.1%and 24%,respectively,compared with the control treatment.Rice moisture decreases with the decrease of soil moisture content,during the whole growth period,canopy relative water content(CRWC)first declined and then increased,and declined sharply at the initial of grain filling,canopy water content(CWC)and canopy equivalent water thickness(CEWT)showed a downward trend.According to the relationship between canopy water index and dry matter accumulation variations,CWC was most closely related to dry matter accumulation.The CWSI of canopy water index is only about 0.1,and the adaptability of rice to drought is weak-So,once the canopy water index drops,water must be added.The biggest soil moister difference between water stress treatment and the control treatment was in shallow soil layers,and the difference was getting smaller with the increase of soil depth.The moisture difference between 0-0.2?0.2?0.4?0.4?0.6m and 0.6?0.8m layers was between 27%?45.2%,10.4%?32.3%,5.4%?18.7%and 3.7%?12.4%,respectively.In addition,the degree of soil moisture variation decreases with the increase of soil depth.In different periods,different depth of soil moisture and the corresponding period of dry weight had significant correlation,0?0.2,0.2?0.4m soil layer showed the best fitting and the highest R2,in the whole growth period,the correlation between soil moisture content and yield in different soil layer decreased with the increase of soil depth,0?0.4m is the optimum soil layer for the diagnosis of water deficit.According to the field water control standard of controlled irrigation model.The study determined that the upper limit of irrigation for the soil layers of 0?0.2m and 0.2?0.4m after the tillering stage is the saturated volume water content of soil,and the lower limit is 76%and 85%of the soil saturated volumetric water content,respectively.These results would provide technical support for monitoring soil moisture and diagnosing rice water deficit using soil sensors.In this study,we compared the responses of rice leaf scale index to water deficit at different leaf positions,and analyzed the leaf scale index and canopy water spectral index to monitor rice water status.The results showed that the changes of stomatal conductance,photosynthetic rate and transpiration rate were as follows:W1>W2>W3,the law of leaf temperature difference showed:W3>W2>W1,there were differences in different leaf positions.At the late stage of grain filling,the photosynthetic rate and transpiration rate of rice under W1 treatment were higher than that of W2 treatment because of severe drought.In the sensitivity of water deficit of different leaf photosynthetic characteristics index,the L1 was most sensitive,the L2 were second,and the L3 were the worst.The variation degree of photosynthetic characteristics of leaves in the whole growth stage was the largest in leaf temperature difference,followed by stomatal conductance.In different stages,different leaf photosynthesis and canopy index Weiguang plant water status(relative water content,water content and equivalent water thickness)have different degrees of correlation,the relationship between canopy water content is the most close,at each leaf position in L1 and L2 of the photosynthetic characteristics of canopy water status can better inversion.While the leaf transpiration rate,photosynthetic characteristic index of leaf-temperature difference can reflect the canopy water content.The law of CWSI of photosynthesis characteristic index value shows:leaf-air temperature difference>stomatal conductance>transpiration rate>photosynthetic rate,CWSI of light drought is the critical value of water deficit,CWSI of leaf-air temperature difference,stomatal conductance,transpiration rate and photosynthetic rate were 0.42,0.32,0.17,0.12,respectively.On the whole,it is suitable to diagnose the water deficit of rice by adopting the variation of L1 leaf-air temperature difference.Among the canopy water spectral index,CWC was the best for water status monitoring,followed by CEWT,CRWC was the worst.Normalized water index based on infrared(NIR)and shortwave infrared(SWIR)is better than canopy water spectral index in monitoring water status.But practically,using leaf-water temperature difference to diagnose rice water status is more accurate and stable than the canopy spectral.