Water-saving Irrigation Of Winter Wheat By Assimilation Of Remote-sensing Data And Crop Model

With the rapid growth of the world's population and the continuous increase in the demand for water resources in industry and agriculture,the scarcity of water resources has become an important factor restricting global sustainable development.China is in severe shortage of water.Per capita freshwater resources are only a quarter of the world per capita.China is a big country in agriculture,and agricultural irrigation water accounts for 62.4%of the total water supply.In recent years,frequent extreme weather has led to increased drought.North China Plain is one of the major food production bases in China.The normal supply of grain in this area also affects China's food security,and winter wheat is the main food crop in North China.In recent years,the drought situation in North China has intensified and has become a major factor limiting winter wheat production in the region.Therefore,how to scientifically grasp the stability of winter wheat production and water-saving irrigation has become the most important issue.To study the relationship between crop water and yield,one of the effective irrigation strategies is deficit irrigation,but the field control experiments are time-consuming and laborious.The AquaCrop model was proposed by Food and Agriculture Organization of the United Nations?FAO?,which is driven by water,and suitable for Beijing area with rainfall and water restriction.This study focused on the assimilation of remote sensing data and crop models which is the hot topic in the remote sensing field,winter wheat as the research object in the National Precision Agriculture Demonstration Base,Beijing,China.In order to reduce the irrigation water consumption,increase the yield and water use efficiency,this paper provides information support for the optimization management of field irrigation schemes from the point of view of crop water use efficiency.The extended Fourier amplitude sensitivity test?EFAST?method was used to analyze the sensitivity of crop parameters of AquaCrop model,the aboveground biomass?AGB?,canopy coverage?CC?and yield of output variables.Two sets of model localization correction parameters were proposed.The yield and water use efficiency were simulated in different irrigation situations.The best combination will be found between irrigation,yield and water use efficiency of winter.Then the best assimilation model would be found by coupling AquaCrop model and the particle swarm optimization?PSO?,simulated annealing?SA?and shuffled complex evolution method developed at the University of Arizona?SCE-UA?algorithm using AGB and CC as state variables.Finally,the winter wheat irrigation scheme is optimized on the regional scale combined with the results of the former two studies.The main conclusions are as follows:?1?Parameter sensitivity analysis is the basis of model localization and application.The EFAST was used to analyze the crop parameters AquaCrop model,analysis of different irrigations.The results show that?1?the parameters relevant to temperature,humidity and increasing in canopy cover?such as stbio,kcb,wp and cgc?,there are high sensitivity for AGB,the sensitivity of these parameters does not vary with changes in crop growth environment.The sensitivity index of parameters relevant to plant density?such as ccs and den?and root development?such as root,rtx and rtnx?has larger effect on the accumulation of biomass under the condition of water stress.?2?The parameters with high sensitivity for CC were related to planting density,emerging time and canopy development?such cgc,mcc,den,ccs and eme,etc.?.?3?The sensitive parameters that have a greater impact on the yield are the harvest index,the start stop time with the critical growth period?such as flo and mat?and the parameters related to biomass,and the sensitivity of the parameters is slightly different under different water condition,there are more sensitive parameters under the condition of water stress.Biomass and yield production parameters,canopy and phenological development parameters were more sensitive to the effects of water stress on yield.?2?Two groups of sensitive parameters are choose,the parameters?P1-rainfed?under water stress and parameters?P2-normal irrigation and excessive irrigation?under no water stress for localization of the AquaCrop model correction.The results show that the parameter P1 and P2 two groups can well predict different years in the Beijing area of winter wheat under the conditions of different water treatment process variables?CC and AGB?and final yield,P1 parameters under the condition of slightly better than the results of model calibration parameters under the condition of P2.?3?On the basis of AquaCrop localization,the relationship between winter wheat yield and yield water use efficiency was detailed simulated under wet,normal and drought years 3 different rainfall year type in different irrigation quantity.Research discovered:?1?under the same irrigation gradient of winter wheat,only 1 water was irrigated,and the annual winter wheat yield was the highest in the three types of rainfall years.?2?when irrigation of 2 water is the highest irrigation yield during the elongation and flowering period.?3?when irrigation of 3 water,the yield was highest during the turning green period,elongation period and the flowering stage.?4?when irrigation 4 water,the first 3 growth periods of more irrigation yield.The water utilization efficiency of winter wheat increased with the increase of irrigation.However,when the irrigation amount of winter wheat increased to a certain extent,the irrigation quantity continued to be increased.?4?AGB and CC are crucial process variables in the growth process of winter wheat.Model to simulate accurately is important for the accuracy of the inversion process variables.11 vegetation index related AGB and CC were select,comparative vegetation index and AGB in the jointing stage,carry flag period,flowering period and filling stage,calculated the grey correlation degree,determination coefficient R² of vegetation index and CC in the whole growth period,respectively select top five largest vegetation index correlation,establish a partial least-squares regression?PLSR?model.Results show that?1?the NDVI?WDRVI?OSAVI?NDRE and GNDV,5vegetation index build PLSR model inversion of the measured CC and CC R² and RMSE were 0.89?n=176?and 12.8%respectively,the high precision and can be used for inversion of winter wheat CC.?2?AGB in jointing stage?NDVI?GNDVI?DCNI?VOGa and MTCI?,the carry flag stage?GNDVI?MTCI?NDRE?DCNI and VOGa?,anthesis?NDVI?GNDVI?NDRE?DCNI and VOGa?and filling stage?NDVI?TVI?OSAVI?NDVI and GI?and the selected PLSR model of vegetation index to construct the R² and RMSE were 0.71?n=48?,0.31 t?hm^-2,0.60?n=48?,0.82 t?hm^-2,0.45?n=48?,1.49 t?hm^-22 and 0.64?n=64?,1.63 t?hm^-2,better accuracy,can be used for inversion of winter wheat AGB.?5?The combination of the remote sensing data and the crop model perfectly combined of point and surface.The accuracy of AGB,CC and yield of winter wheat was improved effectively using AGB and CC as the state variables,and the problem was solved that the assimilation method of single state variable is assimilated with high accuracy of state variables,and the accuracy of other output variables is poor.The R²and RMSE between simulated and measured values of AGB,CC and yield using AGB as the state variable are 0.92?1.26 t?hm^-2,0.31?18.8%and 0.61?0.93 t?hm^-2.The R²and RMSE between simulated and measured values of AGB,CC and yield using CC as the state variable are 0.75?1.92 t?hm^-2,0.77?10.1%and 0.61?0.93 t?hm^-2.The R² and RMSE between simulated and measured values of AGB,CC and yield using AGB and CC as the state variables are 0.92?1.34 t?hm^-2,0.76?10.2%and 0.76?0.80 t?hm^-2.The results show that there are high R² and low RMSE between simulated and measured values of AGB,CC and yield using AGB and CC as the state variables,and the AquaCrop+SCE-UA assimilation method has good application value.?6?Coupling data assimilation algorithm and crop model estimated the yield of winter wheat in Tongzhou District.The assimilation and measured values of winter wheat yield at sampling point reached a significant level?P<0.05?.The values of R²,RMSE and MBE were 0.59 and 1.62 t?hm^-22 respectively and-17.7%,the regional assimilation yield is generally lower than the measured yield.The assimilation and measurement values of winter wheat yield at the sampling point after irrigation optimization reached a significant level?P<0.05?,and the values of R2,RMSE and MBE were 0.62,1.37 t?hm^-22 and-13.3%,respectively.The water use efficiency of winter wheat in Tongzhou District was estimated.After the optimization of irrigation,the yield and water use efficiency of winter wheat generally increased,and the yield and water use efficiency of some samples decreased slightly.