| The issue of the food security and water resources is related to the Political stability and economic development of a county or even the whole world.Despite China's grain production has been presented in the past decade a growing trend in recent years,but its growth is mainly dependent on the high input of material elements that include water resources.In addition,the total irrigated area of China in 2015 was 6 587.26 millions hm2.And effective irrigation area of 2 990.2 millions hm2,accounting for 45%of the total irrigated area.There is a low irrigation efficiency of water resources.How to develop the agricultural water use efficiency,reduce agricultural water use and improve crop water productivity has become a key issue to resolve contradictions between agricultural water and continued high yield.Therefore,it is of great significance to accurately estimate the crop water productivity,which can monitor the status of agricultural water use and manage agricultural water.How to improve crop water productivity has become a key issue to resolve contradictions between agricultural water and continued high yield.The main purpose of this paper is to analyze the water productivity of wheat in Jinzhong during 2014-2015.As the primary data source,Landsat 8 remote sensing,statistics,meteorological data,crop growth period data and ground survey data in 2014-2015 were used in crop information extraction,crop yields rasterizing,actual evapotranspiration estimation and crop water productivity calculation.The main results are as follows:(1)The multi-temporal Landsat 8 remote sensing data were used to extract crops planting information.And the ratio of NDVI between May and June in 2015 was used as the basis for extracting wheat with the threshold value of 1.78.Wheat area was 8208.04 hm2 extracted from Landsat 8 image,and the statistical actual wheat area of 2015 was 7604.2 hm2,the precision was 92%.(2)With the help of stepwise regression for the NDVI of March?April and May in 2015,the regression equation of the NDVI and yield that based on grid was excluded.The final model of yield is:Y = 7.401 + 7.876x1-2.916x2 + 1.442x3The results showed that the yield of wheat in Jinzhong was 2735-8 941 kg/hm2,with an average value of 4581 kg/hm2.(3)A preliminary evaluation of model accuracy was conducted through comparison between daily ET values inversed with the SEBAL model and the values calculated with meteorological data and Penman-Monteith equation.Ground monitored ET values of Taigu?Qixian?Jiexiu and Lingshi werel.64,1.78,1.85,1.72 mm/d respectively,while the model inversed ET value was 1.62,1.58,1.86,1.53 mm/d.The deviation was about 1.2%,10.9%,-0.3%,11.3%.And the average deviation was about 12%.The results were similar to Lanzhou Institute of Plateau Atmospheric Physics' verification of SEBAL model.It was proved that the model is reliable and the result is reasonable.(4)Finally,the wheat water productivity was calculated with the yield and actual ET data.The results showed that the wheat water productivity in Jingzhong was not more than 1.60 kg/hm3,and the regional mean was about 1.07kg/m3.Specifically,the wheat water productivity in Taigu and Qixian was higher,most of which is above 1.00 kg/hm3.And the wheat water productivity in Jiexiu was generally less than 0.85 kg/hm3.Although the wheat planting in Lingshi was more dispersed,the wheat water productivity was high.And the highest reached 2.00 kg/hm3.However,comparing with Yang Jianying's mean water productivity estimates for the winter wheat in the plain from 2011 to 2012,the average water productivity of Jinzhong wheat was less than that of the average of 1.21kg/m3. |
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