Modeling Agricultural Water Productivity In Shallow Groundwater Area

The water conversion process in field and irrigation region is complex under the shallow groundwater condition.Then the contribution of groundwater to water use in field affects the formation process of water productivity.The main project of the study is T exploring the effect of deficit irrigation on water recycle of irrigation field and crop growing.Through field experiment and developing model,the study reveals the impact of different irrigation water amount,groundwater depth and salinity on the water cycle and crop water use in the field.At the same time,the hydrological process at regional scale is analyzed.Main contents and results of the dissertation are as follows:1.Experiments of deficit irrigation on maize were carried out in 2013 and 2014.The parameters of water balance were calculated with the Darcy Law and Water Balance Method.Results showed that the crop evapotranspiration decreased slowly with irrigation water reducing,but the groundwater contribution increased with irrigation water reducing.Then deficit irrigation improves the groundwater contribution.The groundwater contribution to crop water use increased linearly with irrigation water reducing.When the irrigation amount was minimum,the groundwater contribution to crop water use could be up to 15%.The water productivity is similar among various irrigation levels,but the irrigation water productivity increased with the irrigation decreasing.2.Based on considering the water and salt transport in actual root zone and groundwater up flow,the model(Agricultural Water Productivity Management for shallow groundwater,AWPM-SG)was developed with coupling the soil water and salt transport and the crop growing.The AWPM-SG model not only considered the actual water and salt status and its impact on crop growing but also combining the dynamic process.For proving the feasibility of the model,experimental data of maize with lysimeters at Linhe in 2007,2008 and experimental data of maize at Fenzidi in 2016 were used to calibrate and validate the AWPM-SG model.Results showed that the model can simulate the soil water and salt transport and crop growing perfectly in regions with shallow groundwater.3.After calibration and validation,the AWPM-SG model was used to simulate the effect of different irrigation amount,groundwater depth and groundwater salinity on soil water and salt process and its impact on crop growing.The results showed that under same irrigation amount,the groundwater contribution to crop water use and the crop yield decreased with groundwater depth increasing.When the groundwater depth was greater than 3 m,the groundwater contribution to crop water use can be ignored.The water productivity of maize varied parabolicly with the deeper groundwater under same irrigation amount,and the water productivity increased firstly and then decreased with decreasing irrigation under same groundwater depth.Under same groundwater salinity,the soil salinity of root zone increased with groundwater depth decreasing and then the crop growing would be affected.Under same groundwater depth,the crop yield was affected less significant than the crop evapotranspiration with groundwater salinity increasing.Then the water productivity increased slightly with groundwater salinity increasing.With groundwater at 1.5 m,the water productivity of maize with groundwater salinity of 4.0 g/L increased by 0.01kg/m3 than that with groundwater salinity of 1.0 g/L,and the reduced proportion of irrigation water productivity was 0.1kgh/m3.4.The groundwater depth ranged from 0.4 m to 4.24 m in Jiefangzha irrigation district in 2013 and 2014.The averaged groundwater depth in 2013 was 2.03 m and deeper than that in 2012.The spatial distribution of groundwater contribution(F)was related directly with the distribution of groundwater depth.The maximum of F appeared at the west of the study area and the minimum of F appeared at the east and northeast of the study area.The spatial distribution of crop yield was similar with the crop evapotranspiration,which is affected by the distribution of soil salinity significantly.Due to the concentrated rainfall in 2012,the irrigation efficiency in 2012 was less than that in 2013.