Crop water production function based on gene expression programming

A crop water production function has been one of the most significant parameters to improve the use efficiency of agricultural water in irrigation districts. A quantitative relationship between agricultural hydrological elements and yield can be established for the influence of the agricultural hydrological process on crop growth. However, the determination of parameters in the water production function requires a great deal of field experimental data in the water- salt stress gradient treatment. At the same time, there is the complex response of crop yield to the water-salt dynamic processes with the water production function. Therefore, it is necessary to construct the water production functions for the quantitative influence of hydrological factors on the crop yield using soil water-salt dynamic processes. In this study, the new crop water production function was established to integrate the Agro-Hydrological & chemical and Crop systems simulator (AHC) and Gene Expression Programming (GEP), particularly for the water saving and higher yield. The main crops were taken as the research objects, including maize, sunflower, and wheat, which were widely planted in the Hetao Irrigation District. The AHC was selected to simulate the agro-hydrological process and crop growth under different scenarios. Simulation results were used as the input data of the GEP algorithm. Subsequently, the optimal input factor combination was determined to compare the evaluation indexes of the generated data from the GEP algorithm. As such, the crop water production functions were established. Results showed that the optimal input combinations included the groundwater depth, irrigation amount, evapotranspiration (ET), total dissolved solids of groundwater, salt stress, and water content in the root zone soil. Specifically, the sensitive environmental factors varied greatly in the different crop yields. The maize yield was related to the groundwater depth, salt stress in the sowing- jointing stage and the filling-harvest stage, and the soil water content in the jointing-trumpet stage and the trumpet- tasseling stage. The sunflower yield was closely related to the groundwater depth, evapotranspiration, and the salt stress in the sowing-seedling stage, the seedling-budding stage, and the flowering-filling stage, while the soil water content in the budding-flowering stage and the filling-harvest stage. The wheat yield was related to the evapotranspiration, and salt stress in the jointing- heading stage, while the soil water content in the filling-harvest stage. Furthermore, the groundwater was the main water supply source during the maize growth period, when the maize was less resistant to the salt. By contrast, the less irrigation amount resulted in the soil salt accumulation and the salt stress in the initial and end stage of maize growth. Correspondingly, the effect of groundwater on the sunflower yield was similar to the maize, whereas, the sunflower yield was affected by the evapotranspiration, which was related to the dry aboveground biomass accumulation and yield. In addition, the effect of evaporation on the wheat yield was consistent with the effect on sunflower yield. The excessive salt accumulation and water deficit were reduced the wheat yield during the jointing-heading stage and the filling-harvest stage, which were the main growth periods. Meanwhile, the crop yield (predicted yield) was estimated under different irrigation quantities using the crop water production function. The determination of coefficient values between the predicted yields of maize, sunflower, and wheat and their simulated ones by AHC were 0.96, 0.93, and 0.96, respectively, and the mean relative errors were both less than 5%. Therefore, the water production function can be used to accurately estimate the crop yield under the salinity stress. The finding can provide strong references for agricultural water saving and efficient use of irrigation water. © 2022 Chinese Society of Agricultural Engineering. All rights reserved.