Soil Water And Salt Transport Characteristics And Simulations Under Mulched Drip Irrigation Of Maize With Different Soil Water Matric Potentials In The Hetao Irrigation District

The Hetao Irrigation District in the Inner Mongolia is one of the most important bases for commodity grain and oil in China.However,there was a substantial reduction in the total water quantity diverted from the Yellow River in recent years.In order to alleviate the shortage of water resources and help to realize agricultural water saving and soil salinization control in the irrigation district,field experiments were carried out in three three years?2016-2018?in a selected typical saline field,where EC_1:5 of 0-40 cm soil was 1.22dS/m and the pH value was 8.3,which belonged to a moderate salinization level.In the experiment,five different threshold values of soil matric potentials?SMP?were set to trigger the mulched drip irrigation for spring maize,i.e.,-10?S1?,-20?S2?,-30?S3?,-40?S4?,and-50 kPa?S5?.Soil water and salt distributions,growth and water consumption of spring maize under different irrigation treatments were studied.The main findings were summarized as follows.?1?Soil water content was significantly different under different SMP in three growing seasons.An obvious radial distribution of soil water content appeared in the soil profile below the emitter.During the whole growing season,the soil water content in maize root zone fluctuated greatly,but the deep layer was not affected by irrigation and evaporation.The water content of deep soil was relatively stable since the deep soil was not affected by irrigation and evaporation and the groundwater level was shallow.Redistribution of salt occured in soil profile,but the desalination areas were different for different treatments.With the decrease of SMP,the desalination area gradually shrunk.The maximum desalination area of the S1 treatment could reach 60 cm below the emitter,while there was no obvious desalination area in the S5 treatment.?2?When under lower SMP threshold values,plant height and leaf area index?LAI?of maize were relatively lower during the growing season.And premature senility of maize was observed when under the SMP threshold value of-50 kPa.Aboveground biomass,hundred-grain weight,and number of grains per spike increased with the increase of SMP threshold values.When under higher SMP threshold values,higher maize yields were obtained.The yields of treatments of S1,S2 and S3 were significant higher than those of S4and S5?p<0.05?,but there were no significant difference among S1,S2 and S3.With the decrease of SMP threshold value,WUE increased first and then decreased.The highest WUE value was obtained when under the SMP threshold value of-30 kPa.?3?The HYDRUS-2D model was calibrated and validated with experimental data of the treatment of S3 in 2017 and 2018.The results showed that the model simulations were basically in agreement with the measurements,sicne the values of RMSE?root mean square error?and R² between simulated and measured values of soil water contents were 0.042cm³/cm³ and 0.83 in 2017 and 0.037 cm³/cm³ and 0.78 in 2018,respectively.And the simulated and measured values of soil electrical conductivity were 0.052 dS/m and 0.77 in2017 and were 0.047 dS/m and 0.75 in 2018,respectively.This showed that the HYDRUS-2D model was able to satisfactorily simulate the effects of drip irrigation under mulch on the soil moisture and salinity in spring maize field in Hetao Irrigation District,which could provide a technical and data support for the optimization of drip irrigation under mulch in the irrigation district.Generally,both taking into account the yield and soil water and salt,we recommended the SMP value of-30 kPa to be the threshold value to trigger mulched drip irrigation for spring maize production in moderate saline field in the Hetao Irrigation District.