| The shortage of water resources and salinization of soil are important factors that restrict the sustainable development of agriculture in Tianjin coastal area.With the development of economy and society,these problems are increasingly prominent.Drip irrigation under mulch can block the direct contact between soil and atmosphere,reduce the evaporation of soil moisture,and improve the soil moisture content.Moreover,drip irrigation can realize the precise irrigation of the soil in the root zone of crops,which will not cause the secondary salinization.In order to study the distribution and movement of soil water and salt in the coastal area of Tianjin,the maize was taken as the test crop,two irrigation methods of conventional drip irrigation and under mulched drip irrigation were used,and two different irrigation quotas were set.The HYDRUS-2D model was used to simulate the water and salt transport of soil,and the simulated value was compared with the measured value.The results showed that:(1)At the beginning of the experiment,the salt content of the whole soil profile was large,and the distribution of soil salt showed the phenomenon of surface accumulation.Rain and irrigation redistribute soil salinity.In the vertical direction,soil salt moved down with water and accumulated at the bottom of soil;in the horizontal direction,soil salt moved to the edge of membrane with water and accumulated at the edge of mulch.There were obvious desalination area and salt accumulation area under the dripper.The evaporation of soil water caused the salt in the bottom layer of the soil to move upward along the soil capillary water,and the salt content in the root zone increased.At the end of the experiment,the rainfall increased,the soil salt was fully washed,and the evaporation of soil water was reduced,therefore the soil salt showed the phenomenon of bottom accumulation.The trend of soil water content and salt content along the horizontal and vertical direction were basically the same at different sampling points from the emitter.(2)The effect of drip irrigation under mulch was better than that of conventional drip irrigation.During drip irrigation,under the 10 mm irrigation quota,the soil salt content of drip irrigation under the mulch was 7.55% lower than that of drip irrigation.Under the 20 mm irrigation quota,the soil salt content of drip irrigation under the mulch was 11.17% lower than that of drip irrigation.In the process of soil water redistribution,the water content of the mulched soil was higher than that of the uncoated soil,and the effect of soil salt return was better.(3)The irrigation quota had a significant effect on soil salt redistribution.The effect of high irrigation quota treatment on soil salt leaching was better than low irrigation quota treatment.In the process of irrigation,the effect of vertical irrigation water on 0-20 cm soil salt leaching was obvious.The leaching proportion of 20 mm irrigation quota treatment was 28.70%,and that of 10 mm irrigation quota treatment was 16.86%.20-60 cm soil layer soil leaching effect was general,20 mm irrigation quota treatment leaching ratio was 9.62%,10 mm irrigation quota treatment leaching ratio was 6.78%.In the horizontal direction,the closer to the emitter,the better the leaching effect,and the lower the salt content of the soil near the dripper.The leaching depth of 20 mm irrigation quota was about 50 cm,while the leaching depth of 10 mm irrigation quota was about 40 cm.In the process of water redistribution,0-20 cm soil moisture and salt content in the surface layer increased the most than that in the 20-60 cm soil layer.(4)The parameters of HYDRUS-2D model were calibrated with the measured data in 2017.The soil content RMSE was 0.025cm3/cm3,MAE was 0.02cm3/cm3,the soil salt content RMSE was 0.34g/kg,MAE was 0.25g/kg.Based on the measured data in 2018,this paper simulated the soil water and salt transport in the shallow buried area of coastal groundwater,and compared the simulated value with the field measured value.The p value of T test of soil water content and salt content were 0.592,0.752,respectively,which were greater than 0.05,and the RMSE and MAE values were 0.022cm3/cm3,0.014cm3/cm3,0.357g/kg and 0.288g/kg,respectively.The results showed that the HYDRUS-2D model is reliable and can be used to simulate the soil water and salt transport in Tianjin coastal shallow groundwater area. |
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