Study Of Soil Evaporation Under Straw Mulching And Winter Irrigation

Water shortages,less precipitation,and intensive soil evaporation are severe problems in North China.During the seasonal freeze-thaw period,phase transition of soil water content and water-heat coupling make the law of soil evaporation complicated.It is of practical significance for alleviating water shortages and seeking feasible measures to suppress soil evaporation to explore soil evaporation law under surface control measures.The soil evaporation under the 1-2 cm straw mulch thickness monitored by field experiment during the freeze-thaw period from 2017 to 2018 was used to verify the SHAW model’s ability to predict soil evaporation under straw mulch.Based on the soil water and heat data under different straw mulching thicknesses in 2005-2006 and under different winter irrigation quotas in 2015-2016 during the freeze-thaw periods,the SHAW model was used to simulate the soil evaporation and soil freezing and thawing process under different straw mulching thicknesses and different winter irrigation quotas.Based on the soil evaporation,soil water content,and soil temperature data under the different straw mulch thicknesses monitored by field experiments during the freeze-thaw period from 2017 to 2018,the SHAW model’s sensitivity parameters were analyzed.The soil evaporation monitored is used as the dependent variable,and nine meteorological factors affecting the soil evaporation are used as the independent variables.The random forest algorithm constructs the prediction model of soil evaporation in the freeze-thaw period,and the importance of the factors affecting soil evaporation during the three freeze-thaw stages was evaluated.The results are as follows:（1）The inhibiting effect of straw mulching on soil water evaporation during the freeze-thaw period reached 24%–56.7%,and straw mulch reduced the range of daily soil water evaporation by 2.02–2.48 mm.The highest soil water evaporation rate occurs during the unstable freezing stage,and the lowest occurs during the stable freezing stage.When the straw mulch thickness exceeded 10 cm,the effect of increasing straw mulch thickness on daily soil water evaporation was reduced,and the straw mulch thickness is negatively correlated with the accumulated soil evaporation during the freeze-thaw period.（2）When the four soil hydraulic parameters in the SHAW model change negatively,the sensitivity of soil temperature,soil water content,and soil evaporation simulation accuracy is higher,and they are all more sensitive to the pore size index.The simulation accuracy of soil evaporation in the stable freezing stage is less sensitive to soil hydraulic parameters,and the maximum freezing depth is most sensitive to the pore size index.（3）The importance evaluation of factors influencing soil evaporation under straw mulch shows that air pressure and surface soil water content have a more significant impact on soil evaporation during the unstable freezing stage,and air pressure during the stable freezing stage is the most important factor affecting soil evaporation.The main factors are the relative humidity and rainfall during the thawing stage.（4）Winter irrigation increases the soil temperature during the freezing period by0.7-1.0℃,but the soil temperature rises slowly during the thawing period,and the soil profile temperature of the irrigated plots is 0.3-0.9℃lower than that of the unirrigated plot.Winter irrigation increases the water storage capacity of the 0-100 cm soil layer,but when the winter irrigation amount is more significant than 200 m³·hm^-2,the impact on the soil water content of the cultivated layer（0-20 cm）is not apparent.（5）Winter irrigation increased the maximum soil freezing depth by 1.1-8.6 cm,and the amount of irrigation was positively correlated with the maximum soil freezing depth and accumulated soil evaporation during the freeze-thaw period.Irrigation increases the cumulative soil evaporation during the freeze-thaw period by 1.5-12.6 mm,and the increase in soil evaporation is about 15%-18%of the corresponding irrigation amount.The soil evaporation rate in the stable freezing stage is only 19%-31%of the other two stages,and the soil evaporation rate in the thawing stage is the highest.