Study On The Influence Of Sand Mulching On Soil Water Transport In Orchards Based On Hydrogen And Oxygen Stable Isotopes

The water resource shortage is one of the severe challenges facing China’s agricultural development,especially in the northwest region of China.At present,in order to cope with the drought and water shortage environment,the farmers in northwest China have developed a drought-resistant planting method-sand mulching after long-term agricultural practice,and to accurately evaluate the role of sand mulching measures to inhibit the evaporation of soil moisture and improve soil water storage,it is necessary to deeply understand the transport process of soil moisture.This will have important scientific value and practical significance for the future production practice and efficient utilization of agricultural water resources.In this study,the Baifeng peach(Amygdalus persica L.)orchard in Hongyi Village,Anning District,Lanzhou City was selected as the test site.Samples of precipitation,irrigation water,soil and plants were collected during the fruit tree growing season(April to October)in2021.Based on the stable isotope data of hydrogen and oxygen,the temporal and spatial variation characteristics of soil water isotope at monthly scale and after irrigation were analyzed.Using line-conditioned excess(lc-excess)equilibrium equation,lc-excess coupled Rayleigh fractionation model and Craig-Gordon model,the influence of sand covering on soil water evaporation was analyzed qualitatively and quantitatively.Based on the principle of isotope mass balance and MixSIAR model,the infiltration process of soil water was discussed.The main conclusions are as follows:(1)The slope and intercept of soil evaporation line(SEL)in each month of the experimental field are smaller than those of the input water line,which reflects the environmental characteristics of dry climate in this area.The monthly variation of soil water isotope value in the sand mulching plot was small,and the soil water isotope value of 0～30 cm was more enriched than that in depth.After irrigation,the soil water isotope value first increased and then stabilized with depth,which was contrary to the change trend before irrigation.On the whole,the isotopic values of the sand mulching plot were relatively depleted,indicating that the sand mulching measures had a good effect on inhibiting evaporation.(2)The soil water content of the non-sand mulching land varies greatly between months,and the water content is relatively small.The lc-excess value increases with depth regardless of whether sand is mulched or not,which indicates that surface evaporation is more intense,and the average lc-excess value of the sand mulching land is greater than that without sand.The lc-excess coupled Rayleigh fractionation model and Craig-Gordon model were used to calculate the evaporation quantitatively.The results also showed that the evaporation was weaker during sand mulching,which was beneficial to soil water retention.In terms of soil water recharge,the sand mulching land can store "old water" better,and the recharge of the surface layer is greater than that of the middle and deep layer.(3)After irrigation,the peak water content of the sand mulching plot appeared on the fifth day,and the peak water content of the non-sand mulching plot appeared on the third day,and the average soil water content of the sand mulching plot was higher than that of the non-sand mulching plot.The slope of the soil evaporation line of the sand mulching plot is greater than that of the non-sand mulching plot,and the lc-excess value of the sand mulching plot is also larger,and the quantitative calculation results also show that the soil evaporation loss rate of the non-sand mulching plot is greater than that of the sand mulching plot.The average infiltration depth of irrigation water in sand mulching plot is greater than that in non-sand mulching plot,and the amount of infiltration is also greater than that in non-sand mulching plot.(4)Sand mulching has a cut-off effect on the input water of smaller intensity,while sand covering after irrigation has a positive effect on the recharge water and recharge depth,so the sand mulching can be supplemented for high-intensity precipitation during the peach tree growth period.The difference in soil evaporation loss rate between sand mulching and non-sand mulching in August is the largest,so the thickness of the sand mulching can be increased as appropriate in August.Large-scale flood irrigation is not conducive to the development of water-saving agriculture,and changing irrigation methods can improve water use efficiency,such as trench irrigation or night irrigation.