Study On Spatiotemporal Distribution And Utilization Of Soil Moisture Under Scale-like Pit And Mulching Measures Of The Loess Hilly Region

Water resource shortage is a major factor restricting the development of ecological and economy in northern Shaanxi Loess Hilly Area. Rainfall almost is the only source of soil moisture in loess hilly region owing to thick loess and no supplement groundwater recharge to soil moisture, wherefore the full use of rainwater resources is the top priority to solve the ecological and economic development in the Loess Plateau. This paper aimed to investigate the impacts on soil moisture that different engineering and mulching measures in combination with scale-like pit, which is the general soil and water conservation measures in the Loess Plateau, by location monitoring, statistical analysis, survey, mathematical modeling and other measures in a typical dryland jujube orchard. The main reslts were listed as follows:(1) By analyzing the soil moisture change over time during each growing season, the impact of individual rainfall on the vertical soil moisture, and each variation of soil moisture in different measures under different humidity conditions, the mean soil moisture (0～180cm) of scale-like pit+branch mulching, scale-like scale+straw mulching, and soil moisture of scale-like pit with no mulching increased by14.2%,9.4%, and4.8%than controls, respectively. Different measures significantly increase the soil moisture on soil surface (0～20cm) and the main root system activity layer (20～100cm) during the jujube growth stages, especially scale-like pit+branch mulching. The soil moisture oscillations die away at depths less than100cm during individual rainfall. Individual rainfall is not obvious to the soil moisture of the deep. There are no significant differences of the soil moistures in different soil depths of scale-like pit with no mulching when compared with it of the control group at the soil moistures of high, medium, and low humidity conditions.(2) The retain water effects were different for mulching measures combination with scale-like pit during different Jujube growth stages. With the less rainfall before flowering and fruit setting stage, scale-like pit had little effect on the accumulation of rainfall, on the contrary, it increased the invalid evaporation by increasing the contact area with air. When the rainy season coming with the heavy rainfall, scale-like pit weakened the rainfall runoff erosion energy. And at the same time, jujube was in the fruit setting and fruit growing critical period with strong transpiration and intense evaporation. The Scale-like pit has an important role to supplement soil moisture by rainwater harvesting. Coupled with mulching measures to suppress evaporation, it ensured the maximum utilization of rainfall. After the rainfall period, soil moisture is consumed continuously since jujube was in fruit enlargement period. A combination of Scale-like pit and mulching measures has a crucial role at this stage. Just Scale-like pit measure almost has no compensation to0-100cm soil moisture, but has more obvious effect in100-160cm soil moisture. Comparison with the early growth period,20-180cm soil water deficit condition have received varying degrees of ease with scale-like pit measures. And100-180cm soil water deficit condition had exacerbated the trend at late growth period, which showed that the jujube growth consumpted deep soil moisture and leading to soil dry layer in the long term.(3) Using HYDRUS-1D model, this paper simulated the soil moisture movement and distribution under scale-like pit condition, basing on the assumption slope simulation results and joining runoff into rainfall. Comparing the soil moisture simulation results of the sloping fields with no treatment and the scale-like pit measures, it was found that the difference is not significant in10cm,30cm,50cm soil layer, but there are more obvious improvement in70cm,90cm soil layer under scale-like pit condition than no treatment. It indicated that scale-like pit had a marked effect in soil moisture recharge for deep soil, but had no obvious effect in shallow soil due to evaporation and crop consumption. Which needed Special attention was30cm soil moisture. When less rainfall, soil moisture slope no treatment> Scale pit measures. Because scale-like pit increased the invalid evaporation by increasing the contact area with air, which result to greater soil moisture loss. But evaporation and crop transpiration were hardly affected70cm,90cm soil layer soil moisture. And Scale deep pit can increase Soil moisture infiltration. Therefore, scale-like pit soil moisture was significantly higher than the sloping fields with no treatment in the70cm,90cm soil layer.