| Caragana korshinskii artificial forest is a typical plantation species in the Loess Plateau,and the zonal Caragana korshinskii forest in the mountainous area of southern Ningxia is a local unique planting mode.It is of great significance to study the deep soil moisture characteristics of zonal artificial forest in the mountainous area of southern Ningxia for local ecological protection and sustainable management of artificial forest.Aiming at the problem of serious soil moisture deficit in the old belt artificial Caragana korshinskii forest in the loess hilly area,in order to further explore the vertical distribution characteristics of soil moisture in the local Caragana korshinskii forest land over time and its response and balance characteristics to precipitation,to repair the desiccated soil and provide data and theoretical support for the sustainable and high-quality development of artificial Caragana korshinskii forest in this area.The vertical distribution of soil moisture in the 0-1760 cm soil layer was analyzed by field investigation,dynamic monitoring and indoor analysis.From May to October 2022,the soil moisture in the 0-500 cm soil layer was dynamically monitored for six months and analyzed in combination with precipitation.The main conclusions are as follows:(1)The 0-1760 cm soil layer of artificial Caragana korshinskii forest showed a drying state.The distribution depth of soil layer in severe drying state was 500-1120 cm,1200-1540 cm and 1660-1760 cm,and the rest was in extreme drying state.The soil water in 0-200 cm soil layer of Caragana korshinskii forest land was seriously deficient,and the average deficiency degree was 50.93%.The range of 200-1760 cm soil layer was moderate deficit,and the average deficit was 37.61%.(2)The soil water storage in the 0-1760 cm soil layer of the artificial Caragana korshinskii forest land was 1786.03 mm,and the control dry farmland was 2766.83 mm.The soil water storage of Caragana korshinskii was 980.80 mm less than that of farmland.According to the growth of Caragana korshinskii for 22 years,the annual water consumption of Caragana korshinskii was 44.58 mm more than that of dry farmland.This is the direct cause of soil desiccation in the aged artificial Caragana korshinskii forest.(3)The monthly dynamics of soil water storage in 0-500 cm soil layer of Caragana korshinskii forest land was the smallest in May,and the water storage increased first,reached the highest in August,and then decreased gradually.According to the soil moisture variation characteristics of 0-500 cm soil layer during the observation period,0-220 cm soil layer can be divided into water active layer,220-300 cm soil layer can be divided into two-way water movement layer,and 300-500 cm soil layer can be divided into relatively stable layer.The cumulative infiltration of precipitation during the observation period failed to recharge to the depth of 500 cm.(4)The soil water infiltration of Caragana korshinskii forest land was as follows:the infiltration depth of light rain(below 8.2 mm)did not reach 60 cm soil layer,which was surface rapid evaporation rainfall;the infiltration depth of moderate rain(more than 1 1 mm)reached more than 60 cm,which was characterized by shallow slow evaporation rainfall.The maximum infiltration depth of heavy rain 28.2 mm and rainstorm 62.4 mm precipitation reached 140 cm and 180 cm respectively within 48 h,and both of them had obvious trend of continuous migration and infiltration of soil moisture,which was manifested as deep infiltration recharge rainfall.Deep infiltration recharge rainfall under natural conditions is the key to realize the water recovery of deep soil dry layer in loess hilly region.(5)The soil water deficit of Caragana korshinskii forest land showed an increasing trend with the increase of depth in the vertical profile of 0-300 cm soil layer,and its change range gradually stabilized with the increase of soil depth,while in time,it showed a trend of decreasing first and then increasing with time.The water compensation degree in the vertical profile of 0-300 cm soil layer of Caragana korshinskii forest soil showed a trend of ’negative compensation ’ level decreasing with the increase of depth in May,September and October,while in June,July and August,it showed a state of ’ positive compensation’ in the upper layer,’no compensation ’ or ’ negative compensation ’ in the lower layer.(6)During the observation period,the monthly average actual total evapotranspiration of Caragana korshinskii forest land was 72.01 mm,which was slightly higher than the rainfall in the same period.The average ET/P(ratio of evapotranspiration to rainfall)was 1.17,and the soil water storage was finally reduced by 108.52 mm during the whole observation period.On the whole,ET/P showed a trend of decreasing first and then increasing.The total evapotranspiration of soil moisture during the observation period was greater than the rainfall recharge,and the soil moisture showed a ’negative balance’ state. |
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