| In order to investigate the effect of the implement of Grain-for-Green on the spatial distribution of soil moisture and nutrients in water-wind crisscross erosion region,field experiments under different land use types at Liudaogou catchment in Shenmu city were conducted.For the dynamic of deep soil moisture and nutrients under different land-use types,bare land,farmland,alfalfa land,Caragana land,abandoned land in terrace and farmland,alfalfa land,abandoned land in slope were compared in present study.Soil water content and nutrients including soil organic matter,total nitrogen,mineral nitrogen,total phosphorus,available phosphorus were analyzed.At the same time,transformation of land-use patterns were used to study effects of revegetation on the process of water consumption and water recovery in soil profile,indicating the drying and recharging processes.Given the local special features of landform,we studied on the characteristics of soil moisture movement in deep profile of aeolian sand soil and the process of precipitation recharging shallow groundwater through the profile quickly.The main results shows as follows:(1)Under the influence of Grain-for-Green,the change of land use type has a significant effect on soil organic matter and total nitrogen content(P<0.05),the conversion of farmland to shrub land and grassland could increase soil organic matter and nitrogen content.The influenced depth of different land use on different nutrients were different,the influenced depth of that on organic matter content and nitrogen content were 40 cm and 60 cm,respectively,and abandoned land following farmland has the greatest effect on total nitrogen content.The influenced depth of different land use types in slope land on available phosphorus content was greater than sampling depth(200 cm),and the influenced degree was greater than that in terrace land.Through compared the nutrients difference with the returning time goes on in 0~10 cm among different land use types,which found that the content of organic matter and total nitrogen in 2016 was significantly higher than that in 2010(P<0.05)in slope abandoned land,the content of total nitrogen in 2016 was significantly higer than that in 2013(P<0.05)in terrace abandoned grassland,the other land use types has an increasing trend of organic matter and total nitrogen with the increase of years,but no significant difference.(2)The change of land use type has a significant effect on soil water content in soil profile.Comparing soil water content distribution under different land use type in terrace and slope,it was found that the soil moisture of alfalfa land and Caragana land in terrace was obviously depleted in 300~600 cm,and the largest infiltration depth of soil moisture was up to 220 cm after rainy season,and the infiltration depth of precipitation at alfalfa land in slope was up to 260 cm after two wet years.Caragana and alfalfa are deep rooting plants,which can improve soil nutrients in the profile,but consume soil water storage significantly.In the two wet years,the soil water storage in 2016 was obviously increased compared with the previous year,and the recharge of soil water storage in 2017 was smaller than that in 2016.The water content of 0~200 cm of abandoned land,alfalfa land and Caragana land was obviously restored.(3)The transformation experiment of land use types,including the conversion of alfalfa cultivation following typical farmland and conversion soybean cultivation from 10-year-old alfalfa,shows that(1)In the two wet years,the soil dry layer under soybean land below 300 cm caused by alfalfa planting in the early stage was effectively restored,and the soil water storage was obviously increased.The recovery depth reached 300 cm at the end of the growth season in 2016,and exceeded the observed depth(500 cm)by the end of the growth season in 2017.(2)After planted alfalfa,soil water storage decreased by 3.6% in 2017,but the depth of soil water consumption reached 200 cm at the end of the growth season in 2017,which was more than supplemental depth(120 cm),indicating that the process of soil water depletion had begun.With the extension of the plant-years of soybean and alfalfa,the soil moisture recovery and consumption depth may increase continually.(4)The interannual difference of precipitation in water-wind erosion crisscross region on the Loess Plateau was great.During the 4 consecutive years of observation,the maximum annual precipitation was more about 2 times than that of the minimum annual precipitation,the water infiltration process was obviously affected by precipitation.In the regional normal precipitation year(2014)or dry year(2015),the moisture content of coarse soil fluctuates only within 300 cm depth and the variation of water content in 300~600 cm depth was weak.However,the water content at the end of the growth season in 2013 and 2016 was significantly higher than that at the beginning of the growing season.Thanks to the aboundant precipitation in wet years and the high infiltration rate of coarse-textured soil in the region,a large proportion of rainfall transformed into soil moisture and had rapidly movement downward.In the two wet years during the observation period,the rainfall infiltration depth had exceeded the measured depth of 600 cm.From the HYDRUS-1D model simulated results,the rainfall could infiltrate to the maximum depth of 1100 cm and 1200 cm respectively,exceeding rooting zone at the end of the growth season in 2013 and 2016,and exceeded the simulated depth of 1500 cm at the end of the year,soil water continues to move to the deep layer,which could recharge shallow groundwater.Under the special geomorphological conditions of loess and aeolian sand accumulation in this area,the aeolian soil profile may be a “special channel” for recharge of shallow groundwater in the basin. |
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