New measures of deep soil water recharge during the vegetation restoration process in semi-arid regions of northern China

Desertification in semi-arid regions is currently a global environmental and societal problem. This research attempts to understand whether a 40-year-old rain-fed Artemisia sphaerocephala Krasch sand-fixing land as part of the Three North Shelterbelt Program (3NSP) of China can be developed sustainably or not using a newly designed lysimeter to monitor the precipitation-induced deep soil recharge (DSR) at 220 cm of depth. Evapotranspiration is calculated through a water balance equation when precipitation and soil moisture data are collected. A comparison of soil particle sizes and soil moisture distributions in artificial sand-fixing land and neighboring bare land is made to assess the impact of sand-fixing reforestation. Results show that such a sand-fixing reforestation results in a root system being mainly developed in the horizontal direction and a changed soil particle distribution. Specifically, the sandy soil with 50.53 % medium sand has been transformed into a sandy soil with 68.53 % fine sand. Within the Artemisia sphaerocephala Krasch sand-fixing experimental area, the DSR values in the bare sand plot and Artemisia sphaerocephala Krasch plot are respectively 283.6 and 90.6 mm in wet years, reflecting a difference of more than 3 times. The deep soil layer moisture in semi-arid sandy land is largely replenished by precipitation-induced infiltration. The DSR values of the bare sandy land plot and Artemisia sphaerocephala Krasch plot are respectively 51.6 and 2 mm in dry years, a difference of more than 25 times. The proportions of DSR reduced by Artemisia sphaerocephala Krasch are 68.06 % and 96.12 % in wet and dry years, respectively. This research shows that Artemisia sphaerocephala Krasch in semi-arid regions can continue to grow and has the capacity to fix sand. It consumes a large amount of precipitated water and reduces the amount of DSR considerably.