Abstract:

Natural precipitation is the only water source in the semi-arid loess region. This research investigated the characteristics of soil water infiltration following precipitation after replanting deep-rooted， perennial plants in soil with severely depleted moisture levels in the hilly areas of the Loess Plateau. Specifically， the research simulated the cultivation of Medicago sativa， using large-scale soil columns （lysimeters） at the Wangwa Soil and Water Conservation Experiment Station in southern Ningxia. The simulation experiment was based on actual rainfall data from March to October in 2022-2023. The results indicated that： 1） Only 41.67% of all precipitation events resulted in soil water infiltration. The ratio of infiltration to precipitation varied with rainfall intensity： in light rain， moderate rain， heavy rain and torrential rain the infiltration was， respectively， 15.89%， 35.63%， 52.20% and 61.50% of the total precipitation. Infiltration amounts thus showed an increasing trend with increasing precipitation. 2） Precipitation infiltrating to depths of less than 30 cm， to depths of 30-80 cm， and to depths greater than 80 cm， accounted for， respectively， 76.04%， 18.75% and 5.21% of the total precipitation. 3） With respect to the issue of deep soil water depletion， alfalfa cultivation led to a trend of soil water increase in soil water measured monthly for one year old plants， while for two year old plants， soil water measured monthly showed a decreasing trend. The monthly infiltration depth （Z_m） increased with increasing monthly precipitation （P_m） as a quadratic function： Z_m=-0.0101P_m²+3.9426P_m （R²=0.9895）. The study provides data on deep soil water status， useful for planning the replanting and sustainable development of deep-rooted， perennial plants in areas on the Loess Plateau with severely dried deeper soil horizons.

Key words: loess soil region, soil drying, alfalfa, soil water, precipitation infiltration