Soil water dynamics under artificial Caragana microphylla shrub in the loess hilly region of Northwest Shanxi Province

Soil moisture is a key factor for the growth and survival of vegetation in the loess hilly region. Soil moisture dynamics was monitored under artificial Caragana microphylla shrub at 5 ages (5, 10, 20, 30 and 40 years after germination) in the loess hilly region of Northwest Shanxi Province in 2006. The results show decreasing soil moisture content (SMC) under artificial C. microphylla shrub with increasing age. SMC is lowest under the 40-year shrub. SMC under the shrubs is generally lower than under nearby wastelands. Based on monthly trend, SMC gradually decreases from April to June (hitting the lowest point in June), and then gradually increases from August to October. Vertically, SMC in the 0~200 cm soil layer gradually decreases with soil depth, especially in the 40~80 cm soil layer. During shrub growth period, soil moisture circulation is low. It is only 4.63% under the 40-year shrub, which is 2.92% less than that under nearby wastelands. Furthermore, the overall soil moisture balance is negative. It then implies that the artificial C. microphylla shrub is under moisture stress in the loess hilly region. In the long-term, moisture stress could threaten the growth and survival of artificial C. microphylla shrubs in this region.