Change in soil water deficit and soil organic matter consumption over time in rain-fed apricot orchards on the semi-arid Loess Plateau, China

Abstract The impacts of massive reforestation on soil water and soil organic matter (SOM) in the ecosystem are attracting increasing attention worldwide. However, the response of the soil water content (SWC) and SOM after the conversion of agricultural land to economic forestland have not been sufficiently clarified in semi-arid areas. To investigate the influence of land-use change on the SWC and SOM dynamics, we examined the SWC (0–400 cm depth) and SOM (0–60 cm depth) and growth status of fruit trees in three apricot (Armeniaca vulgaris Lam.) orchards of different ages (7, 12, and 22 years) under extensive management, together with those of adjacent cropland (control) on the Loess Plateau, China. The results showed that SWC significantly decreased with increasing stand age, and strong soil desiccation occurred in the 12-year-old apricot orchard after conversion from cropland. The annual growth rate of the dried soil layer between the 12th and 22nd years (12.00 cm y−1) was higher than that between the 1st and 12th years (6.67 cm y−1). The soil water deficit was 498.81 mm over 22 years in the 0–400 cm soil profiles. SOM stock was improved in the short term (7 y) compared with the cropland, and was consumed thereafter. Only the topsoil (0–20 cm soil profiles) experienced SOM consumption in the 12-year-old orchard, but the SOM of all soil layers was consumed in the 22-year-old orchard. In the 0–60 cm soil profiles over 22 years, the SOM consumption was 26.53 Mg ha−1. The length and diameter of peripheral branches generally decreased with increasing stand age; where those of the 22-year-old orchard were 83.87 % and 39.13 % lower than those of the 7-year-old orchard (P