Abstract:To characterize the changes in vertical distributions of soil moisture and nitrate following conversion to apple orchard from cropland in the Loess Plateau, 40 600 cm depth soil profiles were sampled from farmland (as control), 8, 17 and 25 yr old apple orchards in Luochuan county to determine soil moisture content, nitrate concentration and their storage. The results showed that 8 yr old apple orchards were similar to cropland in soil nitrate concentrations (SNC) and residual soil nitrate (RSN), and also presented equal (Jiuxian) or even higher (Huanbai) values of soil moisture content (SWC) and soil water storage (SWS) when compared with cropland. In contrast, the 17 and 25 yr old apple orchards significantly decreased SWS by 150 and 230 mm, respectively, which was mainly associated with the SWC changes in soils deeper than 300 cm. SNCs in the 0-500 cm layers increased significantly with the standing ages of apple orchard, and RSNs accumulated in the 0-600 cm profile were 6 830 and 8 370 kg/hm2, corresponding to 17 and 25 yr old apple orchards, respectively, which were appreciably higher than that of 8 yr old apple orchard (440 kg/hm2) and cropland (695 kg/hm2). Thus, we concluded that converting cropland to apple orchard could result in soil water deficit, especially in > 300 cm soil depth, and nitrate accumulation, so, the strategies including water-conserving and strict controls on N fertilizer should be adopted to mitigate the unfavorable impacts caused by the enlargement of apple orchard in the Loess Plateau.