Assessment of Soil Nutrients in Plant Root Layer of a Saline-Sodic Soil Cropped with Lycium barbarum L. When Drip Irrigated with Saline Groundwater

Drip irrigation is an effective method to utilize waste saline-sodic land with a high water table. For reasonable and sustainable utilization of saline-sodic soil under such conditions, spatiotemporal changes in total nitrogen (TN), total phosphorus (TP), and soil organic matter (SOM) were investigated during the utilization process. The soil was sampled from newly built raised beds before planting (0 y) and beds in three adjacent plots had been planted with Lycium barbarum L. for one (1 y), two (2 y), and three years (3 y), respectively, at the end of the growing season. Soil samples were obtained at four horizontal distances from the drip line (0, 10, 20, and 30 cm) and four vertical soil depths (0–10, 10–20, 20–30, and 30–40 cm). The results showed that the average TN and TP of the soil profile increased with the planting year and were approximately 0.68 and 1.81 g·kg−1 in the soils of 3 y, approximately 84.9 and 42.4% higher than that of 0 y, respectively. SOM decreased in the first growing season and then continuously increased in the following planting years, reaching 8.26 g·kg−1 in the soils of 3 y, which was approximately 38.2% higher than that of 0 y. TN, TP, and SOM contents were high in soils around the drip line and decreased with distance from the drip line. In both horizontal and vertical directions, TN, TP, and SOM varied slightly in soils of 0, 1, and 2 y, while in soils of 3 y, TN and SOM decreased with increased distance in both horizontal and vertical directions and TP decreased obviously only within 10 cm in both directions. This indicated that the contents and distributions of soil nutrients in such saline-sodic soils could be improved with planting year under drip irrigation with local saline groundwater and especially around the drip line as the soil around the dripper was quickly ameliorated.