Shallow sand-filled niches beneath drip emitters made reclamation of an impermeable saline-sodic soil possible while cropping with Lycium barbarum L.

Abstract

The native soils of large areas of the Ningxia Plain in northwest China are saline-sodic, known as takyric solonetz, with very low saturated hydraulic conductivities (ks<0.1mm/d). A 3-year field experiment was conducted to determine if reclamation could be achieved while growing Lycium barbarum L. using drip irrigation where soil beneath the drip emitters, near the plants, was replaced with sand in niches that were 0.2m ground diameter and 0.2m deep. The purpose of sand-filled niche was to increase the area over which infiltration of water occurs thereby reducing the application rates to values that more closely matched the saturated hydraulic conductivity of the native soil. The initial values for ECe, pHs, and SAR of the surface soil was 12dS/m, 9.4 and 44.1(mmol/L)0.5, respectively. After deep tillage, beds (1m wide, 0.5m high) were formed. The drip lines were placed on beds covered with plastic. L. barbarum L. seedlings were then planted. Five water treatments were based on the soil matric potential (SMP), measured with tensiometers installed 0.2m beneath the emitter, used to trigger an irrigation of 5mm: the SMP levels were −5kPa (S1), −10kPa (S2), −15kPa (S3), −20kPa (S4), and −25kPa (S5). The salinity and SAR of the applied water were 2.14dS/m and 6.02(mmol/L)0.5. Considerable reclamation was achieved in three years. The low-salinity and the low-pH zone, which formed under the drip line during the first year, enlarged year by year. The average ECe and pHs in root zone increased with decreasing (more negative) SMP. The average SAR in root zone decreased sharply in the first year, then leveled off in the next two years. After 3 years, S3 and S4 had the better survival (∼80%) and higher fruit yields, around 900kg/ha, which were close to the level in local farmland. Our findings indicated that a sand-filled niche beneath the drip emitter could be adopted for the reclamation of saline-sodic wasteland in Ningxia Plain, northwest China, and an SMP of −10kPa in the first two years and −20kPa from the third year could be used to trigger drip irrigation while cropping L. barbarum L.