Moving salts in an impermeable saline-sodic soil with drip irrigation to permit wolfberry production

Abstract

A saline-sodic wasteland of takyric solonetz is widely distributed across arid regions of Northwest China. The poor soil structure and low permeability (Ks < 0.1 mm d−1) hinder reclamation because the excessive sodium salt occurring mainly in the surface soil layer cannot be leached down by conventional leaching methods, including drip irrigation, without any assistance measure. The objectives of this study were: 1) to characterize salt movement that occurs within the planted ridge due to drip irrigation of varying amounts, and 2) to identify the optimum soil matric potential (SMP) threshold for drip irrigation in order for wolfberry (Lycium barbarum L.) to be successfully produced, based on plant survival and productivity. A three-year field experiment was conducted with wolfberry using drip irrigation on this solonetz soil. The soil was improved by creating shallow sand-filled niches beneath drip emitters. Five SMP levels triggered irrigations of 5 mm: −5 kPa (S1), −10 kPa (S2), −15 kPa (S3), −20 kPa (S4), and −25 kPa (S5). The improved drip irrigation system significantly facilitated soil water infiltration, and redistributed soil salt in the planted ridge. The leached salt accumulated increasingly at the surface layers of the ridge slope and furrow. Irrigating at higher threshold SMP resulted in lower soil salinity in the root zone. Crop evapotranspiration (ET) was affected by different drip regimes, and lower SMP resulted in reduction in irrigation application amount and ET. Deep percolation was always <8 mm during the three–year study. Soil salinity in the root zone at the end of the study under the S1–S4 treatments decreased to <8.9 dS m−1, the salt-tolerant threshold of wolfberry. At the end of the study, wolfberry survival rate and productivity were greatest for the S2–S4 treatments. These results and the greater water use efficiency found with the S3 and S4 treatments suggest using an SMP threshold of −20 kPa to trigger drip irrigation for wolfberry production on this impermeable saline-sodic soil.