Assessment of secondary soil salinity prevention and economic benefit under different drip line placement and irrigation regime in northwest China

This study was conducted in order to evaluate the prevention of secondary soil salinity and the economic benefits of different drip line designs and irrigation regimes in northwest China. A three-year experiment (2008–2010) was carried out in the Xinjiang Autonomous Region of China and included five water treatments and two drip line designs. Irrigation was triggered by the soil matric potential (SMP) threshold at 20-cm soil depth, at −10, −20, −30, −40 and −50kPa for single and double lateral irrigation placements after cotton was established. Soil salinity was significantly affected by the irrigation regime and drip line design. The single line design was more efficient at salt leaching and the areas of low electrical conductivity zones in the soil profile existing throughout the growth season were directly proportional to the SMP threshold. Moreover, the critical SMP value (CSV), which is the lowest SMP threshold that can prevent salinization of soil, was significantly related to soil depth and drip line placement. The lowest CSV of −43kPa was obtained under single line design within the 0–40cm soil depth interval. Seed cotton yields were positively correlated with the SMP thresholds and planting years; and the highest yield of 6.41 Mg/ha was achieved under the double lateral design for SMP of −20kPa in 2010. Economic evaluation showed that total investment cost was around 10% lower for single compared to double lateral design, whereas double laterals produced more net income. From the combined point of economic return and soil salinization prevention, a SMP threshold of −20kPa with double line design was found to be most appropriate for scheduling of cotton drip irrigation and agronomic practices in Xinjiang.