Soil water and salinity dynamics under the improved drip-irrigation scheduling for ecological restoration in the saline area of Yellow River basin

The drip-irrigation scheduled by different soil matric potential (SMP) thresholds at different stages according to soil water and salt management purposes was usually adopted for revegetation in saline-alkali land. To reveal the desalinization mechanism of this multi-stage drip-irrigation scheduling, a 3-year field trial, adopting this method for revegetation, was conducted in an arid saline area. The trial consisted of 5 irrigation treatments marked S1 S5, with their SMP that monitored directly under drip emitter at 0.2 m depth correspondingly controlled higher than -5, -10, -15, -20 and -25 kPa. Results showed the SMP threshold of 5 kPa during the unified irrigation stage induced a leaching fraction (LF) of 42.6% and a minimum recharge amount (MRA) from groundwater of zero, thus resulting the relative desalinization rate (RDR) of 91.8% in 0-120 cm soil layer. When treatment applied, the average electrical conductivity of the saturated soil extracts (ECe) in 0-40 cm among three growing seasons in S1-S5 treatments linearly increased from 0.90 to 1.73 dS/m as SMP threshold decreased from -5 to -25 kPa, resulting from the LF correspondingly decreasing from 18.4% to 2.5% and the MRA increasing from 0 to 21.4 mm. The inter-annual salt dynamic indicated a salt equilibrium state was formed in 80-120 cm soil layer when the SMP threshold was set higher than 10 kPa and that was formed in 40-80 cm soil layer if the SMP threshold was set between -20 and -15 kPa. This study found the SMP threshold controlled the LF and MRA, and eventually determined the dynamics of soil salinity, which explained the efficient desalinization mechanism under the multi-stage drip-irrigation scheduling. A key SMP threshold of 5 kPa for rapid soil leaching stage and that of -20 kPa for precise salt regulating stage were recommended for vegetation construction in the low-lying saline area.