Strategy of subsurface pipe drainage system to alleviate soil salinization based on the DRAINMOD model*

Abstract To investigate the dynamics and influencing factors of water and salt in subsurface pipe drainage (SPD) systems, three field experiments (denoted as E 0.8 , E 1.1 , and E 1.4 ) with different drainage pipe depths (80, 110, and 140 cm, respectively) were conducted in saline farmlands in the Xinjiang Autonomous Region, China. The cumulative water drainage and salt discharge were used to calibrate and validate the DRAINMOD model for simulating water and salt movements in SPD systems. Two indices, the effective leaching water amount ( W e ) and the ratio of the salt discharge rate to the soil desalination rate ( R s / N) , combined with the water drainage rate ( R w ) and salt discharge rate ( R s ), were used to evaluate the effects of salt discharge under different pipe layouts. The experimental results showed that water drainage only started when groundwater completely submerged the subsurface pipes. Furthermore, R s and R s / N increased with decreasing burial depth, while the total salt discharge decreased and R w increased with W e . The relationship among W e , the burial depth of the subsurface pipe ( B ), the groundwater table ( G ), and the R w or R s / N of SPD was quantified under different soil textures. In addition, quantitative formulas for determining the water and salt discharge characteristics of SPD were also established.