Water and salt replacement through soil salt leaching under brackish water conditions with subsurface pipe drainage

To explore the improvement effect of subsurface drainage and brackish water on saline alkali soil, an orthogonal experimental design was used to conduct soil column experiments under nine parameter combinations of the depth of the buried subsurface pipe, irrigation amount and salinity of brackish water. A numerical model of soil water and salt movement was established, and the physical parameters of the soil were verified by using the software HYDRUS-1D. The results indicated that the salinity of the brackish water only affected salt replacement. The salt replacement associated with subsurface drainage decreases with increasing water and salt replacement area at a constant irrigation volume. The salt replacement amount through subsurface pipe drainage increased with the irrigation amount in constant water and salt replacement areas. When the burial depths of the subsurface pipes were 140 and 160 cm and the irrigation amounts were >3180 and 3990 m(3) ha(-1), respectively, the salt discharge through the subsurface pipes was greater than the salt content carried by the brackish water, and the salt content of the soil in the root zone reached the critical salt tolerance value of cotton, which can simultaneously show that the soil salt content would not affect cotton growth.