<i>Effect of subsurface drainage on soil salinity and crop yield under greenhouse in China</i>

Greenhouse is economically profitable, but excessive fertilization has caused soil salinity and food safety issues. Effects of subsurface drainage on soil salinity and crop yield in facility cultivation are rarely found. Technical specifications of drainage system for greenhouse were designed, including spacing, depth, filter and collecting device according to soil properties, crop type and weather conditions. A subsurface drainage system consisting of 11cm diameter plastic tiles, each of 100cm length, was installed at depth of 0.4m with spacing 6m and depth of 0.6m with spacing 8m for evaluating its influence in soil salinity, soil moisture and crop production. During an irrigation cycle, ground surface soil electrical conductivity (EC) and soil moisture had no obvious change in 24 hours after irrigation; soil EC reached peak values after irrigation 2 days in the subsurface drained area, and then decreased over time. The relationship between surface soil moisture and soil EC above the drain can be expressed by the nonlinear equation. Drain spacings up to 8m was found to decrease surface soil salinity from 3.23 to 1.44. Subsurface drainage can significantly increased greenhouse summer tomato yield. It was also found that surface soil EC between two drain tubes was lower than that above the tube. Subsurface drainage was also very efficient in decreasing the number of summer waterlogging days by 75% in subtropical monsoon climate.