Effects of subsurface drainage design on soil desalination in coastal resort of China

Problems in coastal resort development include water logging and soil salinization. Subsurface drainage is useful to remove excess water from subsurface of the soil in order to provide favorable conditions for plant production. However, subsurface drainage systems are needed to be placed at appropriate depths and spacings according to soil types. For this reason, applied field studies were set-up in coastal area of Tianjin. The studies consist of subsurface drainage systems with corrugated plastic pipe drains for which, the drain spacings vary among 6 m, 10 m and 14 m and drain depths among 0.8 m, 1.1 m and 1.4 m. The key performance indicators including the lowering of groundwater table and soil salinity of the layered soils were observed to compare the effects of subsurface drainage design on soil desalination. The results showed a considerable increase of desalination rate that varied as following sequence: T9> T8> T7> T6> T5> T3>T4> T1> T2. At the end of the experiment, T9 (drain depth 1.4 m, drain space 6 m) was the most effective in reducing the salinity by 54.99% in the soil profile of 0-80 cm. Due to subsurface drainage, the groundwater table was reduced gradually among treatments in the sequence of 1.4 m>1.1 m>0.8 m for depths and 6 m>10 m>14 m for spacings. Average soil salinity of different depths of drainage tubes decreased with time; the largest desalination rate was recorded for drain depth of 1.4 m. Likewise, average soil salinity of different spacings of drainage tubes decreased also with time, the largest desalination rate was obtained for drain spacing of 6 m. Based on variance analysis, salt reduction was significantly affected by drain depths; with the optimum as the drain depth of 1.4 m.