Shallow subsurface pipe drainage in Xinjiang lowers soil salinity and improves cotton seed yield

Abstract: Soil salinization seriously restricts the sustainable development of agriculture in the arid area of China. For the purpose of lowering underground water level and soil salinity, increasing farmland crop yield as well as improving agricultural ecological environment, this research investigated the effect of subsurface pipe drainage on soil salinity and cotton yield in soils with mild and moderate salinization in cotton field covered with plastic mulching film under drip irrigation. A complete random plot design was used in the year of 2010. The soils were irrigated by water from well and the irrigation water had the salinity of 0.65 g/L, lower than that of fresh water. The cotton was planted in mild and moderate salinization soils with subsurface pipe drainage as the treatment and also in similar soils without drainage as the control. Plastic mulching film covered 6 rows of cotton and 2 drip irrigation tubes. The cotton was planted in 2010 and its seed yield was determined at the harvest stage. The electric conductivity (EC) and pH value of subsurface drainage were measured during the growth period of the cotton. The results showed that the cotton seed yield, EC and pH value of subsurface drainage could be affected by different degree of soil salinization. The subsurface drainage significantly (P<0.05) reduced the soil salinity. During the period of cotton growth, the salinity profile of soils with mild and moderate salinization was characterized by changes in the salt accumulation from its surface to the lower depth of soils. The desalinization ratio was 90.89% in the 0-20 cm, 59.87% in the 20-40 cm, 38.75% in the 40-60 cm, and 32.11% in the 60-80 cm for the moderate salinization soils, and 50.96% in the 0-20 cm, 42.69% in the 20-40 cm, and 18.48% in the 40- 60 cm for the mild salinization soils. It was apparent that the desalinization ratio in the 0-20 cm layer was highest than the other layers. The salinity of the moderate salinization soils decreased significantly (P<0.05) to mild saline level via salt removal through subsurface pipe drainage. The change of EC under subsurface pipe drainage ranged from 7.53 to 11.16 dS/m, and the value of pH value varied from 7.08 to 8.20. In addition, through subsurface pipe drainage, the cotton yield of the mild and moderate salinization soil was increased by 25.3% and 55% (P<0.01) compared with the control without drainage, respectively. However, the cotton yield was not significantly different between the mild and moderate salinization soils (P>0.05). This study indicated that the shallow subsurface pipe drainage technology could greatly improve soil condition, control soil salinity, and enhance crop yield. Furthermore, since the pipe was buried in soils, leaving more soil surface space for crop and thus having the potential of increasing economic benefits. It suggested that the shallow subsurface pipe drainage technology combined with the drip irrigation under plastic mulch can be an effective method for exploration and utilization of saline soil in Xinjiang.