Soil physiochemical properties and subsurface pipe drainage effect of paddy field in low wetland of Sanjiang plain

Abstract: Sanjiang plain is located in the east of Heilongjiang Province. Sanjiang plain is the low plains formed from confluence and alluvial of Heilongjiang, Songhua River and Wusuli River. Problems often occur in low wetlands such as low-lying, clay, concentrated rainfall, flooding, resulting in crop production reduction. In addition, in the harvest season, the soil is too wet, agricultural machinery is difficult to operate in the wet soil. This study investigated the soil physiochemical properties of low farmland and introduced subsurface drainage technique widely used in the Southern China to the field in order to solve the problems above. The study was carried out in Sanjiang 859 Farm in Heilongjiang. The rice was planted for 15 years. The soil organic matter content (58.14 g/kg) in 0-15 cm was higher than the other places (30 g/kg). However, the alkaline N, available P and K were low. In the experimental field, we set up a plot buried with subsurface pipe. The spacing of pipe was 10 m and the buried depth was 70 cm. The slope gradient was 1/1000. The pipe diameter was 25 cm. The experiment started from the spring of 2016. A plot without subsurface pipe was designed with the same size with that with subsurface pipe. The irrigation in both plots was same: shallow period with surface water depth of 3-5 cm and irrigation when the surface was dry. At the end of tillering stage of rice, the surface was dried and at the initial maturing stage the soil was drained. The soil was samples for physiochemical property measurement. The rice yield was determined. The results showed that the soil texture was clay. The clay content was more than 40%, the effective porosity was low (6.40%-7.81%). Soil aeration and water permeability were poor, especially the parent material where was almost airtight and watertight. The soil water content was high, and in the natural state it was more than 40%. The soil bulk density was low and the topsoil was 0.93 g/cm3. The soil hardness was low and the liquid index was 0.38-0.61. The whole soil was in the plastic state, and the mechanical bearing capacity was poor. It was possible to improve the permeability of the soil by setting up the subsurface pipe in the meadow marsh soil. The distance from the subsurface pipe had an effect on the soil drainage effect, and the closer the distance from the subsurface pipe, the better the effect of soil drainage, the more obvious the decrease of water content. In the rice field with subsurface pipe at tillering stage, the soil surface was dry while the control without pipe was still wet. The yield of rice treated with subsurface pipe was 8.06% higher than that without subsurface pipe. This study provides technical support for improving soil condition in the low plains.