Spatial Variability of Soil Salinity under Subsurface Drainage

Abstract

In the coastal area of eastern China with monsoon climate and high water table, soil salinity exhibits strong spatial heterogeneity at the field scale. Using basic tools of geostatistics and geographic information systems (GIS), we explored the spatial characteristics of soil salinity under rain-fed conditions and subsurface drainage. The results showed that (1) spatial variability in soil salinity could be reduced significantly by leaching with rain water and subsurface drainage (LD) during the rainy season. The variability in soil salinity after LD decreased from strong to moderate. (2) After LD, soil salinity remained at more than 0.85 g/kg irrespective of values before the rainy season. In other words, it was almost impossible to remove all the salts in the plow layer. (3) Spatial heterogeneity of soil salinity showed a homogenizing tendency based on the critical point of 7 g/kg. Soil salinity less than 7 g/kg (79% of samples) homogenized to within 1.5–2 g/kg under LD and that more than 7 g/kg decreased to 1.5–4.5 g/kg. However, at this level, most salt-tolerant crops could grow. (4) The homogeneity was also reflected in the transformation of salinity grade in different areas. Before LD, the moderately and heavily saline (2–10 g/kg) soil area accounted for 88% of the pilot field in which the heavily saline area constituted 57.45% of the total salt load within the 0- to 30-cm layer; after LD, the mildly saline (1–2 g/kg) area was dominant with more than 75% ratio, contributing 65.24% of total salt load. (5) Intensive and frequent rainfall and long-term LD may reduce the spatial variability in salinity and allow for better reclamation and utilization of saline land. These results provide a scientific basis for integrated management of water and agricultural production.