Abstract
Over three million hectares of salt-affected soils characterized with high salinity and sodicity caused serious land degradation in Songnen Plain, northeast China. Soil salinity–sodicity heterogeneous distribution under microtopography is usually influenced by several environmental factors. The side direction movement of soil water driven by water from depression is the key factor that aggravates the soil salinization under microtopography in dry condition. In this study, the differences in surface soil salinity–sodicity (0–10 cm) between dry year and wet year were compared, and the relationship between soil salinity–sodicity and environment factors such as ground elevation, surface ponding time, surface ponding depth, and soil moisture at four soil layers (0–10, 10–30, 30–60, and 60–100 cm) were analyzed using redundancy analysis (RDA) and simple correlation analysis (Pearson analysis) for two different hydrological years. Analyzed soil salinity–sodicity parameters include soluble ions (Na+, K+, Ca2+, Mg2+, CO32−, HCO3−, Cl− and SO42−), salt content (SC), electrical conductivity (EC), sodium adsorption ratio (SAR), and pH. Results showed that values of SAR, Cl−, and SO42− were significantly higher in dry year than in wet year, while Ca2+, Mg2+, K+, and HCO3− showed the opposite results. Values of Na+, CO32−, and EC were significantly higher at higher ground elevation gradient (20–40 cm) in dry year than wet year. Redundancy analysis indicated that spatial distributions and variations of salinity and sodicity in surface soil layer were related with environmental factors of ponding depth, ponding time and ground elevation in wet year, and they were related with ground elevation, ponding depth, ponding time, and soil moisture at 30–60 and 60–100 cm soil layer in dry year. Ponding depth and ground elevation rank first and second as the influential factors of the spatial distribution and variation of soil salinity–sodicity in wet year. However in dry year, primary and secondary influential factors are ground elevation and soil moisture at 60–100 cm soil layer.
Highlights
Salt-affected area covers about 1 ˆ 109 ha in the world [1]
Parameter values of sodium adsorption ratio (SAR), Cl, and SO4 2 ́ were significantly higher in dry year (2007) than in wet year (2005) (p < 0.05), while Ca2+, Mg2+, K+, and HCO3 ́ showed the opposite results (Table 1)
The results showed that 51.6% of soil salinity–sodicity spatial distribution was explained by these seven environment variables during the wet year, whereas 68.8%
Summary
Salt-affected area covers about 1 ˆ 109 ha in the world [1]. Songnen Plain, northeast China, is one of three major saline-sodic soil distribution. Water 2016, 8, 227 regions in the world. The area of saline-sodic soil is about 2.57 ˆ 106 ha, approximately 22.62% of its total area [4,5]. The area of saline-sodic soil is increasing at an annual rate of 1.35 ˆ 104 ha. The salinization land accounts for more than 20% of the total area and has been changed into wasteland [6]. Soil salinization has caused serious soil degradation, which negatively influences the economic development and decreased the yield of local crops
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