Influence of Reclaimed Water Quality on Infiltration Characteristics of Typical Subtropical Zone Soils: A Case Study in South China

Irrigation with reclaimed water (RW) can alleviate water scarcity and improve the environmental and economic benefits. However, RW contains a large number of salts, suspended particles, organic matter, etc., which can affect soil infiltration. Previous studies focused on the examination of this effect in alkaline soils, but the infiltration change of acidic soils has seldom been investigated. This study selects four typical types of soil in the subtropical area in the south of China and designs experiments using different concentrations of RW to examine the influence of RW on the infiltration of various acid soils. The short-term impact is examined based on a one-dimensional horizontal method, and the long-term infiltration characteristics are measured by a Mini Disk infiltration meter with one year’s RW irrigation. Results show that RW irrigation can restrain the short-term infiltration of red soil while accelerating that of purple soil, aquic soil and paddy soil. Regarding the long-term effect, the cumulative infiltration of red soil increases with the decline of the concentration of RW, while there is no unique trend for the other soils. After one year’s RW irrigation, physical properties such as soil particle size distribution, texture and EC have changed. For red soil, EC increased significantly with RW irrigation, from 46.7 µS/cm to 101.07 µS/cm. However, regarding aquic soil, EC decreased from 157.05 µS/cm to 123.20 µS/cm. Moreover, the infiltration rate coefficient of red soil and aquic soil exhibits a significant positive correlation with RW concentration (p < 0.01), while the silt content shows a significantly negative correlation (p < 0.01). Furthermore, soil infiltration parameters c and S value of the purple soil, paddy soil, is significantly negative correlated with pH value (p < 0.01). The results reflected that appropriate RW quality for irrigation is different among various soil types, which will influence the sustainable application of RW. It can shed insights into solving the water scarcity issue and improving water sustainability in subtropical regions.