Effects of reclaimed water irrigation with different water quality on surface soil macro-pores

Reclaimed water plays a crucial role in the water resource of agricultural irrigation. Reclaimed water is the high demands for the sustainable water usage in the field. A comprehensive analysis is also required to elucidate the relationship between reclaimed water and soil dynamics in the short- and long-term implications. However, there are great variations in the physical properties and internal pores within soil during irrigation, due to the different concentrations of nutrients and harmful substances. Previous exploration has been focused mainly on the impacts of reclaimed water on soil health and structure merit. In this study, a 1.5-year outdoor experiment of field irrigation was conducted to explore the degradation of soil under reclaimed water irrigation with different water quality. The surface soil of 0-20 cm depth was set as the focus layer of soil after water irrigation, in order to constitute the primary rooting zone for the major crops, such as winter wheat and summer maize. A systematic investigation was then performed on the structure parameters of soil pores in the surface soil layer (0-20 cm). The soil's physical and chemical properties were compared (pH: potential of hydrogen, EC: electrical conductivity, SAR: sodium adsorption ratio, soil macropore, and macropore structure) after irrigation with the reclaimed water of different water quality (W1: pretreated domestic sewage, W2: reclaimed water 1, W3: reclaimed water 2, and W4: tap water). The results showed that: 1) The physical and chemical indexes (such as SAR and Na⁺ content) in soil increased after 1.5 years of reclaimed water irrigation, compared with the fresh water. But the SAR and pH indicators were significantly improved, whereas, there was no change in the rest. No salinization of surface soil was found in the short-term irrigation of reclaimed water with different water quality. 2) The total porosity of soil remained constant (P<0.05) after reclaimed water irrigation. The macro-porosity and macropore connectivity (equivalent pore diameter D>50 μm) of surface soil was improved by 120.76%,131.23% and 49.69%, respectively, in the W1, W2, and W3 treatment, compared with the W4. The proportion of connected pores and connectivity index also increased. But reclaimed water irrigation significantly blocked the tiny pores in the soil, leading to the soil's hydraulic properties. 3) The soil connectivity was improved after reclaimed water irrigation. The number of connecting channels between pores also increased for the more complex pore network and the soil aeration. In summary, the short-term reclaimed water irrigation cannot lead to the serious soil degradation. However W1 treatment was harmful to the soil from the perspective of long-term irrigation. The soil aeration was then improved to reduce the standards of water quality for a better impact on the soil.