Impacts of long-term saline water irrigation on soil properties and crop yields under maize-wheat crop rotation

Saline water is widely used as an alternative water resource for agriculture to overcome the freshwater shortage in arid and semiarid regions. But long-term using of the saline water for irrigation would negatively affect soil properties and crop production, and the salinity of the irrigation water should be properly managed to reduce the risks. In this study, saline water with five levels of electrical conductivities (ECiw) at 1.3 (CK), 3.4, 7.1, 10.6, and 14.1 dS·m−1 were used to irrigate winter wheat and summer maize with annual double cropping system in the North China Plain (NCP) from 2006 to 2019, to decide the threshold value for long-term using saline water. Crop yields and soil salinity were continuously examined from 2006 to 2019, and soil physicochemical properties were monitored in 2018 and 2019 after 12 years’ saline water irrigation. Results showed that soil salinity in the 0100 cm layer could be maintained at a low level using saline water with ECiw at 3.4 dS·m−1. Soil salt accumulated in winter wheat seasons could be leached from the main root zone in the following summer maize seasons, which were rainy in this region due to the monsoon climate. No significant difference was observed in grain yields for treatment with ECiw at 3.4 dS·m−1 compared to CK treatment. The electrical conductivity of the saturated soil extract (ECe), soil pH, sodium adsorption ratio, and bulk density within the top soil layer of 030 cm increased with the increase in ECiw, whereas the soil organic carbon, porosity, macroaggregates (> 0.25 mm) content, and activities of catalase, urease and alkaline phosphatase decreased, indicating the long-term using saline water irrigation deteriorated soil properties. But the difference in soil properties between the treatment of ECiw at 3.4 dS·m−1 and the CK was not apparent. There were reductions below 5% in relative grain yields and soil quality index (SQI) with ECiw lower than 3.17 and 3.10 dS·m−1 compared with CK treatment, respectively. Comprehensive consideration to maintain a stable crop production and benign soil quality, ECiw of 3.10 dS·m−1 for long-term saline water irrigation was recommended as the safe utilization threshold in the NCP.