The effects of applying manure on soil physical properties and crop yield under long-term saline water irrigation

To maintain the soil quality under long-term saline water irrigation, application of manure was carried out to examine the influences of manure on soil physical properties. The long-term saline irrigation was conducted from 2015 to present at the Nanpi Experimental Station in the Low Plain of North China Plain, which including 4 irrigation treatments, which were: irrigation once at jointing stage for winter wheat with irrigation water containing salt at 1 g L⁻¹ (as fresh water), 3 g L⁻¹, 4 g L⁻¹ and 5 g L⁻¹, respectively; maize was irrigated at sowing using fresh water. Under all those irrigation treatments, manure application was conducted, with treatments without manure application as control. Results showed that under long-term irrigation with saline water, the application of manure increased the soil organic matter contents, exchangeable potassium, available phosphorus, and total nitrogen contents in the 0-20 cm soil by 46.8%, 117.0%, 75.7%, and 45.5%, respectively, as compared with the treatments without manure application. The application of manure reduced soil bulk density, increased the proportion of water stable aggregates and the amounts of bacteria, fungi, and actinomycetes for the tillage soil layer compared with the controls. Due to the salt contained in manure, application of manure had dual effects on soil salt contents. In winter wheat season, the application manure increased soil salt contents. During summer maize season, due to the high salt leaching effects under manure application, salt contents were significantly reduced which resulted in the smaller difference in salt contents between the manure and the non-manure treatments. The improvement in soil structure under manure application increased soil desalination rate by 38.3%, 14.7%, and 21.3% as compared with the treatments without manure application for soil layers of 0-40 cm, 40-100 cm, and 100-200 cm, respectively, during the summer rainfall season. Due to the higher salt contents during winter wheat season under manure application, yield of winter wheat was slightly decreased as compared with the control. In contrast, the yield of summer maize was improved by 3.9% under manure application, due to the increased soil nutrient contents and the effective salt leaching. The annual yield of winter wheat and summer maize was similar for treatments with and without saline water application. The results from this study indicated that manure application helped to maintain soil physical structure which was important for long-term utilization of saline water. In practice, it was suggested to use manure with low salt contents to reduce the negative influences of saline water irrigation on soil properties to achieve sustainable saline water use.