The effects of applying manure on soil physical properties and crop yield under long-term brackish 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; maize was irrigated at sowing using fresh water. Under all those irrigation treatments, manure application were 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%, 117.02%, 75.7%, and 45.5%, respectively, as compared with the treatments without manure application.The application of manure reduced the bulk density of 0-10 cm soil layer, increased the proportion of water stable aggregates in 0-20 cm soil layer, and improved soil fertility and maintained soil structure of tillage layer. The application of manure significantly increased the amounts of bacteria, fungi, and actinomycetes in the soil microbiota of 0-20cm soil by 73.8% as compared without manure applictaion. 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 to 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 without manure application. In contrast, the yield of summer maize was slightly improved under manure application, due to the increased soil nutrient contents and the effective salt leaching. 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.