Study On The Migration And Adsorption Behavior Of Nitrogen And Phosphorus In Soil After Biogas Slurry Irrigation

With the continuous development of society,livestock and poultry breeding are developing rapidly due to the growing demand for agricultural products of people.The manure and urine produced by intensive farms were dealt with by anaerobic digestion,and the product biogas slurry were widely used in slurry irrigation soil because of its rich in nitrogen,phosphorus,potassium and other nutrients and trace elements.Biogas irrigated soil has become the main disposal of biogas slurry because of the rapid development of livestock and poultry breeding in Chongqing.Although the environmental pollution caused by direct discharge of biogas slurry can be reduced and the soil properties can also be improved by slurry irrigation soil,the potential threat to the soil and groundwater would be created with unreasonable or excessive biogas irrigation.As one of the main types of soil,purple soil is the largest distribution area and the main production base of agriculture and forestry animal husbandry products.However there are few studies on the biogas irrigation in purple soil at present,the dynamic adsorption environmental behavior of nitrogen and phosphorus after biogas irrigation was not fully grasped.Therefore,the adsorption and migration behavior of ammonia nitrogen?NH₃-N?and total phosphorus?TP?in different soil types and under different biogas slurry irrigation load was studied in this paper from time and depth scale.The changes of soil properties?soil nitrogen and phosphorus content,soil enzyme activity,soil structure and soil composition?after biogas irrigation were investigated to further grasp the pollution risk of biogas irrigation on soil and the surrounding environment.The main conclusions are as follows:1)The soil nitrogen and phosphorus capacity was significantly affected by biogas slurry irrigation load.The NH₃-N and TP adsorption in purple soil gradually decreased with the increase of biogas irrigation load.The NH₃-N and TP adsorption behavior of purple soil shows the following three stages,strong adsorption,adsorption capacity decreased and stable stage with low adsorption capacity.There is a risk of NH₃-N migration to the depth of the soil trend under 382.2 m³/hm²·d?T₁?and biogas irrigation load should be controlled not more than 191 m³/hm²·d?T₂?.However,TP was mainlyadsorbed and trapped in the soil surface?0³5cm?with a weaker migration ability to the soil depth.2)The soil nitrogen and phosphorus capacity was significantly affected by soil type.The sorption capacity of purple soil on NH₃-N and TP was the strongest and the river sand was the weakest with the possibility of soil nutrient loss.The NH₃-N depth migration velocity in different soil is sorted as follows:river sand >sandy soil > purple soil 2 > purple soil 1,And that of the TP is sorted as follows : river sand >sandy soil >purple soil 1 > purple soil 2.The migration of TP and NH₃-N in sandy soil is faster than that in Clay soil.3)The soil urease,phosphatase,and invertase activity was improved significantly after biogas irrigation and the changes of phosphatase activity was affected by biogas irrigation load.Under T₂ load the soil phosphatase activity was increased significantly,and it would be inhibited under higher load biogas irrigation.The urease and invertase activity was gradually increased with the increase of biogas irrigation and was decreased with the increased depth of profile.4)The soil NH₄⁺-N and available phosphorus?SAP?content was significantly increased and the fertility of the soil was raised after biogas irrigation.However,The test under 382.2 m³/hm²·d?T₁?would lead to the risk of the atmospheric environment and groundwater environment.Scanning electron microscope?SEM?pictures showed that the soil porosity increased significantly,and it's beneficial to improve soil structure and improve microbial activity.After biogas irrigation the components of purple soil were basically the same with before but the content of some component had different changes.The content of quartz was relatively reduced and the content of illite was increased with the more obvious changes under higher biogas irrigation load.The intensive livestock farms biogas irrigation effects on soil properties and the NH₃-N and TP dynamic adsorption and migration behavior in the soil layer was studied in this paper.The research has important theoretical significance and practical value to determine the biogas irrigation and provide theoretical basis and technical support to master the migration process of nitrogen and phosphorus NH₃-N and TP.