Characteristics Of Water And Nutrient Transport In Layered Soil With Piggery Effluent Irrigation

With the rapid development of intensive livestock and poultry breeding industry in China,the amount of livestock and poultry feces and sewage has increased sharply,which leads to the increasingly prominent environmental problems of agricultural non-point source pollution.The return of feces and sewage to the field has become an important way to solve the current resource utilization of livestock and poultry waste.It is of great significance for the utilization of aquaculture wastewater and the protection of water and soil environment to reasonably control the process of aquaculture wastewater returning to the field and understand the law of soil solute transport under the complex soil configuration of aquaculture wastewater irrigation.In this study,loam clay in sandy soil layer configuration of subtropical hilly region was selected as the research object,piggery effluent and tap water were used as irrigation sources,and one-dimensional soil column vertical infiltration simulation irrigation test was used to study the effects of interlayer thickness(5,10,15,20 cm)and the position of of interlayer(the upper boundary of interlayer was 5,10,15,20 cm from the soil surface)on the soil water infiltration characteristics and nutrient distribution under different soil configurations of aquaculture wastewater infiltration.The main research results were as follows:(1)Two kinds of water quality were used to irrigate the soil with different interlayer thicknesses.Under the same infiltration time,the migration distance of soil wetting front,the cumulative infiltration amount and the infiltration rate all showed a trend of first decreasing and then increasing with the increase of the interlayer thickness.The results found that when the thickness of irrigation interlayer of piggery effluent and tap water was20 cm and 15 cm respectively,the soil infiltration capacity was the weakest and the infiltration inhibition effect was the best.Under the same water quality irrigation,the characteristic value of infiltration rate of each layer thickness treatment was as follows:initial infiltration rate>average infiltration rate>stable infiltration rate,and the relationship between the cumulative infiltration amount through the lower interface of the interlayer and the thickness and time of the interlayer could be well fitted by a binary quadratic equation(R~2>0.995).(2)The interlayer of soil could intercept nutrients,especially nitrogen and phosphorus.When the aquaculture wastewater was used to irrigate the soil with different interlayer thickness,the maximum interception rate of organic matter in the interlayer was 12.66%,and the interception rates of alkali-hydrolysed nitrogen,total phosphorus and available phosphorus were 5.06%～17.61%,21.21%～34.49%and 27.13%～51.38%,respectively.The nutrient interception of 10～20 cm interlayer thickness was the most.Compared with tap water,when the same interlayer thickness was irrigated by aquaculture wastewater,the interlayer had a better effect on the same nutrient accumulation.(3)Two kinds of water quality were used to irrigate the soil with different interlayer positions.Under the same infiltration time,the closer the interlayer was to the soil surface,the smaller the migration distance of soil wetting front,cumulative infiltration and infiltration rate were.The characteristic value of infiltration rate of interlayer position 5 cm were significantly lower than those of other interlayer treatments(p<0.05).Therefore,when using piggery effluent to irrigate 20 cm interlayer thickness and 5 cm interlayer position,using tap water to irrigate 15 cm interlayer thickness and 5 cm interlayer position,the corresponding water resistance and seepage reduction effect was the best.Linear equation was used to fit the relationship between soil cumulative infiltration and wetting front advance distance(R~2>0.999),and binary quadratic equation was used to fit the relationship between soil cumulative infiltration across the lower interface of interlayer and time and interlayer position(R~2>0.998).The fitting accuracy was extremely high.(4)When the aquaculture wastewater irrigated the soil at different interlayer positions,the interception degree of each nutrient at the interlayer was different.The p H value and total nitrogen interception degree of the interlayer were low,but the other nutrients interception effect was obvious.The maximum interception rate of organic matter and alkali-hydrolysed nitrogen was 5.26%and 20.40%,respectively.The interception rates of total phosphorus and available phosphorus were 28.14%～34.32%and 33.20%～42.79%respectively.The nutrient interception of 10～20 cm in the interlayer was the highest.(5)The optimal model of layered soil water infiltration was screened and the model of layered soil nutrients was fitted.The relationship between the migration distance of wet front of layered soil with time could be fitted by a power function(R~2>0.978),and the relationship between the characteristic value of soil infiltration rate and interlayer parameters could be fitted by a quadratic equation with one variable(R~2>0.739).Kostiakov model was the best model for layered soil water infiltration,followed by Horton model,while Philip model was not applicable.The relationship between the average relative value of soil nutrient content and the thickness or position of interlayer could be well fitted by quadratic equation with one variable.The relationship between nutrient interception per unit thickness and interlayer thickness or position was fitted by logarithmic equation,and the relationship between average nutrient interception per unit thickness and interlayer thickness or position and interlayer water content could be fitted by quadratic equation.