Effects Of Long-term Irrigation With Reclaimed Water From Dairy Industry On Soil Quality

Shortage of water resources has long been a problem affecting our national economy and people’s livelihood.Therefore,the 14th Five-Year Plan outlines"to strengthen agricultural water saving and efficiency,encourage renewable water use."Huhhot city is short of water and a large amount of reclaimed water is produced by the vigorous development of dairy industry.Using reclaimed water for irrigation can not only alleviate the shortage of agricultural water,but also save groundwater resources.For a long time,there is little research on dairy industry reclaimed water in the field of reclaimed water,so this paper mainly studies and evaluates the effects of irrigation on soil quality.Taking the downstream dairy reclaimed water irrigation area of Huhhot and Linger Shengle Economic Park as the study area,this paper has set up five typical irrigation areas with different water quality,namely:dairy sewage irrigation area（W1,W5）,dairy reclaimed water irrigation area（ZG）,well water irrigation area（JG）,dairy reclaimed water and well water irrigation area（HG）,waste land as the control area（CK）,and collected soil samples from 0-10cm,10-30cm,30-50cm,50-70cm and70-90cm respectively before the autumn harvest in October 2020 and before planting in April 2021,and determined effective nutrient indicators（alkaline nitrogen,ammonium nitrogen,nitrate nitrogen,available phosphorus,available potassium）and salinity indicators(EC₂₅,Na⁺,K⁺,Ca²⁺,Mg²⁺,CO₃^2-,HCO₃^-,Cl^-,SO₄^2-),calculates SAR and ESP,and obtains 16 indexes in total.The change of soil available nutrient index and soil salinity index in different soil layers of typical irrigation areas were analyzed,and the comprehensive influence of irrigation with wastewater and reclaimed water from dairy industry on soil quality was quantitatively evaluated by using soil quality index（SQI）,so as to provide reference for rational irrigation with reclaimed water from dairy industry.The main conclusions are as follows:（1）The quality of soil comprehensive fertility has been improved to varying degrees by the irrigation with dairy sewage and reclaimed water.Dairy wastewater and reclaimed water could significantly improve soil available phosphorus and nitrogen availability（P<0.05）in 0-90cm soils,and the effects on soil available nitrogen and potassium were different.Soil available phosphorus was increased by 0.9 to 3.3 times,and soil nitrogen availability was significantly increased by 7.3%to 18.26%for ammonium nitrogen and 102.72%to 638.55%for nitrate nitrogen.（2）According to the results of water-soluble salt ion detection,the contents of Na⁺and SO₄^2-(Na⁺between 0.3 times and 5.3 times,SO₄^2-between 0.7 times and 5.1 times)in the soil have been significantly increased compared with well water irrigation,and the proportions of Na⁺/cation and SO₄^2-anion have been increased(Na⁺between 7.2%and19.8%,and SO₄^2-3.5%and 5.2%).Compared with well water irrigation,the soil electrical conductivity of dairy sewage and reclaimed water irrigation increased significantly by 0-90cm（the increase range was between 18.41%and 88.03%）and SAR（the increase range was between15.04%and 591.11%）.By analyzing the soil salinization degree,it was found that the soil salinization risk was prominent under irrigation with dairy sewage.Through the redundancy analysis,it was found that Na had the greatest effect on the nutrient factors of all irrigation treatments（except HG）and CK,and all showed negative correlation.（3）Through the compatible evaluation of soil quality with effective nutrients and salts,the SQI values of each irrigation treatment are in order as follows:ZG（0.38）>HG（0.37）>JG/CK（0.36）>W5（0.35）>W1（0.33）,indicating that the soil quality under the sewage of dairy industry has decreased and that under the irrigation with reclaimed water of dairy industry has improved.Based on the spatial distribution of SQI,it is found that the soil quality below 10cm in the sewage irrigation area of dairy industry is low,which is easy to aggravate the salinity in spring after overwintering.Dairying reclaimed water can obviously improve the quality of topsoil,and salinization mainly concentrates below 30cm soil layer,which has little effect on crops at seedling stage.The SQI value of mixed irrigation of well water and dairy reclaimed water is similar to that of well water after overwintering,so it is recommended to use mixed irrigation of well water and dairy reclaimed water.