Researchon The Effect Of Positional Application Of Biogas Fertilizer On Tomato Quality And Soil Environmental Quality For 3 Consecutive Years

Biogas fertilizer is rich in trace elements and nutrients such as N,P,K,etc.It is an organic fertilizer with comprehensive nutrients,which can replace chemical fertilizers to a certain extent,reduce the amount of chemical fertilizer and improveits efficiency.It plays a positive role in improving the yield and quality of agricultural products,and improving the physical and chemical properties of soil.With the utilization of biogas fertilizer,the pollution problems such as excessive content of heavy metals and antibiotics in soil are becoming more and more serious,which are due to the unscientific use of biogas fertilizer.In order to reduce the influence of external environmental factors,the greenhouse was used as the test site in this study,tomato was selected as the planting object.Biogas fertilizer and chemical fertilizer with equal nitrogen content were applied,and the nitrogen content was 170kg·ha^-1.A total of 5 experimental groups were set up with biogas fertilizer treatments:BF1（tomato planting）,BF2（not tomato planting）,chemical fertilizer treatments:CF1（tomato planting）,CF2（not tomato planting）,no fertilizer treatment CK（planting tomato）.Through the comparative study on the changes of tomato plant growth,fruit yield and quality,heavy metals,as well as soil physical and chemical properties,heavy metals and antibiotics in each experimental treatment for three consecutive years,the pollution of soil heavy metals,potential ecological hazards and health risks of tomato intake were evaluated,and the maximum bearing years of soil heavy metals were estimated,so as to provide corresponding theoretical basis for the long-term safe application of biogas fertilizer.The following conclusions are drawn:（1）In this study,the application of biogas fertilizer with N content of 170 kg·ha^-1for three consecutive years was better than the application of chemical fertilizer with equal N content and no fertilizer in promoting tomato plant growth,increasing fruit yield and improving fruit quality;The continuous cropping of tomato will affect the growth,reduce the yield and quality,and the application of biogas fertilizer can slow down this downward trend.The stems and fruits of tomato plants have different absorption effects on different heavy metal elements.Heavy metal elements Cu,Zn,Cd,As and Hg were detected in the plant stem,while only heavy metal elements Cu,Zn and Cd were detected in the fruit.The content of heavy metal in fruit was lower than that in plant stem.The contents of Cu and Zn in tomato fruits treated with biogas fertilizer were higher than those treated with chemical fertilizer and no fertilizer,and the content of Cd was lower than that treated with chemical fertilizer and no fertilizer.In the three-year experiment,the content of Cu in tomato fruits treated with biogas fertilizer increased by 4.54%,and the contents of Zn and Cd decreased by 8.01%and 36.11%respectively.The content of heavy metals in tomato fruit of all experimental treatments did not exceed the limit index of"National Food Safety Standard for Contaminants in Food"（GB2762-2017）.（2）In the three-year experiment of this study,the initial value of soil p H is 7.72,and the soil p H value of each experimental treatment showed a downward trend year after year,which decreased by 2.94%～5.53%in three years.The downward trend of soil p H in biogas fertilizer treatment was slow.The content of soil organic matter in biogas fertilizer treatment increased year by year,the content in the third year increased by 7.17%～8.84%compared with the initial content,and the content of soil organic matter in chemical fertilizer treatment and no fertilizer treatment decreased year by year.The application of biogas fertilizer and chemical fertilizer for three consecutive years can significantly increase the content of total nitrogen in soil.After the three-year experiment,the contents of Cu,Zn,As and Hg in the soil treated with biogas fertilizer increased by12.91%～19.64%,10.77%～17.08%,9.28%～10.07%and 4.93%～7.04%respectively compared with the initial value,the content of Cd decreased slightly,there was accumulation of some heavy metals in soil.The content of heavy metals in the soils of all experimental treatments was lower than the screening value of soil pollution risk for agricultural land in the"Soil Environmental Quality Agricultural Land Soil Pollution Risk Control Standard（Trial）"（GB15618-2018）.Antibiotics（tetracycline,oxytetracycline,and chlortetracycline）were not detected in all experimental treated soils.（3）The single factor pollution index of heavy metals in all experimental treatments was less than 1,and the Nemero comprehensive index was less than 0.7,it shows that the application of biogas and chemical fertilizers with the current nitrogen concentration has a low degree of soil heavy metal pollution and is relatively safe;The environmental risk index of single pollution of soil heavy metals was less than 40,and the comprehensive environmental risk index RI of heavy metals and multi elements was less than 150,it shows that the potential ecological risk of heavy metals in soil was slight.Under the current nitrogen content of 170 kg·ha^-1,the maximum bearing years of Cu,Zn and As in tomato soil were 35a,45a and 73a respectively,and the maximum bearing years of Cu,Zn and As in non tomato soil were 22a,27a and 67a respectively;The health risk index of heavy metal intake for adults and children of all the experimentally treated tomatoes was less than 1,indicating that the consumption of tomatoes grown under the current conditions caused a lower health risk for adults and children.