Effects Of Biogas Slurry Application On Soil Physical And Chemical Properties And Antibiotic Residues Of Rubber Plantation

Soil resources are the basis of sustainable agricultural development.As a good filter and purification medium of forest ecosystem,the quality of forest soil has attracted more and more attention.In Hainan Province,with the vigorous development of the agricultural ecological cycle model of returning biogas slurry to farmland,some environmental problems began to emerge,among which soil antibiotic residues caused by improper application of biogas slurry,soil degradation and hardening of rubber plantation,and pollution of groundwater sources have gradually become the focus of attention.In this study,the effects of biogas slurry application on soil physicochemical properties,antibiotics and microorganisms were the main contents.Firstly,the effects of long-term digestion of biogas slurry on different vegetation types of soils in large-scale pig farms in Hainan Province were investigated,and the problems caused by the digestion of biogas slurry in large-scale pig farms at the present stage were analyzed.Taking rubber plantation as the main research object,the effects of different gradient biogas slurry on soil physical and chemical properties of rubber plantation were systematically studied through field experiments.At the same time,the relationship between soil physical and chemical properties,antibiotics and microorganisms of rubber plantation after biogas slurry application was further explored.In field experiment,rubber plantation with good growth and the same age was selected as the test object.Four gradients of biogas slurry application were set up.The amount of biogas slurry applied every 667 m2 was 30 m3(T1),60 m3(T2),90 m3(T3)and blank control(TO).Reasonable analysis of the test results and summary of the best application frequency and amount of biogas slurry in rubber plantation were conducted,which provided a scientific basis for the further popularization and application of the model.The main conclusions are as follows:1.The results of the effect of different gradient biogas slurry on soil physical and chemical properties of rubber plantation for one year showed that the annual average growth rates of organic matter,total nitrogen,total phosphorus,alkaline hydrolysis nitrogen and pH value increased with the increase of the application amount of biogas slurry for one year,and the annual average growth rates were the highest at the T3 treatment gradient(organic matter 35.1%,total nitrogen 39.2%,total phosphorus 416%,alkaline hydrolysis nitrogen 26.1%,pH value 14.7%),followed by the T2 and T1 treatment gradients,i.e.T3>T2>T1.The annual average growth rate of water content,catalase activity and urease activity increased first and then decreased with the increase of biogas slurry application rate,and showed the highest annual growth rate under the gradient of T2 treatment(water content 14.5%,catalase activity 13.6%,soil urease activity 26.8%),followed by the gradients of T1 and T3 treatment,that is,T2>T1>T3.In addition,when the amount of biogas slurry was T3 treatment,the activities of soil catalase and urease were lower than that of the blank treatment T0,and the average annual growth rate was negative(soil catalase 2.5%,urease 11.6%).Therefore,when the amount of biogas slurry was T3 treatment,the application of biogas slurry would inhibit soil enzyme activity.2.The results of the experiment on the effect of biogas slurry application on antibiotic residues in rubber plantation soil showed that the phenomena of antibiotic residues in soil caused by long-term and large-scale application of biogas slurry were obvious,and it was necessary to control the frequency of application or improve the irrigation method of biogas slurry.In the experiment of "Change of soil physicochemical properties,antibiotics and microorganisms in rubber plantation after biogas slurry application" from December to February,no antibiotics were detected in T3 treatment group after the first application of biogas slurry,and 12.79 ng/g antibiotics(Fluoroquinolones antibiotics(FQs)5.23 ng/g,Tetracyclic antibiotics(TCs)7.56 ng/g)were detected after the second application of biogas slurry.After three consecutive application of biogas slurry,24.22 ng/g of antibiotics(FQs 12.92 ng/g,TCs 11.3 ng/g)were detected again in T3 treatment group,which indicated that the application of biogas slurry in T3 treatment group was too large and the content of antibiotics was too high.Continuous application of biogas slurry with this gradient would lead to the occurrence of antibiotic residues in soil.3.The results of analysis of biogas and soil samples from large-scale pig farms showed that the main antibiotics detected in the biogas of five pig farms were sulfadiazine antibiotics(SAs)(sulfadiazine,sulfamethoxazine,sulfamethoxazine)and TCs(oxytetracycline,aureomycin).The total concentration of antibiotics in biogas samples ranged from 9.93 ng/mL to 22.85 ng/mL,the concentration of SAs ranged from 3.98 ng/mL to 5.24 ng/mL,the concentration of FQs ranged from 2.56 ng/mL to 3.26 ng/mL,and the concentration of TCs ranged from 2.02 ng/mL to 16.31 ng/mL.No chloramphenicol antibiotics(CAPs)were detected in all biogas samples.4.The results of changes of soil physicochemical properties,antibiotics and microorganisms in rubber plantation after biogas slurry application showed that no antibiotics were detected in the soil on the 30th day after the application of biogas slurry,and the soil physical and chemical properties and the total amount of soil microorganisms increased with the increase of the amount of biogas slurry applied.The monthly growth rate was T3>T2>T1.On the 60th day of biogas slurry application,12.79 ng/g of antibiotics were detected in T3 treatment.At this time,the monthly growth rates of water content,pH value,total nitrogen,total phosphorus and total potassium were still T3>T2>T1;the monthly growth rates of total microorganism,organic matter,alkali hydrolyzed nitrogen,available potassium,catalase and urease were changed to T2>T3>T1.On the 90th day of application of biogas slurry,24.22 ng/g of antibiotics were detected again in T3 treatment The monthly growth rates of pH,total nitrogen,total phosphorus and total potassium were still T3>T2>T1;the monthly growth rates of water content,organic matter,alkali-hydrolyzed nitrogen,available potassium,catalase and urease were T2>T3>T1;and the monthly growth rates of total microorganisms were T2>T1>T3.The results showed that because of the excessive amount of biogas slurry and the high content of antibiotics in T3 treatment,the continuous application of biogas slurry with this gradient would lead to the occurrence of antibiotic residues in soil,thus reducing soil quality.In summary,when the annual application rate of biogas slurrg in rubber plantation is about T2 gradient,the soil quality of rubber plantation is the best,and there is no antibiotic detection in the soil,the number of soil microorganisms is relatively the highest,and the condition of soil factors is the best.