Dynamic Changes Of Manure Nutrients And Heavy Metals In Large-scale Farms And Evaluation Of Safe Application

Entering the 21 st century,China has a higher requirement for the ecological environment construction.With the current sternly situation,issues concerning agriculture,countryside and farmers need to be solved by the large scale livestock breeding.However,in the process of breeding,a large amount of excrement cause pollution to the ecological environment.With the accumulation of heavy metals in the farmland,it not only affects the normal growth of crops but also may eventually threaten human’s healthy diet.In order to make a full use of the organic manure resources of excrement in agricultural safety production,it is necessary to have a comprehensive understanding of the dynamic changes in the contents of heavy metals and nutrients in large-scale of livestock and poultry farms in Yuncheng City.A total of 53 pig manure samples and feed were collected from 4 different large-scale pig farms in Yuncheng in August,October,December 2018,and January,March,and May 2019,and nutrients such as N and P and heavy metals were carried out.The contents of Hg,As,Fe,Cd,Cu,Zn,Pb,Cr,and Ni were determined as follows: The average contents of BOD5,COD,ammonia nitrogen,total phosphorus,and suspended matter in the feces were 20693,34454,1254,and 217,15403mg/l,the concentration of pollutants discharged from each breeding site has not reached the pollutant emission standards for livestock and poultry breeding(GB18596-2001).The average contents of heavy metals Hg,As,Fe,Cd,Cu,Zn,Pb,Cr,and Ni in feces were 0.016,5.25,2552,0.297,270,1203,2.39,9.52,5.17 mg/kg.According to the agricultural sludge pollutant control standard(GB4284-2018),except for some sites where the emissions of zinc exceeded the standard,other indicators were qualified.Analysis of the average monthly content of heavy metals in pig manure samples: Hg,Cd,Cu content was highest in October 2018,As,Zn,Pb,Ni content was highest in December 2018,and Cr and Fe were in January and March 2019,respectively Hg,As,Cu were the lowest in January 2019,and Cd,Zn,Pb,Cr,and Ni were the lowest in March 2019.The content of heavy metals in pig feed showed: Zn> Cu> Cr> Pb> Ni,and other than Cu meeting the standards,other indicators did not meet the "Specifications on the Safe Use of Feed Additives"(Ministry of Agriculture Announcement No.2625).Cu and Zn in pig manure are the main factors affecting the terms of service about the soil.Based on the above calculation,Cu content in agricultural soil in Shanxi Province is within 134 a and Zn content is within 191 a,which can exceed the soil environmental quality agricultural land soil pollution risk control standards.Therefore,it is a must to have a strict control about the hog feed,such as,ensuring that the amount of heavy metals added in the feed is within a reasonable range.In this way,it can effectively decline the overrun of heavy metals in hog feed.At the same time,it will also bring good ecological and environmental benefits for the scientific use of pig manure as organic fertilizer.