Study of the Characteristics of the Accumulation,Migration,and Transforma-tion of Heavy Metals in a Feed-Pig Manure-fermented Biogas Liquid-Paddy Soil System in the Brown Soil Area of the Huaibei Alluvial Plain
To explore the impact of swine manure and digestate on the accumulation and migration of heavy metals in soil and to study the changes in heavy metal content in soil systems from feed-swine manure-fermented digestate-rice paddies,a field experiment involving digestate was performed on rice paddies in the brown loam area of the Huabei alluvial plain.Two experimental groups were set up,with the digestate(BS)and chemical fertilizer(CF)applied as controls.This study analyzed the distribution of heavy metals in feed and pig manure at different fertility stages in pigs,focusing on the effects of the return of biogas to the field on soil heavy metals and environmental factors.The results revealed differences in the contents of the heavy metals Cu and Zn in feed at different fertility stages,and the accumulation of Cu and Zn in pig manure was positively correlated with that in feed.The Cu and Zn concentrations in the nursery pig manure exceeded the agricultural sludge standard by 14.6％and 53.9％,respectively.The average contents of the heavy metals Cu,Zn,Cr,Cd,Asm,and Pb in the biogas were 0.092 2,0.545 6,0.018 9,0.000 98,0.004 5,and 0.005 1 mg·kg-1,respectively,and none of them exceeded the limits of the standard for irrigation water(GB5084-2005).After the application of the full amount of biogas(BS)to the rice field,the con-tents of Cu,Zn,Cr,and As in the 0-20 and 20-40 cm soil layers were lower than those in the chemical fertilizer(CF)treatment,and the contents of Pb and Cd were elevated,with average Cd concentrations of 14.73 and 15.07 mg·kg-1,respectively,which significantly exceeded the limits of the Standards for Risk Control and Management of Soil Contamination of Agricultural Land.The accumulation of Cu and Zn was closely negatively correlated with the amount of biogas Cu and Zn,and the As concentration was negatively correlated with the Cu and As in the digestate.Redundancy analysis revealed that in the different soil layers,the soil total nitrogen(TN),electrical conductivity(EC),and pH negatively affected the accumulation of Cu,and the water content(MC)positively affected the accumulation of soil Cu and Pb.
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