Effect of roxarsone metabolites in chicken manure on soil biological property

Roxarsone (ROX), an organoarsenic feed additive, occurs as itself and its metabolites including As(V), As(III), monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA) in animal manure. Animal manure improves soil biological property, whereas As compounds impact microorganisms. The integral influence of animal manure bearing ROX metabolites on soil biological quality is not clear yet. Herein, the effect of four chicken manures excreted by chickens fed with four diets containing 0, 40, 80 and 120 mg ROX kg^-1, on soil biological attributes. ROX addition in chicken diets increased total As and ROX metabolites in manures, but decreased manure total N, ammonium and nitrate. The elevated ROX metabolites in manures increased soil total As, As species and total N, and increased first and then decreased soil nitrate and nitrite, but did not affect soil ammonium in manure-applied soils. The promoting role of both soil As(III) and ammonium on soil microbial biomass carbon and nitrogen, respiration and saccharase activity, were exceeded or balanced by the inhibiting effect of soil nitrate. The suppression of soil catalase activity by soil As(V) was surpassed by the enhancement caused by soil nitrate and nitrite. Soil urease, acid phosphatase and polyphenol oxidase activities were not suitable bioindicators in the four manure-amended soils. Soil DMA did not affect soil biological properties, and MMA was not detectable in all manure-amended soils. The above highlights the complexity of joint influence of soil As and N on biological attributes. Totally, when ROX is used at allowable dose in chicken diet, soil biological quality would be suppressed in manure-amended soil.

Toxicity of synthetic chelators and metal availability in poultry manure amended Cd, Pb and As contaminated agricultural soil

Chelating agents added to contaminated soils may increase solubility and phytoextraction efficiency of soil metals. However, they can create negative effects on soil biological quality. A 90-day incubation experiment was conducted to evaluate mixed effects of chelating agents and poultry manure on changes in available Cd, Pb and As, CO2-C efflux, microbial biomass C, dissolved organic C (DOC), and N mineralization in metal-polluted agricultural soil. Application of poultry manure resulted in a considerable increase in soil pH, DOC, CO2-C efflux, net N mineralization, net N nitrification, and microbial biomass C compared to those in unmanured soil. Availability of arsenic increased twice in manure amended soil due to changes in pH and DOC. However, adding poultry manure did not affect the concentrations of available Pb and Cd compared to those in control soil. Chelating agents increased CO2-C efflux, DOC, and metal availability but decreased microbial biomass C and net N mineralization. Maximum decrease in microbial biomass C, net N mineralization, and net N nitrification, was observed in EDTA applied soil possibly due to high metal availability to soil microorganisms. Overall results revealed that the application of synthetic chelators in combination with poultry manure enhances available As and demonstrates better environment for soil biota.