The contrasting effects of alum-treated chicken manures and KH<inf>2</inf>PO<inf>4</inf> on phosphorus behavior in soils
Citation
Huang, L., Yang, J., Xu, Y., Lei, J., Luo, X., Cade-Menun, B.J. (2018). The contrasting effects of alum-treated chicken manures and KH2PO4 on phosphorus behavior in soils. Journal of Environmental Quality, [online] 47(2), 345-352. http://dx.doi.org/10.2134/jeq2017.08.0314
Plain language summary
Chicken manure is high in nitrogen (N) and phosphorus (P), so can be a valuable alternative to chemical fertilizer. However, the ratio of N to P in chicken manure is low compared to crop needs for N and P. This means that adding chicken manure to meet crop N requirements will add too much P to soil. This extra P can be lost from soil to water, causing water quality problems. Alum is commonly added to chicken manure in North America, China and elsewhere, before spreading the manure on soil. This is done because alum binds with P, stabilizing it in soil, preventing it from being lost from soil to water but still keeping the P available for crops. This study used chicken manure from two different sources, free-range chickens and intensively-farmed chickens, because the manures from these sources had different N to P ratios and different organic matter concentrations, due to differences in animal diets. When alum treatment of these two manures was compared with alum-treated chemical fertilizer, it showed that the organic matter in the manure could interfere with the ability of alum to bind with P, depending on the chicken diets, which limited the effectiveness of alum to stabilize P in soil and prevent its loss to water.
Abstract
Alum [KAl(SO4)2×12H2O] is often added to chicken manure to limit P solubility after land application. This is generally ascribed to the formation of Al-PO4 complexes. However, Al-PO4 complex formation could be affected by the matrix of chicken manure, which varies with animal diet. Alum was added to KH2PO4 (as a reference material) and two manures from typical chicken farms in China, one from an intensive farm (CMIF) and another from freeranging chickens (CMFR). These were subsequently incubated with soils for 100 d to investigate P transformations. Alum reduced water-soluble colorimetrically reactive phosphorus (RP) from soils amended with manure more effectively than in soils amended with KH2PO4. Alum addition lowered Mehlich-3 RP in soils with CMFR but had no influence on Mehlich-3 RP in CMIF- or KH2PO4-amended soils. A comparison of P in digested Mehlich-3 extracts with RP in undigested samples showed significantly increased P in digests of alum-treated CMFR only. Fractionation data indicated that alum treatment increased P in the NH4F-RP (Al-P) fraction only in soils with KH2PO4, but not in soils with manure treatments. Furthermore, NaOH-extracted nonreactive P was markedly higher in soil with alum-treated CMFR relative to normal CMFR. The CMFR manure was assumed to contain higher concentrations of organic P because these chickens were fed grains only. These results suggest that the formation of alumorganic P complexes may reduce P solubility. By comparing alumtreated KH2PO4 and manures, it appears that organic matter in manure could interfere with the formation of Al-PO4 complexes.