The Contrasting Effects of Alum‐Treated Chicken Manures and KH₂PO₄ on Phosphorus Behavior in Soils

Abstract

Alum [KAl(SO)⋅12HO] is often added to chicken manure to limit P solubility after land application. This is generally ascribed to the formation of Al-PO complexes. However, Al-PO complex formation could be affected by the matrix of chicken manure, which varies with animal diet. Alum was added to KHPO (as a reference material) and two manures from typical chicken farms in China, one from an intensive farm (CMIF) and another from free-ranging 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 KHPO. Alum addition lowered Mehlich-3 RP in soils with CMFR but had no influence on Mehlich-3 RP in CMIF- or KHPO-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 NHF-RP (Al-P) fraction only in soils with KHPO, 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 alum-organic P complexes may reduce P solubility. By comparing alum-treated KHPO and manures, it appears that organic matter in manure could interfere with the formation of Al-PO complexes.

Characterizing the phosphorus forms extracted from soil by the Mehlich III soil test

“…The colorimetrically-determined MRP concentrations in the M3 extracts ranged from 29 to 378 mg kg −1 , representing 47–100% of the P concentrations determined by ICP (Table 5 ). This is also consistent with previous studies [ 9 – 12 , 14 – 16 ]. However, previous reports have suggested that the differences between colorimetry and ICP are greater at lower concentrations [ 10 , 12 , 13 ].…”

“…The ratios of orthophosphate monoesters to diesters (Mono:Diester ratio, Table 6 ) were similar for the control, N and untreated poultry litter (PL) treatments (~ 7), but were lower than the alum-stabilized PL treatment (15.7). This reflects the much higher concentration and percentage of myo -IHP in the M3 extract after alum treatment, which is consistent with previous reports that alum stabilizes myo -IHP in poultry litter, potentially limiting its decomposition or loss in soil [ 15 , 16 , 43 – 45 ].…”

“…The clear differences in myo -IHP concentrations in M3 extracts of the alum-treated and untreated AR soils fertilized with poultry litter suggests that more research is needed to determine the long-term implications of the widely-used practice of alum treatment. Although alum treatment has been shown to reduce water-extractable P compared to untreated litter [ 15 , 16 ], the build-up of high concentrations of myo -IHP in soils may affect soil fertility over time. Research is also needed to determine any possible adverse effects from the transport of alum-stabilized myo -IHP to water bodies, for example by erosion.…”

“…Unlike colorimetry, ICP determines total P in solution, which includes both MRP and molybdate-unreactive P (MUP), with MUP being the difference between ICP-determined P and MRP. Higher P concentrations in M3 extracts with ICP analysis than with colorimetric analysis have been widely reported, suggesting MUP is common in M3 extracts [ 9 – 16 ].…”

“…Notably, differences have been observed in M3 P measured by colorimetry and by ICP. For example, Huang et al [ 15 , 16 ] reported much larger MUP concentrations in M3 extracts of soils fertilized with poultry litter stabilized with alum [(Al 2 SO 4 ) 3 ·14H 2 O] than in M3 extracts from soils fertilized with untreated poultry litter. However, studies across a range of soils show no clear patterns for MUP concentrations in M3 extracts; concentrations were not consistently higher with ICP analysis than with colorimetric analysis, and they were not consistently associated with soil properties such as pH, organic matter or cations [ 11 , 13 , 14 ].…”