Effects of different organic wastes on phosphorus sorption capacity and availability in soils

Abstract: Farm in suburban area that supports dense livestock operations is important land to recycle organic wastes. Soils in this area received animal wastes and sewage sludge are vulnerable to release a large amount of dissolved phosphorus in surface runoff owing to the gradual saturation of the soil's phosphorus sorption capacity. The objective of this study was to evaluate phosphorus sorption (based on Langmuir isotherms) and availability of phosphorus (as water soluble and available phosphorus) in 4 soils incubated for 6 months with pig manure-rice straw compost, biogas residue, pig manure, chicken manure, domestic waste compost, 2 sources of sewage sludge, or KH2PO4, added to soils on a phosphorus-equivalent basis (100 mg P/kg). Phosphorus isothermal adsorption experiment was applied to evaluate the maximum adsorption capacity of the incubated soils, and both water soluble phosphorus and available phosphorus were used to assess phosphorus release potential of the soils. Results showed that all the phosphorus sources had a negative effect on phosphorus sorption and a positive effect on phosphorus availability in all soils. However, the effects on phosphorus sorption and availability in the soils varied with the phosphorus sources because of differences in their mineral components. The decreases in maximum phosphorus sorption in the pig manure-straw compost, and pig manure-treated soils (9.03%-15.60%) were similar with those in KH2PO4 treated soils (10.59%-16.63%). The decreases in biogas residue, chicken manure, and domestic waste compost treated soils (5.09%-9.84%) were much lower (P<0.05) than the KH2PO4 treated soil. The decreases in sewage sludge-treated soils (4.32%-6.77%) were consistently the lowest for all incubated soils. The effects of pig manure-straw compost, biogas residue, pig manure, and KH2PO4 on water soluble phosphorus were, in most cases, greater (P<0.05) than those of other phosphorus sources. However, the effects of phosphorus sources on soil available phosphorus were relatively small. The declined values of maximum soil phosphorus sorption induced by applications of organic wastes were negatively correlated with total iron, aluminum and calcium contents in the applied organic wastes. The increased values of soil water soluble phosphorus induced by applications of organic wastes were negatively correlated to the input of calcium from these relatively high calcium sources. It suggested that increasing concentrations of iron, aluminum, and calcium in the applied organic wastes can alleviate negative impact of phosphorus on the environment when organic wastes are recycled in soil. The results provide a guideline for reasonable rate of organic waste application in the suburban areas.