PHOSPHORUS PHOSPHORUS LEACHING LEACHING IN IN SOILS SOILS AMENDED AMENDED WITH WITH PIGGERY PIGGERY EFFLUENT EFFLUENT OR OR LIME LIME RESIDUES RESIDUES FROM FROM EFFLUENT EFFLUENT TREATMENT TREATMENT D. D. M. M. Weaver Weaver & G. G. S. S. P. P. Ritchie Ritchie Abstract Abstract Phosphorus Phosphorus (P) (P) in in wastes wastes from from piggeries piggeries may may contribute contribute to to the the eutrophication eutrophication of of waterways waterways if if not not disposed disposed of of appropriately. appropriately. Phosphorus Phosphorus leaching, leaching, from from three three soils soils with with different different P sorption sorption characteristics characteristics (two (two with with low low P retention retention and and one one with with moderate moderate P retention) retention) when when treated treated with with piggery piggery effluent effluent (with (with or or without without struvite). struvite). was was investigated investigated using using batch batch and and leaching leaching experiments. experiments. The The leaching leaching of of P retained retained in in soil soil from from the the application application of of struvite struvite effluent effluent was was determined. determined. In In addition. addition. P leaching leaching from from lime lime residues residues (resulting (resulting from from the the treatment treatment of of piggery piggery effluent effluent with with lime lime to to remove remove P) P) was was determined determined in in comparison comparison to to superphosphate superphosphate when when applied applied to to the the same same three three soils. soils. Most Most P was was leached leached from from sandy sandy soils soils with with low low P reten- reten- tion tion when when effluent effluent with with or or without without struvite struvite was was applied. applied. More More than than 100% 100% of of the the filterable filterable P applied applied in in struvite struvite effluent effluent was was leached leached in in sandy sandy soils soils with with low low Pretention. Pretention. Solid, Solid, inorganic inorganic forms forms of of P (struvite) (struvite) became became soluble soluble and and potentially potentially leachable leachable at at pH pH < 7 or or were were sorbed sorbed after after dissolution dissolution if if there there were were sufficient sufficient sorption sorption sites. sites. In In sandy sandy soils soils with with low low P retention. retention. more more than than 39% 39% of of the the total total filterable filterable P applied applied in in recycled recycled effluent effluent (without (without struvite) struvite) was was leached. leached. Soil Soil P increased increased mainly mainly in in surface surface layers layers after after treatment treatment with with effluent. effluent. Sandy Sandy soils soils pre-treated pre-treated with with struvite struvite effluent effluent leached leached 40% 40% of of the the P retained retained in in the the previous previous application. application. Phosphorus Phosphorus decreased decreased in in surface surface layers layers and and increased increased at at depth depth in in the the soil soil with with moderate moderate P retention retention after after leaching leaching the the struvite struvite effluent effluent pre-treated pre-treated soil soil with with water. water. The The soils soils capacity capacity to to adsorb adsorb P and and the the soil soil pH pH were were the the major major soil soil properties properties that that affected affected the the rate rate and and amount amount of of P leaching. leaching. whereas whereas the the important important characteristics characteristics of of the the effluent effluent were were pH. pH. P concentration concentration and and the the forms forms of of P in in the the effluent. effluent. Phosphorus Phosphorus losses losses from from soils soils amended amended with with hydrated hydrated lime lime and and lime lime kiln kiln dust dust residues residues were were much much lower lower than than losses losses from from soils soils amended amended with with superphosphate. superphosphate. Up Up to to 92% 92% of of the the P applied applied as as superphosphate superphosphate was was leached leached from from sandy sandy soils soils with with low low P retention. retention. whereas whereas only only up up to to 60% 60% of of the the P applied applied in in lime lime residues residues was was leached. leached. The The P source source contributing contributing least least to to P leaching leaching was was the the lime lime kiln kiln dust dust residue. residue. The The amount amount of of P leached leached depended depended on on the the water-soluble water-soluble P content. content. neutralising neutralising value value and and applica- applica- tion tion rate rate of of the the P source. source. and and the the pH pH and and P sorption sorption capacity capacity of of the the soil. soil. Keywords: Keywords: phosphorus, phosphorus, leaching, leaching, lime lime residue, residue, piggery piggery effluent, effluent, struvite. struvite. INTRODUCTION INTRODUCTION Phosphorus Phosphorus (P) (P) loss loss from from soils soils by by leaching leaching or or runoff runoff contributes contributes to to the the eutrophication eutrophication of of waterways waterways (Sas, (Sas, 1989). 1989). Nutrients Nutrients contributing contributing to to eutrophication eutrophication have have their their source source in in fertilisers fertilisers applied applied to to agricultural agricultural land, land, industrial industrial wastewaters, wastewaters, or or intensive intensive rural rural industries, industries, such such as as piggeries piggeries (Raper, (Raper, 1983). 1983). A single single piggery, piggery, for for example, example, contributes contributes about about 10% 10% of of the the total total P load load to to the the Peel-Harvey Peel-Harvey estuarine estuarine system system in in Western Western Australia Australia (Humphries (Humphries & Bott, Bott, 1987). 1987). Pollution Pollution from from piggeries piggeries may may arise arise because because common common methods methods of of effluent effluent disposal disposal include include spray spray irrigation irrigation or or discharge discharge to to waterways waterways after after settling settling in in ponds. ponds. Unfortunately, Unfortunately, these these methods methods do do not not always always remove remove sufficient sufficient P to to prevent prevent eutrophication, eutrophication, particularly particularly if if the the effluent effluent is is irrigated irrigated onto onto soils soils which which have have a low low sorption sorption capacity capacity for for P. P. Lime Lime and and bauxite bauxite residues residues have have been been used used to to remove remove P from from effluent effluent (Weaver (Weaver & Ritchie, Ritchie, 1987, 1987, 1993). 1993). Lime Lime treatment treatment can can decrease decrease the the P concentration concentration of of effluent effluent so so that that it it is is less less likely likely to to enrich enrich waterways waterways with with nutrients. nutrients. The The waste waste sludge sludge (lime (lime residue) residue) resulting resulting from from lime lime dosing dosing of of effluent effluent also also requires requires disposal. disposal. Possible Possible disposal disposal methods methods include include its its use use as as a source source of of P for for plants plants or or to to ameliorate ameliorate acidic acidic soils. soils. In In either either case, case, the the use use of of this this material material may may be be constrained constrained by by its its P leaching leaching charac- charac- teristics. teristics. The The quantity quantity of of P leached leached from from soil soil when when effluent effluent or or lime lime residues residues are are applied applied will will depend depend on on the the forms forms of of P in in the the source source material, material, P application application rate, rate, the the P sorption sorption characteristics characteristics and and pH pH of of the the soil, soil, and and P uptake uptake by by plants. plants. Both Both effluents effluents (Payne, (Payne, 1986) 1986) and and soils soils have have widely widely different different properties properties that that may may affect affect P losses. losses. In In