Impact of chemically amended pig slurry on greenhouse gas emissions, soil properties and leachate

The effectiveness of chemical amendment of pig slurry to ameliorate phosphorus (P) losses in runoff is well studied, but research mainly has concentrated only on the runoff pathway. The aims of this study were to investigate changes to leachate nutrient losses, soil properties and greenhouse gas (GHG) emissions due to the chemical amendment of pig slurry spread at 19kg total phosphorus (TP), 90kg total nitrogen (TN), and 180kg total carbon (TC) ha^-1. The amendments examined were: (1) commercial grade liquid alum (8% Al₂O₃) applied at a rate of 0.88:1 [Al:TP], (2) commercial-grade liquid ferric chloride (38% FeCl₃) applied at a rate of 0.89:1 [Fe:TP] and (3) commercial-grade liquid poly-aluminium chloride (PAC) (10% Al₂O₃) applied at a rate of 0.72:1 [Al:TP]. Columns filled with sieved soil were incubated for 8mo at 10°C and were leached with 160mL (19mm) distilled water wk^-1. All amendments reduced the Morgan's phosphorus and water extractable P content of the soil to that of the soil-only treatment, indicating that they have the ability to reduce P loss in leachate following slurry application. There were no significant differences between treatments for nitrogen (N) or carbon (C) in leachate or soil, indicating no deleterious impact on reactive N emissions or soil C cycling. Chemical amendment posed no significant change to GHG emissions from pig slurry, and in the cases of alum and PAC, reduced cumulative N₂O and CO₂ losses. Chemical amendment of land applied pig slurry can reduce P in runoff without any negative impact on nutrient leaching and GHG emissions. Future work must be conducted to ascertain if more significant reductions in GHG emissions are possible with chemical amendments.