The Fate of Pig Slurry Phosphorus Applied to a Sandy Loam Soil under No-Till Cropping in Southern Brazil

Repeated phosphorus (P) inputs can lead to the accumulation of surplus P in soil with enhanced potential risk of transfer and accelerated eutrophication of aquatic environments. Intensive pork production in Rio Grande do Sul in southern Brazil results in the generation of large quantities of P-rich waste in the form of pig slurry, which is used to fertilise crops. The aim of this study was to assess and quantify the impact of repeated application of pig slurry P over 8 years (2000-2007) on the fate of P in a sandy loam soil maintained under a mixed cropping regime. In a replicated field trial, pig slurry was applied at three rates (20, 40, and 80 m3 ha-1), which resulted in cumulative P inputs over the 8-year period of 628, 1256, and 2511 kg P ha-1. Slurry inputs of 20, 40, and 80 m3 ha-1 resulted in the accumulation of 368, 936, and 2039 kg P ha-1 in soil to 60 cm, respectively. A combination of soil storage (59-81 %), crop removal (7-14 %), and total P transfer in surface runoff (5-15 %) accounted for most of the P applied in pig slurry over 8 years. Our results highlight the potential environmental impacts of runoff P losses in long-term waste-amended and intensively managed subtropical coarse-textured soils. Measures to minimise soil erosion and P transfers from land to water bodies are of utmost importance.