Fate of phosphorus applied to soil in pig slurry under cropping in southern Brazil

Abstract

Strongly weathered soils (such as Oxisols), are inherently phosphorus (P) limiting and highly P-sorptive thus requiring continued P inputs for productive agriculture. Constant P inputs result in accumulation of soil P with increasing risk of eutrophication of waterways. The state of Santa Catarina is the largest pork producer in Brazil. Production is concentrated in confined systems, with large generation of nutrient rich waste, commonly utilised as fertiliser. The objective of this work was to investigate and quantify the impact of long-term P inputs in pig slurry to a high P-sorbing Oxisol under cropping in southern Brazil. Fifteen years of pig-slurry addition resulted in P accumulation and vertical movement down the soil profile in proportion to application rates, but significant effects were confined to the 0–20 cm soil layer. Phosphorus accumulated mainly in inorganic forms. Slurry input rates of 25, 50, 100, and 200 m 3 ha −1 y −1 resulted in accumulations of 25, 57, 106, and 159 kg P ha −1 y −1 (0–40 cm), of which only 8, 10, 23, and 28 kg P ha −1 y −1 were organic P forms. Mass balance showed that between 62 and 94% of the P inputs in slurry were accounted for in grain exports (7–35%), soil storage (58–83%), minimal amounts were estimated in crop residues ( < 1%), while the remainder (6–38%) was presumed to have been lost in drainage by overland flow.