Phosphorus in the runoff of soils with contrasting textures influenced by soil slope and pig slurry application

Abstract

The objective of this study was to quantify the losses of water, sediments and phosphorus (P) fractions by surface runoff as a function of terrain slope and P rates applied in two soils with contrasting textures. Six field trials installed in 2015 were evaluated in 2018 and 2019, in a Nitisol and in a Cambisol, with 642 and 225 g kg−1 of clay. Averages of 0, 55, 110 and 220 kg ha−1 year−1 of P were applied superficially, corresponding to 0, 32.5, 65, 130 m³ ha−1 year−1 of pig slurry. Pig slurry was applied under three terrain slopes at each site: 10%, 20% and 30% in the Nitisol and 15%, 25% and 35% in the Cambisol. After natural rainfall events, the drained solution was collected and the flow volume, amount of sediments and fractions of dissolved reactive P (DRP), particulate P (PP) and total P (TP) lost by surface runoff were determined. At the beginning of 2019, soil samples were collected in the 0–10 and 10–20 cm layers and the Mehlich-1 extractable P was determined. Increase in terrain slope substantially increased the losses of water, sediments and P. Considering the highest slope of each site, the losses of water, sediments and TP in the Nitisol were 35.3, 13.5 and 21.8 times higher than in the Cambisol. Mehlich-1 extractable P in the Nitisol was 1.7 times higher than that observed in the Cambisol. DRP represented about 73% of the total P lost, but the participation of PP increased with the increase in slope. It was concluded that the Nitisol undergoes higher losses of water, sediments and P by surface runoff, compared to the Cambisol, much due to the higher rainfall volume, rate of transported material, lower water infiltration in the soil profile and accumulation of P in the surface layer of the soil.