Phosphorus mobility and degree of saturation in oxisol under no-tillage after long-term dairy liquid manure application

The main way of manure use is its application to croplands near livestock farms as a nutrient source to enhance crop production. However, if incorrectly applied, the manure can become an environmental problem due to phosphorus losses to water bodies. This study aims: i) to assess the mobility of phosphorus downward in the soil profile; ii) to evaluate the long-term influence of dairy liquid manure (DLM) application under no-tillage on phosphorus adsorption; and iii) to suggest an environmental threshold for soil phosphorus. The experiments were conducted at two experimental stations of the ABC Foundation, Paraná state, Brazil. One site had a dystrophic red-yellow oxisol (sandy oxisol), sandy clay loam texture soil with 13% slope. The other site had a dystrophic oxisol (clayey oxisol), clayey texture soil with 10% slope. The experiments started in November 2005 and May 2006 in the sandy oxisol and clayey oxisol soils, respectively, in areas where the no-tillage system had been practiced for over 15 years. Treatments consisted of four rates of DLM (0, 60, 120, 180 m3 ha−1 year−1). Soil samples were collected in 2014 at six depths (0-10; 10-20; 20-30; 30-40; 40-50; 50-60 cm). The effect of DLM on downward phosphorus mobility in the soil profile was observed up to 50 cm in the sandy oxisol soil. In the clayey oxisol soil, the phosphorus in soil solution was affected by DLM application up to 20 cm. A reduction in the binding energy was observed in both soils with the application of DLM. The maximum phosphorus adsorption capacity decreased only in the sandy oxisol soil. It was possible to determine the change point only for the sandy oxisol soil at 62.2% of DPSResin (degree of phosphorus saturation with resin extraction) and 34.2% of DPSMehlich (degree of phosphorus saturation with Mehlich extraction). This corresponds to 188 mg kg−1 of soil resin P and 103 mg kg−1 of soil Mehlich-1 P, at the soil surface (0-10 cm). These values for this type of soil, are recommended as an environmental threshold for phosphorus.