Vertical distribution of phosphorus fractions and the environmental critical phosphorus level in acidic red soil under long‐term fertilizer and lime application in southern China

Background Phosphorus (P) deficiency in acidic red soil restricts crop yield. However, long‐term application of phosphate fertilizer can cause potential environmental risks due to the accumulation of P in the soil. Aims Our aim was to determine the distribution characteristics of P fractions in acidic red soil profiles and the environmental risk of soil P losses after application of organic fertilizer and lime, and analyze the key factors driving P distribution in the soil profile of acidic red soil. Methods Based on the long‑term applicationof fertilizers and quicklime in the acidic soil under wheat–maize rotation system, contents of soil Olsen‐P and CaCl2‐P, as well as pH, at multiple soil layers between 0 and 50 cm depths were monitored. The environmental critical P levels were determined using a two‐segment linear model. Results During 1990–2010 and 2011–2014, application of phosphate fertilizer or quicklime on acidic red soil significantly (p < 0.05) increased the annual average aboveground biomass of wheat and maize and P recovery efficiency. Soil Olsen‐P and CaCl2‐P contents increased with the application of phosphate fertilizer, especially in combination with manure, and the increase mainly concentrated at the 0–20‐cm soil layer. The environmental critical Olsen‐P content was 99.7 mg kg−1. The Olsen‐P contents at different soil layers were mainly affected by cumulative P and organic P inputs, but were less affected by soil pH. Conclusions The application of organic fertilizer and lime can prevent the acidification of red soil, and the application of organic fertilizer should reduce the total phosphate fertilizer input to prevent rapid accumulation of P and risk of P loss in leachate while still improving the crop utilization rate of P fertilizer. Thus, this strategy should help achieve the concomitant goals of high crop yield and environmental protection.