Phosphorus Fertilizer Efficiency and Phosphorus Availability in No-Till Subtropical Oxisols

The P use efficiency can be influenced by the fertilizers type used, the fertilizer application method, and the initial soil P availability. Clayey Oxisols with a low, medium, and high initial P content were used to grow crops over three years. The treatments included seven P sources [single-superphosphate, triple-superphosphate, Yookarin, Mosaic, Shell, Yoorin, Bayóvar, and a control treatment (no P fertilization)] applied in two methods [fertilization system (100% in winter crop); crop fertilization (50% in winter; 50% in summer crop)]. Crop yield, soil available P content, and agronomic efficiency index (AEI) of fertilizers and soil test critical value (STCV) for P were assessed. The cumulative grain crop yield for treatments receiving soluble fertilizer was 75% higher than partially soluble fertilizers. This difference decreased in soils with medium (10%) or high initial P content (2%). P content of the soil with low initial P content increased with time, especially with the use of partially soluble fertilizers (Yoorin and Bayóvar). The AEI was especially high in the soils with low or medium P content treated with soluble fertilizers. The STCV of P extracted by anion exchange found for the 0 − 0.1 and 0 − 0.2 m soil layer was 26.2 and 18.2 mg dm⁻³ and can be used as reference values to assess soil P availability. In no-till subtropical Oxisols, soluble P fertilization as crop system is crucial when soil P levels are below the STCV. However, in soils rich in available P, fertilization methods and P sources have minimal impact on crop yields.