Critical levels and sufficiency ranges of phosphorus in Pinus taeda plantations in southern Brazil

Pinus taeda plantations in South America have been cultivated on soils of low natural fertility, especially phosphorus (P), increasing the necessity for phosphate fertilisation. The proposition of critical levels (CL) and sufficiency ranges (SR) of P in the needles and soil in P. taeda plantations can assist in decision making on the rational use of phosphate fertilisers, reducing the cost of production and P fertiliser losses. This study aimed to propose critical levels and sufficiency ranges of P in P. taeda plantations in southern Brazil. The study was conducted in 12 plantations of P. taeda subject to fertilisation and non-fertilisation. The parameters height, diameter at breast height, mean annual increment (MAI), P concentration in the needles, available P in the soil, pH, soil organic matter, sand and clay were evaluated at mid-rotation and end-of-rotation. The CL and SR of P in the needles and soil were calculated. The use of a Bayesian approach to boundary analysis allowed us to propose values for CL of P in the needles and soil in P. taeda plantations in southern Brazil. The CL of P in the needles relative to the MAI was 1.6 g P kg−1. The CL for P in the soil was 5.2 mg P dm−3. The use of CL will allow foresters to reverse any P deficiency, ensuring adherence to the adjusted phosphate fertiliser recommendations, reducing production costs and possible P fertiliser losses in P. taeda plantations.