Changes in topsoil, standing litter and tree nutrient content of a Pinus patula plantation after phosphorus and potassium fertilization

A major goal for sustainable forestry management is to prevent a decline in soil fertility over time. The impact of phosphorus (P) and potassium (K) fertilization on the nutrients in the foliage, standing litter and topsoil (0 to ?10?cm) at the end of the third crop rotation (at age 15?years) was determined. Three quantities (20/20, 40/40 and 80/80?kg?ha^?1) of both P and K fertilizer was applied at different stages of stand development (all at planting, all post-pruning at age 5?years, or applying 20/20 at planting and the rest post-pruning). The results showed that the effect of P fertilizer was more pronounced than the effect of K fertilizer. Compared to the control, the application of 80/80 PK fertilizer increased the concentration of plant available P (Bray II) in the first ?10?cm of the topsoil from 3 to 12?mg P kg^?1 and increased the foliar P level to 0.13%. The foliar P as well as the concentration of plant available P in the topsoil increased when the fertilizer was applied post-pruning. The split application of either 40/40 or 80/80 PK fertilizer increased the stemwood P concentration by 50%, compared to the 23?mg P kg^?1 on the control plots. Application of the 40/40 and 80/80 quantities of fertilizer increased the dry mass (DM) of the standing litter layer by 27?Mg DM ha^?1 (35%), which also affected the P and K content per hectare. A larger proportion of the applied fertilizer-K than fertilizer-P was removed from the site in stemwood and stembark, indicating that the re-application of K in the subsequent rotations will be important for sustainable production.