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

Abstract

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.