The Effect of Long-Term Mineral Fertilizers Treatment on the Pine Diameter Growth at Plantings in the Burnt Clear-Cuts with Sandy Soils. I. The Consequence of the 30-Year Annual Treatment of Potash Fertilizers on the Pine Diameter Growth and Wood Quality

The paper considers the problem of restoration of forest communities, destroyed by timber harvesting and subsequent fires. The study object was a 53-year-old pine crop seeded in 1961 in a burnt clear-cut of the heather type with sandy soils. The work objective was the research of the aftereffect of the 30-year annual potash fertilizers treatment on the pine di-ameter growth and wood quality. The fertilizers (potassium chloride (K), superphosphate (P), urea (N)) were applied annually from 1967 to 1996. The experimental design was: con-trol (without fertilization), K, PK, NK. The aftereffect of potash chloride on the increment of the basal area growth of a tree stem, which was more informative than the increase in diameter, was observed until the end of the investigations. The effectiveness of the potassi-um aftereffect on the average periodic mean annual basal area growth was significantly higher than at the period of supplementary fertilizers. Over the entire observation period (from the age of 15 years to 53 years) the potash fertilizer provided an increase in the basal area of an average tree by a factor of 1.2 compared to the control indicator. However, the phosphate-potassium (by a factor of 1.7) and nitrogen-potash (by a factor of 1.9) fertilizers proved to be more effective. The annual potash chloride application for 30 years had not affected significantly on the average number of layers in 1 cm of wood and the average ra-dial increment. The addition of phosphorus and nitrogen to the fertilizers deteriorated the studied parameters, but simultaneously caused the increase in the proportion of latewood. Nitrogen-potash fertilizers provided the maxima of a mean diameter and a growing stock but reduced the wood density.