Soil fertility rehabilitation in young Pinus radiata D. Don. plantations from northern Spain after intensive site preparation

Soil fertility and tree nutrition of young Pinus radiata were examined four years after harvesting, site preparation and planting in a hilly area of northern Spain. Conventional stem-only harvesting was compared with highly mechanized techniques applied in the region, such as (a) whole-tree harvesting and humus layer removal, and (b) whole-tree harvesting and humus layer removal followed by down-slope deep ploughing. For the study, 58 plantations of Pinus radiata were selected which were located at sites with similar climatic conditions, on slopes often exceeding 35% and on soils with similar properties, developed from argillite. Whole-tree harvesting negatively affected the physical properties and fertility in the rooting soil layer over a period of some years, because of the severe soil disturbance and accelerated erosion which took place. Soils, whose bulk density was increased at the time of site preparation, still showed values high enough to be restrictive to tree growth after a period of four years. A very low rate of recovery was observed for organic matter, total N and S and exchangeable Ca, whose contents remained very low even four years after site preparation. In these soils, exchangeable K increased over this time, most probably as a consequence of the rapid release of this element from logging residues and soil organic matter decomposition. intensive site preparation also affected the nutrition and growth of young trees. The removal of organic components and deep soil disturbance led to deficiencies of P, S and N in foliage, as well as potentially toxic levels of Mn, which were associated with symptoms of chlorosis, needle loss and poor growth. (C) 1999 Elsevier Science B.V. All rights reserved.