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 n orthern Spain. Conventional stem-only harvesting was compared with highly m echanized techniques applied in the region, such as (a) whole-tree harvesti ng and humus layer removal, and (b) whole-tree harvesting and humus layer r emoval followed by down-slope deep ploughing. For the study, 58 plantations of Pinus radiata were selected which were located at sites with similar cl imatic conditions, on slopes often exceeding 35% and on soils with similar properties, developed from argillite. Whole-tree harvesting negatively affe cted the physical properties and fertility in the rooting soil layer over a period of some years, because of the severe soil disturbance and accelerat ed erosion which took place. Soils, whose bulk density was increased at the time of site preparation, still showed values high enough to be restrictiv e 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 c ontents remained very low even four years after site preparation. In these soils, exchangeable K increased over this time, most probably as a conseque nce of the rapid release of this element from logging residues and soil org anic matter decomposition. intensive site preparation also affected the nut rition and growth of young trees. The removal of organic components and dee p 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 chl orosis, needle loss and poor growth. (C) 1999 Elsevier Science B.V. All rig hts reserved.