Nutritional aspects of exotic forestry in New Zealand: The uptake , cycling and removal of mineral nutrients by crops of Pinus radiata
- Forest Research Institute, Rotorua
Evidence is presented that the cycling of nutrients in Pinus radiata plantations on a pumice soil will retard serious depiction of nutrients at least until the end of the second crop.
Of the quantities of nitrogen, phosphorus, potassium and calcium taken up from a pumice soil by P. radiata forest, at least 85% is returned to the soil as litter and wash from the tree crowns in rain, and as slash from thinnings, prunings and clear felling. This slash returns more nitrogen, phosphorus and potassium to the soil than is removed in logs.
There are seasonal fluctuations in the nutrient content of foliage and living bark as well as progressive changes in foliage, bark and wood as the tissues age. Levels of all nutrients in bark fall as it becomes older: the same is true of wood except for calcium. This results in reduced demands on soil reserves of nutrients during the latter part of the life of each crop when the greatest part of dry matter accumulation is in the form of heartwood.
Nutrient additions from outside the forest in rainfall are likely to be offset by losses through leaching.
Soil nutrient reserves of potassium and calcium seem adequate for a number of tree crops but supplies of nitrogen and phosphorus will largely depend on their release from soil organic matter which forms stable complexes with allophane in these soils. Fungal activity associated with tree roots does seem capable of destroying these complexes and releasing nutrients.