New Zealand Journal of Forestry (1980) 25(2): 217–228
©New Zealand Institute of Forestry
The role of fertilisers in the future of West Coast exotic forests.
D. J. Mead , G. Mew and R. E. Fitzgerald
Exotic forestry on the West Coast faces difficulty in meeting wood demands after a reduction in the indigenous forest cut. The situation is acute because of the small size of the exotic estate (14 200 ha), its age distribution (only 1400 ha >20 years old), the species used, and their generally poor growth rates. Fertilizers offer one method of overcoming these difficulties.
The region is characterised by a moderately warm but extremely wet climate and by problems associated with topography, low soil fertility, and the influence of man. Recent soil surveys, backed by analyses of soil and of pine foliage,have identified the physical and nutrient limitations to growth of exotic tree species over a 4000 km1 area in the region.
Trials have been established (maximum trial period, 14 years) to find ways of overcoming limitations of low levels of N, P, K, Mg, and B. Results indicate that, in order to produce sawlogs of pine on short rotations, heavy repeated dressings of N and P fertilisers will be required on many sites. In addition, wet pod-zolised soils usually require drainage and additions of K and Mg may sometimes be necessary. Gold-dredge tailings are often deficient in B as well as N and P; legumes have shown promise as a method of supplying N on such sites.
Fertiliser management prescriptions involve the use of soil analyses prior to planting and careful monitoring of foliage nutrient levels during rotations to ensure healthy trees and minimum fertiliser wastage. The choice of fertiliser materials must take into account the method of application and potential for leaching losses on the various sites.