Use of fertilisers at establishment of exotic forest plantations

This paper reviews New Zealand research and experience with fertilisers at establishment of plantations of exotic tree species and outlines current manage-ment practice. The first commercial use of fertilisers at establishment was made in the mid-1960s during planting of radiata pine on P-deficient clay soils. Currently c. 6000 ha of new plantings are fertilised annually. The main fertiliser elements are P, N and B. All are applied manually on an individual basis in order to minimise stimulation of competing vegetation. The most common practice is to place the fertiliser in a spade slit some 15 cm from the base of the seedling within 3 to 8 weeks after planting. Phosphorus is applied to radiata pine at establishment mainly on weathered and leached clays and podsolised sands in the Auckland region and on strongly leached alluvial gravels in the Nelson region. With minor variations application rates are (as P) 17 g/seedling in the Auckland region and 6-10 g/seedling in the Nelson region. Most P is applied as superphosphate (8-10 % P). Responses to P tend to be enhanced by site preparation methods involving weed control and deep soil cultivation. Spot applications of P at establishment are usually effective for only 3 to 4 years. Nitrogen is applied at establishment of radiata pine on podsolised soils, skid sites where topsoil has been removed and on strongly leached alluvial gravels. The most common application rate is c. 15 g/seedling of N applied as urea, or diammonium phosphate where both N and P are required. Nitrogen is used in the establishment of Eucalyptus spp. on a range of sites with up to 30 g/seedling of N (as urea) being used. Establishment applications of N tend to be effective for only 1 to 2 years. Boron is used to a limited extent in the establishment of radiata pine on strongly leached soils formed from alluvial gravels and granite in the Nelson region. It is usually applied in the form of boronated superphosphate to give 0.8 g/seedling of B. These applications are usually effective for only 3 to 4 years