The response of growth and foliar nutrients to fertilizers in young Eucalyptus globulus (Labill.) plantations in Gippsland, southeastern Australia

Abstract

Fertilizer trials, which included rates of application of up to 400 kg ha −1 N, 200 kg ha −1 and 200 kg ha −1 K, were established in experimental plantations of E. globulus at three sites in Gippsland, southeastern Australia. These sites cover a range of annual rainfall and soil fertility, from 620 mm on a deep infertile sand, to 1000 mm on a rich gradational clay loam. Early growth at all sites was significantly increased by the addition of fertilizers and by age 4 years was consistently best at the highest combined rates of N and P. Foliar N and P concentrations were significantly increased at all sites by combined additions of N and P at Age 1, but were insensitive to treatment at Ages 2 and 4. Relationships between foliar nutrient concentrations and growth were site dependent. Correlations between foliar nutrients and growth in the same year were strongest at Age 1. Foliar nutrients at Age 1 were also strongly associated with growth at later ages at all sites. The best growth was associated with foliar concentrations at Age 1 of about 2.5% N and 0.23% P. Additions of P, alone or with N, consistently decreased foliar N P ratios at Age 1 to between 11 and 12 whereas N and P additions resulted in foliar N P ratios of 15 to 16 at Age 4. These ratios indicate a greater requirement for P than N in the first year suggesting that the N P ratio of fertilizers should be 1:1 within the first year, increasing to 2:1 in later applications. General recommendations for fertilizer addition in the routine establishment of E. globulus are presented. Mean tree volumes at Age 4 ranged from 0.014 to 0.019 m 3 in control treatments and from 0.031 to 0.055 m 3 at the highest rate of fertilizer addition. Growth responses to fertilizers were greatest, in both absolute and relative terms, at the most fertile site and appeared to be constrained by unfavourable soil texture and limited water availability at the other sites. Because the responses of E. globulus are site specific, detailed assessments of fertilizer requirements on soil types other than those described here require the establishment of further trials. A schedule for the establishment and monitoring of such trials is proposed.