RESPONSE OF <em>EUCALYPTUS</em> <em>DEGLUPTA</em> TO PHOSPHATE FERTILISER

Abstract

An experiment was installed in 3 - to 4-31- old plantations of Eucalyptus deglupta in the Tawau residency, Sabah, Malaysia. Rock phosphate was applied to plantations on three soil types at five rates of elemental phosphorus (0, 50,100, 200 and 400 kg P ha^-1). Height and diameter measurements were made on trees prior to application of fertiliser and at intervals over three subsequent years. Samples of foliage were taken for chemical analysis 12 months after treatments had been applied. Phosphorus concentrations in foliage of unfertilised trees differed between soil types but application of P fertiliser increased foliar P concentrations over all soils. Within each soil type, increases in foliar P concentrations were linearly related to current annual increment in wood volume during the 12 months after samples had been taken. Growth responses were evident within 12 months of fertiliser application and increased thereafter. Three years after treatment, increases in mean annual increment in wood volume were linearly related to the logarithm of the quantity of fertiliser applied, up to a maximum of four m³ ha^-1 at the highest application rate of 400 kg P ha^-1. Soil type (site quality) had no influence on this relationship. Growth rates of E. deglupta in Sabah have been below expectations and establishment of new plantations is not likely to be profitable, even with enhanced growth from P fertiliser. However, marginal returns on investment
in P fertiliser application to existing stands on good sites are high and an application of 100 kg P ha^-1 is recommended.