Growth response of four tropical plantation timber species to increasing phosphorus supply and assessment of phosphorus requirements using foliar analysis

Abstract

An understanding of the comparative nutritionalrequirements of important timber species isfundamental in the development of sustainable systemsfor the production of wood from plantations on manyinfertile, highly weathered soils in the humidtropics. We established a field experiment comparingthe responses of four highly-valued cabinet timberspecies (Cedrela odorata, Agathis robusta,Flindersia brayleyana and Castanospermumaustrale) to phosphate fertiliser on a soil very lowin chemically extractable phosphorus (4 mg P/kg soil). Similar soils derived from Palaeozoic metasedimentsare widespread throughout the humid tropics ofnorthern Australia, south-east Asia and thesouth-western Pacific, and are typical of those onmany sites available for plantation forestry in theregion. Phosphorus fertiliser treatments (rangingfrom 0 to 300 g P/tree) were applied soon afterplanting to all four species, as was a basalfertiliser dressing supplying adequate levels of allother mineral nutrients. Two species (F.brayleyana and C. australe) maintained goodgrowth even without additional P and showed little orno response in growth or foliar P concentration toincreased P supply. The other two species (C.odorata and A. robusta) responded strongly inboth growth and foliar P concentration to increasingP supply. In these responsive species, chemicalanalysis of foliage at 17 months after planting wasshown to have potential diagnostic and prognosticvalue. Phosphorus concentrations less than 0.30% drymatter (DM) in the petiole plus rachis of young matureleaves of C. odorata, and less than 0.19% DM inthe distal needle leaves of A. robusta, wereassociated with diminished growth of these two speciesboth at the time of sampling and 21 months later. Theresults indicate that there are significantdifferences in the ability of tropical tree species toacquire and use phosphorus, and consequently thatsimple prescriptive applications of phosphorusfertiliser to young plantations, irrespective of soiltype or tree species, are often inefficient.