Paper presented at 19th IUFRO World Congress, August 1990, Montreal, Canada

Influence of Soil Organic Matter Content on the Responsiveness of Eucalyptus grandis to Nitrogen Fertiliser

Published in: South African Forestry Journal
Volume 156, issue 1, 1991 , pages: 23–27
DOI: 10.1080/00382167.1991.9629083
Author(s): A.D. NobleInstitute for Commercial Forestry Research, South Africa, M.A. HerbertInstitute for Commercial Forestry Research, South Africa

Abstract

It is widely recognised that the inherent nitrogen (N) mineralisation capacity of a soil is directly related to the organic matter content. Consequently, in estimating the N requirements of Eucalyptus grandis at planting this mineralisation potential must be taken into account in order to obtain a judicious and cost-effective use of inorganic nitrogenous fertilisers. This study was conducted to determine the relationship between organic carbon (OC) content in the topsoil and the responsiveness of E. grandis to N fertilisation applied at planting. The relative basal areas and N content in the leaves were determined in four different N-P-K fertiliser trials conducted on soils with an OC content ranging from 2,3% to over 10%. A highly significant inverse relationship was observed between OC content of the soil and the relative response to applied N in terms of basal area at four years. Soils with a low (> 2 %), intermediate (2,5-5 %) and high (< 5 %) OC content were effectively associated with average relative response increases to applied N of 55%, 24% and 5% respectively. The optimum level of nitrogen and phosphorus fertilisation for soils with an orthic diagnostic topsoil horizon containing a clay content between 38 and 61% can be extrapolated on the basis of soil organic carbon in order to obtain maximum fertiliser efficiency. A highly significant relationship was observed between OC content and N levels in the leaves of E. grandis, indicating a critical N level of 2,9%. These results clearly show the influence of soil OC on the response to N fertilisation and N levels in the leaves of E. grandis.

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