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New Zealand Journal of Forestry (1995) 40(1): 33–37
©New Zealand Institute of Forestry

Research article
Recent developments in assessment of nutrient deficiences in Pinus radiata using colour imagery

A.J. Thorn , P.N. Beets , S.T. Olykan and L.A. Morris

Identification of nutrient deficiency in plantation forest species has traditionally relied on recognition of change in foliar colour and tree growth pattern and confirmation by chemical analysis of foliar tissue. Colour photography allows qualitative comparisons between a standard colour and the spectral characteristics of the material, since the human eye and photographic film are sensitive to the same region of the spectrum.

Image-processing techniques designed to quantify the occurrence of specific colours in a photographic image were used to assess the degree of nitrogen deficiency induced experimentally in Pinus radiata D. Don seedlings. Results were found to be positively correlated with foliar nitrogen concentration (r2 = 0.62) in non-water-stressed plants, but the relationship was not consistent when water stress was imposed.

Classification of radiata pine canopy characteristics from oblique colour photographs, using an image-processing system and a simple clustering algorithm, was found to be highly correlated (r2 = 0.82) with visual scores for symptoms known to have been induced by magnesium deficiency.

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