Use of foliage sulphate concentrations to predict response to urea application by Douglas-fir

Abstract

The foliage from 11 Douglas-fir fertilizer installations in the American Pacific Northwest were chemically analyzed to find a possible parameter to predict response to nitrogen application. It was found that the trees with high foliar sulphate sulphur reserves had a high response to nitrogen fertilizer while those with low foliar sulphate sulphur reserves had a low response. The basis for the assessment was the known biochemical relationship between nitrogen and sulphur in protein and the necessity for adequate foliar sulphur concentrations for nitrogen to be utilized by the plant. Foliar sulphate sulphur concentration was found to be a better single parameter for determining fertilizer nitrogen requirements than foliar nitrogen concentration.