NITROGEN STRESS IN BIRCH SEEDLINGS .2. N,K,P,CA, AND MG NUTRITION

In a series of experiments with nitrogen stress, optimum and supra‐optimum nitrogen supply, N, K, P, Ca, and Mg have been analysed in leaves, stems and roots of birch seedlings (Betula oerrucosa Ehrh.). Growth rate was strongly and linearly correlated with the nitrogen status of the seedlings within the whole sub‐optimum range. Seedling weight was equally strongly correlated with nitrogen status, although exponentially. Various expressions for growth rate and nitrogen status give similar results. Nitrogen efficiency (dry matter produced per unit nitrogen) decreased with increasing nitrogen status, but nitrogen productivity (dry matter produced per unit nitrogen and time) increased up to optimum. The maintenance of a stable nitrogen status in the seedlings and a stable growth rate requires an accurate and closely controlled technique of nitrogen addition. Because of the exponential relation between seedling weight and sub‐optimum nitrogen status and a rapid decrease in the supra‐optimum range, a strict control of the optimum status is necessary to maintain maximum growth. Copyright © 1979, Wiley Blackwell. All rights reserved