Effects of inorganic nitrogen forms on growth of Eucalyptus globulus seedlings

Eucalyptus globulus plantations are being established in many temperate regions of the world in soils which vary widely in the availability of ammonium and nitrate forms of inorganic N. Little is known about the capacity of E. globulus to utilize these N forms. In this poster we examine the N requirements of nonmycorrhizal seedlings grown with adequate phosphorus in a N-free yellow sand in the glasshouse. A factorial design with three N fertilizers [(NH4)2S04, Ca(N03)2 and NH4N03] and 10 N rates in four replicate blocks was set up and plants harvested after nine weeks of growth. There was a significant growth response to all fertilizers. However, growth of nitrate fed plants was depressed at fertilizer N rates that were just deficient for plants supplied with ammonium-N or ammonium plus nitrate-N. The growth responses showed narrow optimum ranges of N fertilizer rates. Symptoms of nitrate-toxicity included thick, stunted, dark blue-green leaves with necrotic tips. Foliar N concentrations increased three-fold from N-deficiency to N-adequacy indicating a useful relationship for N deficiency diagnosis for juvenile leaves_ Since E. globulus seedlings are inefficient users of N03-N, other forms of N should be used to maximize growth in nurseries and young plantations