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

Diagnosis of nitrogen deficiency and toxicity of Eucalyptus globulus seedlings by foliar analysis

The relationship between shoot growth and foliar nitrogen (N) in E. globulus seedlings was studied in the glasshouse to determine standard values for N deficiency and toxicity diagnosis. Seedlings were grown for 9 weeks in yellow sand, at 10 rates of N, applied as ammonium sulphate, calcium nitrate or ammonium nitrate. Shoot dry weight (DW) increased linearly with N rate for all forms of N in the deficiency range. Seedlings continued to respond to higher rates of ammonium and ammonium nitrate than to nitrate. Maximum shoot DW for nitrate fed plants and ammonium nitrate fed plants were 51% and 84% respectively of ammonium fed plants. Total N concentration in the youngest fully expanded leaf (YFEL) ranged from 1.0% to 3.3% in deficient and adequate plants. The critical N concentration for deficiency diagnosis (corresponding to 90% maximum yield) in the YFEL, determined from these growth response curves averaged over all N forms, was 2.6% N. For ammonium nitrate fed plants, total N concentration in the YFEL for the severely deficient, deficient, adequate, and toxic ranges were 4.3%. High total N concentrations were associated with growth depression and toxicity symptoms, which differed with N form. For nitrate fed plants, a total N concentration above 3.3% in the YFEL was associated with severe growth depression, and leaf tip necrosis. The adequate concentration range for ammonium nitrate was similar to values found on a field trial with 7 month old E. globulus trees grown on an exforest site