Effects of different nitrogen forms and ratios on growth of male Populus tomentosa seedlings

ObjectiveInvestigating growth response of male Populus tomentosa seedlings to different nitrogen forms and ratios aims to provide theoretical basis for improving nitrogen use efficiency and recommendations for N fertilizer management of male P. tomentosa.

MethodMale P. tomentosa 331 seedlings with narrow crown feature were transplanted in containers and different forms of nitrogen fertilizers were applied. The effects of seedling growth, physiological structure and nutrient accumulation of P. tomentosa were measured. The treatments included seven N forms, which were five nitrate (NO₃^-) to ammonium (NH₄⁺) ratios of 0:100, 75:25, 50:50, 25:75, and 100:0, one single form N treatment (amide nitrogen) and a control with no fertilizer. Seedling height, root-collar diameter (RCD), biomass, leaf structure, root morphology, and leaf nitrogen (N), phosphorus (P) and potassium (K) concentrations were measured periodically during the growing season.

ResultThe height and RCD of P. tomentosa seedlings increased initially and then stabilized with the increase of NO₃^--N to NH₄⁺-N under the same nitrogen level. When the proportion of nitrate nitrogen reached 50% and above, the seedling height and RCD tended to be stable, with an average of 189.33 cm and 21.84 mm, respectively. The biomass of root and stem also increased with the increase of NO₃^--N to NH₄⁺-N, but 75:25 treatment (0.84) had significantly greater root to shoot ratio than treatment 100:0 (0.68). NO₃^--N fertilizer obviously promoted the growth of total leaf thickness and fine root of P. tomentosa. Root length and root surface area of fine roots with treatment of 50% or more nitrate were significantly greater than those of other treatments. 50:50, 75:25 and amide nitrogen treatments could effectively promote N accumulation for stems and roots, but the P concentration of seedlings under amide nitrogen treatment was significantly lower than that of others.

ConclusionNO₃^--N fertilizer can significantly promote the growth and nutrient accumulation of male P. tomentosa 331 seedlings, the optimum ratios of NO₃^--N to NH₄⁺-N were 50:50 to 75:25 for different nitrogen form fertilizers.