Variation analysis of growth traits of four poplar clones under different water and fertilizer management

To determine appropriate quantities of water and fertilizer required for early growth of hybrid poplar cuttings, we recorded the growth traits of four clones grown under four factors (irrigation and nitrogen, phosphorus, and potassium fertilizers), each with four levels, using an orthogonal experimental design. A logistic model was used to estimate growth in height. The growth curves for tree height were sigmoid, and the model R2 values were greater than 0.9, which indicated that the fit was highly significant. ANOVA results for tree height and basal diameter indicated that all sources of variance showed significant differences (p < 0.001). The average tree height and basal diameter for all the four clones under the different treatments ranged from 155.39 to 235.04 cm, and from 13.71 to 17.42 mm, respectively. A highly positive correlation between the extreme k value and tree height was observed, suggesting that the k value was an accurate estimation of tree height. For model parameters, the earliest average time point for the onset of the rapid growth period of poplar clones was 131 d, and the highest average increment in tree height during the rapid growth period was 138.78 cm. The highest average tree height for all clones under each factor was 219, 210.51, 200, and 201 cm when treated with either 1200 mL of water applied every third day, 3 g of nitrogen, 0 g of phosphorus, or 0 g of potassium, respectively. The most suitable treatment for the early growth of hybrid poplar cuttings, as suggested by the developed logistic model, was 1200 mL of water applied every third day and three applications of 1 g nitrogen (in the form of CH4N2O).