Nutrient Dynamics And Fertilization Technology Research Of Triploid Populus Tomentosa

Triploid Populus Tomentos, widely planted in the north of Yellow River, is an ideal tree species for the pulpwood and plywood with the characteristics of short rotation, fast growth, excellent quality and anti-disease.With the spreading of Triploid Populus Tomentos, higher-standard management measure is required. However, there is no scientific management model of Triploid Populus Tomentos at present, especially on the nutrients dynamics in a rotation period, nutrients requirement by the tree and nutrients depletion in the forest soil.Provinces of Hebei, Henan and Beijing, most suitable for the growth of Triploid Populus Tomentos, were selected for the tree nutrition and fertilization experiments. Random block design in Henan and Beijing experimental plots and an orthogonal design of L16(45) in Hebei were conducted to study the growth habit of Triploid Populus Tomentos, nutrients dynamics in the leaves, soil nutrients depletion without fertilization, limiting nutrients for the tree growth, and fertilization effects for the past three years. Results showed that:1) Nutrients concentrations in the leaves of Triploid Populus Tomentos varied in a growing season, with total N 20.15-25.42 g/kg, P 1.15-2.03 g/kg, K 5.20-12.04 g/kg, Ca 6.98-17.95 g/kg, and Mg 3.31-5.63 g/kg, respectively.2) Nutrients concentrations in the leaves of Triploid Populus Tomentos varied with tree age. With increasing tree age, N, P and K concentrations in the leaves of Triploid Populus Tomentos decreased, but Ca and Mg concentrations did not change much.3) Very significant differences were found between different clones of Triploid Populus Tomentos for K, and significant differences for N and Ca in the leaves, but there were no significant differences for P and Mg in the leaves.4) There were significant differences between different site conditions for the nutrients concentrations in the leaves and tree growth of Triploid Populus Tomentos. N, P, K and Ca concentrations in the leaves and tree growth parameters (height, DBH and volume) were higher in Henan experimental plots than those in Beijing, but Mg concentrations in the leaves were lower in Henan experimental plots than that in Beijing.5) With increasing tree age, soil nutrients concentrations showed different change regulation in different soil layers. Soil organic matter and hydrolyzed N increased with the year in the soil layer of 0-20cm, but decreased in the soil layer of 20-60cm. Soil available P decreased with the year in all soil layers. Soil rapidly available K increased with the year in the soil layer of 0-20cm, but there was no obvious change in the soil layer of 20-60cm.6) Correlations between nutrients concentrations in the leaves and tree growth parameters (height and DBH) were found, with higher correlation coefficients between N, P and K concentrations and tree growth parameters, but lower correlation coefficients between Fe, Mn, Cu and Zn concentrations and tree growth parameters. This may indicate that N, P and K were the limiting nutrients for tree growth of Triploid Populus Tomentos.7) Fertilization effect experiments in Wei County of Hebei Province showed that the optimal recipe of Triploid Populus Tomentos was 460 g CO(NH2)2, 150 g Ca(H2PO4)2 and 75 g K2SO4 per tree.It is the first time for the present study to clarify the nutrients dynamics in the leaves of Triploid Populus tomentosa in a growing season, with different tree ages, under different site condition and between different clones, respectively. Nutrients dynamics in the forest soil were also studied. The nutrients limiting the growth of Triploid Populus tomentosa were N and P, and the optimal fertilization recipe was finally reached. The results provide a scientific basis for the management of Triploid Populus Tomentos.