Nutrient Dynamics And Fertilization Experiment Of Triploid Populus Tomentosa

The nutrients dynamics in the leaves of Triploid Populus tomentosa were studied in three most suitable growth areas of Hebei,Henan and Beijing.Fertilization experiments with an orthogonal design (L₁₆4⁵) were also conducted in the experimental plots located in Hebei Province.The main results were as follows:Compared with the control of duple clone,nitrogen concentrations in the leaves of Triploid clones S11,S1,S6,S3,S7,S8 and S4 were significantly higher.Significantly higher K concentrations and lower Ca concentrations were also found in all 11 triploid clones.Nutrients concentrations in the leaves of Triploid Populus Tomentos varied regularly in a growing season,with total N 20.72-31.89 g/kg,P 1.21-1.91 g/kg,K 8.13-12.81 g/kg,Ca 8.27-17.95 g/kg,and Mg 4.21-6.91 g/kg,respectively.No matter pre- or post- leaves fallen,higher N,P,K and Ca concentrations but lower Mg concentrations were found in the leaves of Triploid Populus Tomentos with fertilization than those without fertilization.The application of P and K fertilizers did not lead to the luxury uptake of P and K by Triploid Populus tomentosa.Fertilization significantly increased the biomass of Triploid Populus tomentosa and thus increased the flux of external cycling of major nutrients.The application of superphosphate made considerable quantity of Ca transfer from trunk,branch and root to leaves.Based on N,P and K concentrations in the leaves of Triploid Populus tomentosa from July to October in the third year after plantation,nutrition diagnosis standards of DRIS graphic and index methods were successfully established with high accuracy.The optimal N/P,N/K and K/P ratios were 19.116±1.270,3.054±0.289 and 6.356±0.651,respectively.Diagnostic accuracy reached 80%with the analytical data in September for return test.The nutrients requirement by Triploid Populus tomentosa was in the order of N>K>P,which was in accord with the actual application rate of fertilizers. Nutrients concentrations in the leaves of Triploid Populus Tomentos varied greatly in different growth status with higher coefficients of variation(CV),especially in low-yield plantations.The highest CV was found for Zn concentration,which was 37.30%,48.37%and 66.40%for high-,medium-,and low-yield plantations,respectively.Except for Mg,nutrients concentrations in the leaves tended to increase with increasing tree yield.Based on the average and standard deviation of nutrients concentrations in the leaves of high-yield plantations,the classification standards and critical indices were put forward as follows:N,25.00g/kg;P,1.50 g/kg;K,8.00 g/kg;Ca,9.00 g/kg;Mg,4.00 g/kg;Fe, 250 mg/kg;Mn,40 mg/kg;Cu 10 mg/kg and Zn 30 mg/kg.There were significant positive linear correlations between tree growth and N,P,K concentrations in the leaves.The positive linear correlation between tree growth and Ca concentration in the leaves did not reach the significant level.A negative linear correlation between tree growth and Mg concentration was also found.According to the partial correlation coefficients,the effect of N,P,K concentrations in the leaves on tree growth was N>K>P.The responses of different growth indices of Triploid Populus tomentosa to fertilization varied in the order of volume > breast-height basal area > diameter at breast height > height.After fertilization, the initial response occurred in the first year of fertilization,and the greatest response appeared in the second year.The fertilization effect decreased in the third year.Tree DBH and height increment effects with fertilization were significant.The DBH increased by 18.7%,and height by 9.4%most compared with those without fertilization.There were very significant differences of the DBH and volume growth between different fertilization treatments.Changes of the DBH annual growth were completely consistent in 16 fertilization treatments,with the maximum values appearing in the second year.The maximum values of height annual growth appeared in the third year except for fertilization treatment 12,whose maximum value appeared in the second year.Taking the volume growth and potassium fertilizer into consideration,the best schemes of 4-year-old Triploid Populus tomentosa were:urea 230g/tree + superphosphate 150g/tree.