The Growth And The Root Morphology Of Young Eucalyptus Urophylla×E. Grandis Forest To Different Kinds Of Fertilizers

Fertilization plays an important role on cultivation of Eucalypts plantation. To enhance the Eucalypts production for commercial use, at the same time avoid the forest soil productivity from going down, fertilizer use efficiency and safety should be concerned. In this study, we planted Eucalyptus urophyllaxE. grandis seedlings. The objective of this research was to investigate the response of E.urophyllaxE. grandis young forest to different kinds of fertilizers, the root morphology and biomass as affected to fertilizers, the microorganism distribution and enzyme activity in the rhizosphere. The results were as follows.(1) Fertilization affected the height and diameter growth of E.urophyllaxE. grandis young forest. Among phosphate fertilizer, urea, and special Eucalyptus fertilizer, special Eucalyptus fertilizer positively affected the growth of E.urophyllaxE. grandis seedlings, while the urea negatively affected the height and diameter of seedlings. The varied quantity of phosphate fertilizer did not result in the difference of the seedlings growth. E.urophyllaxE. grandis seedlings did not show significant difference under different initial stand density. It might be due to the uncorrelated relationship in unclosed stand.(2) Fertilization improved E.urophyllaxE. grandis seedlings root extension, especially at horizontal direction. The root extended vertically ranging from32cm to57cm, while horizontally from57cm to86cm. Horizontal root distribution was larger than vertical distribution. The effects of different types of fertilizers on E.urophyllaxE. grandis seedlings root growth varied. Phosphate fertilizer showed high impact on the root vertical distribution. Special Eucalyptus fertilizer most affected the root horizontal distribution and the length of first class lateral root. Urea most affected the number of root tips, while least affected the length of first class lateral root.(3) The effect of fertilizers on E.urophyllaxE. grandis seedlings total root biomass were mainly due to the amount of phosphate fertilizer. The biomass of different root classes varied under different fertilizers. Fertilization did not affect the root of class0～2.0mm and2.1～5.0mm, but affected the root class of5.1～10.0mm and>10.1mm. As the root diameter class increased, the biomass showed rising trend.(4) The microorganism in rhizosphere soil of E.urophyllaxE. grandis mainly distributed in the0-20cm root layer. The deeper as the soil was, the less the bacteria, fungi and actinomycetes were. The enzyme activities (invertase, urease, andcatalase) were also the most in the soil layer above20cm deep, showing the same trend with microorganism.(5) Fertilization showed highly significance on bacteria in rhizosphere soil of E.urophyllaxE. grandis. Fertilization also affected actinomycetes significantly, while, no effect on fungi was found. Among phosphate fertilizer, urea, potash fertilizer and special Eucalyptus fertilizer, urea affected bacteria the most. A small amount of urea improved the activity of bacteria, but large amount inhibited the bacteria activity. The special Eucalyptus fertilizer positively affected the activity of actinomycetes.(6) Fertilization significantly affected all the microorganism in rhizosphere soil of E.urophyllaxE. grandis. Compared with invertase and urease, the catalase was affected less. Among the four fertilizers used, urea showed the top influence and phosphate fertilizer the bottom, with potash and special Eucalyptus fertilizer being the second and third. Urea negatively affected invertase activity. The activity of urease was the highest at3g of urea.