Effects On Soil Properties And Tree Growth Of Multi Generation In Eucalyptus Urophylla E. Grandis

With the fast-growing and high-yield,also short rotation cycle and high economic efficiency, eucalyptus is one of the main forest types in Guangxi. At present,the eucalyptus has entered the stage of multi generation update. Therefore, to explore the eucalyptus plantation soil physicochemical properties and the growth of multi generation update has become an important subject to be solved. In Guangxi Gaofeng plantation Liuli department, We measured the physical and chemical properties of soil and tree growth of multi generation update in Eucalyptus urophylla×E.grandis. The results are as follows:(1)The density of multi generation update in Eucalyptus urophylla×E.grandis forest soil (0-60cm soil) is0.998～1.605g/cm3.With the increase of soil depth,the rule is the first generation less than the second generation, the third generation of minimum, but the differences are very small. The total porosity of soil is42.56%～61.03%, of which the non capillary porosity occupied1/5～1/3, decreasing as increasing soil depth and update primary. Soil permeability is17.46%～46%and decreases with the increase of soil depth and update generation time. Soil water holding capacity, capillary water holding capacity and minimum water holding capacity followe by25.87%～71.19%,19.33%～33.73%and12.36%29.89%.Each of them decreases with increasing soil depth and update generation time.(2)The PH value of multi generation update in Eucalyptus urophylla×E.grandis forest soil (0-40cm soil) is4.33～5.62. The PH value slightly increases with soil depth increasing, but slightly decreasing with increasing generation time. The soil organic matter content is9.02-49.99g/kg, decreasing as increasing soil depth, but the difference of each generation is very slight. The soil total nitrogen(N)、 total phosphorus pentoxide(P20s)、 total potassium oxide (K2O) followe by0.54～1.58g/kg、0.35-0.86g/k、9.03～19.93g/kg. In addition to the total K20is increasing with the increase of soil depth, the other decreasing as increasing soil depth and generation time. The available N、 P、 K are44.4～180mg/kg、0.47～2.81mg/kg and20.2～120.8mg/kg, respectively. These values decreasing with increasing soil depth and generation time.The exchangeable Ca、 Mg are90.8～227.5mg/kg and9.0～23.9mg/kg, decreasing with increasing soil depth and generation time. The effective Cu、Zn、 B followe by0.72～1.95 mg/kg、0.61～1.10mg/kg and0.14～0.29mg/kg, decreasing with increasing soil depth and generation time.(3)The mean DBH in first generation second generatio、third generation of5-year-old Eucalyptus urophylla×E.grandis forest are14.8cm11.3cm and10.2cm, respectively. With the increase of slope position and update primary, the mean DBH in9.7%-23.6%significant decline. The average height are18.9m、15.4m and14.1m, along with the slope position and update primary increasing in8.4%～18.5%significantly decreasing. The stand average volume are204.6m3/hm2、127.7m3/hm2and97.6m3/hm2, respectively. Along with the slope position and update primary increasing, the stand average volume in23.6%～37.6%significant decline. Research result shows that, the multi generation update in Eucalyptus urophylla×E.grandis forest causes varying degrees of soil compaction and soil fertility decline, with increasing generation time. That is not conducive to improve the physical and chemical properties of forest soil, which is one of the main causes of the stand productivity decreasing. Therefore, it is necessary to delve deeper in Eucalyptus management measures.