Response of Soil Fertility Quality to Continuous Cropping of Eucalyptus urophylla Plantation in Northern Guangxi

The soil of 3 generation of Eucalyptus urophylla plantation in northern Guangxi was studied. Based on the determination of 20 soil physical and chemical properties, the minimum data set of soil fertility quality evaluation of Eucalyptus forest land was selected by principal component analysis, and the quality evaluation of soil fertility was carried out. The results show that the physical and chemical properties of the 3^rd generation E. urophylla plantations are significantly lower than that of other generation forest. Soil water holding capacity, capillary porosity, organic matter, total phosphorus, available phosphorus, available potassium and effective elements in the 1^st and 2^nd generation are significantly higher than those of 3^rd generation E. urophylla plantations. The minimum data set of capillary porosity, organic matter, total phosphorus, available phosphorus, available potassium, available boron, available calcium and effective zinc are selected as the minimum data sets for evaluating the soil fertility quality of E. urophylla plantation. The results show that the 2^nd generation (0.785) > 1 ^st generation (0.642) > 3 ^rd generation (0.566). The soil quality increases first and then decreases. After 2 generations, the soil physical and chemical properties are significantly degraded. Therefore, after the 2^nd generation forest harvesting, it is necessary to replenish the element content decreased by continuous planting in order to achieve the fast-growing and high-yield production of E. urophylla.