Soil characteristics of Eucalyptus urophylla × Eucalyptus grandis plantations under different management measures for harvest residues with soil depth gradient across time

The clear-cut burning method for forest clearing has been widely used in Eucalyptus plantations in Southern China for successive planting generations. Harvest residues can provide a considerable nutritional supply for Eucalyptus plantations by affecting soil fertility qualities. Thus, harvest residue management is crucial. This study aims to investigate the effects of different management measures for harvest residues on the soil fertility of Eucalyptus urophylla × Eucalyptus grandis plantations and the changes in soil characteristics at different times and soil depths. We selected an evergreen broad-leaved forest (CK0) and a third-generation E. urophylla × E. grandis plantation (CK) as the control. The experimental plots were burned and retained the harvesting residue after CK harvesting. Soil samples were obtained one month, one year, and five years after burning (B1, B2 and B3, respectively) and retaining (R1, R2, and R3, respectively) the harvest residues. All measured soil properties were significantly affected by depth, stand, and interactions, except for the pH value. Discriminant analysis showed that the effects of different stands on the primary physicochemical properties of soil were higher than those on the microelement and biological characteristics. Varying stands had a significant influence on the primary physicochemical properties of soil across time. All stands were classified into four grades according to soil quality assessment values. The findings showed that CK0 obtained the highest score for grade I, followed by R2 (grade II); B1, R1, and R3 (grade III); and CK, B2, and B3, which had the lowest grade. Soil parameters were affected not only by soil depth but also by different management measures for harvest residues across time. In addition, although no significant difference was found in soil fertility quality between burning and retaining harvest residues in the short term (about a month), the soil fertility quality of a forest retaining harvest residues was significantly higher than that of a forest burning harvest residues in the long term.

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