Objective Effects of tea cultivation practices on the makeup and stability of soil aggregates that affect the fertility and quality of the land were analyzed for the optimization of plantation management and ecology.

Method At two tea growing areas in eastern Fujian, a forestland (FD) and a plantation operated under the conventional practice (CT) and one under organic farming (OT) were surveyed to analyze the differentiations on the soil structure. Using the wet screening method, soil aggregates at the locations were separated by the sizes of >5 mm, 2~5 mm, 1~2 mm, 0.5~1 mm, 0.25~0.5 mm, and <0.25 mm. Proportions of the varied particle sizes were calculated, and stability indicators monitored.

Result The macro-aggregates (i.e., >5 mm) accounted for 27.84~78.16% of the total and was dominant on the forestland as well as at the plantations (P<0.05). They were significantly lower in the soil of CT by 32.73~56.51%. And the CT lots had significantly more particles of 0.5~1 mm and 0.25~5 mm than did FD (P<0.05). But no significant differences in size distributions between the soils at FD and under OT. The moisture holding-stable particles (R0.25), mean weight diameter (WMD), and geometric mean diameter (GMD) of the soil aggregates at the different sites were generally ranked as FD>OT>CT, but opposite on fractal dimension (D). The MWD and GMD of CT soil aggregates were significantly lower than those of FD but not significantly different between those of OT and FD. The composition and stability indicators of the aggregates were closely related to the organic matter, total nitrogen, alkaline nitrogen, pH, and bulk density of the soil. And pH and bulk density were the major factors as indicated by a redundancy analysis (RDA).

Conclusion After converting a forestland for conventional tea cultivation, the macro-aggregates, MWD, and GWD of the soil at the land were significantly reduced. However, if organic farming was implemented at the plantation, a significantly improved sustainable agriculture could be expected.