Soil Quality Assessment for Sustainable Management: A Minimum Dataset for Long-Term Fertilization in Subtropical Plantations in South China

Restoration plantations in subtropical regions, often established with fast-growing tree species like Acacia auriculiformis and Eucalyptus urophylla, are frequently developed on highly weathered soils characterized by natural phosphorus (P) deficiencies. To investigate strategies for mitigating nutrient imbalances in such ecosystems, a long-term (≥ 13 years) fertilization experiment was designed. The experiment involved three fertilization regimes: nitrogen (N) fertilizer alone, P fertilizer alone and a combination of N and P (NP) fertilizer. The objective of this study was to investigate the effects of long-term fertilization practices on soil quality in subtropical plantations through a soil quality index (SQI). Principal component analysis (PCA) was used along with a literature review to select a minimum dataset (MDS) to calculate SQI. Three physical indicators (silt, clay, soil water content), three chemical indicators (soil organic carbon, inorganic nitrogen, total phosphorus), and two biological indicators (microbial biomass carbon, phosphodiesterase enzyme activity) were chosen as MDS from a total dataset (TDS) of eighteen soil indicators. Our study showed that long-term fertilization did not significantly change the soil quality as measured by SQI in both Acacia auriculiformis (p=0.25) and Eucalyptus urophylla (p=0.45) plantations. However, investigations of individual soil indicators in the MDS suggested that P addition through fertilization (P and NP regimes) strongly increases the P pool in the subtropical plantation soil. The MDS provided a strong representation of the TDS data (R2=0.81), and the SQI was positively correlated with littermass (R2=0.37). These findings suggest that the MDS can serve as a quantitative and effective tool for long-term soil quality monitoring.