Development of a soil quality index for Camellia oleifera forestland yield under three different parent materials in Southern China

Camellia oleifera is used to produce tea oil, which is also known as oriental olive oil. Camellia oleifera forestland in southern China displays low yield per unit area, which seriously hinders the production of tea oil. This decreased production is primarily a result of improper planting site and lack of scientific guidance. However, during soil quality assessment, selection of soil indicators from a single soil physical and chemical attribute or specific site resulted in little practical guidance. To assess soil quality scientifically, a total of 142 sampling sites in southern China under three types of parent materials, killas, sandstone, quaternary red clay, were investigated for 23 indicators representing soil physical, chemical and biological properties. Data were analyzed by factor analysis, discriminant analysis and regression analysis. Killas had the highest total nitrogen (TN), available potassium (AK), available magnesium (AMg), available manganese (AMn), available copper (ACu), available zinc (AZn), unease and sucrase, while quaternary red clay had the highest bacteria, actinomycetes and fungi concentrations. Seven indicators, bulk density (BD), sand content, soil organic matter (SOM), available phosphorus (AP), AK, available iron (AFe), and acid phosphatase (ACP) were combined in a minimum data set (MDS) for assessing soil quality under different parent materials. The soil quality index (SQI) of soils that originated from killas, sandstone, quaternary red clay were 0.71, 0.62, 0.54, respectively, which were significantly correlated with the SQI based on all 23 indicators (R-2 = 0.733) and oil yield (R-2 = 0.694). Soils originating from killas were considered most suitable for planting of C. oleifera since they had the highest soil quality among those, investigated herein. Measures should be taken to improve soil fertility of soils originating from quaternary red clay, which showed nutrient deficiency and had the lowest SQI.