Objective  To analyze the effects of three important factors of soil nutrients, planting years and methods (understory and no understory) on oligosaccharide content which is one of the core index of Morinda officinalis quality, provide the theoretical and data supports for cultivation of M. officinalis which is one of the “Four Southern Herbs” in China.

Method  This study selected eighteen no understory planting sites in the genuine producing area of M. officinalis in Deqing County, Guangdong Province. Soil samples and M. officinalis samples of different growth years were collected by random multi-point sampling method. The contents of soil nutrients and oligosaccharides in M. officinalis flesh root were determined to analyze the relationships of soil nutrient contents, growth years and oligosaccharides content of M. officinalis. In addition, samples in understory and no understory planting sites were collected to explore the quality differences of M. officinalis by principal component analysis.

Result  The pH value was highly negatively correlated with sucrose content (P<0.01) and positively correlated with oligosaccharide content (P<0.05). Total phosphorus, available phosphorus and available potassium in soil were positively correlated with the contents of 1-kestose and nystose (P<0.05). The sucrose content of 3-year-oldM. officinalis was significantly higher than those of other growth years, and 1-kestose content of 4-year-old M. officinaliswas significantly higher than that of 2-year-old M. officinalis. The understoryM. officinalis showed better quality than that of no understory.

Conclusion  Improving the contents of available P and available K in soil can improve the quality of M. officinalis. The quality of 4-year-old M. officinalis is the best in our study. Understory planting can improve the quality of M. officinalis.