Abstract: Under the condition of long-term management, the soil obstacle problem of eucalyptus plantation in the lower tropical region frequently occured. The identification and evaluation of soil fertility obstacle factors in main eucalyptus producing areas based on soil types, and the development of regional management and fertilization strategies for forest rights owners can provide a theoretical basis for the improvement of soil fertility, which is of great significance to ensure the high quality and sustainable development of Guangxi plantation industry. In this paper, a total of 298 typical soil samples of red soil, yellow soil and red soil in the main planting areas of eucalyptus plantations in northern Guangxi in the past three years were collected and analyzed. Cluster analysis combined with principal component analysis was used to screen the main obstacle factors from 15 soil fertility factors. The obstacle degree model was introduced to quantitatively analyze the obstacle factors of different soil types. The results showed that the main obstacle factors were different in different soil types. In red soil, there were four severe obstacle factors, which were pH, total phosphorus, available manganese and available boron, among them, pH barrier was the highest (28.20%), and soil total nitrogen was the mild disorder factor. In yellow soil, pH, total nitrogen, available manganese and available zinc were the severe obstacle factors, among them, pH barrier was the highest (36.53%), and total potassium was the mild disorder factor. In the red soil, there were three severe obstacle factors, total potassium, available magnesium and available zinc, among them, available magnesium barrier was the highest (40.72%), and the mild obstacle factor was organic matter and available manganese. Due to the widespread application of formula fertilizer in short-cycle plantation management in Guangxi, the available N, P and K nutrients of the three main soil types in this region are relatively sufficient, and the soil problems are concentrated in acidification, low phosphorus, partial trace elements loss and other common problems. However, due to the different site conditions in different regions, it is suggested that the forest right owners should develop business strategies according to the local conditions and soil types in order to reduce the occurrence of soil obstacles.

Key words: membership function, soil nutrient, short-period plantation, soil barrier factor, obstacle degree model