Delineating soil management zones in rubber plantation using multisource data of environmental variables

Abstract: A rubber planation of the state farm in Hainan Island, China is traditionally managed with unified soil practices (e.g. fertilization, cultivation). This inevitably results in an inefficient use of resources since it ignores soil heterogeneity (e.g. variability in soil fertility and environmental conditions) of the rubber plantations. Soil management zones can be used to overcome the limitations above of the uniform soil management practices. However, studies on soil management zones are mainly carried out at the field scale. Additionally, data of some soil properties used to delineate soil management zones are difficult or expensive to acquire. This study selected easily available environmental variables and aimed to evaluate their validity in delineating soil management zones of rubber plantation at regional scale. Four types of environmental variables, including terrain attributes (elevation, slope, and aspect), parent materials, climate factors (precipitation and temperature) and vegetation index (normalized difference vegetation index), were selected as data source, and principal component analysis as well as fuzzy-C means clustering algorithm were applied to delineate soil management zones for a rubber plantation with an area of approximately 26000 ha. Two indices, fuzzy performance index (FPI), and normalized classification entropy (NCE) were used as criterion to determine the optimal number of soil management zones. Results showed that the optimal number of soil management zones for the rubber plantation was three. To test the validity of the soil management zones, 486 soil samples were collected and analyzed for 12 soil properties including pH, soil organic matter (SOM), total nitrogen (TN), available phosphorus (AP), available potassium (AK), exchangeable calcium (Ca), exchangeable magnesium (Mg), available sulfur (S), available copper (Cu), available ferrum (Fe), available manganese (Mn), and available zinc (Zn). One-way analysis of variance was employed to test the difference in the soil properties and environmental variables among the three soil management zones. Statistically significant differences in selected soil properties (except Zn) and environmental variables were found among the three management zones. In addition, the mean coefficients of variation (C.V.) of the soil properties and the environmental variables in the three management zones were much lower than that obtained before the management zones were applied to the rubber plantation. The results above verified that easily available environmental variables could be used to delineate soil management zones for rubber plantation at the regional scale. Further, the management practices corresponding to the characteristics of each zone should be adopted to improve the soil management efficiency of the rubber plantation.