Purpose To evaluate the nutrient suitability and spatial variability characteristics of three typical tobacco-planting soils in Yunnan Province.
Methods In the spring of 2020, three representative tobacco fields, dominated by paddy soil, purple soil, and red soil, were selected in Chuxiong Yi Autonomous Prefecture, Yuxi City, and Qujing City, respectively. A 300 meters long transect was established in the center of each field, and soil samples were collected at 5 m intervals at a depth of 0-20 cm. Soil pH, organic matter, alkali-hydrolysable nitrogen, available phosphorus, and available potassium contents were determined. Comprehensive evaluation of the suitability of soil nutrients in each tobacco-planting soil was conducted by combining the fuzzy mathematics membership function and entropy weight method, and spatial variability characteristics of soil nutrient indices and suitability were explored by using semi-variance analysis method.
Results Except for alkali-hydrolysable nitrogen, all nutrient indices of the Chuxiong paddy soil were significantly higher than those of the Yuxi purple soil and the Qujing red soil (P<0.05), and its overall spatial variability was also higher. By calculating the soil feasibility index (SFI), the Chuxiong paddy soil exhibited the highest nutrient suitability, followed by the Qujing red soil, with the Yuxi purple soil performing the worst. The total proportions of sampling sites of three typical tobacco-planting soils belonging to grades Ⅰ and Ⅱ (SFI≥0.7) were 96.72%, 68.85%, and 14.76%, respectively. Regarding spatial structure, the spatial dependence of all nutrient indices and SFI was strongest in the Qujing red soil tobacco field, with correlation ranges falling between 13 and 77 m; the nutrient indices of the Chuxiong paddy soil might exhibit monotonic spatial trends, as their correlation ranges were close to or even exceeded the total length of the investigated transect, while SFI showed a purely random distribution; obvious “hole effect” were revealed in the semi-variance of all nutrient indices and SFI of the Yuxi purple soil, suggesting potential variations at multiple scales.
Conclusion Among the three typical tobacco-planting soils in Yunnan Province, the Chuxiong paddy soil had the highest SFI, indicating its highest suitability for tobacco planting. Nevertheless, a pure-nugget effect was observed in its SFI semi-variance. Future research efforts are needed to optimize sampling strategies for further characterization of its spatial structure. These findings provide important implications for the refined production and management of tobacco in Yunnan Province and its surrounding regions.
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