Spatio-temporal Characteristics of Available Boron Content and Its Influencing Factors in Tobacco-growing Soils in Chongqing

In order to provide a scientific basis for the regulation and management of soil boron, this work studied the spatial and temporal characteristics of available boron content in tobacco-growing soils in Chongqing and its influencing factors. A total of 2,513 soil samples from the tillage layer (0-20 cm) were collected from 11 tobacco-growing regions in Chongqing, with measurements and analyses of available boron and other physical and chemical indicators. The relationship between available boron content and factors such as altitude, soil type, soil parent material, and soil physical and chemical properties was also examined. The results indicated that the overall available boron content in Chongqing’s tobacco-growing soils is relatively high, with an average value of 0.63 mg/kg. The regions of Qianjiang, Shizhu, Fengdu, Pengshui, and Youyang exhibited relatively high soil available boron content, while the regions of Fuling, Fengjie, Wushan, Wuxi, Wulong, and Wanzhou had suitable levels. Compared to data from a decade ago, the available boron content in Chongqing's tobacco-growing soils has increased by 152%. Soils derived from fluvo-aquic soils and yellow soils demonstrated higher available boron content, whereas those developed from alluvial soils had lower levels. There was a very significant positive correlation between 0.25-0.5 mm particle size aggregates and soil available boron. Altitude, soil pH, organic matter, and available potassium were all found to have significant effects on available boron content. In conclusion, adjusting soil pH and organic matter content can be effective measures to regulate soil available boron. For regions with high soil available boron content, such as Qianjiang and Shizhu, reducing the application of boron fertilizer can help avoid toxicity due to excessive boron levels. Conversely, in regions with low soil available boron content, such as Wulong and Wanzhou, increasing the amount of boron fertilizer is necessary. This study provides a theoretical foundation for the scientific application of boron fertilizers in tobacco-growing areas in Chongqing.