Objectives The spatial and temporal distribution and the influence factors of soil nutrient contents reflects the rationality during a certain period of tobacco cultivation. The study will provide theoretical basis for scientific fertilization strategy in high-quality tobacco production of Dali Prefecture.
Methods In 2012 and 2022, total of 1131 and 4512 top soil samples were collected in the tobacco fields of the plain area in Dali Prefecture, Yunnan Province. The location, altitude, soil texture and pre-crop information of each sample were investigated, and the physical and chemical properties were analyzed. The data of the second soil census in 1982 was used as reference. Geostatistics were used to analyze the spatial and temporal distribution of available Zn, Mo and B contents in 1982, 2012 and 2022, and regression analysis and random forest model were used to quantify the main factors affecting the changes of soil available Zn, Mo and B contents.
Results In 1982, 2012 and 2022, the average available Zn content was 2.35 mg/kg, 3.50 mg/kg and 4.35 mg/kg, respectively, showing an increasing trend; The available Mo content was 0.18 mg/kg, 0.14 mg/kg and 0.11 mg/kg, respectively, exhibiting a downward trend. The available B content was 0.26 mg/kg, 0.63 mg/kg and 0.58 mg/kg, respectively, showing a rising first and then decreasing trend. The nugget values of available Zn and B in 1982, 2012 and 2022 were 50.8%, 45.5%, 31.8% and 41.3%, 39.4%, 33.8%, respectively, showing moderate spatial autocorrelation, and the available Zn and B contents were low in the middle and high in the outskirts of the test area geographically. The nugget values of available Mo were less than 25%, and showed a decrease trend from high in the southeast to low in the northwest. The available Zn and B contents were significantly higher in the plains than in the mountainous areas; the available Mo content was significantly higher in the clay than in the sand and loam soil, and the available B content was higher in the loam than in the other textures of soils. Soil pH, organic matter, available N, P and K, and the altitude strongly affected the spatial and temporal variation of the three elements. The main influencing factors were available P and altitude (interpretation rate 20.5% and 16.8%) for Zn, altitude and available N (interpretation rate 13.7% and 12.8%) for available Mo, and available N and K (interpretation rate 17.6% and 15.6%) for available B.
Conclusions The soil available Zn, Mo and B contents in tobacco-growing fields in Dali Prefecture show a general increase, compared to 40 years ago, and are graded at V (rich), II (deficient) and III (moderate) levels at moment, respectively. All the Zn, Mo and B content were affected by topographic feature, soil texture and fertility. In general, Zn application should be appropriately controlled, B application be maintained, and Mo application be increased. However, Zn and B application should be considered when the previous crops are grain crop and rape, and Mo should be applied when following legumes crop, for the high-quality tobacco production in the test area.
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