The spatiotemporal variation of soil available phosphorus and phosphorus application strategy in tobacco field of Dali, Yunnan Province

Objectives This study investigated the spatiotemporal variation of soil available phosphorus (AP) in tobacco-growing areas of Dali Prefecture, Yunnan Province, aimed to provide a scientific basis for phosphorus management friendly to high-quality tobacco production and sustainable environment.

Methods The total tobacco planting area in Dali Prefecture is around 3.23 × 10⁴ hm². 256, 633, 1244 and 2332 soil samples were collected from the five typical tobacco planting counties of Dali in 1999, 2012, 2018 and 2022 respectively, for determination of soil AP content. Geostatistics and GIS technology were used to analyze the spatiotemporal variation of soil AP in the five counties over the four decades. Finally, a general phosphorus application strategy was proposed based on the soil AP content in 2022.

Results The average soil AP content in the tobacco-growing areas of Dali trended to increase over the last 40 years. The average soil AP increased from 8.09 mg/kg in 1982 to 43.92 mg/kg in 2022, with an increase of 4.42 times. The soil AP content in most tobacco planting area belonged to ‘low’ grade (<20 mg/kg) in 1982, and over 50% of soil belonged to ‘medium’ grade (20–40 mg/kg) in 1999−2022. The nugget effect of soil AP increased from less than 25% to 41.45% over the last 40 years, indicating a weakening influence of natural factors such as topography and an increasing impact of human factors such as fertilization. In 2022, 34.21% of the total area were high and even extremely high in soil AP, mainly distributed in the north of Midu, west of Xiangyun, southwest and northeast of Binchuan.

Conclusions The soil AP content in Dali tobacco-growing areas has significantly increased on average over the past four decades due to fertilization. Most tobacco fields should reduce or even stop phosphorous fertilizer application.