Objective The aims were to clarify the contents and enrichment patterns of selenium (Se) in the paddy soil-rice system, as well as their interrelationship mechanisms, is of great significance for the efficient utilization and potential development of soil Se resources and the development of Se-rich agricultural products.

Method This paper collected 24,278 sets of corresponding paddy soil-rice samples from the southern Hunan region, and measured the total Se, organic matter, cation exchange capacity, pH, total copper, and total zinc in the soil, as well as the total Se, total copper, and total zinc in the rice. Through ordinary kriging interpolation, extreme gradient boosting model and Shapley additive explanation, correlation analysis and other methods, the relationships between parent material, soil properties, climatic factors (sunshine duration, precipitation) and soil Se and rice Se were analyzed.

Result The average Se content in the soil of southern Hunan was 0.514 mg kg⁻¹, and the average Se content in rice was 0.053 mg kg⁻¹, with an average enrichment coefficient of 0.118, indicating that the region had high soil Se content and abundant Se rice resources. The spatial distribution of soil Se showed a pattern of being high in the middle and southern parts, and low in the eastern, western and northern parts. The distribution of rice Se content was highly consistent with that of soil Se, and the enrichment coefficient showed a belt-like distribution from the southwest to the northeast. Parent material had a significant effect on the Se content and enrichment coefficient of soil and rice (P < 0.05). The soil Se content was extremely significantly positively correlated with organic matter, soil copper and zinc content (P < 0.01), and significantly negatively correlated with pH and rice copper (P < 0.05). The rice Se content was extremely significantly positively correlated with soil copper, rice copper and rice zinc (P < 0.01), and extremely significantly negatively correlated with soil organic matter and cation exchange capacity (P < 0.01). The enrichment coefficient was extremely significantly positively correlated with rice copper and rice zinc (P < 0.01), and extremely significantly negatively correlated with soil organic matter and copper (P < 0.01). The XGBoost model prediction showed that soil zinc and organic matter were key factors affecting the soil Se content. Rice copper had the greatest impact on the rice selenium content. Soil organic matter and rice copper had a greater impact on the enrichment coefficient.

Conclusion The paddy soil Se resources in southern Hunan are abundant, and the rice's selenium-enriching ability is strong. Agronomic cultivation measures such as improving soil organic matter, cation exchange capacity and pH can be taken to further develop selenium-rich agricultural products in a reasonable and scientific way.