基于随机森林模型与SHAP算法的渝东北烟区土壤交换酸含量影响因素分析研究

The analysis of influencing factors of soil exchangeable acidity content in northeast Chongqing’s tobacco area using Random Forest model and SHAP algorithm

【背景和目的】土壤交换酸含量在农业生产中对于指导施肥和调节土壤pH具有重要作用,研究环境因子(气候、地形、成土母岩)和种植年限对土壤交换酸(Exchangeable Acidity, EA)含量的影响。【方法】以重庆市东北烟区为研究区,对该区中483个采样点的土壤交换酸数据进行统计分析,构建随机森林(Random Forest, RF)模型并结合Shapley Additive exPlanations(SHAP)算法,探讨影响土壤交换酸含量的主控因素。【结果】(1)研究区土壤交换酸含量在1.56~27.50 cmol/kg之间,与降水、日照时数、坡向、种植年限呈极显著负相关性。二叠系石灰岩发育的土壤交换酸含量显著高于三叠系石灰岩发育的土壤。(2)RF模型可解释土壤交换酸含量空间变异的64%,影响因子对土壤交换酸含量的重要性为气候>成土母岩>种植年限>地形。(3)SHAP算法揭示了土壤交换酸含量在不同气候条件下存在明显的阈值效应。当年均降水量、日照时数和均温分别超过1250 mm、1290 h和12℃时,会导致土壤交换酸含量的减少,反之则会促使其增加。【结论】气候是影响土壤交换酸含量变异最重要的环境因素,其中降水和日照时数是最重要的气候因子,研究结果可为烟田土壤酸化管理调控提供参考。

[Background]Exchangeable acidity content is crucial for guiding fertilizer application and regulating soil pH in agricultural practices.This work aims to clarify the effects of environmental factors(climate,topography,parent materials)and planting years on soil exchangeable acidity(EA)content.[Methods]In this paper,the soil exchangeable acidity data of 483 sampling points in the northeast tobacco area of Chongqing were statistically analyzed.The random forest(RF)model was constructed and combined with Shapley Additive exPlanations(SHAP)algorithm to explore the main controlling factors affecting soil exchangeable acidity content.[Results](1)In the study area,the exchangeable acidity content ranged from 1.56-27.50 cmol/kg and showed a significant negative correlation with precipitation,sunshine duration,slope direction,and planting duration.The content of exchangeable acidity was significantly higher in soils developed from Permian limestone than that in soils developed from Triassic limestone.(2)The RF model accounted for 64%of the spatial variation in exchangeable acidity content.The influence of environmental factors on exchangeable acidity content was:climatic factors>parent materials>planting years>topography.(3)The SHAP algorithm indicated that soil exchangeable acidity content had obvious threshold effect under different climatic conditions.When mean annual precipitation,sunshine hours and mean temperature exceed 1250 mm,1290 h and 12℃,respectively,soil exchangeable acidity content decreased and vice versa.[Conclusion]Climate is the predominant environmental factor influencing soil exchangeable acidity variation,with precipitation and sunshine duration being the most influential variables soil exchangeable acidity.The research results can provide reference for the management and regulation of soil acidification in tobacco fields.