Comprehensive evaluation of soil fertility in mango orchards with different microtopographies in karst areas

【Objective】To evaluate the soil fertility characteristics of mango orchards in different microtopographies using different evaluation methods ，and to provide scientific reference for the precise evaluation of soil fertility in mango orchards in karst areas.【Method】Setting up 4 kinds of microtopographic sample plots in mango orchards in typical karst areas of Tianyang District，Baise City of Guangxi，10 soil chemical indexes were screened as evaluation indexes，and principal component analysis，fuzzy mathematics，improved Nemero index and soil fertility comprehensive evaluation methods based on rough set theory were applied to evaluate soil fertility in different microtopographies，and to analyze the differences between the evaluation results of different fertility evaluation methods. Linear fitting was conducted fertility evaluation index and yield，and the effects of microtopography and environmental factors on comprehensive soil fertility were explored through redundancy analysis.【Result】The soil fertility indexes of the main components of different microtopographies were presented as slope（0.87，very high fertility）>pass（0.59，medium fertility）>transition zone（0.48，medium fertility）>depression（0.39，low fertility）；the fuzzy mathematics soil fertility index showed that the soil fertility of different microtopographies were all at a high level or above（0.68-0.82）；the Nemero soil fertility index showed that the soil fertility of different microtopographies were all at a medium level or above（0.26-0.46）；the rough set theory soil fertility evaluation index was presented as slope（0.67，high fertility）>pass（0.50，medium fertility）>transition zone（0.37，low fertility）>depression（0.35，low fertility），which was relatively accurate and had the highest degree of linear fitting with yield. The results of redundancy analysis showed that the topographic factor explained 34.15% of soil fertility and the environmental factor explained 23.30%.【Conclusion】Based on the evaluation results of different evaluation methods，the soil fertility of mango orchards in different microtopographies is basically presented as slope> pass>transitional zone>depression；based on the rough set theory，the results of the comprehensive evaluation of the 3 conventional fertility evaluation methods are relatively accurate，and the effect of distinguishing between the different microtopographic fertility levels is fine. The difference of soil fertility in different microtopographies is affected by both topographic factors and environmental factors，among which topographic factors have greater influence.