Soil fertility characteristics in Zanthoxylum bungeanum planting area of Chongqing with the analysis of fuzzy synthetic evaluation

The purpose of this study was to reveal the soil quality and spatial characteristics of Zanthoxylum bungeanum in Chongqing and provide references for Zanthoxylum bungeanum ash fertilization management. Forty-five soil samples were collected from main Zanthoxylum bungeanum ash areas in Chongqing, and 13 indexes including pH value, bulk density, organic matter, available phosphorus, alkali-hydrolyzed nitrogen, rapidly available potassium, available copper, zinc, iron, manganese, boron, molybdenum, and sulfur were determined. The fuzzy comprehensive evaluation method was used to evaluate the soil quality, and the spatial variation characteristics of each index were analyzed using the semi-variable function. The results showed that the variation coefficients of each nutrient index ranged from 14.8% to 171.4%, indicating that the nutrient content distribution in this region was not balanced. The spatial correlation of available phosphorus, iron, boron, and sulfur was weak, which was mainly affected by random factors. The membership degree of available zinc and available iron was the highest, with values of 0.89 and 0.91, respectively. The membership degree of available boron and organic matter was low, with the values of 0.15 and 0.34, which indicated that the contents of available zinc and available iron were rich. However, the contents of available iron and organic matter were low. Overall, this area had 51.1% medium-fertility soil, in which 42.2% was higher than the average fertility, 6.7% of the and was lower than the average fertility. The comprehensive soil fertility index presents a spherical semi-variable function in space, and the fitting degree is very high.