Objective  To explore the effects of different coupling modes of water-fertilizer on root zone soil quality and water use of Coffea arabica under shade.

Method  C. arabica was chosen as test material, under 30% shading degree, three irrigation levels (W_H: 1.2 Ep, W_M: 1.0 Ep, W_L: 0.8 Ep) and three fertilization levels (F_H: 530.00 kg·hm⁻², F_M: 353.33 kg·hm⁻², F_L: 176.67 kg·hm⁻²) were completely designed with a total of nine treatments. The response laws of soil nutrient, microbial quantity, enzyme activities, dry mass and irrigation water use efficiency in root zone of C. arabica to water-fertilizer regulation were analyzed, and soil quality was comprehensively evaluated by combining membership function with factor analysis, and then the optimal water-fertilizer coupling mode of C. arabica was found by TOPSIS comprehensive analysis.

Result  Irrigation level and fertilization level had significant effects on soil nutrient, microbial quantity, enzyme activities (except catalase in autumn), root dry mass, stem dry mass, total dry mass and irrigation water use efficiency of C. arabica root zone. The average seasonal values of nitrate nitrogen, available phosphorus and available potassium contents in F_HW_L treatment were the highest. The average seasonal values of soil microorganism quantity and enzyme activities were the highest in F_MW_H treatment. Compared with F_LW_L treatment, F_HW_L treatment increased the average seasonal values of soil nitrate-nitrogen, available phosphorus and available potassium contents by 72.61%, 154.01% and 7.37%, respectively; F_MW_H treatment increased the average seasonal values of soil bacteria, fungi and actinomycetes number by 121.81%, 61.73% and 41.43%, respectively, and increased the average seasonal values of urease, catalase and phosphatase activities by 46.67%, 42.74% and 22.55%, respectively. There was a significant positive correlation between soil nitrate nitrogen content and catalase activity. The number of soil bacteria, fungi and actinomycetes were significantly positively correlated with the activities of urease, catalase and phosphatase, respectively. The combination of membership function and factor analysis showed that soil quality index of F_MW_H treatment was the highest (0.75). The total dry mass (38 011.50 kg·hm⁻²) of F_MW_H treatment was the highest, and the irrigation water use efficiency (7.88 kg·m⁻³) of F_MW_L treatment was the highest. However, TOPSIS method showed that the comprehensive benefit (soil quality, dry matter and irrigation water use efficiency) of F_MW_M treatment ranked the first, followed by F_MW_H treatment.

Conclusion  Under 30% shading degree, F_MW_M treatment was the best coupling mode of water-fertilizer for improving soil quality and promoting efficient production of C. arabica .