Partially replacing chemical fertilizer with manure improves soil quality and ecosystem multifunctionality in a tea plantation

Substituting chemical fertilizer with organic alternatives has been proven to improve soil fertility and crop yield and mitigate adverse environmental effects. However, the impact of different organic materials, such as animal-sourced organic fertilizer (AOF) and plant-sourced organic fertilizer (POF), on soil quality index (SQI) and ecosystem multifunctionality (EMF) in perennial systems like tea plantations remains unclear. This study evaluated the impact of partially substituting (30 %) chemical fertilizer with AOF (SM, sheep manure; PM, pig manure; CM, cow manure) and POF (SC, soybean cake) on soil properties, enzyme activity, enzyme stoichiometry, SQI, and EMF in a tea plantation of China. Partial substitution with AOF improved soil pH, total C content, and β-1,4-glucosidase, β-1,4-N-acetylglucosaminidase, L-leucine aminopeptidase, and acid phosphatase activities. In contrast, chemical fertilizer alone (CF) and POF substitution reduced these parameters. Compared with the control, CF, and POF, AOF substitution treatments effectively alleviated soil microbial C limitation but increased N limitation. Additionally, all fertilizer treatments enhanced the SQI and EMF of the tea plantation. Among the organic treatments, partial substitution with AOF resulted in the maximum increase in SQI (60 %–134 %) and EMF (157 %–177 %) compared with no fertilization, while POF substitution resulted in a comparatively lower improvement (53 % in SQI and 50 % in EMF). Random forest modeling identified five soil variables and eight enzyme variables as key contributors to the differences in EMF under partial organic substitution. Partial least squares path modeling further revealed that the changes in enzyme properties and microbial metabolic limitations directly influenced EMF in these treatments. Thus, the study proves that partially substituting chemical fertilizers with organic fertilizers, especially composted manure, enhances the soil quality and ecosystem functionality of tea plantations. These findings provide a scientific basis for developing effective soil management strategies to improve crop production sustainably.