Influence of environmental and agronomic variables on soil microbiome in citrus orchards: A comparative analysis of organic and conventional farming system

Crop health and productivity depend on the structure and functionality of soil microbiota associated with the root system of plants. The agricultural policy of the European Union promotes organic farming systems to ensure environmental sustainability and food safety. The objective of this study was to investigate the impact of organic farming on soil microbiome in citrus orchards. The soil microbiota of eight conventionally and seven organically managed commercial citrus orchards across eastern Sicily was characterised using Illumina sequencing and BeCrop® primers for PCR amplification. The structure (diversity and relative abundance) and functionality of soil bacterial and fungal communities depended primarily on the sampling site. Other variables influencing the soil microbiome included soil total carbon content, seasonality, rootstock genotype, soil tillage and irrigation system. The latter three exerted differential effects on either bacterial or fungal communities. Conversely, age and visible health status of the tree had negligible influence on both communities. The differences between organically and conventionally managed citrus orchards accounted for a significant proportion of the variability, indicating a relevant effect of the farming system on soil microbiome. Organically managed orchards compared to those managed conventionally exhibited higher microbial diversity and a unique composition of nutrient-cycling microbes. In particular, organic farming promoted beneficial microbial functions, such as nitrogen fixation and phosphorus solubilization. Findings provide insights into the dynamic and complex interactions between environmental variables and soil microbial communities in citrus orchards, confirming the potential of microbial diversity as an indicator of sustainability in agricultural systems.