Soil microbiome diversity under annual and perennial crops in conventional and organic agriculture.

Microorganisms in agricultural soils play a key role in nutrient recycling and nutrient availability for plants. The diversity and abundance of these microorganisms and the subsequent microbiological processes can however be influenced by different factors. This includes among others the crop type grown on the field, the farmers’ agricultural field management and various soil parameters as these farming processes may highly affect the soil microbiological diversity and abundance. Some farming practices aiming at increasing crop yield such as ploughing or nitrogen fertilization might actually endanger soil processes provided by microorganisms supporting crop yield. It is therefore important to better understand the complexity of soil microbial abundance and diversity – including bacterial, fungal and protist – in relation to agricultural soil management.

The objective of this study is to determine the structure of the microbiota (including bacteria, fungi and protists) in agricultural soils in Skåne, Sweden, across different farming conditions and soil characteristics.

To achieve this, soil samples were collected from agricultural fields with the primary focus on two crops:  small grain cereals (annual) and ley (perennial). Samples were collected from a total of 25 farms including conventional farms and organic farms, varying in time since transition, to account for potential differences in farming practices. The soil samples were incubated using soil chips to observe the abundance of the various types of microorganisms. We also compared microbial morphodiversity with molecular biodiversity measurements. In addition, the soil characteristics such as pH, organic matter and electrical conductivity were determined for correlation analysis with microbiological presence/abundance.

The abundance of microbiological groups examined via microscopic analysis in soil chips proved to be highly variable within crop types and agricultural field management (conventional/organic). However, time since transition to organic farming practices might influence the abundance for the microbiological groups with an increase in abundance for older organic farms. In addition, the analysis of soil parameters such as pH, soil organic matter and electrical conductivity also showed to be highly variable within crop types and agricultural field management.

This study shows that abundances of microbiological groups in various types of agricultural soils might be highly variable, in which the years of organic farming, but not the categorical farming practices tend to affect microbiological group abundance.