Culturable microbial communities associated with the grapevine soil in vineyards of La Rioja, Spain

The definition of soil health is complex due to the lack of agreement on adequate indicators and to the high variability of global soils. Nevertheless, it has been widely used as synonymous of soil quality for more than one decade, and there is a consensus warning of scientists that soil quality and biodiversity loss are occurring due to the traditional intensive agricultural practices.

In this work we monitored a set of soil parameters, both physicochemical and microbiological, in an experimental vineyard under three different management and land use systems: a) addition of external organic matter (EOM) to tilled soil; b) no tillage and plant cover between grapevine rows, and c) grapevines planted in rows running down the slope and tilled soil. Monitoring was performed in the soil top-layer (10 – 20 cm depth) and in the deeper layer (20 – 30 cm). The monitored physicochemical parameters were: pH; soil organic matter; total N; C/N ratio; soil texture; soil temperature and humidity; and the biological parameters: soil respiration (CO₂ efflux using the chamber technique) and microbial populations of the following microbial families: yeasts, decomposers of organic matter (actinomycetes), nitrogen fixing bacteria and total aerobes.

Results showed that the EOM dosage was correctly adjusted and maintained the soil biochemical equilibrium and fertility. With regard to microbial populations, it was shown that the vineyard soil is a relevant yeast reservoir that conserved its yeast populations above 10⁴ CFU/g dry soil. Results also showed that the most abundant microbial family was the nitrogen-fixing bacteria located in the soil top-layer, and remarkably, this population showed the highest values during the humid period and in the soil that received EOM, whereas the tilled soil on slope showed the lowest values. It is worth noting that the measured parameter of CO₂ efflux showed higher values in the soil deeper layer, proximate to the grapevine rhizosphere, than in the upper layer, and it did not correlate with microbial populations. This could be explained by the fact that soil mesofauna is more abundant in the deeper, warmer and more humid soil layer than in the upper layer, and to the abundance of plant roots in the soil deeper layer. In summary, in this work it is shown that an adequate EOM addition to the vineyard soil can contribute to its microbial richness, which is regarded as a parameter associated with soil health.

Acknowledgment: Financed with the Project EOM4SOIL of the E.U. H2020-EJP SOIL Program.