Soil health: Hello, is there anybody down there?

How much life is in your soil and how hard is it working for your crops? It is a tough question to answer. That is why our Soil Biology and Soil Health Partnership has looked at ways to measure the size and activity of soil microbial biomass – a key indicator of soil health.

Focusing on two biological indicators already used in commercial labs, the research team examined an extensive data set from agricultural mineral soils to establish ‘typical’ values for UK conditions. Until now, guidance has relied heavily on data from the United States.

Potentially mineralisable nitrogen (PMN) – a measure of the amount of nitrogen readily decomposed under controlled (anaerobic) conditions (625 arable soils tested).

Solvita® respiration burst (CO₂-C) – a measure of the amount of carbon dioxide (CO₂) released when a dried soil is rewetted (1,803 arable and 310 grassland soils tested).

• As expected, there was very little activity in the subsoil, compared with the topsoil
• Soil texture had little influence on microbial activity, meaning a set of typical values could be created for all mineral soil textures (<20% soil organic matter)
• Separate guideline values for grass and annual cropped fields are required (and have been developed for CO₂-C)

In 2021, further work will test and further refine the guideline values. Once finalised, the results will help people benchmark soils and target measures to improve microbial activity.

This article is based on project report 91140002–11, entitled: Developing UK-relevant benchmarks for the soil health indicators: Potentially mineralisable nitrogen and Solvita respiration burst.

Funded by AHDB and BBRO, the five-year Soil Biology and Soil Health Partnership is a cross-sector programme of research and knowledge exchange. It helps farmers and growers maintain and improve the productivity of UK agricultural and horticultural systems, through better understanding of soil biology and soil health.