If you want to know how healthy you are, there are a myriad of tests and tools to help you ‘quantify’ your
body condition – blood pressure, body mass index and cholesterol level, for example. Now there is a move to
develop ways to quantify the health of your soil, too.
In 2016, AHDB and BBRO funded the five-year Soil Biology and Soil Health Partnership. With its focus on soil health, one goal is to produce a toolkit to assist with its measurement and management. One of the first tasks was to review what could be measured and how practical it was to measure it. A broad range of indicators (physical, chemical and biological) has been assessed by the research team, including:
• Common indicators: pH, routine nutrients, bulk density and penetrometer resistance
• Less common indicators: visual evaluation of soil structure (VESS), soil organic matter/loss on ignition (LOI), respiration and earthworms
• New indicators: total nitrogen, microbial biomass carbon, potentially mineralisable nitrogen (PMN), DNA measures (e.g. of pathogens), nematodes and microarthropods
With so many soil attributes available for measurement, a simple way to bring the most relevant ones together was essential – enter the ‘soil health scorecard’. The team has identified threshold values associated with each attribute. When the results from the various field measurements are entered into the scorecard (currently an Excel spreadsheet), a traffic-light system flags up whether anything requires investigation (red), monitoring (yellow) or, if things are good, where no action is needed (green). To test the approach, a network of seven experimental sites has been established. The sites represent a range of soil management histories, soil types, soil organic matter additions, pH levels, drainage statuses/structures, climatic conditions and rotations (including grass leys, cereals, sugar beet and potato production).
A research case study, available on the AHDB website, has been developed for one of these sites. Located at Harper Adams University, it is a fascinating and unique long-term experimental site. Established in 1991, on a sandy-loam soil (‘Wick’ soil series), the site provides an extreme test for the prototype scorecard. It has a long history of repeat organic material additions (at recommended rates) in a predominantly arable rotation (cereals and potatoes). In fact, cumulative organic matter inputs range from 0 t/ha to 129 t/ha. Prior to the latest round of funding, the site had received support from a variety of sources: most recently, via the WRAP digestate and compost in agriculture (DC-Agri) field experiment (wrap.org.uk/content/digestate-andcompost-agriculture-dc-agri).
Five organic material treatments have been applied (Table 1). These include annual applications of cattle farmyard manure (FYM), cattle slurry, green compost, green/food compost and food-based digestate. There is also a control treatment, which has received manufactured fertiliser only. Fertiliser was also applied across treatments to ensure that nutrient supply did not limit crop growth. Initial measurements of topsoil physical, chemical and biological properties were made in October 2017 and a soil health scorecard was produced (Table 2).
In terms of soil organic matter (SOM), the thresholds set were based on those considered typical for the soil type and climate. Unsurprisingly, the control – which received no applications of organic matter – had a relatively low SOM content. The light-textured soils responded well to the application of organic materials, particularly bulky materials, such as FYM and green compost. Key nutrients were also measured – extractable phosphorus (P), potassium (K) and magnesium (Mg). Thresholds were based on values taken from AHDB Nutrient management guide (RB209). Levels of nutrients were relatively low in the control. Levels were higher across the organic matter treatments.
The soils at this site are inherently high in extractable P, and management strategies would need to consider this across all treatments, especially the FYM treatment. Visual Evaluation of Soil Structure (VESS) scores from the topsoil (top 30 cm) were also good at the site. VESS is a straightforward and quick way to test soil structure in three simple steps – soil removal, soil assessment and soil scoring. The soil quality score produced can help highlight where soil structure needs to be improved. Ideally, each distinct soil layer should be assessed separately, and management focused on the worst performing, ‘limiting’ layer. A score of 1 or 2 is good, a score of 3 is moderate and shows the soil requires monitoring, and a score of 4 and 5 indicates that management action is required.
Further information on VESS can be found, at: sruc.ac.uk/info/120625/ visual_evaluation_of_soil_structure
Counts of the number of earthworms (total number of adults and juveniles) showed that all treatments were associated with an active population – more than eight per pit is an ‘active’ population for arable or ley/arable soils. The application of bulky organic materials was also shown to improve topsoil bulk density (at 5–10 cm depth), from 1.4 g/cm3 on the control treatment to 1.3 g/cm3, where either FYM or green compost had been applied. The plan is to repeat the sampling process for three more years of arable cropping (winter wheat, potatoes and spring cereal). The impact of additional organic material applications on a wider range of soil quality indicators will also be investigated.
Other long-term sites in the network are also using the approach to determine the effect of crop rotation, pH, tillage and drainage status on soil health.
The main strength of the scorecard is that it breaks down the challenge of improving soil health into manageable pieces. It can focus attention and guide management interventions to improve the overall health status of the soil. During the remainder of the partnership, the soil health scorecard will be refined and tested across the experimental sites, and in consultation with the project’s eight farmer research innovation groups. A set of indicators, which can be used to measure soil health in the field directly or indirectly (i.e. through sending samples away for analysis), will be developed by the project. Critically, the research will also improve understanding of the relationship between each component of soil health and crop yield.
One of the most exciting areas of activity is the development of more robust indicators, benchmarks and thresholds for biological properties. The 2018 annual report includes details of innovative developments in molecular biology that are yielding ways to measure the soil biological community, including the presence and distribution of soilborne pathogens.
Information on the project can be accessed via ahdb.org.uk/greatsoils