Soil Health: Let's get physical (and chemical and biological)

In 2016, AHDB and BBRO funded the five-year Soil Biology and Soil Health Partnership. With its focus on soil health, one ambition 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 howpractical it was to measure it. The next task was to identify asimple way to bring the most relevant attributes for measurement together – enter the ‘soil health scorecard’. Currently developed in Excel, the team has identified threshold values associated with each attribute. When the results from the various field measurements are entered into the scorecard, a traffic-light system flags whether anything requires investigation (red),monitoring (yellow) or, if things are good, where no action is needed(green). One of the first tasks was to review what could be measured and how practical it was to measure it. The next task was to identify asimple way to bring the most relevant attributes for measurement together – enter the ‘soil health scorecard’. Currently developed in Excel, the team has identified threshold values associated with each attribute. When the results from the various field measurements are entered into the scorecard, a traffic-lightsystem flags 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. One of these is a long-term experimental site at Harper Adams University. 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.

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. Table 1.

Table 1. Organic material treatments applied at the Harper Adams University trial site

Initial measurements of topsoil chemical, physical and biological properties were made in October 2017 and a soil health scorecard was produced (Table 2).

Table 2. Example soil health scorecard for the Harper Adams University trial site

**Attributes that showed a statistically significant difference between treatments (P<0.05)

In terms of soil organic matter (SOM), the thresholds set were based on those considered to be ‘typical’ for the soil type and climate. Unsurprisingly, the control – which received no applications of organic matter – had a relatively low SOM content. The lighttextured 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 take this into account 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 www.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 of earthworms – 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 a further three 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 will also use the approach to determine the effect of crop rotation, pH, tillage and drainage status on soil health. Information on the project can be accessed via ahdb.org.uk/greatsoils In 2016, AHDB and BBRO funded the five-year Soil Biology and SoilHealth Partnership. With its focus on soil health, one ambition is toproduce a toolkit to assist with its measurement and management.