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Measuring and managing soil health

Publication Date: 
14 May 2018

Article first published in Grower Magazine, May 2018

Do you know how to tell if your soil is healthy or if it needs a boost? Audrey Litterick, Earthcare Technical, gets to grips with methods for measuring soil health

Many farmers and growers are considering management changes with a view to improving the health of their soils. But, before you start to plan and implement major changes, it’s important to define the health of your soils as they are now. Only if you have good baseline data can you effectively evaluate the impact of management changes on your soils.

Soil health is critically important to growers because there is a direct relationship between well-functioning, healthy soils and reliable good yields of quality crops. Soil health therefore has a clear impact on profit margins. Many growers have become aware that their soils have suffered following years of intensive cultivations with little or no organic matter returns.

AHDB have been investing in the GREATsoils programme since early 2015. The first, three-year, part of the programme was led by The Soil Association and involved Earthcare Technical Ltd. and Organic Research Centre. The project aimed to inspire and support fruit, vegetable and salad growers to develop the abilities and confidence to assess the health of their soils and take practical action to improve management strategies. Here, we’ll take a look at what we mean by the term “soil health”; the most appropriate soil health measurement techniques for growers will be described, and we’ll have a look at the ways in which one grower is looking to measure and manage soil health.

Soil health defined

Soil health can be defined as “the capacity of soil to function as a vital living system, to sustain plant and animal productivity, maintain or enhance water and air quality, and promote plant and animal health”. It has physical, chemical and biological components, all of which can be measured in various ways:

  • Physical components include soil structure and the degree to which water infiltrates down through the soil profile;
  • Chemical components include soil pH, crop nutrient indices and soil organic matter content;
  • Biological parameters include earthworm numbers, soil respiration and the degree of diversity in microorganism populations.

The results obtained when we test soil health are strongly affected by the ways in which we manage our soils. Some aspects of your soil cannot be changed, such as soil depth and soil texture (the relative percentages of sand, silt and clay), but it is worth being aware of these properties too since they can impact strongly on the way in which soils behave under different management regimes.

How to measure soil health

Soil health is complex. You cannot assess it adequately by looking at a single measure. There are a wide variety of soil assessment methods and techniques available. An important element of initial work in the GREATsoils project was to work with growers to identify the best methods for use in UK soils, to evaluate them and then test them in the field. Key methods include;

  • Physical – soil compaction test; infiltration test; visual evaluation of soil structure; full soil profile investigation
  • Chemical – soil pH; extractable P, K, Mg; base cation saturation ratio; soil trace elements; soil organic matter (Loss-on-ignition)
  • Biological – earthworm counts; soil respiration; soil foodweb.

Key outputs and future work under GREAT soils

Aside from around 46 practical grower and adviser workshops conducted over the three years of the project, a range of guidance notes, case studies, videos, webinars, grower blogs and reports on the field trials/field labs have been published, all of which are available at www.ahdb.org.uk/greatsoils

Case study: Balbirnie Home Farms

David Aglen is Farms Manager at Balbirnie Home Farms, a 1200ha mixed farming enterprise in rural Fife. His soil is a moderately varying sandy loam with a sandy subsoil. This allows a varied rotation which includes carrots, potatoes, cabbages and cauliflower as well as combinable crops, grass and forage crops for the cattle enterprise.

David said, “Nurturing the fragile structure of these soils while growing mechanically intensive crops is becoming a major driver of the rotation. An absolute minimum level of cultivation is used for the establishment of the combinable crops along with a vegetable and root crops only being grown one year in four across the 900ha of cropped land.”

David is keen to maintain or increase soil organic matter levels on the cropped fields and to that end chose to look at the impact of using chopped straw and green compost on soil health as part of the GREATsoils project.

For the trial, David chose a 10ha field with a sandy loam topsoil which he felt was in need of some organic matter. The field was in an arable/vegetable rotation, with carrots and potatoes each being grown roughly one year in six and cereals and cover crops being grown in intervening years.

Trial facts

After carrot harvest in April 2017, the field was divided into four treatment areas. The eastern half of the field had chopped straw applied at approximately 50 t/ha and the western half no straw. The northern half of the field had compost applied at 20 t/ha and the southern half had no compost.

Soil physical, chemical and biological assessments were made prior to the 2016/17 carrot crop, during carrot growth, at barley growth stage 31 in 2017, and after barley harvest in October 2017.

Trial findings

Bulky organic materials can have multiple benefits to soil health including:

  • liming value (in some cases);
  • nutrient value (P, K, Mg, S and trace elements);
  • organic matter which can improve soil water holding capacity, soil structure, nutrient retention and the activity of soil organisms including microorganisms and larger soil fauna such as earthworms.

Regular inspections of soil structure, through frequent test digs and allocation of structure scores (e.g. VESS) can give quick, useful indications of the physical aspects of soil health, but these can have limited value where intensive cultivations are regularly carried out.

Earthworm counts are a useful indicator of soil biology when taken regularly at similar times of the year, every year. AHDB provide a guide to counting earthworms at www.ahdb.org.uk/greatsoils

Soil respiration measurements are a relatively new method for estimating the biological life in soil on farms; further results must be gathered on different farms, soil types and growing systems in order to learn how to interpret the data gained and take actions based upon it.

David’s view

"While there are well-established laboratory methods for soil chemical analysis and a range of practical methods for measuring soil physical properties, we are now seeing methods emerge for soil biological analysis. David feels that some of these tools have started to provide him with the reassurance that the innovations he’s introducing to his mechanically intensive vegetable production system are having a positive impact on the health of his fragile soil."

Further reading

Full report: https://potatoes.ahdb.org.uk/node/643077

AHDB GreatSoils: https://ahdb.org.uk/projects/GREATsoils.aspx

AHDB Soil Testing Videos:

 

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