How healthy is your soil?

In celebration of World Soil Day, December 5, 2021, we want to help farmers around the world to better understand their soil.

Our soils are an incredible resource – they have a remarkable ability to clean water and help mitigate climate change, they support biodiversity and are the reason we can grow nourishing food. However, the ability of soil to deliver these benefits has been compromised by widespread intensive farming – so much so it’s been estimated we have only 50 harvests left until our topsoil is degraded beyond repair. But not all is lost. Every day, farmers are transitioning to more sustainable farming practices which can not only prevent further deterioration of the land but can regenerate it too. 

But where do you start? You can’t manage what you don’t measure – a clear indication of the health of your soil can help show you where to go next and illustrate the effectiveness of new management practices. Here are three simple soil tests from the Global Farm Metric that you can do to understand, manage and protect the health of your soil and the vital services it provides.

These tests indicate the state of your soils in terms of structure, the amount of organic matter and biodiversity. You can do this in your garden or allotment, or on your farm. 

On farm scale, choose three fields that are representative of your land (e.g. with different soil types or different enterprises such as arable or permanent pasture). Follow the sampling protocols – time of year and weather (e.g. after heavy rainfall or frost) can sometimes affect your results, so tests are best done throughout the year, when soil is moist and not waterlogged or frozen. Let’s get digging!

Worm count 

You may already know that earthworms are critical for soil structure, resilience to pests and pathogens (including aphids), nutrient cycling and biodiversity. Lesser known, is that there are three ecological groups of earthworms which uniquely influence soil functions: surface, topsoil and deep burrower. Identifying the prevalence of earthworm types can indicate what practices would be beneficial for your soil health. 

The following protocol has been developed by Jackie Stroud in collaboration with the Sustainable Soils Alliance, Earth Watch Europe, UK Centre for Ecology and Hydrology, University of Sheffield and SRUC. Read full instructions here and find out more via the website and social media (@wormscience).

You will need:

• spade and ruler
• mat
• pot for worms
• a bottle of water
• notebook

Steps:

• Select where you will test your soil.
  • For larger areas, dig five soil pits per field in a ‘W’ shape. 

  2. At each soil pit spot check the soil surface for the presence of middens and record results.

  • • Middens are heaps of biological material (usually 2-5 cm mounds of plant residue and earthworm ‘droppings’) left behind by deep burrowing (anecic) earthworms which have enhanced soil organic matter and ability to cycle nutrients.
    • Learn more about identifying middens here. 

  3. Dig a 20cm x 20cm x 20cm soil pit and place soil onto a mat and place each whole earthworm you find into the pot.

  Record the following:

  1. 1.  Are pencil size vertical burrows present? 
     2. Total number of (adult and juvenile) earthworms 
     3. Total number of adult earthworms (usually only a few – return juveniles to soil pit);
        only adults have a saddle (the reproductive ring near the head). Top tip: a saddle can be more obvious on the underside of the earthworm. 
     4. The number of each type of adult earthworm (surface, topsoil, deep burrower) 
     5. Use the identification key found here.

  4. Return all worms to the soil pit and back fill with soil.

  5. Upload your results, find interpretation support and community results at www.uksoils.org.

Soil structure

Good soil structure can allow the roots of crops and plants to penetrate deep into the earth, improve water availability and soil aeration. This is vital for healthy crops, reducing water use, preventing agricultural run-off into nearby water systems and improving soil biodiversity. 

This test, developed by Aarhus University, UEM and SRUC, assesses soil structure based on the appearance and feel of a block of soil dug out with a spade. Find out more here.

You will need:

• spade (20 cm wide, 22-25 cm long)

Optional:

• light coloured plastic sheet, sack or tray (50×80 cm)
• small knife
• camera

Steps:

1. Sample between three and 10 locations across a field, depending on size.
2. Extract a soil block one spade’s depth and width.
3. Examine soil structure by manipulating the soil block to see how easy it is to break up.
4. Use the VESS scorecard to record a score for topsoil and subsoil.

The VESS Scorecard can be found here. The scale ranges from 1 (friable soil) to 5 (very compact). Scores may fit between Sq categories if they have the properties of both.

Scores of 1-3 are usually acceptable whereas scores of 4 or 5 may require a change of management. 

Soil infiltration

Testing the rate water seeps into the soil can give a good indication of soil structure which can affect root penetration, water availability to plants and soil aeration. These properties can help increase biodiversity in the soil and produce a healthy crop, as well as reduce the risk of soil erosion which can contaminate nearby water courses. You can measure soil infiltration using the drainpipe test. This is best done a day or two after rainfall – testing on already saturated ground can be quite a challenge!

You will need:

• two short lengths of pipe 10cm in diameter and 20cm long
• a hammer or mallet
• a stopwatch
• 5 litres of water

Steps:

1. Drive the pipe halfway into the ground using the hammer or mallet, leaving 10 cm standing above the ground.
2. Pour in roughly 800 ml of water to a depth of 10 cm.
3. Start the stopwatch immediately and measure the time taken for water to drain into the soil.

Results:

• For light and medium soils (typically associated with ‘good’ health), it should take about 2-5 minutes for water to drain away.
• Areas with heavy clay soil and poorer structure can take 20 minutes or longer for the water to drain away.

How to improve:

• Consider the use of cover crops in the winter and planting an herbal lay with oat, lucerne, chicory and/or red clover which have deep tap roots that help break up compacted soil. Keeping soils productive can also make them more resistant to compaction, increase nitrogen fixation and soil organic matter.
• Avoid cultivation when soils are wet – this helps to keep existing aeration intact.
• Continue to monitor! This can help you find out what’s working for your land and what’s not.

Achieving our climate goals is dependent on everyone being able to do better. Measuring your soil health can help you to improve your sustainability and productivity, whether you’re a small-scale producer in Wales or a industrial dairy farmer in Australia.

But there are many more indicators of sustainability we should be measuring. The Global Farm Metric is a whole-farm framework for measuring sustainability on all farms around the world, assessing biodiversity, air and climate, water, productivity and more. This January 2022, the Global Farm Metric Research Tool (UK) will be made freely available to assess on-farm impacts. Be the first to know by signing up to the Global Farm Metric newsletter here.