Increase Soil Organic Matter – GOV.UK

Why soil organic matter is important

The floors are a mixture of:

• mineral matter (sand, silt and clay) – their ratio determines the texture of the soil
• air
• the water
• organic material

Organic matter is a small but vital part of soil. It is composed of :

• living organisms, such as bacteria, fungi, plant roots, and small animals
• decaying plant or animal tissue

Organic matter is important for better soil fertility and structure, and for overall soil health. To increase organic matter levels, you can:

• add organic materials such as solid or liquid manure, plants or crop residues
• reducing soil drainage or cultivation to slow the breakdown of organic matter

You must follow the agricultural rules for water. These require you to take steps to prevent manure, fertilizer or soil from entering water bodies.

Where to increase soil organic matter

Priority :

• soil with less than 15% organic matter in the top 15 cm
• arable or root crops where the previous growth of the crop is destroyed (usually by plowing or spraying) before planting

The benefits of soil organic matter

Soil with more organic matter can absorb and hold more water. This can improve crop productivity and reduce:

• tillage and irrigation costs
• flooding, as water moves more slowly across the landscape after heavy rains
• erosion and runoff
• greenhouse gas emissions
• need for fertilizer, as nutrients are recycled more efficiently
• the use of pesticides, as more organic matter will reduce pests and diseases

Soils low in organic matter are more prone to wind erosion, especially sandy soils. The increase in organic matter will bind topsoil to help prevent wind and associated airborne particle pollution.

Before you start increasing soil organic matter

Use a runoff and soil erosion risk assessment to verify and record:

• fields with eroded soil or streams
• wind erosion – look for buried seedlings and blown soil in hedges or ditches, or on nearby roads

Soil pits are a quick way in the field to check your soil for:

• shallow rooting depth
• slow water infiltration
• low number of earthworms
• poor or weak soil structure

Read a guide to visually check the floor.

How to Measure Soil Organic Matter Levels

Take soil samples and send them to a lab for analysis. Compare the results with findings from your soil pits and soil mapping data.

For accurate results:

1. Sample areas with roughly the same soil type and history.
2. When fields include more than one soil type, sample each separately.
3. Collect 25 individual soil cores, in a clean plastic bag, to form a bulk sample of approximately 0.5 kg.
4. Take the cores in a “W” pattern, with 5-7 cores along each leg of the “W”.
5. Avoid uneven areas of terrain, such as manure piles, pylons, walkways, headlands, and around trees.
6. Sample at the same time each year, but do not sample if the soil is waterlogged or very dry.
7. Do not sample within 3 months of spreading manure or slurry as this will affect organic matter levels.

Take grassland cores at 7.5cm depth and topsoil cores at 15cm. A plowed layer is usually 23 cm deep, but if the soil in this layer is mixed, a 15 cm sample will be representative.

If you are using a no-till or no-till crop, nutrients can accumulate near the surface of the soil. A 15 cm sample may give too high readings, so sample at about 23 cm. Read a guide to sampling different cultures.

Your lab results should also include soil texture. Clay content influences the amount of organic matter a soil can normally store. Use your results to identify fields with below average soil organic matter.

How to Add Organic Matter to Soil

You can:

If your soil is slow to warm up in the spring and delays germination, sow later. The overall benefits for growing higher levels of organic matter should balance this out.

Add organic matter to soil from:

• animal manure and slurry, from your own farm or imported from elsewhere
• digestate (material left over from anaerobic digestion of biodegradable materials, such as household food waste)
• manure or specialty crops
• composts and biosolids
• paper and wood crumble
• slaughterhouse and food processing by-products

Check to see if you can get financing for new precision manure spreading equipment.

You can allow soil organisms to mix with the added organic matter, instead of using machinery. Use this natural process only when:

• the condition of the ground is good
• the risk of runoff is low
• earthworms are abundant

Using lab results, add to areas low in organic matter. You should follow best practices for using sewage sludge on your land. You may also need a land application permit.

Record organic matter inputs with a nutrient management plan. It will help you:

• avoid wasting money by using too much fertilizer
• optimize crop yields
• minimize nutrient pollution of water and air

Use cover crops or green manures and catch crops on land at high risk of pollution, instead of slurry or fertilizer.

Use ground cover and low-emission spreading equipment, such as a hose or drag shoe, to prevent soil crusting when slurry is applied to bare soil. Low-emission spreading equipment will limit ammonia loss and ensure more nutrients reach the soil.

How to Reduce Soil Organic Matter Loss

You can:

• add harder organic materials with a high carbon to nitrogen ratio like straw, crumbled paper, sawdust or wood shavings
• switch to no-till or no-till agriculture, to disturb the soil less

• reduce soil compaction caused by livestock and machinery

• manually disturb streetcar lines to reduce soil erosion and runoff
• maintain plant cover to insulate the soil against seasonal and daily warming

You can convert naturally moist topsoil to:

pest control

More soil moisture and surface material can increase slugs, as well as beneficial pest predators. Find out how to control slugs.

How to tell if soil organic matter is increasing

Dig 20cm deep soil pits and look for darker colored topsoil. As organic matter increases, its color becomes similar to that of uncultivated topsoil, such as nearby hedgerow embankments.

There will be more earthworms in the soil. Read a fact sheet on how to count earthworms.

You will also see:

• deeper root penetration, especially through finer roots
• visible pores or spaces in most soil blocks or aggregates
• looser, grainier soil consistency with no visible compaction layer

You will be:

• notice less surface water runoff and soil lost from your fields during heavy rains
• be able to work and use machinery on your land for longer periods of time without damaging the ground
• use less water withdrawn from natural sources for irrigation during prolonged dry periods
• record higher than average levels of organic matter for your soil type and clay level