The number of earthworms that are visible in a spade full of soil is an important indicator of soil health, farmers were told at an event in Cullybackey on Tuesday.
Becky Wilson from Farm Carbon Toolkit said 10 to 15 worms per spade indicates good biological activity within soils which benefits soil structure, organic matter levels, water infiltration and plant growth.
“In grassland, it might initially seem that you don’t have that many, but worms tend to hide until you start to break the soil apart.
Set the worms on your spade or a bag as you pick them off,” she said.
Wilson explained there are three main types of earthworms in agricultural soils which fulfil different functions.
Litter dwelling earthworms are usually around the size of a matchstick and are a dark pink colour. They are found near the surface, have a role in carbon cycling and are prey for birds.
Topsoil earthworms are slightly bigger and are a yellow or light green colour. These worms move horizontally within soils and create a network of burrows. This helps improve soil structure and nutrient availability for plants.
Finally, deep-burrowing earthworms are larger again and have a dark red head with a flat tail. They make deep vertical tunnels up to a metre below the surface.
“There are not a lot of these worms in arable fields because they do not like cultivation. They are like nature’s plough as they improve air movement, water infiltration, and give roots access to nutrients,” Wilson said.
Farmers were told that heavy applications of slurry can be detrimental to earthworms, but light coatings can be beneficial to worm populations as slurry helps lift organic matter levels in soils.
Wilson also urged farmers to be wary of chemical additives that are being marketed as a way of improving soil biology. She said there is often little or no independent research to back up claims made by manufacturers.
“The best tools for improving soil biology in grassland are livestock. You already have everything you need without buying anything in,” she maintained.
Host farmer Will Frazer outlined how he has taken various steps to improve earthworm numbers in his soils.
This includes applying lime to low-pH soils, cutting back on chemical fertilisers, and switching from set stocking to a rotational grazing system.
He has also started leaving a higher residual grass cover after each grazing event, with his post-grazing target now being 1,800kg of dry matter per hectare.
Over 300 types of soil on NI farms
There are 308 different soil types in NI, a leading expert on grassland and forestry has said.
Professor Jim McAdam said the most detailed soil survey available shows NI has twice as many soil types as England and Wales, even though it is 11 times smaller in terms of area.
The most common soil type in NI is gleyed soils, making up 56% of the area. “These are sticky clay soils that are heavy. They are potentially fertile, but they are hard to manage,” McAdam said.
Available figures suggest 14% of soils in NI are peat, although McAdam said this is currently under revision and will most likely increase as more data is published.
He told farmers at the event in Cullybackey that NI soils tend to have high organic matter content, so they contain vast stores of carbon.
“Carbon in vegetation is pretty insignificant. Around 96% or 97% of carbon on our farms is in the soil. It is a valuable asset. Farmers need to get credit for managing it,” McAdam suggested.