Angus Soil & Nutrient Network: 2nd meeting event summary

The second meeting of the Angus Soil & Nutrient Network was held during the middle of January 2020 at the Finavon Hotel, Forfar – a bit warmer than an on-farm meeting at this time of year!

The main focus for the event was ‘The Living Fraction of the Soil’.

The evening was spent discussing soil biology which is crucial to maintain soil health and fertility, as well as being responsible for nutrient cycling and organic matter decomposition.

There were 4 main points covered at the meeting:

What makes a soil?

The meeting started with an interesting and fun group discussion about what the difference is between soil and stone, with the main variance being that the soil is living where a stone is not.  The soil is made up of parent material, organic matter, air and water. Organic matter can be split down further as it is made up of a mixture of organic substances and structures with different biological origins, decomposition rates, stages of decomposition, modification and different ages.

Soil organisms and their role in the soil

There are trillions of different organisms within the soil, each playing a vital part in keeping the soil healthy and productive.  Their main purpose is to decompose organic matter, dissolve soil minerals, aerate the soil and increase permeability, control harmful organisms and increase the efficiency of plant nutrient uptake being a few.  Most soil organisms require this organic matter for both energy and carbon.  Every time an organism eats another one it excretes excess nutrients which is then readily available to the plant.  Organisms found in soil tend to specialise in their role and therefore a diversity of living things is important for soils to function healthily.

What are Micro, Meso and Macro fauna?

Micro Fauna
Micro Fauna are tiny single-celled organisms which decompose organic matter making the nutrients available to other organisms for example Rhizobia and Streptomyces.

Micro Fauna – Fungi
There are two main types of fungi in the soil, the first being Saprophytic fungi which decompose organic matter into fungal biomass, CO2 and small molecules.  The second being mutualistic fungi such as arbuscular mycorrhizae which form an association with plants to provide nutrients and water in exchange for Carbon.

Meso Fauna
There are many different types of meso fauna within the soil. Protozoa require space in the soil for living /feeding. They primarily feed on bacteria making them responsible for controlling bacterial populations and nutrient cycling.
Nematodes feed on plants, bacteria, fungi, protozoa and each other. Again they help to cycle nutrients, and healthy soils will contain a diverse mix of nematodes.

Macro Fauna
The main Macro species found in the soil is the earthworm.  There are 3 species of earthworms that can be found in UK soils:

• Epigeic, which are found on the surface and consume high levels of compost
• Endogenic, which burrow horizontally in the top soil
• Anecic, which are the largest worm in the UK but can often be absent from arable soils. They burrow down 2m deep which can assist with drainage root penetration, aeration and nutrient cycling. Micro Fauna Micro Fauna are tiny single-celled organisms which decompose organic matter making the nutrients available to other organisms for example Rhizobia and Streptomyces.

Measures to Improve Soil Biology and Organic Matter

• Reduce Soil Disturbance

Tillage can affect organic matter in 2 ways, firstly by physically disturbing and mixing the soil and secondly incorporating the plant residue into the soil profile. This can reduce the total Carbon and Nitrogen concentrations within the soil, microbial biomass and simplifies microbial community’s structure. On the whole, micro faunal groups are unchanged by tillage, whereas macro faunal groups can be highly inhibited.

• Increase Plant Diversity

Ecosystems require diversity just like humans needing a balanced diet to be healthy. The plants feed the soil and the soil feeds the plant, if a soil is not healthy then both partners are going to suffer. Weeds are natures response to a lack of plant diversity, nutrient or soil imbalances

• Living Roots

Living roots are the most easily accessible energy source for soil microbes. Different rooting structures and plant species are key, for example arbusular Mycorrhizal fungi will not form an association with brassica plants. To keep levels of mycorrhizae inoculum in the soil high they need a living plant to survive.

• Soil Cover

If you can’t see the soil, that is a good thing! Crop residues and living plants act as a living and dead armour for the soil which help in reducing soil erosion, increasing infiltration as well as providing habitats for beneficial arthropods.

The evening then finished with a slaking demonstration, showing the difference in aggregate stability between a soil which is intensively managed and one that has been in grass for 7 years. The two aggregates are the same soil type and were dug from the same field just 10m apart.  The video below shows what happened.