The bug benefits

Published 9 October 15

Soil bugs play a vital role in supporting soil structure and plant growth on grassland farms but farmers must look after their soil to reap these benefits, warns a leading soil expert. Dr Debbie McConnell, AHDB Dairy R&D Manager, finds out why on behalf of Forage for Knowledge.

Soil is full of life. One small handful of soil contains more organisms than the total number of humans who ever lived on Earth, but what are these creatures and how do they influence our soil?

Speaking at a recent AHDB-BGS meeting, soils expert Dr Elizabeth Stockdale outlined the range of organisms in a typical handful of grassland soil. “It is packed with billions of organisms, such as bacteria, fungi, nematodes, mites, springtails, earthworms, insects and millipedes, most of which are too small to see with the naked eye.”

Dr Stockdale, the main author of the AHDB website healthygrasslandsoils.co.uk, explained that these organisms played many essential roles in the soil including:

  • Powering nitrogen fixation
  • Recycling nutrients into plant available form
  • Developing a sponge-like structure to regulate water retention and drainage.

“These organisms influence most of the processes which take place in the soil and, as a result, are essential for plant growth – no plant will grow in a sterile soil,” she comments.

So how can farmers help encourage these organisms in the soil?

“Just by having plants in the soil all year round you are helping these bugs survive,” explained Dr Stockdale. “Plants release carbohydrates and sugars into the soil through their roots, which provide a food source for other organisms.”

Other organisms then consume these bacteria and fungi, breaking them down into vital nutrients such as nitrate and phosphate, which are readily available for the plant roots to absorb. As a result, the organisms benefit from the plant roots and vice versa.

Adding organic matter such as farm yard manure (FYM), composts and slurry is also important to encourage soil biology, providing a key source of energy for many organisms. This is backed by recent research at the Agri-Food and Biosciences Institute, showing that earthworm populations were five-times higher on plots that received slurry each year than those that only received inorganic fertilisers.

However, to get this benefit, Dr Stockdale advises managing organic manure inputs carefully. When earthworms come into contact with slurry, the high concentration of ions can extract body fluids from shallow skinned earthworms by osmosis, killing the worm. The risk is much lower with farmyard manure, as the nutrients are less concentrated.

“Organic matter input is important so try and make sure most fields across the farm receive some. With slurry, try a little and often approach to minimise any detrimental impact on soil organisms,” she said.

Another key factor to help soil organisms survive is good soil structure. “When soils are compacted, the air spaces are squeezed out, removing oxygen which is vital for organisms to survive,” said Dr Stockdale.

“Regularly assessing soil structure and soil testing is something every farmer can do themselves to make sure their soil can support a range of soil organisms which in turn will aid grass growth, nutrient use efficiency and water retention.”

 

Who’s who in the soil environment:

Soils 1

Earthworms. There are three main types commonly found in UK soils: epigeic, endogeic and anecic. Anecic earthworms are particularly good at improving soil structure, making large vertical channels throughout the soil. 

 

Soils 2

Mites are the smallest (usually less than 1mm) and also the most diverse group of arthropods in soil and therefore show a very wide range of feeding habits and lifestyles. The presence of these microarthropods markedly increases decomposition rates across a range of environments. 

 

Soils 3

Nematodes are microscopic roundworms with a diameter of <50μm. Different species of nematodes play different roles in the soil. Some feed of plant residues while others break down bacteria and fungi in the soil into vital nutrients.

 

Soils 4

Fungi. Fungal hyphae are usually 2-10μm in diameter, but can extend to up to a kilometre in length. Fungi are involved in a large number of interactions and processes in soil. They are often found in close proximity to plant roots. 

 

Soils 5

 

Bacteria are single-celled prokaryotes. The large majority of bacteria existing in soil (>95%) are not culturable and so for a long time could not be studied. Bacteria in the soil often have the ability to ‘slow down’ metabolic activity and maintain activity in a dormant state, even under conditions of very low energy and nutrient availability