The subject is complex, explains speaker Jackie Stroud, soil scientist at Rothamsted Research. “There are ten common species of earthworm and they can be divided into three ecological groups, each with a different role: epigeic live on the surface and break down organic matter; anecic or burrowing worms make permanent vertical burrows and create piles of casts or middens that can be teeming with microorganisms; and lastly endogeic worms mix organic and mineral components together in the topsoil.
“In all my years digging soil pits I always find the endogeic worms, even in heavily worked soil, so I am very cautious about using ‘earthworm numbers’ as an indicator of soil health without identifying the species.”
Jackie has been working with farmers on the #60minworms survey to help inform a ‘traffic light’ system that will determine soil health by the species present.
Amanda Bennett, Resource Management Scientist (Soils) for AHDB, is also speaking. She comments that soil health (in an agricultural context) means that there is a good balance of physical, chemical and biological properties providing the continued ability to support agricultural production and reduce impacts on the environment.
She says: “Within the AHDB-BBRO Soil Biology and Soil Health Partnership we are looking to test and validate a range of physical, chemical and biological indicators for soil health, across a range of production systems and soil types. This is being done at long-term experimental research sites as well as on-farm; the findings will help farmers better understand what makes a healthy soil and which management practices can help maintain or improve soil health in the long-term.”
Land management to encourage earthworms is one of those recommendations. Good earthworm populations have been associated with more resilient soils.
“Taking resilience to mean the ability of the soil to recover more quickly from an extreme event such as heavy rainfall, then good soil structure is a key part of this,” Amanda continues. “Earthworm burrows provide drainage channels and pathways for roots to follow, which may result in roots being able to access nutrients deeper in the soil profile. In addition, less soil disturbance allows fungal mycelial networks to establish more fully, which can release nutrients and make them more accessible for uptake by plants.”
Although ‘min-till’ regimes have been shown to benefit earthworms, Amanda says other considerations need to be taken into account. She says: “A lack of cultivation allows earthworm populations to build up and, in particular, the anecic earthworms to establish their permanent vertical burrows without disturbance.
“However, there are a number of pros and cons to any cultivation approach and whilst minimum tillage may result in less disturbance of the soil biology, farmers need to consider a number of other variables in selecting their cultivation and soil management approach.”
Felicity Crotty, Principal Soil Scientist at the Game and Wildlife Conservation Trust, is also speaking. She comments: “Earthworms provide many benefits. While it has been estimated that 90% of all water infiltration is due to earthworms they also have an important role in nutrient cycling. A meta-analysis has shown that increased earthworm numbers could actually provide a tangible yield benefit to crops.
“I like to think of earthworms as the emblem of a healthy soil – if there is a healthy earthworm population then it is likely the other soil fauna will also be abundant and healthy.”
The association between organic matter, yield and worm populations was investigated by an AHDB research project. The study concluded that the addition of organic matter improved yields and earthworm numbers but no direct link was made between the two.
Amanda continues: “The build-up of organic matter in the surface of the soil can act like a sponge, helping to reduce surface runoff even without the specific activity of worms. However, they do have an important role, not just in physically creating drainage channels but also in redistributing organic matter in the soil.”
Jackie agrees: “The number of middens, which indicate the presence of anecic worms such as L.terrestris, could be used to assess soil health. The soil beneath these food stores is literally crawling with life – other types of earthworms and mesofauna – and this translates into improved soil structure, with better aggregation and porosity.”
Jackie and the other speakers, including Nick Voulvoulis, Director of the OPAL Soil Centre at Imperial College London, will be sharing their insights at "Waiting for Worms" a Water and Soil Health Special Interest Group event to be held at Morley Farms, Deopham Road, Morley St. Botolph, Wymondham, NR18 9DF on 16th May 2018.
Find out more at www.agritech-east.co.uk.
Image:Felicity Crotty, Jackie Stroud, Amanda Bennett