Initial monitoring of earthworm numbers at Lower Smite Farm
Caroline Corsie (assisted by farming volunteers Carol Greenow and Sarah Giles)
Lower Smite Farm
Lower Smite Farm, the HQ for Worcestershire Wildlife Trust, is a 65ha mixed farm (of which 15 ha are permanent pasture), an average size for Worcestershire, and has been owned by the Trust since 2002. Lower Smite Farm is also a Flagship site for the Trust and aims to demonstrate how biodiversity can be significantly enhanced alongside a changing commercial farming environment. The farm is in an ELS/OELS/HLS agreement (Agri-environment schemes funded by the UK Government and the European Union (EU) and currently under review) all the land is managed with the aim of maximising year round food supplies and habitat for wildlife. Half the land is in the second year of organic conversion (fully organic from August 1st 2011). The ‘conventional’ land currently grows cereal crops such as maize and winter wheat for a neighboring dairy farmer who also carries out the majority of tractor work. No insecticides or slug pellets are applied.
Soils
The arable soils are deep silty loams, and nutrient contents average as follows: Phosphate Index 1.5, Potash Index 3, pH 6.3 and soil organic matter 3%. The soils retain moisture and are relatively free draining but winter cropping is favoured commercially since the ground lies wet in the spring and is very prone to compaction and capping (forming a hard crust which impairs plant germination) after spring sowings. All in all, the soil health is not great and structure is poor. Our core objective is to restore soil health and soil biodiversity: the capacity of soil to function as a vital living system. The term ‘fertility’ is avoided, since gains here could be achieved entirely through the use of artificial inputs and to the detriment of soil flora and fauna.
Aim
Our aim is to increase earthworm numbers throughout the farmed land by at least 30% over five years and soil organic matter by 3%. Various ‘green manure’ mixes have been sown to kick start the humus building process including chicory (deep root to break pans), red clover (legume) and cock’s-foot grass (prolific roots). Some areas will also receive well rotted farmyard manure. Grazing animals are integrated where practical. On the conventional land, well rotted farm yard manure is applied prior to sowing maize or winter wheat (roughly one in three years). Cultivations are limited by the neighbour’s machinery to ploughing or discing (not ideal).
Earthworms provide a major contribution to soil health by three main means:
1. Biological: digesting organic matter (e.g. dead leaves) and converting into rich humus.
2. Chemical: ingesting soil which is excreted as nutrient and mineral rich casts 5 times N(nitrogen), 7 times P(phosphorus), 11 times K (potassium) than adjacent soil).
3. Physical: burrowing keeps soil open, maintains aeration and drainage (something a grower cannot achieve with mechanical tillage).
Method
All samples were taken on the same day (7th September 2010)
Six sample pits of 20x20x20cm were dug in each test area (Soil animals are predominantly found in the top 8cm)
No expellant solution used (soil moist throughout)
Soil was placed on plastic sheet and carefully stripped to check for worms
Worms were placed in plastic container
Worms identified using the Key to common British Earthworms (Opal). Soil returned to pit.
Sample Areas (all taken on 7th September 2010)
1. Winter wheat stubble
2. Fallow (uncultivated for 9 months)
3. Ryegrass (RG) + red clover + recycled household compost (five month old). Previously one year fallow. Compost applied two months prior to sampling). Cut and mulched on 21st June
4. Rye grass + red clover ley (also five month old, previously one year fallow). Cut and mulched 21st June.
5. True Couch Elytrigia repens: a dense area of couch within a failed green manure crop. Cut and mulched 21st June
Sample areas 1 and 2 were adjacent to each other in ‘South Meadow’
Sample areas 3, 4 and 5 were all within field ‘Thistle East’
Results
Sample area | Ave number of worms | X (times) more than plot 1 (winter wheat stubble) |
1.winter wheat stubble | 1.33 | |
2. fallow | 5.7 | 4 |
3. RG/ red clover + compost | 8.33 | 6 |
4. RG/ red clover | 13.7 | 10 |
5 .couch | 16.3 | 12 |
Summary
The soil was moist throughout.
The majority of worms were less than 2cm long and did not have clearly defined saddles so were juveniles (about 80%).
Species found included Green worm Allolobophora chlorotica; Grey Worm Aporrectodea caliginosa ; Redhead worm Lumbricus rubellus and Black-headed worm Aporrectodea longa.
1. Winter wheat stubble: The winter wheat stubble had the least worms. This stubble was also bare of weed/plant growth as a result of earlier herbicide application
2. Fallow: The nine month old fallow was easier to dig than the wheat stubble and more ‘friable’. The fallow had a cover of arable weeds dominated by winter wheat volunteers (wheat from spilled wheat seed), annual meadow grass Poa annua, scarlet pimpernel Anagallis arvensis, charlock Sinapis arvensis, nipplewort Lapsana communis and smooth sow thistle Sonchus oleraceus.
3.RG/red clover + compost. Worms were harder to find in soil samples from the red clover/rye-grass/household compost area than the adjacent red clover/ryegrass (without household compost). Rye-grass growth was taller and lusher where compost was added but the red clover was less vigorous and swamped by the rye-grass (this may have been because the compost helped retain more moisture during the very dry spring/early summer).
4. Rye-grass/ red clover: this soil showed clear signs of worm activity (worm tunnels) and was friable
5. Couch: The couch plot was the hardest to dig and extract worms from due to the /tangle of both live and dead roots. More worms were found in this plot than any other.
Comments
Worms do ‘less well’ in acid conditions (particularly less than pH6)
The phosphate levels are low and at this level farmers would be advised to apply extra (which is mined in Morocco and is a non re-newable resource)
The potash levels in the soil are moderate.
The soil organic matter level is ‘moderate’ for arable land (could be 1% or less on Cotswold brash) but is not high enough to bind the topsoil and prevent capping and improve moisture retention. Soil organic matter is converted to humus (worms/microbes/fungi etc). Arguably we should be monitoring humus content/soil microbes. Our aim is to get to at least 5% organic matter in five years and then retain it.
The overall trend is for more worms where food is available for them (and other soil critters) e.g. mulching green manures, prolific root growth of ryegrass, root nodules and nitrogen fixing from clovers all contributing to a more active soil environment. The wheat stubble only had ageing/dead wheat roots (we do not apply slug pellets since these can also kill worms as well as slugs and snails). The clover/rye grass crops are generating increasing amounts of fresh/ageing/decaying roots in the soil profile and this should result in increasing worm counts. The ‘higher’ worm count in the couch was ‘unexpected’ but the couch is also a prolific rooter (so providing cellulose/decaying organic matter)
Future steps
Further small trials have been held since this experiment and in future pits will be filled with a dilute solution of biodegradable washing-up liquid to encourage the earthworms to come to the surface without harming them (an expellant).
Sample numbers will be increased to six per crop type and statistical analyses applied.
Surveys will be linked to soil type.
A full survey will be implemented in spring 2011.
