I’ve become very interested in learning more about soil recently. My PhD research project is on water pollution from agriculture, so it makes sense to broaden my understanding of soil as its erosion ultimately leads to reduced water quality.
This post is about what I learnt at a recent soil and water event; as someone who knows relatively little about soils, I found it very valuable, and I hope that sharing this will be useful to others as I think we could all do with knowing a bit more about the substance that we rely on so heavily.
The UK only has 30-40 years of fertile soils left if we continue to degrade oils at current rates.
This is really rather scary. If we lose our soils, we lose our ability to produce food.
For those who need to see a monetary figure to envisage how important this issue is (after all, we are in the era of ‘Natural capital’), soil erosion is costing ~£165 million every year in the UK alone. I imagine that this is probably an under-estimation as farmers with poor soils will be suffering from lower yields, and I’m not convinced that all of these losses have been taken into account here as they’d be difficult to calculate (please correct me if I’m wrong!).
According to a UN-backed study, fertile soils are being lost at rate of 24bn tonnes a year through intensive farming as demand for food increases
However, awareness surrounding soil does appear to be improving; plans have emerged for a bill to ensure that farmers protect and enhance the health of their soils (although who knows to what extent this will work or how stringent it will be)!
Why is soil important?
‘Soils provide anchorage for roots, hold water and nutrients. Soils are home to myriad micro-organisms that fix nitrogen and decompose organic matter, and armies of microscopic animals as well as earthworms and termites. We build on soil as well as with it and in it.’
– International Soil Reference and Information Centre
Here are some of the main functions of soil:
- Food and other biomass production
- Environmental Interaction e.g. storage, filtering, and transformation
- Biological habitat and gene pool
- Source of raw materials
- Physical and cultural heritage
- Provides a platform for man-made structures e.g. buildings, highways
“The nation that destroys its soil, destroys itself” – Franklin Delano Roosevelt
What should ‘good’ soil look like?
There are different types of soil (e.g. clayey, sandy, silty etc.) so it varies slightly, but typically soil should consist of 45% mineral matter, 25% air, 25% water, and 5% organic matter. Air is vital as it allows free draining of rainwater whilst enabling earthworms to move through the soil. If water cannot move through the soil this results in compaction and loss of biological matter.
Sand has large particles, which means bigger pores – this allows water to drain more freely, but it also means that nutrients may leave more readily. On the opposite end, clayey soil has very small particles so it isn’t as free-draining and easy to handle than sandy soil, but it retains its nutrients more so may be more fertile.
Essentially, how good your soil is depends on which type of soil you have, but if it crumbles into ‘breadcrumbs’ and has plenty of pores then that’s likely to be good. Earthworm presence is also a great indicator of soil health.
Signs of ‘bad’ soil
These are just a few of the signs I have learnt about thus far – I’m sure there are others depending on the soil type, but here are some key signs to look out for:
- Standing water – if you see water standing in the fields, this may mean that the soil isn’t draining properly
- Surface capping – if there is a ‘crust’ on the first 0-5mm of topsoil, this may be preventing water from flowing through the profile. This tends to occur in light/silty soils
- Subsurface compaction – If you dig a hole with a spade and you see that there aren’t many pores in the section around 20cm deep, your soil may be compacted. It may break into angular pieces rather than flaking into round ‘breadcrumbs’
Most farmers carry out soil tests at some point or speak to their agronomists – if you’d like to learn more, it may also be worth getting in touch with your local FWAG/CFE/CSF advisor and they’ll either be able to help or point you in the right direction.
Causes of soil erosion
Here are just a few farming practices that may lead to increased risk of soil erosion:
- Over-usage of heavy machinery
- Late sown winter cereals (leading to poor cover over winter)
- Keeping pigs outdoors over winter
- Planting crops at the wrong time of year
- Tilling too often
- Lack of vegetation
What can farmers do?
The most important thing is that farmers match their land use with land capability – Jo Oborn, FWAG
Maize, a valuable feed crop for dairy farmers, seems to be particularly problematic at the moment. This is because it often seems to be grown on soils that aren’t suitable which leads to extreme run-off events.
There is also a lot of talk about using minimum/no tillage, however, Jo Oborn of FWAG suggested that in particularly degraded soils farmers may need to get the soils functioning again before they begin minimum tilling. Cover crops are also a very useful way to provide all-year round cover for soil, however, again, this may not be appropriate for every farm.
Surface capping can be prevented by drilling earlier in the year, using cover crops, using coarser seed beds or having a primary cultivation. Subsurface compaction can be prevented by rotating crops, planting early varieties, sub-soiling, or ploughing. However, it is vital that every farm uses the method(s) that are appropriate for their individual farms.
Essentially, every farm is different; in fact, every field seems to be different, so there isn’t a ‘one size fits all’ solution.
Anyway, this has been a very brief whistle-stop blog post containing a few of the issues our soils are facing; please read some of the links below if you’re keen to learn more!
Please note: I am by no means claiming to know much about soil myself in this post as it’s a massively complex subject; I’m just sharing what I’ve learnt so far. I’d love to continue learning about soils, so please get in touch if you have anything to add!
Thanks to Campaign for the Farmed Environment (Mark Smith), FWAG South-West (Jo Oborn), and Catchment Sensitive Farming (Lucy James) for holding the event which has inspired me to write this post.