Soil health is becoming a regular discussion point for farmers and advisors, but what does it really mean? Personally, I like the US Dept of Agriculture definition, which states that it is “the continued capacity of soil to function as a vital living ecosystem that sustains plants, animals and humans”. That definition clearly relates to the fact that only living things can have “health” and looking at soil in that way should give us a new perspective on how and why we should care for it. It is becoming increasingly clear that our relative neglect of the soil biology has impacted on the chemical and physical properties too.
Properties that determine soil health include both fundamental and dynamic factors or qualities. Some factors are derived from a soil’s basic characteristics, whilst others are strongly influenced by the management over time. For example, a sandy soil will naturally drain faster than a clay soil and it will have a lower nutrient holding capacity (CEC). These characteristics are not easily changed by management, but one focus for soil health research must be to use appropriate techniques on different soil types that improve the soils function.
The principles of Regenerative Agriculture are very closely aligned with improving soil health and practitioners often move away from synthetic inputs much faster than they anticipated. It is not a simple solution and it will take some time to get a degraded soil back into good health, but the benefits are being seen across the globe on both arable and livestock farms. The basic principles of Regenerative Agriculture are:
As I sit here and write this at the beginning of January 2020, the last few months have been extremely challenging on farms across the country. Winter rainfall totals are well up on typical levels and the land is struggling to cope in many areas. At a recent farmer meeting in the Midlands, of the 30+ farmers in the room there was not a single hectare of Winter Wheat planted and those that had OSR in the ground were very worried about that too.
- Living roots in the soil for as much of the year as possible – these roots are feeding the soil biology with their exudates, facilitating the building of soil aggregates and releasing previously unavailable nutrients
- Cover soil at all times with living plants or crop residue – mimic nature and protect the soil surface from the impact of the weather (sun, wind and rain)
- Minimise or eradicate soil disturbance – reduce or replace tillage by using direct drilling or broadcasting cover crops
- Increase diversity in your rotation – grow a wider range of cash and cover crops that affect soil resources in different ways
- Incorporate grazing animals back into the rotation where possible – the impact of grazing animals on the biological processes should not be underestimated.
When the biology present in the soil is affected by sudden changes to the ecosystem (by cultivations or the effects of a fungicide/pesticide/fertiliser), the overall soil health could be affected. When these practices are the norm, the soil becomes dependent upon the artificial amendments and the biological processes are continually impaired. By adopting a more biologically sensitive approach, many natural systems can be repaired and these will perform many of the functions more efficiently than mechanical or chemical intervention.
The simple fact that a healthy soil produces better crops also leads to an expectation that inputs can be reduced over time, with many growers choosing to cut out some inputs altogether, particularly insecticides. Organisms under stress (plants and animals) will succumb to disease and pest pressure far more quickly than robust, healthy specimens. Healthy soils will slow down the rate at which stresses such as drought, waterlogging, heat and nutrient deficiency will affect growing crops, so the need for intervention/ expenditure will be reduced.
Reducing the level of chemical inputs going onto and into the soil is likely to speed up the rate of improvement in soil health, as products such as fungicides, pesticides and even fertilisers can often be detrimental. A healthy soil should have a good balance of bacterial and fungal activity, but modern farming techniques seem to favour bacteria at the expense of fungi. A key part of a healthy soil is the Arbuscular Mychorrizal Fungi (AMF) network that forms symbiotic relationships with the roots of most plants. These crops have a mutually beneficial trade of photosynthetic carbon to the AMF in exchange for nutrients e.g. P and N. It is important to recognise that AMF cannot complete their life-cycle without a host plant, which is another reason to increase diversity in both your rotation and in cover crop mixes. Obviously, cultivation is unhelpful for AMF, but several trials have shown that no-till farming alone is a poor replacement for no-till and keeping active roots in the soil via cover crops. The soil cover and active roots feed the biology, which then combine to provide many of the services for which steel and horsepower have been relied upon.
A classic example of how biology can affect the function of a soil is in water management. It is the AMF hyphae that excrete the long carbon chain glycoprotein, glomalin, which both facilitates soil aggregation and increases carbon storage within the soil. These aggregates will combine to produce a mix of large and small spaces in the soil (Macro and Micro-pores) that regulate the passage of water. Micro-pores hold water in the soil through adhesion to the surface of the particles, whereas macro-pores allow water to pass through the soil profile, leaving room for air/ oxygen. It is essential for a healthy soil to have a mixture of pore sizes so that it is able to hold water, but it can also regulate the amount and not become waterlogged and anaerobic. These pore spaces also allow room for roots and fungal hyphae to have good access to the widest possible area.
Another useful benefactor of these pore spaces will be Earthworms, one of the most visible of the countless organisms that will be living in healthy soils. They are a useful measuring tool for the improvement as they can be counted very easily and, in simple terms, an increase in worm numbers equals better soil health. It is worth doing a little bit of worm research as there are a number of different types and a useful website is The Earthworm Society of Great Britain (www.earthwormsoc.org.uk). Earthworms play a huge role in the build up of soil organic matter as some species pull down soil residue from the surface, deep into the soil profile where it gets processed further by a number of organisms.
Be under no illusion that managing soil health is easy but there are farmers rewriting the rule book on what can be achieved and the benefits that can be delivered. A simple acceptance that a “Healthy Soil” is a living thing will go a long way to setting us off on a better path.
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