Organic Matter (OM) is a key component that influences soil structure and workability, crop germination, nutrition and yield, writes Nick Everitt of Ely, Cambs-based Everitt Contractors.
Organic matter is the engine that drives all major functions. It does this partly by feeding earthworms fungi and other organisms that make a better environment for crop roots to explore the soil for water and nutrients. 1cm³ of soil can contain up to 30m of fine fungus threads. A good earthworm population can produce up to 30t/ha of digested humus and nutrient-rich earth, and up to 150 air/drainage holes/m² down to a depth of 2m.
Manure needs to be well rotted or, better still, composted. This can easily be achieved on the farm by turning, and increasing the temperature up to as high as 70°C. By doing so, it will kill weed seeds and pathogens making the product more readily available to the soil and young plants.
By using FYM, trials have shown an increase in yields in all crops that could not be achieved by fertilisers alone. Adding regular amounts of FYM increases yields in cereals by 0.5–1.75t/ha and potatoes by 5t/ha+. Benefits can be greatest with spring crops often when rooting environment is challenging. FYM
consistently increases yields the most but compost and anaerobic digestion (AD) are almost as effective. Diseases are suppressed and dry matter improved, hence making fertilisers and nutrients more readily accessible to growing plants. Water holding capacity is improved as is drainage/infiltration. Soil holds water without feeling wet as OM can hold six to seven times its own weight in water. 1 per cent of OM in the soil equals 230,000-litres/ha of water holding capacity.
OM also helps to prevent capping, slumping, compaction and erosion. It stabilises sands and silt based soils and makes clay more ‘loamy’.
Close to surface
High levels of OM mean a greater flexibility and also a buffer against mismanagement. Maintaining a high concentration of OM close to the surface and avoiding deep incorporation will have the most influence. Ploughing should be avoided as this burns off high amounts of existing OM, buries FYM where it can’t work (due to lack of oxygen), and will dilute the amount applied resulting on the OM having little effect on the soil structure.
Protection of the soil surface is a key factor as it is the surface that bears the impact of rain. In a heavy storm raindrops may have a velocity of 9m/sec and the impact pressure of such raindrops at the soil surface can be as much as 900psi, forcing the oxygen out of the soil. Although leaving OM/debris on the surface may not look as pretty as your neighbour’s ploughed field, yours will be protected. In addition, every time you cultivate the soil you release around 30 per cent carbon, depleting OM and destroying worms, roots and their drainage channels. Research has shown a 50 per cent increase in humus in soil that hasn’t been cultivated for 7–8 years (ie direct drilled).
OM can save diesel and time by reduced tillage and draft and less irrigation. Even a small amount of OM reduces draft, lowers fuel consumption and provides longer working windows, especially in challenging seasons. It provides a large store for nutrients and helps reduce their leaching.
Regular monitoring of OM should be considered as important as checking for pH status and P&K – the contents of OM and the many benefits it provides, far out way the nutrient value.
|OM content/Water Holding Capacity||Value of nutrients/t|
|Cattle FYM||6–8||3–4||8–9||2.5–3||1.8–2||Moderate to high||£10+|
|Duck FYM||10–15||8–9||15–16||4–5||3–4||Moderate to high||£25– £30|
|Horse stable waste/ Compost||7 – 8||5 – 6||6 – 7||High||£10+|
|Pig FYM||7–8||6–7||8–9||3–4||1.8–2||Moderate to high||£10–£12|
|Broiler/turkey litter||30+||25+||18+||8||4 – 5||Low||£30+|
|Green waste/compost||7.5||3–4||5–6||2–3||3–4||Very high||£9|
|· N is slowly released (25 per cent in spring, summer, autumn and winter = 100 per cent) depending on temperature and moisture (compared with 40–50 per cent in granular fertiliser)|
· 60 per cent of P and 90 per cent of K is available to the next crop in the first year of application (compared with 4–10 per cent of P and 40 per cent of K in granular fertiliser)