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Organic Matter

Rothamstead Research Station has been the base for a series of experiments over the last 150 years that have concluded that by increasing soil organic matter levels, drought stress in plants can be alleviated. It has also shown that heavy soils can be made more workable and light soils more manageable and nutrient retentive by increasing the organic matter.

It has also been observed that Nitrogen and Phosphate metabolism are more effective and that they are available to the crop more consistently throughout the growing season in soils of high Organic Matter Content. There appears to be some effect on limiting the amount of these elements lost to the crop due to leaching during the winter period. This suggests that there is significant environmental benefit from increasing organic matter content of agricultural soils, thus limiting the loss of Nitrates and Phosphates into water systems and avoiding the subsequent problems associated with eutrophication.

Anecdotal evidence suggests that increasing Organic Matter Content in soils has resulted in an increase of earthworm populations. Dr Kevin Butt from the Department of Environmental Management, University of Central Lancashire, conducted scientific research into this phenomenon in the regeneration of reclaimed land, and his results confirmed this theory. Increases in earthworm populations ultimately lead to increased conversion of soil organic matter into usable crop nutrients, thus reducing the need for highly soluble mineral fertiliser input. It also improves soil drainage and general soil health.

More recent work by Dr Nortcliff at Reading University has also shown that there is a range of beneficial effects from applications of organic matter to the soil. It has been shown that these applications cause improvements in the chelation of nutrients and also to the cationic exchange capacity of the soil, thereby improving nutrient metabolism and uptake, and reducing risks of nutrient leaching. The previously observed improvements to moisture retention, workability and nutrient uptake have been further confirmed.

Two important trace element deficiencies, namely boron and iron, occur mainly in soils of low organic matter content. The various chelates associated with soil organic matter are a major source of available iron. Boron deficiency occurs in sands and light loams, and is leached easily from these soil types following wet winters and springs.

Many sludges and effluents contain useful levels of organic matter. In many cases, this can help to supplement or replace the traditional application of Farm Yard Manure, which is no longer available as livestock numbers and management has reduced its production.

Observations on many sites across the UK suggest that since the recycling of high organic matter wastes to land programme has been operated, many of the heavier and poorly structured soils have improved very significantly. It has been noted that there has been a steady yield increase, an improvement in topsoil drainage on some fields and there has been a reduction in the power consumption required for cultivations. The effects on lighter, sandy soils has also been significant, with a noticeable increase in nutrient and water retention, and a more consistent supply of both major and minor nutrient to the crop.

Interest in the value and importance placed in the addition of organic matter to agricultural soils is in alignment with the thrust of the Soil Action Plan (Defra; May 2004), which reports that since the early 1980’s over 18% of soil organic matter has been lost from agricultural land. The maintenance of Organic Matter levels will enhance soil microbial populations, act as a buffer against surges in crop nutrient elements and reduce the effects of drought. Soil microbes are important in the metabolisation of crop nutrients, especially Nitrogen, and will assist in converting applications of Nitrogen into forms available for uptake by the crop, reducing risks of volatilisation and leaching.