Lewis Grassland Trials
The deep peat soils on the west coast of the Isle of Lewis offer a unique challenge for grass growth. Unlike most mineral soils these organic peat soils have little or no structure. In wet weather conditions they become quickly saturated, whereas during periods of drying weather they become solid in nature. Moreover their acidity and low nutrient availability add to the challenge of growing a respectable grass crop.
A considerable amount of research was carried out during the 1920s and 1930s at the Macaulay Demonstration Farm just outside Stornoway to increase productivity for dairy on such peat soils. The vital importance of liming, using shell sand, was noted. However, it was also observed that although perennial ryegrass was present in the sown grass, it was not thriving.
There is currently a grassland trial ongoing, funded by The Lewis Endowment Fund, at mid-Borve on the west coast of Lewis which is aimed at testing less conventional grasses and clover species for the establishment of a grass sward on a peat soil. Timothy and Reed Canary Grass are both tolerant of wet conditions and these are being compared with the more conventional Perennial ryegrass. The following videos show how the trial has developed and results noted.
The present trial at mid-Borve on the west coast of Lewis is aimed at testing less conventional grasses and clover species for the establishment of a grass sward on a peat soil. Timothy and Reed Canary Grass are both tolerant of wet conditions and these are being compared with the more conventional Perennial ryegrass.
Before establishment of any crop, including grass, it is essential to assess the state of the soil, particularly with regard to compaction. The texture of the soil ie the amounts of sand silt and clay mineral matter can be assessed by hand although more accurately by laboratory test. The soil structure, and resistance to compaction, will be dependent on the interaction of these mineral components with the soil organic matter. If you want to learn more about this then this Technical note from SRUC may be useful: (TN656): Soil Information, Texture & Liming Recommendations
On peat the organic component dominates the soil and so drainage and aeration are primarily dependent on the density of the peat material. As is the case with all soils they should not be worked when in a wet condition as this will lead to severe compaction.
Peat soils are normally acidic. However crop growth is not affected by the acidity to the same degree as in more mineral-dominated soils. Where on a mineral soil the pH should not be allowed to drop below 5.8 the equivalent threshold for a peat soil is pH 5.1.
Peat soils are comprised primarily of organic matter which is derived from partially decomposed plant material. The organic material accumulates due to the wet, cold and acidic conditions. It has been realised that, on an international level, such peat accumulations are important in that they have immobilised huge amounts of atmospheric carbon. Severe physical disruption of these peat soils could lead to their degradations and resultant release of carbon dioxide to the atmosphere. However, the establishment of long term grass crops is likely lead to further carbon accumulation due to the organic matter in the grass root system.
A number of materials can be used for liming, the most common being ground limestone. However, other materials such as shell sand are used for liming on the Western Isles. The ability of a liming material to counteract soil acidity is determined by their neutralising value. The speed at which they work is normally dependent on the particle size of the material; a fine powder liming product will work more quickly in raising soil pH than a larger, granular material.
Most agricultural liming products, including shell sand, are based on calcium or magnesium carbonate compounds. It is worth noting that it is carbonate that neutralises the soil acidity; calcium sulphate or magnesium sulphate have virtually no effect on soil acidity.
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