Why apply lime?

The application of lime is one of the oldest and most important methods of improving a soil and dates back hundreds of years. Without lime the land will neither respond to fertiliser nor produce the quantity or quality otherwise achieved where lime is applied regularly. Table 1 shows the optimum pH for the more common crops sown in Ireland.

Table 1 – Optimum soil pH for Crops

Crop Optimum pH
Potatoes 5.5 – 6.5
Permanent Pasture 5.5 – 6.5
Oats 5.5 – 7.0
Rye-grass mixture 5.5 – 7.0
Oilseed Rape 6.0 – 7.5
Wheat and Maize 6.0 – 7.5
Peas and Beans 6.0 – 7.5
Barley 6.5 – 7.5
Field Vegetables 6.5 – 7.5
Field Brassica 6.5 – 7.5
Beet 6.5 – 8.0

When sowing a crop it is essential to have the correct pH in the soil for optimum growth and profit. It is commonly accepted that most crops prefer a slightly acidic to neutral soil (6.0 – 7.0) and it is at these pH’s that soil nutrients are most available to the crop. Table 2 shows the effects of soil pH on the availability of N, P and K to a growing crop.

Table 2 Effect of soil pH on the availability (%) of N, P and K

pH 4.5 pH 5.0 pH 5.5 pH 6.0 pH 7.0
Nitrogen (N) 30% 43% 77% 89% 100%
Phosphorus (P) 23% 31% 48% 52% 100%
Potassium (K) 33% 52% 77% 100% 100%

Teagasc studies have shown that in a wheat crop, where soil pH is raised by 1.0 (i.e. 5.5 to 6.5) a yield increase of 2t/ha was achieved.

Using lime improves the “life” of the soil. Farmyard manure contains valuable plant foods which, when rotted, become available to the growing crop as nutrients. Using lime increases the rate at which these nutrients are broken down and made available for plant uptake.

Application of lime makes tillage cultivations easier, and drainage and soil aeration better by causing small particles of soil to stick together into larger particles.

Using lime will improve the microbial activity in the soil. Earthworms are more active in a neutral (i.e. 6.0 – 7.0 pH) environment, thus improving aeration and drainage, and enabling better use of organic matter by the earthworm in the soil.

Liming also helps to overcome “Sod Pull”. This can occur in grassland when the cow pulls at the grass during grazing. After the cows leave the paddock, if the pasture has a lot of up-rooted sods around the field, sod pull has occurred. Low pH is one of the main reasons for sod pull. This happens when the roots begin to turn up and lose their hold on the soil due to poor aeration and surface acidity. Over a period of time root development deteriorates. Applying lime will help the proper branching and overall development of roots.

Gran – Lime provides a valuable source of available calcium. The calcium in Gran – Lime is 100% water soluble and available to the soil and plants. This is hugely beneficial to the soil and especially to farmers with min-till systems or vegetable crops. It also is a source of Magnesium, which can help to reduce the risk of grass tetany.

How can lime be lost in the soil?

  1. Rainfall
    Lime is lost from the land mainly through rainfall. Rain and soil water are charged with carbon dioxide (carbonic acid), which dissolves the lime contained in the soil. Some of this dissolved lime finds its way down into the soil drainage system thus being lost from the soil. Teagasc figures state that from to 100 and 250kg/acre of ground limestone per annum may be lost, depending on the rainfall, soil type and the amount of lime initially in the soil.
  2. Crops
    An average crop of hay or silage utilises 75kgs/acre of lime.
  3. Livestock
    A mature bullock utilises nearly 25kgs/acre of lime according to Teagasc trials.
  4. Fertiliser
    Continuous use of fertilisers, such as Sulphate of ammonia, and to a lesser degree, Urea, tends to use up lime in the soil.

Can over-liming be dangerous to the land?

Over use of lime can be dangerous and may create a lot of problems in the soil.

  1. Nutrient Imbalance
    Applying too much lime to the soil can lock up trace elements. When over-liming occurs the pH is lifted to a level that becomes too alkaline. This results in vital trace elements becoming locked up. Consequently, the roots don’t take up enough nutrients that ultimately may contribute to trace element deficiencies in plants and animals. Applying the correct amount of lime to achieve optimum pH with a ‘little and often’ approach is the best way to avoid this and ensure all the nutrients are made available. This is done by using Gran-Lime.
  2. Root Crops
    Over-liming can also have an adverse effect on root crops such as beet, turnips and swedes. Again, similar to grassland, the important trace elements are not made available to the root system because of over-liming and the crop may suffer from lack of plant nutrients such as B (Boron), Fe (Iron) and Mn (Manganese).
  3. High Molybdenum (Mo)
    In areas that are high in Mo (Molybdenum) it is dangerous to apply lime. There are many areas throughout Ireland that are high in Mo. Applying too much lime to high Mo soil and dramatically raising the pH makes more Mo available to the plant. As a result, this may induce copper deficiency. Land with high levels of Mo should not rise above a pH of 6.0. In such a situation with a low pH, Gran – Lime can be used as it is a very controlled way of liming, i.e. it allows you to maintain the optimum balanced pH for your soil with the ‘little and often’ approach.

Applying Lime

Before applying lime it is essential to have the soil sampled so that the lime requirement can be accurately determined. Most Irish land is lime deficient. Many of the soils are sour and acidic, and in need of occasional dressing. The most common ways of raising a soil pH are by spreading ground limestone or a granulated lime product.
In recent years the popularity of Gran-Lime has grown as an alternative to spreading ground limestone. It is a much more convenient, cleaner and accurate way of raising soil pH. Use Gran – Lime at the beginning of each growing season to maintain optimum pH of between 6 and 6.5 and therefore get full benefits from fertiliser application.
For tillage, use appropriate rate of Gran – Lime to suit the crop rotation and history of cropping. Give priority to lime-sensitive crops within the rotation such as sugar beet, peas, beans, wheat and barley.

Best results for reseeding are achieved by spreading Gran – Lime at the time of reseeding grass so that it can aid the decomposition of the previous sward, which would cause acidity. For min-till systems and for vegetable production, Gran – Lime’s ‘little and often’ approach is required because of emphasis on soil structure, aeration and available calcium.
Surface acidity (within the top 5cm) often occurs in grassland due to high rainfall and the use of nitrogenous fertiliser. This reduces the availability of fertiliser phosphorus. For this reason it is better to apply ‘little and often’ rather than one large application at irregular intervals.

Peat Soils
The optimum pH for grass growth on peat soil is not as high as it is for normal mineral soils. This is because peat soils do not contain the toxic elements that are present in clay soils.

View more information on Gran-Lime and application rates.