Lime is a vital nutrient and must be applied where required if farm productivity is to be maintained. Where the soil pH drops in either grassland or tillage crops it will result in poor utilisation of applied fertilisers and organic manures.
Phosphorus is the most expensive nutrient and its availability is very sensitive to low soil pH. In grassland it will result in poor recycling of soil mineral nitrogen (N) and poor survival of productive perennial ryegrass and clover swards. In cereal crops the most sensitive crop to low soil pH is barley followed by wheat.
Liming soils has many indirect beneficial effects such as soil structure. For example, liming an acid soil increases the population of bacteria, fungi and earthworms, which are responsible for the breakdown of soil organic matter. The decomposition of soil organic matter will assist in soil crumb formation and improve the environment for plant root development and nutrient uptake. It is widely recognised that liming heavy soils improves soil structure and reduces stickiness, lightens cultivations and makes it easier to prepare a satisfactory seedbed.
Lime is continually being lost from the soil and needs to be maintained as part of a nutrient management programme. For example, drainage water can remove approximately 250-625kg/ha/yr depending on the soil type. Light, free-draining soils will lose lime more quickly than heavy retentive soils. Therefore, light land needs extra attention, especially where the soil is not a limestone soil. Crops and livestock also remove lime. For example, a crop of first-cut silage can remove approximately 190kg/ha/yr.
The application of lime has declined from over 1.5m tonnes per year in the 1970s and early 1980s to around 0.5-0.8m tonnes in the past decade. In order to reduce soil acidity and maintain adequate lime status we should be applying in the region of 1.5m tonnes annually.
That means that we are only applying between 30pc to 50pc of our annual requirement, which is needed to maintain an adequate soil pH level throughout Ireland.
Farmer soil samples tested through Teagasc reflect this reduction in lime usage as 60pc of grassland soils are below a soil pH 6.0 and 40pc of tillage soils are below a soil pH 6.5. Lime is being forgotten about on Irish farms and the postponement of lime applications will only build up future soil problems and add to the costs of production.
Maintaining the correct soil pH will increase the microbiological activity of the soil and will result in a whole series of responses.
1.Applied fertilisers will give a better response on soils maintained at the correct soil pH. Where two bags of 0:10:20 are applied on well-limed soils, it will give the same return as three bags spread on land needing lime;
2.The more productive and high yielding perennial rye grasses will thrive resulting in maximum sward productivity;
3.When lime is applied to land with a low soil pH the equivalent of two bags of 27pc N will be released each year for several years. This is due to the beneficial effects of liming on soil life (eg, bacteria, earthworms etc) and better nutrient recycling from soil sources.
Soil Analysis & Liming
Routine soil sampling should be carried out once every three to five years to check soil pH and apply lime where required. Soil laboratory analysis will tell us exactly the amount of lime to apply and is the most reliable method to determine the lime for your particular soil type.
Lime and Fertilisers
Generally when a crop is performing poorly it is attributed to a shortage of one of the major nutrients, such as nitrogen (N), phosphorus (P), potassium (K) or magnesium (Mg). Lime can be overlooked, yet its effect on the efficient use of both minor and major nutrients is enormous because of its effect on soil pH.
Fertilisers are now a significant proportion of production costs and we must look at the soil pH in order to maximise the return from every kilogramme of applied N, P and K. For maximum return from applied nutrients it's essential to maintain soil pH within the optimum range pH 6.5-7.0 for tillage crops and pH 6.3-6.5 for grassland soils.
Timing of Lime application
Ground limestone can be applied at any convenient time of the year. For lime-sensitive crops such as beet, cereals and maize, apply lime two years before sowing. If lime has not been applied it should be spread after spring ploughing so that it can react with the soil and be thoroughly mixed with soils during spring cultivations.
In grassland, apply lime and keep grazing animals off the grass until the lime is well washed in.
In silage land, apply before mid-March for first cut or within one week after cutting on land being closed for a second cut.
Liming and slurry applications
Applying slurry on recently limed soils should be avoided as it will result in a loss of nitrogen through accelerated ammonia volatilisation. Where lime is applied, slurry should not be applied until the lime is well washed into the soil. The same holds true for lime and urea applications – avoid spreading urea on recently limed soils to reduce the loss of N.
Liming and Grass Reseeding
Lime is an essential for good grass production and is a basic requirement during grass seedling establishment. In addition, sufficient lime levels are required to maintain good grasses and clovers growing in the sward. Grass reseeding offers a good opportunity to correct acid soils. Identify fields that are to be reseeded in the current year and apply lime in advance of reseeding. This will give plenty of time for the lime to be washed in and will also assist with the breakdown of the turned-in sod.
Where lime recommendations are greater than 7.5t/ha, half of the lime should be applied now and the remainder applied at reseeding time. Early lime application will help insure against poor grass establishment and yield.
Cost of Lime
Lime costs in the region of €22/t (delivered and spread). Based on this price lime only costs €8-10/ac/yr to maintain the soil's pH status once it has been brought to satisfactory level. It's a small annual cost to incur.