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The importance of Lime

Posted on 23 March 2016

Why should lime be applied?

Soil is an essential raw material from which most food is produced. Having soil in good condition is vital for efficient and productive growth of grass and crops. Correcting the pH of the soil by applying lime is a simple and effective way to increase grassland productivity as acidity in soil reduces nutrient availability. Having soil too alkaline can also adversely affect crop production. It is therefore vital to regularly monitor the chemical and physical properties of the soil and correct any imbalances.

Why test soil pH level?

As a result of adding fertiliser to land and leaching by rainwater, the top layers of the soil may become acidic over time. To ensure that the correct amount of lime is added to the soil to correct soil pH it is important to test the soil and calculate levels appropriately.

When is the best time to test soil?

The best time to test soil is between October and March. Do not sample within 9-12 months of liming or within three months of a slurry, farmyard manure or artificial fertiliser application.

How should a soil sample be taken?

Twist a sampling auger / soil corer down to 7.5 cm for grassland and 15cm for arable crops. Take multiple cores, 25 recommended, in a W pattern across the field avoiding gateways and feeding areas. Seal bags, label them clearly with your name, field name, Farm Survey Number and field number and send to laboratory. Samples should be taken on a regular basis every 4-5 years. If fields are very large, a separate sample should be taken for every 4ha (10 acres). A lime requirement will usually be included as part of the results. It should be noted that the lime requirement ONLY refers to year 1.

What is an ideal soil pH?

The optimum pH for grass growth in mineral soils is in the range 6 - 6.5. For vegetable growth and for some cereal crops the pH may need to be slightly higher. However, optimum pH for peaty soils will be in the range 5.3-5.8.

How should lime be applied?

Whenever possible, tillage should be used as a tool to incorporate lime into the soil. The better lime is worked into the soil, the larger the surface area exposed to it meaning there is a more rapid reaction between soil and lime. However, in the case of permanent grassland, a surface application of lime is the only suitable method.

How long will it take the lime to react?

Lime should be applied to the seed bed, correcting the pH for the next growing season. Soil pH may begin to change within a few weeks. If arable crops are sown using minimal cultivation techniques, lime should be applied as early as possible as reaction time will be slower. Lime can be applied to established grassland in autumn or early spring and may take 9-12 months to take effect.

Granular lime will react much more quickly than loose agricultural lime. Up to 30% of basic ground limestone reacts in year 1 with the corresponding value for granulated lime being 95%.

Dr Norman Weatherup 
Grassland & Organic Technologist

Click for more information on G-Lime granulated lime.