Liming to improve soil health and nutrient availability

Date published: 25 September 2024

Now is a good time for farmers to consider applying lime to productive grass and arable fields on their farms. With high periods of rainfall and consistent wet weather, water passes through the soil which can leach essential nutrients such as calcium, causing soils to become more acidic and less productive.

The College of Agriculture, Food and Rural Enterprise’s (CAFRE’s) arable ground is tested annually. Grassland fields tested every three years to assess pH, identify any deficiencies and target lime, phosphorous and potassium applications to meet optimum crop requirements.

This autumn, where conditions allow, the farm will apply bulk ground limestone based on recommendations from the most recent soil analysis report with a target of pH 6.2 for mineral grasslands (or pH 5.5 for peat soils).

Arable fields on the farm are targeted towards a pH of 6.5 for mineral soils (or pH 5.8 peat soils). The target pH is 0.2 units above the optimum pH to allow for inconsistencies across a field.

The Hill Farm Centre at Glenwherry has land which is designated or classified as Species Rich Grassland. Lime is never applied to these fields as it will reduce the species composition from a biodiversity perspective and release Carbon to the atmosphere.

Lime contains calcium carbonate which when applied will raise soil pH and improve soil health. This increase in soil pH will ensure better use of nutrients - improving grass and crop productivity. Lime is also a soil conditioner which improves soil structure and neutralises the acids generated from the mineralisation of nitrogen fertilisers.

However, soils which are classified as peat with a very high organic matter do not have the same requirement for liming as over applying lime to peat soils can release carbon to the atmosphere, increasing greenhouse gas emissions and reducing diversity in species rich grasslands.

Farmers who have taken part in the Soil Nutrient Health Scheme (SNHS) in Zones 1 and 2 will have received their soil analysis reports and will be ready to act on the recommendations for lime this year.

While participation in the SNHS is now a conditionality of receiving future farm support, the information you receive from the scheme will allow you to correct deficiencies, cost-effectively apply nutrients in line with what your crop requires and improve farm productivity, economics and soil health.

Further help on how to interpret your soil analysis and how to make best use of the results can be found in the SNHS training, which is available on the CAFRE website.

Your soil analysis report will recommend the amount of lime each field requires to achieve optimum pH. Points to bear in mind are:

1. Prepare a farm liming plan based on your soil analysis report. If the recommendation is more than 2t/acre of lime to be applied, apply half now and half again next year or in two years’ time.
2. Target fields with the greatest requirement first (the most acidic).
3. Lime can be applied at re-seeding or cultivation, incorporating it into the seedbed or on the surface of existing grass swards.
4. Lime can be applied at any time during the year but ideally at the end of the year as applying slurry after liming can lead to a loss in nitrogen.
5. Bulk calcium ground limestone is a persistent material which reacts longer over time due to the larger particle sizes whereas granulated (prilled) lime products (less than 0.1mm particle size) are more reactive and can be applied with a fertilizer spreader. At low pH levels a bulk application is often needed to raise pH to the optimum. At higher pH levels annual applications of granular products can be beneficial as a way of maintaining pH levels at closer to optimum.

If you have not obtained a soil analysis report inside the last four years aim to soil test your fields this winter and at least three months after your last slurry or fertiliser application.

For soil samples outside of the SNHS, bags and augers can be requested and collected through your local DAERA Direct office by phoning 0300 200 7850. You can then post off your soil samples and pay NRM directly by debit or credit card.