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The value of lime

February 18, 2022

Our farm inputs are becoming increasingly expensive and need careful consideration. The use of Lime is one such input, however the application of lime to increase soil pH will increase the availability of expensive Nitrogen and other nutrients and so this year more than ever represents an excellent investment.

Soil Testing:

As a first step check the nutrient status of your soil. This should be done once every four years.

Take a good representative soil sample from across the field using a soil auger. Do this during the winter months to avoid recently sown fertiliser or organic manure which will give high false readings. Sample to a depth of 7.5-10mm (3-4”) for grass crops and 15cm (6”) for cereal crops. Samples must be sent off to a laboratory for analysis and this can be arranged through a DAERA Direct office or a local fertiliser or seed merchant. 

The analysis report which you receive will tell you what the pH, phosphate, potash and magnesium status is in the soil sample and how much lime, phosphate and or potash is required to correct an imbalance and grow the next crop.

Soil pH and Lime:

Soil pH is a measure of soil acidity and this has a major impact on plant growth. It should be taken as a priority to correct the pH.

Plants favour growing in soils with particular pH ranges. The optimum soil pH for grassland production in mineral soils is just over 6.0. The optimum soil pH for cereal crops growing in mineral soils is 6.5-7.0.

Nutrients are more readily available to plants growing in soils with an optimal pH. Earthworms and microorganisms live in the soil breaking down dead plant material and organic manures and as a consequence release nutrients for plant growth. They don’t work well if there is a low soil pH.  

Applying lime will increase the soil pH. An application of 5 tonnes of bulk ground limestone per hectare, costing £130/170, should bring a non-productive low pH soil back into full productivity and provide an excellent return on the investment for 5-10 years.

Fergal Watson at Cloughey on the Ard’s Peninsula tests his soils regularly and applies lime to keep his average soil pH above 6.0. Fergal says “it’s important for me to keep the pH of my soil above 6 as I grow a range of crops including barley, beet, beans, wheat and grass. I don’t allow the pH of my soil to fall below 6.0 as it will result in poor crop growth and yield.”

Ground Limestone takes up to six months to noticeably raise the soil pH and affect crop growth. It works best if worked into the bare soil when a new crop or grass reseed is being sown but will also be effective if spread directly onto an established grass sward. The fineness and neutralising value of the product determine the speed of action.  Granular limestone which is very finely ground has a role to play during the growing season as it works quickly and can be spread on crops and grass by the farmer using a conventional fertiliser spreader.                                          

Lime should not be spread within three months of spreading manure or urea fertiliser because a chemical reaction occurs with the lime and some of its neutralising ability is lost. Nitrogen fertiliser however can be sown three weeks after liming in the springtime.  

Contact your local CAFRE Development Adviser based in a DAERA Direct office to discuss issues regarding your soil nutrient status.