Padraig Shevlin is regional manager with the Glenside Group, which is based in Britain but has been working with Irish farmers for 18 years.

Padraig explained what he believes all farmers should be aware of before they start taking autumn soil samples. He said there is no point taking soil samples shortly after spreading slurry. Usually when a farmer identifies a paddock as poor-performing, it is because performance is not up to scratch and the field is not growing enough grass. Padraig believes that before you call in the machinery contractors, you should walk the field with a spade in your hand and assess the soil you are working with. He says you should be looking at the three fundamental properties of soil – physical, biological and chemical. All three are linked to soil productivity.

Physical

The physical properties focus on soil structure. Padraig said: “When sinking a sharp spade into the ground you should not have to apply excess force. If you do have to apply a good deal of force, it is a sign of compaction. Of course it will be harder to sink the spade in very dry weather but it should not feel like concrete. Compacted soil will be structureless and clay particles will be clumped together in a tight mass.

“Compacted soil will feel very heavy compared to well-structured soil because it is so compact and has little or no air present. There is very little plant root presence in this soil. This type of soil will suffer from drought in the summer because there is no pore space to hold water and air. It will be more likely to get poached in the winter time because water will be slow to drain down and just sit on top. Cracking of the soil during the summertime is an indicator of compaction as well as iron residues in the soil. Compacted soils are much slower to heat up in early spring, leading to slower grass growth.”

Biological

Padraig believes soil should be full of living organisms that continually enhance its structure. He said: “When you turn over a sod of earth the first thing you should see are earthworms. If you don’t come across any, you may have a problem. Earthworms eat their way through soil and mix the material with mucus in their guts. This helps to improve soil crumb structure. They help to introduce more air into the soil and mix soil throughout the different horizons. The Earthworm’s body waste adds to soil fertility. If soil is compacted, earthworms will find it far more difficult to travel through it and do their job.”

Chemical

Padraig then explained how to assess the chemical properties of a soil: “When assessing the chemical properties of soil, you are looking at its ability to hold and exchange nutrients. Clay and humus particles are negatively charged anions, or in other words they repel each other. Calcium, magnesium, potassium and sodium are all positively charged cations and are attracted to the negatively charged clay and humus particles. Because of this attraction the cations stick on to the clay and humus particles and are readily available for plant up take.”

The Cation Exchange Capacity (CEC) is a measure of how well a soil can hold and exchange plant nutrient cations. The CEC can be linked with soil fertility because if the soil is strong at holding positively charged nutrients, they won’t be easily leached. Sandy soils tend to have a low CEC, whereas clay soils and soils with a high organic content have a high CEC. In order to have soils with a good CEC, you need an adequate amount of clay, particles, organic matter and pH. CEC does not measure fertility. It measures the ground’s ability to hold nutrients. Light soils are easier to balance, but you need to work hard to keep them balanced. Once heavy soils are balanced, it is easier to keep them balanced.

Correcting your soil

The pH is a measure of how acidic or alkaline a substance is. Padraig claims that a high pH soil is not necessarily high in calcium. He feels that the pH measure itself will not give you a sufficient guide to calcium status.

Glenside’s Albrecht soil survey looks at the cations (calcium, magnesium, potassium and sodium) that are deficient in the soil and gives detailed advice on how to correct each deficiency to arrive at the desired base solution. Padraig says that in most cases there is an abundance of phosphorus already tied up in the soil that could be used but is not available for plant growth.

He advises that if farmers work on achieving a balanced biological active soil with the correct quantities of calcium, magnesium, sulphur, and potassium, then combined with a pH of 6.8 this phosphorus will become more readily available for plant growth.

Recommendations

Padraig says every field in Ireland he evaluates is different and requires different recommendations.

Variations to the cost of fixing an issue can range generally from €35-€100 per acre, but this can vary hugely. Calcium is needed for plant growth, cell division and elongation. Padraig said: “If calcium levels are very low, you should apply high-calcium calcareous lime. Farmers should be aware of the type of lime that they are being supplied with. Magnesium is required for energy transfer reactions in the plant and is an essential constituent of chlorophyll.”

Padraig says when magnesium levels are low you should apply products like Kieserite or Patentkali. These are mixes that contain magnesium, sulphur and potash.

Sulphur forms part of some essential amino acids, the building blocks of protein. Low levels of sulphur in the soil can effect plant growth by decreasing the efficiency of nitrogen utilisation as sulphur is active in the conversion of inorganic forms of nitrogen into usable forms of N. Caution should, however, be displayed in using high levels of sulphur on low pH soils.

Because sulphur is an acidic product, it can reduce this pH further.