Lime - an old but gold technology
Although one of the older technologies available, the correction of soil pH through the application of lime to acidic soils still remains a practical nutrient management solution and is the foundation for addressing soil fertility challenges on Irish farms.
That’s according to Dr. Patrick Forrestal, Senior Research Officer at Teagasc Johnstown Castle, who delved into the benefits of liming at the Teagasc National Beef Conference on November 19.
Pointing to the importance of taking soil samples and making use of the results, particularly in regard to soil pH, Dr. Forrestal said: “For mineral soils of productive grassland, the target is to be in a 6.3-6.5 pH range and clover will particularly benefit from the higher soil pH levels.
“If there is known issues around high molybdenum then we don’t recommend going above pH 6.2 and for peat soils – soils with an organic matter content greater than 20% - the target is a pH of 5.5.”
Liming benefits
By bringing soil pH to the optimum, Dr Forrestal explained, many benefits will ensue, including an increased availability of phosphorus and nitrogen, a heightened capacity to support legume crops such as clover, and emissions reductions from applied fertiliser nitrogen can occur.
Presenting data from a trial conducted in Teagasc Johnstown Castle, Dr Forrestal illustrated how increasing the pH of acidic mineral soils has the potential to unlock the soil’s phosphorus (P) reserve.
“Soils in Ireland, even within the first 10cm, can have several hundred kilograms of total phosphorus. However, the vast majority of that phosphorus is unavailable to the plant, but there are things we can do to help make that phosphorus we already have more plant available.”
One of these things is correcting soil pH through the application of lime to acidic soils, with Dr Forrestal adding: “As we increase the soil pH, plant available phosphorus levels increase, particularly when we go above pH 6. If you can unlock that P with lime, it’s a good spend and gives the potential to save on phosphorus fertiliser and to keep any new phosphorus fertiliser plant available for longer. It is not uncommon for liming to increase the availability of P by one index.”
Figure 1: Liming acidic mineral soils increases soil phosphorus (P) availability
Clover establishment and greenhouse gas emissions
Volatile fertiliser markets and a requirement to reduce chemical nitrogen usage on farms has seen more and more farmers opt to include white clover within grassland swards.
To avail of the clover’s benefits, namely biological nitrogen fixation, it must be maintained within the sward and it was on this point where Dr. Forrestal highlighted the importance of soil pH.
“Soil pH has an important influence,” he added, before providing details of another research trial from Teagasc Johnstown Castle which examined the relationship between soil pH and dry matter (DM) yields of grass-white clover swards grown in plots of various soil pH (5.5 to 6.8) levels. In summary, and as presented in figure 2 below, this study showed that as soil pH increased, so did the quantity of grass-white clover yield produced.
Offering tips to farmers trying to increase the proportion of clover present within their swards or to establish new reseeds, Dr Forrestal said: “Many swards will already have some clover in them, you can give them a boost using lime. If you are going to establish new reseeds, most of which have some clover seed within, lift the soil pH first. That’s a key first step, try and get the pH up initially.”
Figure 2: Effect of pH on yield of a direct drilled grass clover sward (150kg N/ha)
In addition to benefits in terms of phosphorus release and its role in supporting clover establishment, Dr. Forrestal also touched on research from Teagasc Johnstown Castle which has examined the emissions saving from increasing soil pH.
On this significant piece of work, he said: “New research from Johnstown Castle has also shown that as the soil pH was increased, the amount of nitrous oxide emissions coming from a fertilised soil decline. Correcting soil pH can also help reduce greenhouse gas emissions from soil.”
If you were unable to attend the Teagasc National Beef Conference and would like to see Dr. Patrick Forrestal’s full presentation, a recording is available to view below:
Alternatively, Dr. Forrestal’s full paper from the Teagasc National Beef Conference is available to read here