Sitting here on a Friday, surrounded by colleagues taking calls from lime contractors across the UK, I thought it would be worthwhile to address the importance of correcting your pH. With the earlier harvest, land being clear and the need for some rain before OSR cultivations can really begin in many areas of the UK, there's a good opportunity for lime to be applied.

What is pH and what causes it to change over time?

Soil pH is a measure of acidity and alkalinity, which is related to the hydrogen ion concentration in the soil. Put simply, the lower the soil pH, the higher the hydrogen ion concentration. The natural pH of most arable soils in the UK varies from about pH 4 (very acidic and when most crops will fail), to pH 8.0 or just over (soils rich in calcium or magnesium carbonate). Where these carbonates are naturally low in the soil, the pH will drop and become more acidic over time.

What leads to acidification?

• The leaching of calcium and magnesium through the soil due to rainfall leaves a higher concentration of hydrogen ions attached to the clay particles

• Plant growth and root activity where cations (such as calcium, magnesium and potassium) are taken up by the crop leaves a higher concentration of hydrogen ions in the root zone

• Root exudates, such as citric acid and the production of organic acids from organic matter

• The mineralisation of organic matter and nitrification (where nitrogen is converted into nitrate)

• The application of ammonium containing fertiliser, where ammonium is converted to nitrate. 

What are the benefits of liming to the correct pH?

• Improves crop yield

• Improves availability of the major nutrients

• High rates of lime can improve soil structure

• Improves break down of organic matter by improving conditions for soil bacteria

• Improves nitrogen fixation for legumes, clover and lucerne

• Reduces the impact of acidification of ammonium fertilisers

• Control of disease, such as club root, if application timed correctly
  
  

What pH should I target? 

A pH of 6.5 is beneficial for most arable crops, with this level serving as a good 'middle-ground' for safeguarding yield, particularly when supported by timely nutrient applications. 

Maintaining a suitable pH level also protects the availability of nutrients to the plant. At a pH of between 6.5 – 7, most nutrients are readily available. Although they may not be at the most favourable levels, a suitable soil pH means that there is enough of an overlap to avoid causing deficiencies.  

If you leave pH levels in an acidic range, you risk foregoing a good yield. On the other hand, allowing your pH to sit well above 7 risks the availability of vital nutrients such as manganese and iron. Because of this, it's crucial that well-planned, detailed management is undertaken to help keep soils at optimum levels.

Managing your pH with precision lime applications

Through SOYL's nutrient mapping service, we are able to provide growers with GPS sampling, analysis and soil maps which, when combined, provide detailed soil nutrient information to help you make informed decisions about your farm business.

By accurately identifying variations in pH levels, you can reduce your lime expenditure, improve yield where nutrients or acidity are proving problematic, create a management plan to justify nutrient usage and reduce your environmental impact. For instance, in areas identified as having an existing high nutrient status, applications can be eliminated, avoiding unnecessary use and reducing overall costs.

Once you have a greater understanding of the makeup of your soil, you can put together variable rate application plans to get the most from your field. Our team at SOYL can support you with this, whether you wish to take control of your own nutrient applications or, as mentioned above, make use of our UK-wide contractor services.

To find out more, or speak to one of experts about your own farm situation, get in touch with our team. 

​Gavin Campbell​
Applications team leader