Have you considered correcting your pH with lime?

We experience many different scenarios during the farming year while providing support and files to over 100 lime contractors from across the UK. After what has been a very hectic few weeks dealing with lime contractors desperate to get onto clear land, I thought it would be worth writing a short blog on liming and things to consider when it comes to some of the common UK arable crops.

Why is correcting pH important?

Soil pH can seriously affect crop growth which can significantly affect final yield. However, crops vary in their sensitivity to soil pH and thus their ability to reach full potential depends very much on the plant. Oilseed rape, sugar beet, barley and peas are examples of this. Sugar beet, for example, will yield considerably less at pH6. If you are aware you have acidic areas within a field from nutrient mapping and they have not been limed 12 months before beet planting, consider a granular lime product for a quick fix to the problem.

The optimum pH in most arable rotations is around 6.5 as this covers the majority of crops. Most will grow well in a pH range of between 6 and 7 without having too much of a detrimental impact on yield, especially if nutrients are being applied fresh every year.

Correcting soil pH is also vitally important for the availability of nutrients to the plant. Most nutrients are fully available (or close to) between a pH of 6.5 - 7. Although not all nutrients are at 'optimum' availability at this range, there is enough overlap to reduce the chance of deficiency due to pH levels. 

Leaving pH levels at acidic levels can result in large yield penalties but on the flip side, increasing to a pH of above 7 can be costly and reduce the availability of some nutrients. It's imperative that careful and detailed management is undertaken to maintain soils at the optimum level, while not over-liming.

Soil pH also influences the utilisation of applied fertiliser. The table below shows the affect soil pH has on the crops ability to utilise applied N, P and K fertiliser. It is based on an application of 220 kgN, 80kg P and 80kg K at a cost of £220 per ha (August 2017 pricing):

How does lime work?

All limestone products are made up of calcium and magnesium carbonates responsible for neutralizing acids in the soil. The calcium carbonate equivalent (CCE) represents the sum of the calcium and magnesium carbonates in a liming material. The higher the CCE, the greater the acid-neutralizing value of the lime.

In order for lime to work to maximum efficiency, the carbonates must come into contact with the acids in the soil. Smaller-sized particles react faster to neutralize the soil, as shown in the table below. Ideally, the maximum particle size should be 2.4mm – any above this are unlikely to have much impact on soil pH. This is why, when ordering lime from any supplier, you should find out the neutralising value and the particle size of the product.

Due to the dustiness of the fine lime particles, it is commonly granulated or prilled to make it more easily spreadable.

Disease management

Clubroot control can be helped by liming at an appropriate time to reduce the consequences of the disease. Ground Lime will add calcium ions (Ca2+) and raise soil pH. These, combined together, will reduce the impact of clubroot on a brassica where the cases of disease are mild to moderate.

High pH soils have been linked to the worst cases of scab in potato ground. The lower the pH of the soil, the better the disease will be controlled. Research has found that scab is best controlled at a pH between 5 and 5.2, however this is far from doable in a normal arable rotation including potatoes. Because of this, planning lime applications into your rotation is important.

Soil types

The soil type of your field or farm should be a factor when considering liming rates. If you compare a sandy soil against a heavy clay soil, for example, they have very different structures and would require different lime management techniques.

Heavy clay soils have the ability to hold onto the calcium and magnesium ions supplied by the liming product, so will continue to displace the hydrogen ions. On such soil it would be suitable to apply once every four years, as long as the correct liming product is used.

In comparison, a sandy soil will not hold the calcium and hydrogen ions due to their free draining nature. On such soil types, it would be more appropriate to apply lime more regularly at lower doses.

Key points

• ​Consider your rotation- do you grow acid sensitive crops?
  
• What soil type are you on?
• Always ask about NV values of lime to ensure this is accounted for.
• Make sure you know the particle size of the lime being supplied.
• Could a product such as Magnesium Limestone be beneficial? Always check Magnesium levels.
• Do you need a quick result for one year? Consider the possible use of a granulated lime.

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Gavin Campbell
Applications team leader

For specific advice for your business related to this blog or any other aspect of precision crop production get in touch with SOYL.