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Small changes in soil health can have big impact on arable productivity – with nutrition a key driver, say researchers. Even a small deviation... Soil health critical to environment and grower profitability

Small changes in soil health can have big impact on arable productivity – with nutrition a key driver, say researchers.

Even a small deviation away from a target pH of around 6.5 can have a significant impact on soil biology, nitrogen utilisation, uptake of key nutrients and the emission of injurious gases such as carbon dioxide and nitrous oxide.

“We’ve got to bring soil management and liming into the 21st century,” says Omya chief agronomist David McLellan, who is a member of the AHDB’s RB209 fertiliser use steering group.

“Understanding the impacts of pH on soil, its biology, ability to make nutrients available to plants and the potential environmental harms of ignoring it, is key to changing the industry’s misplaced complacency around the topic.”

Recent data from the Professional Agricultural Analysis Group (PAAG) indicates that 41% of UK arable soils have a soil pH of less than 6.5 and 57% of grassland soils have a pH of less than 6.0.

“Over the past 40 years, there has been a dramatic decrease in the production and the use of agricultural limestone,” says Mr McLellan.

“The 2022 British Survey of Annual fertiliser use shows that of almost 7000 farms/fields surveyed, only 8.2% applied lime in 2022 and all this is against a backdrop of soil pH falling steadily in recent years.”

Increased productivity

Virtually any indicator of productivity and soil health you will see that every one of them is adversely affected by poorly managed soil pH, explains Mr McLellan.

“This is not only hitting growers hard now in terms of lost production and the purchase of costly inputs they don’t really need, it’s also storing up major environmental problems at many levels for the future.

“A soil at pH 5.5 will achieve only 77% of the Nitrogen uptake one at the optimum pH 6.5 would. That’s like 1.0kg of N out of every 4.0kg you buy, doing absolutely nothing or the bags you’re buying being only 75% full. It has that much impact.

“If your soil biology is suffering as a result of poor pH management, no amount of nitrogen is going to deliver the yields you want because the soil is out of balance and all the nitrogen gets locked before the plants can get anywhere near it.”

Regular liming also improves soil structure and soil water retention, adds Mr McLellan.

“Unlike some agents that can reduce pH such as magnesium, Calcium actually pushes clay particles apart and this aids aeration and water flow through the soil rather than it being trapped and creating anaerobic conditions.

“This encourages the soil biology to thrive and encourages strong root growth, but it also improves soil water retention and availability for plants.

“Calcium is also essential for the proper functioning and health of plant tissues, being essential for opening the stomata and allowing the plant to maintain its transpiration even in hot weather.”

Reactivity is key

In terms of maintaining the optimum pH, big strides forward have been made in recent years with a greater understanding of the importance of reactivity, says Mr McLellan.

“For a long time, we’ve just talked about the neutralising value of treatments and the cost per unit value of this and we’re only just starting to think about reactivity, but this is potentially one of the most important elements of a successful liming programme.

“Reactivity is the speed at which a product can raise pH and it’s linked to the surface area that is able to come into contact with the soil.

“A granulated lime is made of micronised powder which, in the case of Calciprill, is made up of particles just 150 microns in size. This breaks apart very rapidly and increases the surface area that is available to react with the Hydrogen ions.

“This ultrafine product outperforms coarser limestone treatments with the rapid reaction bringing soil pH to an optimal level very quickly – usually within six weeks – and the effect is longer lasting than with coarser agricultural lime.”