Reducing soil acidity by increasing its pH before drilling winter crops will improve nutrient availability – and boost yields.
More than half of all arable fields are below the target pH 6.7 recommended in AHDB’s Nutrient Management Guide (RB209), suggest results from NRM laboratories which analysed more than 50,000 soil samples from June 2022 to May 2023.
“Nearly 25% of the samples were pH 5.8 or lower, which is extremely low for most arable crops,” says NRM soil and crop nutrition agronomist Sajjad Awan. “While only around a fifth were in the more acceptable target pH range of 6.5 to 7.0.”
The findings reflect industry studies which suggest arable land is only limed on average once every 12 years – way less often than the traditional recommendation of once every three to five years.
Multiple factors
Longer-term data from the NRM study suggests that the pH of arable soils dropped sharply in 2022/23 compared with previous years. There could be multiple factors behind the drop in pH from arable soils this year, says Mr Awan.
“It might be due to weather, an increase in samples from lower pH soils or from specific management systems. There are so many variables and the information provided with each sample is not sufficient to allow us to draw firm conclusions.”
The results highlight the importance of correct soil acidity, says British Sugar’s LimeX business manager Glenn Carlisle. Rectifying pH issues will improve the utilisation of the soil’s nutrients, in particular phosphate and nitrogen.
“Maintaining optimum soil pH ensures all the nutrients required for plant growth are at their most available, which will drive yield and may allow savings on fertiliser inputs,” adds Mr Carlisle.
Growers should soil test each field at least every three years. “It makes sense to time soil sampling ahead of the most acid-sensitive crops in the rotation, such as sugar beet or barley.”
Crop performance
“Most testing takes place on stubbles after harvest. But taking samples earlier, using the tramlines, will mean results are available faster – so liming and fertiliser decisions can be made well ahead of time.
It is a case of matching your requirement with an appropriate liming product, says Mr Carlisle. Particle size as the critical factor for a grower seeking to remedy a pH issue before it affects crop performance.
Research by the University of North Carolina shows that pH continues to drop after lime coarser than 0.84mm is applied.
In contrast, finer particles between 0.15 and 0.18mm will react within six months and hold pH at that level, and even finer lime will increase pH immediately, peaking at eight months before beginning a slow decline.
Particle size
LimeX has a very fine particle size. It is a co-product of the sugar purification process in British Sugar’s factories, where calcium carbonate is created by chemical processes to remove organic matter and nutrients from sugar juice.
“You end up with a very fine particle-size lime product, making it very reactive. In the Ag-lime Quality Standard tests, it scores 100% for reactivity, meaning that 100% of the product you put on land will do the job of pH amendment.”
LimeX’s particle size is between 0.002mm-0.015mm at that spec. Given the right conditions after application, pH should rise within 4 to 6 weeks, whereas other products can take 6-12 months before acidity levels improve.
Multiple factors
“The additional benefit of the fine particles size and high reactivity is that the available calcium increases much more quickly. That benefits soil flocculation and conditioning, which improves aeration, drainage and microbial activity.”
Calcium is an often overlooked but incredibly valuable macronutrient, helping crops combat disease.
LimeX has additional nutrient value, says Mr Carlisle. Each tonne has 9kg of phosphate, 8kg of magnesium and 7kg of sulphur.
Regular testing yields results
Arable farmer James Forrest tests any new land he takes on – and usually applies LimeX within the first year if he has any doubts about soil acidity.
“It’s very good at correcting acidity, and we like the benefits of its nutrients,” he says. “There isn’t any fixed policy for when we put it on, but I would expect to apply it every five to seven years.”
Mr Forrest operates two spreaders, which allows him the flexibility to apply LimeX at the best time. They also sample the fields themselves, having previously dabbled in precision sampling before moving away from it.
“If we have been farming the land for a while, we tend to know where the problem areas are to concentrate on. If we have even the pH across a field, then a blanket application works well.
“However, on new fields we have taken on, we will up the rate for areas that are particularly low.”
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