“When growers are up against it, liming is one of the first jobs to slip down the list of priorities,” admits Stephen Hill, chairman of the Agricultural Lime Association.
Ideally, soils should be professionally tested after harvest, he advises.
“It’s better to take a representative number of spot samples than a composite one if you’re trying to identify specific low pH areas.”
Never test after applying fertiliser and aim to maintain an average pH of 7 on arable land, says Mr Hill.
“This has taken on greater significance with the arrival of Soil Management Plans and agri-environment schemes.
Toxic elements such as aluminium become free within the soil solution if the pH drops too far.”
The supply and sale of liming products, either ground or screened chalk, is regulated, so growers are right to seek assurances about any purchase.
“Materials from quarries vary.
If you are offered lime you should receive a specification, analysis or data sheet.
If you don’t, question the product suitability – the price may be the only thing that is right.”
Neutralizing value and grading, which reflects the grinding fineness, are both important, he adds.
“The higher the NV, the better the product.
“As a finely ground product is quickest to react, you are looking for a high percentage passing through a 3.35mm sieve.”
He recommends 95% passing 3.35mm, plus 30% through a 150 sieve.
“Ask for the Reactivity Value, too, as this depends on the fineness of milling.
It tells you how reactive the lime will be.”
Buyers should also check the specification for the amount of inert silica.
“It has no benefit to the soil, but the content can vary from 1-2% up to 20-30%.”
It is easy to compare values, he says.
“Divide the price by the known NV to get the unit cost.
Then examine the proportion passing through 150.
Ideally, this will be 40%, but look for a minimum of 30%.”