Lime deficiency hits production of dry matter

HOWEVER COMPLICATED a fertiliser plan you produce, when grassland is short of lime, dry matter production will be severely limited.

Independent soil adviser Josephine Scamell says such problems can be severe in many areas including Cornwall, south-west Scotland and Cumbria, where soils are prone to being short of calcium. But it must be checked regularly and topped up, on all except extreme chalk soils, more often than currently practised on many farms for best use of fertiliser.

“A 10% saving on fertiliser applications will usually make testing soils worthwhile,” she adds. “And where there is a chronic calcium shortage, it could be reducing silage yields by 20%. One indicator of a chronically low soil calcium status is a wet, structureless, squashy silage; another can be low milk volume.”

There are two reasons why lime status falls and applications are needed. Firstly, calcium is taken off in grass that is eaten or conserved, and on average 0.6% of total dry matter is calcium, she says.

The second reason is that acidity is increased. This occurs when organic matter degrades and acidic fertilisers are applied. “Many common fertilisers – including triple super phosphate and ammonium sulphate – are acidic.”

Ms Scamell advises testing every two or three years, depending on soil type. A few full trace element analyses costing about 80 each are worthwhile relative to the cost of fertiliser, she says. Back these up with standard DEFRA soil tests, including phosphate, potash, magnesium and pH, on other fields.

These tests should be done before spring fertiliser is applied or preferably at least two months after an application in the autumn.

When a field needs liming, putting on a large dose every five years is not advisable. “A small dose of 1t/acre every two years is better and will keep soil microbial activity up,” she says.

“Lime can be applied in autumn/winter or early spring when land is chronically short. But avoid putting it on spring reseeds.”

There are different sorts of lime and specifications available, adds Ms Scamell. “Good quality lime should be a good colour. And, even if you don”t fully understand the detail, request the spec sheet before buying as the seller will then have to provide evidence of what is being supplied.

“If in doubt, use a good quality, white, calcium carbonate lime, and don”t use a magnesium – dolomitic – lime unless you know you need to. Where soils are prone to being sticky, avoid dolomite.”