Dairy farmers question benefits of lime

That was the question, sort of, Western Dairy's consulting scientist Martin Staines attempted to answer at last week's annual Spring Field Day, in relation to a five-year experiment at Vasse Research Station.

Dr Staines and research scientist Ruairi McDonnell have challenged a widely-held belief that lime should be applied to ryegrass pasture when soil tests show a pH level below 5.5 to improve production.

While application of lime to trial plots in 2011 and monitoring since had shown rapid and significant improvement in soil pH levels - in contrast to untouched control plots which became "extremely acidic" in that time - there was no corresponding increase in pasture production, Dr Staines said.

Statistical evidence of increased pasture production was only detected for the first time this year, and then only for trial plots where lower application rates of lime were mixed into the topsoil to a depth of 10 centimetres five years ago, he said.

And even then, the increase was at best modest, calculated at an extra tonne of pasture per hectare maximum - a lift from 7.5 to 8.5t/ha - and half a tonne on average, said Dr Staines, presenting his latest findings on the liming trial.

"We are saying that for ryegrass based dairy pastures soil pH alone is not enough to make profitable liming decisions,'' he said.

"The old adage, that when soil pH is below 5.5 apply lime, needs revisiting.

"I can imagine some of you are not very happy about that because you have been saying that for many, many years," he told dairy farmers attending the field day.

Brunswick White Rocks dairy farmer and WAFarmers dairy section president Michael Partridge said he had "spent a lot of money on lime on my pastures over the years".

"I could have bought a beach house with the money. I might have been better off doing that, is that what you are telling us?" he asked.

Dr Staines stressed the findings applied only to ryegrass pasture which was tolerant of acid soils and could cope with exposure to soluble aluminium.

It was probably the aluminium build-up, a function of declining pH levels, which caused the primary adverse impact of increasing acidity to less tolerant pasture types such as clover because the aluminium was toxic to the roots of many plants, Dr Staines said.

Ryegrass comprised 90 to 95 per cent of WA dairy pastures and deteriorating pH levels in the control plots, from an average of 4pH five years ago to 3.7 this year, was only just starting to have a detectible adverse impact on ryegrass production, he said.

Dr Staines said the test was initiated to establish if liming actually improved profitability in dairying.

The dairy industry appeared to have adopted a Wheatbelt cropping standard of 5.5pH as its own, but there was "surprisingly little" research on soil pH impact on dairy pastures to support this, he said.

Pasture root depth was much shallower than commercial Wheatbelt crops and ryegrass much more tolerant of acidic soils, he pointed out.

A total of 48 plots were set up in 2011 and treated with a single application of calcium chloride at rates of 1.3, 2.6, 3.9, 6.5 and 13 tonnes per hectare.

On half the plots the lime was left on the surface and on the other half the lime was worked into the topsoil.

Soil pH was monitored and ryegrass cut from the plots and calculated at a tonnage per hectare equivalent in 2011, 2013 and earlier this year.

While the experiment clearly showed more immediate and marked improvement in soil pH from plots with lime worked in, compared to those with lime left on the surface, there was no detectable pasture production increase in 2011 and 2013, Dr Staines said.

He said the dairy industry needed to decide whether further study was warranted.

"Is that where you want to invest your money," he asked.

If so, the trial should be replicated on other soil types with the aim of creating an index to identify, if possible, at what point liming adds sufficient value to pasture production to cover cost, he said.

Helen Golder, from NSW dairy research and consultancy company Scibus, was another field day presenter.

She explained findings from feeding transition trials on ruminal acidosis, commonly called grain poisoning, which is estimated to cost farmers $350 per cow a year.

Up to 11pc of lactating cows in the first 100 days of milking suffer from acidosis in the rumen - the first of a cow's four "stomachs" - causing lameness, loss of milk production, a drop in milk solids especially fat content, loss of condition and decreased fertility, Dr Golder said.

Transitioning cows quickly over a day or two from pasture to silage and other feeds, particularly those containing large amount of grains or sweet suger-based content such as molasses, turnips or fruit, without sufficient roughage significantly increased risk of acidosis, she said.

Dr Golder said cows were particularly susceptible at calving when they were often off their feed but given access to grain during milking.

Ruairi McDonnell outlined similar findings from associated investigations being conducted at Vasse into alternative starch sources to feeding wheat and barley to cows to counter the annual drop in milk production with a transition from pasture to "conserved forage".

Mr McDonnell said a 10-day gradual transition period and supplementary feeding with maize as a more slowly degrading source of starch significantly reduce the risk of acidosis inherent in feeding wheat, barley or oats.

But maize was not readily available to WA dairy farmers so the work was looking at four other concentrates, Mr McDonnell said.