‘Compounds like 27:2.5:5 will not solve soil fertility issues’

90% of the soils analysed by Teagasc in 2015 had sub-optimal levels of soil pH, phosphorus (P) and potassium (K).

According to Teagasc’s John Maher, addressing these soil fertility issues will have a positive impact on the returns generated at farm level. These benefits will occur through increased grass growth and improved nitrogen fertiliser utilisation.

Speaking at a recent Heavy Soils Programme open day, the Teagasc Dairy Specialist said: “Nationally, our P and K indices are in the wrong place and there’s €500/ha up for grabs if we can fix soil fertility on the average farm.”

Maher continued to say that there are 10 farms currently enrolled in the Teagasc Heavy Soils Programme and the soil fertility levels of these farms are worse than the national average.

“Soil fertility is by far the greatest challenge facing these farms. They have been able to grow their cow numbers; but soil fertility is the one thing that is working against them,” he said.

Five steps to improving soil fertility

Maher also touched on the five steps farmers should use to improve the soil fertility levels on their farms.

1. Soil testing

The first step, he said, is to soil test and, as we approach November, December and January, it’s nearing a good time to carry out this task.

“By soil testing, you find out where your soil is in terms of pH, P and K. It’s the first step in addressing a soil fertility issue.”


2. Address the pH problem first

Maher added: “Spreading lime should be prioritised and it’s the cheapest.” The quantities spread should be based on the results outlined in the soil test results.

Traditionally, farmers spread lime in the back end of the year. However, Maher suggested that those operating on heavy ground should do so when the opportunity arises.

You may not be able to travel on heavier soils during the back end of the year, so the strategy needs to change.

“If you have taken surplus grass out as bales, it may be the ideal opportunity to apply lime. It’s that kind of approach, rather than waiting until the back end of the year, that farmers may need to take to address soil pH issues.

“It’s going to make a lot more sense to spread lime during May, June or July when you actually have the chance to travel on the land,” he said.

3. P and K

After addressing a soil pH issue, Maher said the next step was to focus on correcting low P and K index paddocks on the farm.

“If you are at index 1 or 2 for P and K, you are well below the line and your grass is going to under-perform. You really need to be at index 3 or 4 to maximise growth.”

The average dairy cow, he said, will take 6 units of P out of the soil every year. If the farm is stocked at 2.5 cows per hectare, that’s a 15 unit withdrawal of P from each hectare every year.

Without accounting for slurry, that withdrawal will require an application of 2.5 bags of 18:6:12 per hectare just to maintain the soil’s P levels.

“If the farm is at index 1 in terms of P, it will require double that – the equivalent of five or six bags of 18:6:12 per hectare,” he said.

4. Targeting slurry

For fields that have been identified as being index 1 and 2 for P and K following soil testing, Maher suggested that farmers should target these fields with slurry applications.

“We have to be conscious of what else is available on the farm. Slurry should be applied on the fields that are index 1 and 2,” he stated.

tractor, Hi-Spec slurry (vacuum) tanker

5. Compound fertilisers

Maher added: “18:6:12 is an old-type fertiliser, but its make up in terms of N:P:K is right for fixing a soil fertility problem.

“That’s why it was invented many years ago and that’s what most of you require. Spreading 27:2.5:5 or 24:2.5:10 will not fix soil fertility issues.

The idea of spreading compounds like 27:2.5:5 or 24:2.5:10 to fix a P problem simply won’t work. They are maintenance products and they just don’t have the horsepower.

If you are already at index 3 or 4 and you spread 27:2.5:5 across the season, you will probably get close to maintenance levels. But if you are not there, you cannot fix soil fertility by spreading these products,” he said.