‘If you don’t know the soil fertility levels, spreading fertiliser is a waste of money’

Farmers should soil test every field on their farm, as they could be wasting money on fertiliser, according to Grassland Argo’s Dr Stan Lalor.

“If you don’t know the base line soil fertility levels, spreading fertiliser is a big waste of money,” the soil fertility expert said at a recent Teagasc Green Acres farm walk in Co. Laois.

The farm walk was attended by over 300 farmers and Lalor told the crowds in attendance that soil tests are essential to get an understanding of soil fertility levels of all the fields on the farm.

The Grassland Agro representative said that the soil’s pH and fertility levels all need to be considered before farmers spread fertiliser.

Just spreading 18:6:12 (N:P:K) may not the right solution just because you have always done it that way.

Lalor said that Irish soils tend to be acidic and, a low soil pH has a negative impact on the biological activity of the soil along with reducing the amount of Phosphorous (P) and Nitrogen (N) available.

Grassland farmers should aim to have all their soils in a pH range of 6.2-6.5, he said, as at these levels there will be a higher level of output and a better response to the fertiliser applied.

However, research carried out by Teagasc in Johnstown Castle shows that 90% of all Irish soils either have a low pH, P or K status.

Lalor also said that farmers should aim for soil index of 3 for both Phosphorous (P) and Potassium (K).

“Fertiliser programmes should show farmers that they can save money and increase output on the high index soils on their farms, while also targeting the low index fields,” he said.

Lalor said that slurry and farm yard manure is the cheapest way to raise the soils P and K levels and 1,000 gallons of slurry is the same as a 50kg bag of 5:5:30 (N:P:K), he said.

He also said that silage removes a high level of P and K from the soil and as a result these fields should be targeted with slurry applications.

If slurry is not available, Lalor said that farmers should then consider using compound fertiliser containing both P and K.

But, he said that the timing of P and K spreading can have an impact on the efficiency of the compound fertilisers.

“Farmers should target their P applications early in the year and should have between 50-75% of P spread as early as possible.

“It is a good idea to spread 50-75% of the P early as it is essential for spring grass growth, but farmers should hold back a small quantity to spread later in the summer to give grass a P boost,” he said.

“K is also important for grass growth, however if you spread too much K in the spring, it can tie up Magnesium in grass and cause grass tetany. Farmers should aim to spread K fertilisers later in the year,” he said.

Five steps to manage soil fertility:
  • Soil test
  • Address and lime and pH issues
  • Focus on managing soil Phosphorous and Potassium levels
  • Use slurry where possible
  • Use compound fertiliser when slurry is unavailable