Spreading Phosphorous but getting no response? Maybe its to do with the under lying rock

Some farmers are spreading Phosphorous and are getting no visible response in terms of soil index or grass production, according to Teagasc Dairy Advisor Ger Courtney.

Speaking at the Irish Grassland Association summer tour, the Killarney-based advisor said it is particularly a problem for farms based along the Cork and Kerry border.

Courtney said that the problem occurs due to the underlying bedrock found on farms located along the border joining both Munster counties.

The underlying bedrock contains Aluminium and Iron, he said and these elements bind with Phosphorous making it unavailable to the soil and the plants roots.

Teagasc research shows that having the correct soil pH is important for the release of Phosphorous in the soil.

But, Courtney added that even when the pH is at the optimum level of 6.3 for grassland soils, farmers will still struggle to build up the soil Phosphorous index.

“It takes a long time to increase the Phosphorous indexes on these soils as the sink needs to be filled,” he said.

However, Courtney said that this problem is quite site specific, but research work carried out in Teagasc Johnstown Castle shows that 90% of Irish soils have either a lime, Phosphorous or requirement.

And, this has an impact on the overall farm productivity of both grass-based and tillage farms.

It also showed that only 10% of Irish grassland soils had the right levels of nutrients to maximise grass or tillage production on an annual basis.

Addressing low soil fertility:
  • Soil sample the whole farm to see what nutrients are required.
  • Complete a nutrient management plan – Provides information on the levels of lime, P and K required.
  • Target low pH soils first – Grassland soils should have a pH between 6.3-6.5.
  • Use slurry and farm yard manure on fields low in P and K.
  • Artificial P and K may be required – The farm must stay within cross-compliance requirements.

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