Phosphorus levels far from optimal

85% of soil samples were sub-optimal for at least one major nutrient in 2018, according to Mark Plunkett – specialist in soil and plant nutrition in Teagasc.

Mark was speaking at the Fertilizer Association of Ireland’s spring seminar last week where the association launched its fourth technical bulletin – the efficient use of phosphorus in agricultural soils.

Tillage soils

54% of soils on tillage farms are in index 1 and 2 for soil phosphorus (P), 25% are in index 3 and the remaining 22% are at index 4.

This means that just 25% of tillage soils are at the optimum level of P.

Mark explained that up until 2018 the data would suggest that soils were mined for P and potassium (K). Last year, there was a reduction in the number of soils in index 1 for both P and K.

Grassland soils

60% of grassland soils fall into index 1 and 2 for P. Just 22% of grassland soils are at optimal P – index 3. The remaining 18% have high P levels and are in index 4.

The percentage of grassland soils which fall into index 4 for P has declined by 50% since 2007. Mark explained that this can greatly reduce the risk of P loss to water.

However, as P reserves were drawn down Mark added that soils in index 1 and 2 increased from 40% to 60%.

2018 improvements

Improvements were seen in 2018 samples. Soils in index 1 and 2 on grassland farms improved by 4%.

Fertiliser programmes unbalanced

Mark urged attendees at the conference to put effort into a fertiliser plan, as the data he provided suggested that over the last decade fertiliser programmes have not been balanced and did not deliver adequate P inputs to replace P offtakes.

Production from these soils is therefore reduced.