Soil testing survey reveals important grassland fertility trends

The end of March this year was marked by the successful completion of the European Exceptional Adjustment Aid (EAA) funded Soil Sampling and Analysis Scheme.

The scheme was delivered by the Agri-Food and Biosciences Institute (AFBI) to farm businesses across Northern Ireland.

Almost 20,000 fields were soil sampled across the whole of Northern Ireland over the recent autumn/winter season using Global Positioning Satellite (GPS) technology to record field locations and sampling transects.

The scheme had two components. The first was a Northern Ireland scheme, known as the ‘Open Scheme’, to which all livestock farmers in Northern Ireland were eligible to apply.

The second component, the ‘Catchment Scheme’, was targeted at farmers within specific geographical areas of the upper River Bann catchment.

Over 1000 farm businesses who were successful in applying to the scheme received their soil sample analysis reports by the first week in April 2018.

The analysis reports contained detailed information about soils (i.e. pH, phosphorous and potash status) which will enable participating farmers to target the application of slurry, manure and chemical fertiliser more accurately.

This will help to maximise grass yields, improve soil fertility and increase farm profitability; while also reducing the potential for negative impacts on water quality.

Liming

The reports also contained recommendations for liming.

A preliminary analysis of the results from the scheme indicates that 43% of farmed grassland (excluding rough grazing) across Northern Ireland is under-limed with a total lime requirement of 1.2 million tonnes, requiring an expenditure of £30 million (€34.4 million).

Correcting this soil acidity problem could potentially increase grass dry matter (DM) production by some 1.73 million tonnes over the next five years, with a feeding value worth up to £216 million (€248 million) and thus representing an almost seven-fold return on the lime investment.

Taking a typical 100 acre (40ha) grassland farm, lime application costing £1,440 (€1,655) would result in an increased grass yield of 86t DM (i.e. an extra 1t DM/ha/year for five years on 43% of the grassland area, i.e. 17ha).

Dairy

As expected, grassland used by the dairy sector has a major phosphorus (P) over-supply problem with 50% of fields at soil P indices greater than 2⁺. But grassland used for beef and sheep production also has a significant P over-supply problem.

The results indicated that 40% of fields, on both lowland and disadvantaged land areas (DA), and 30% of fields in severely disadvantaged areas (SDA), have soil P indices greater than 2⁺.

Over-use of P, and particularly of chemical fertiliser P, where not required, not only is detracting from farm profits; but, is exacerbating water quality problems.

Results of these soil tests demonstrate opportunities to save on fertiliser P inputs and to make better use of slurry P – another major benefit of the programme.