Soil testing is “critically important” in managing and assessing phosphorous (P) availability in all soils, according to an award-winning professor.

Prof. Mike McLaughlin, who was originally from Co. Antrim, is a research professor with the University of Adelaide, Australia and an adjunct senior research fellow with Teagasc. 

His research includes soil and environmental chemistry and he was also responsible for the establishment of the Fertilizer Technology Research Centre at the University of Adelaide in 2007.

According to Prof. McLaughlin, if a high soil test value comes back and the land in question is in the top phosphorous tier “there is probably no need to apply fertiliser P”.

“But soils in the very lowest tier will need a fair chunk of added fertiliser, in order to get crops up to their full yield potential.

“The reason for testing is to get a measure of phosphorous availability from previous fertiliser applications,” he added.

McLaughlin told the Teagasc Tillage Edge podcast that he believes a lot of farmers may not be adding phosphorous because of the cost.

“If this went on for decades, soil P test results would slowly decline and crop yields would also decline in step with this trend,” he warned.

Soil analysis

Meanwhile, Teagasc has also advised that up-to-date soil analysis will be required to apply fertiliser phosphorous in 2023.

The agency said that if samples are greater than four-years-old, growers should take fresh samples the coming weeks in order to plan and tailor crop fertiliser requirements.

It also highlighted that crop yields from harvest 2022 were above average for most crops.

This will have resulted in increased offtakes of phosphorus and potassium (K), and Teagasc has outlined that it is very important to assess crop P and K offtakes and soil fertility over the coming weeks.

According to its analysis of 3,794 tillage soil samples in 2021 there was a slight decline in fertility on tillage farms when compared to the previous year’s results.

Latest figures indicate that 18% of Irish soils have optimal pH, P and K values (a 6% year-on-year decrease); 61% have a pH >6.5 (a 13% decrease); 57% of soils are at P index 1 and 2 (a 7% increase); and 32% are at K index 1 and 2 (a 2% decrease).

Therefore, test results are necessary to dictate the recommended rates of lime to correct soil pH to the optimum pH 6.5 for a cereal crop rotation.

However, where crops such as oilseeds, beans or beet are part of the crop rotation, a target pH of 6.8 is recommended.

Teagasc has recommended that where possible lime should be applied to correct pH levels based on the results of a recent test report.

It also suggests that optimum soil pH improves function from better structure to improving nutrient recycling and availability.

Growers have been advised to use organic fertiliser where available to reduce fertiliser bills in 2023 and add organic matter to tillage soils. 

These materials include cattle or pig slurry, poultry manures, composts or dairy sludge’s from the milk processing industry.