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Positive Indications: Have we begun to turn a corner with National Soil Fertility?

The 2018 annual review of soil sample results prepared by Teagasc is showing some improvement in soil fertility after years of decline or stagnation. The review tracks trends in soil fertility between 2007 and 2018. The analysis show significant improvements in soil pH over the last few years and a halting of the decline in soil phosphorous (P) and potassium (K) levels, with some indication of improvements in 2018.

pH and Lime

For a number of years Teagasc and other industry partners have targeted advisory programmes at improving soil pH through increased lime usage.  Across all farm enterprises there has been a large increase in the number of soils in the optimum soil pH range for grassland mineral soils (pH 6.3 or greater).  In the 2014-16 period 37% of soils tested were in this range, whereas in 2017-18 this figure had risen to 54%.  This large improvement in soil pH will have significant positive effects on the industry.  As well as increasing grass and crop yields, the improvement will lead to improvements in nutrient uptake efficiency of applied fertilizer and organic manures.  This can lead to a reduction in losses of nutrient to water and air thereby improving water quality and lowering emissions of greenhouse gasses.

Mark Plunkett, Teagasc Soil & Plant Nutrition Specialist said: “improvements in soil pH levels are a reflection of the targeted advisory programmes promoting application of ground limestone. Average national lime use over the last 5 years has  increased by 211,000 tonnes per year  from the previous 5 years and currently stands at approximately  1 million tonnes.

Phosphorus and Potassium

An examination of soil P and K levels across all farming systems show that just 38% and 45% of soil samples respectively, had sufficient P and K for optimal grass and crop production (≥ index 3). However, the 2018 soil results show some signs of improvement, especially for K where the proportion of soils with low K levels has decreased across all farming enterprises. These data show 40% and 50% of soils with sufficient P and K (≥ index 3) respectively, with very little difference between grassland farming enterprises (dairy vs. drystock).

Dr. David Wall, Soil Fertility Researcher at Teagasc Johnstown Castle said; “we must not look at one year’s results in isolation as increased N-P-K compound fertilizer use on grassland farms over the last 4-5 years have not yet been reflected in soil P, which is naturally slow to respond.  However, it appears that soil K levels are beginning to respond positively with an increase of 10% in soil with optimum K for plant production in 2018.  This is a positive result as it indicates a halt to the steady decline in soil K, especially over the last 5 years, some of which may have been as a result of increased grass utilization and the removal of high quality baled silage from paddocks being routinely grazed.”

Progress is evident on all enterprises.  Tillage farms have consistently had the highest soil fertility levels over the last ten years.  When fertilizer usage dropped substantially from 2007 onwards the most significant declines in fertility happened on dairy farms where off-takes are highest. However, in recent years higher incomes and an increased focus on soil fertility has led to faster improvements on dairy farms than on beef and sheep farms. 

Pat Murphy, Head of Environment Knowledge Transfer in Teagasc said; “these positive trends in national soil fertility represent a foundation to build on, as soil fertility is a cornerstone of our grass based animal production systems and critical for enhancing crop yields and quality into the future”.  Farmers should focus on soil fertility on soils where additional yields can be achieved and utilized to feed livestock.  However, we need to ensure that we value and protect our more extensively farmed land where an increase in soil fertility could be detrimental to biodiversity and would devalue the land for future results based Agri-environment schemes.