The right fertiliser, for the right field, at the right time

With margins tight and nutrient limits under pressure, Catherine Kilmartin, Climate and Sustainability Advisor, Teagasc, Mullingar, explains why this winter is the ideal time to review your soil sample results and turn them into a practical Nutrient Management Plan (NMP) for 2026.

One of the most cost-effective actions you can take on your farm is to build and maintain healthy, well-balanced soils. A soil-led plan helps ensure you buy the right fertiliser, for the right fields, at the right time.

Soil samples are a vital tool on every farm. They tell you, field by field, where to target lime, phosphorus (P) and potassium (K). Teagasc recommends soil sampling every four years, with one sample per 5 hectares, to keep information accurate and to remain compliant with fertiliser regulations. Recent Teagasc results show that around half of Irish soils are not at target for pH, P or K. Without up-to-date soil tests, fertiliser decisions are little more than guesswork.

The first priority on any farm should be to correct lime deficiency. Correcting soil pH unlocks nutrients already in the soil and greatly improves the response to applied fertiliser, particularly P. Teagasc research shows that improving soil pH, P and K from low to optimum can increase nitrogen use efficiency from about one-third to nearly two-thirds. Lime is one of the best value investments you can make yielding a return of around €6 per €1 spent.

Using your soil results, work with your advisor to build a NMP that suits your farm. Develop a lime plan over three to four years, decide on field-specific fertiliser strategies to reach and maintain Index 3 for P and K, and plan how to make best use of organic manures.

Organic manures

Organic manures should always be targeted first. Cattle slurry and farmyard manure (FYM) are valuable sources of P and K, especially for Index 1 and 2 fields and silage ground. Applying slurry in spring using low emission slurry spreading maximises nitrogen recovery and improves overall efficiency.

Chemical fertiliser

When it comes to chemical fertiliser, choose the right product for the job. On Index 3 soils, apply maintenance rates to replace nutrient offtakes where required. For nitrogen, protected urea should be the default choice. Teagasc trials show it matches CAN for yield and grows on average 13% more grass than standard urea. It also reduces nitrous oxide emissions by around 71% compared to CAN, and ammonia losses by up to 78% compared to straight urea. On top of that, protected urea is cheaper per kilo of effective nitrogen, helping stretch budgets further.

Timing

Finally, match product choice with correct placement and timing. Calibrate spreaders, use tray tests, avoid spreading before heavy rain and always respect buffer zones. Pair protected urea (with sulphur where needed) with the correct compound fertiliser, such as 0-7-30, 10-10-20 or 18-6-12, based on soil test results.

A NMP, underpinned by accurate soil samples, will prioritise the use of lime, ensure that organic manures are recycled appropriately and advise you to switch from CAN to protected urea. Such a plan will cut fertiliser costs, reduce greenhouse gas and ammonia emissions by 7-8%, protect water quality and deliver the best return per euro spent.

The Teagasc Signpost Advisory Programme

Catherine Kilmartin is a Climate Advisor working on the Teagasc Signpost Advisory Programme. Catherine is based in Mullingar and supports farmers in counties Cavan and Westmeath. The Teagasc Signpost Advisory Programme provides enhanced advisory and training support to farmers to help them to select and implement climate and sustainability actions that are appropriate and impactful on their farms.