Summer nitrogen usage, clover and slurry

Recent rain, recovering grass growth rates and good clover content mean farmers need to focus on maximising nitrogen (N) utilisation across the farm, Teagasc Climate Action and Sustainability Advisor, Liz Duffy shares some key tips.

In this article, I will focus on knowing your N allowance, applying fertiliser N as protected urea and reducing the quantity of fertiliser N if you have clover in the swards.

Reducing the quantity of fertiliser N and the form of fertiliser N that you apply will both contribute to reducing your greenhouse gas emissions this summer. Additionally, using low emissions slurry spreading (LESS) to apply slurry will increase recovery of N from slurry and replenish phosphorus (P) and potassium (K) removed by silage.

Nitrogen strategy for June

For all grass-based livestock systems, the Grass10 campaign publish a really useful weekly newsletter giving the state of play for the dairy and drystock systems from the Pasturebase Database. Subscribe to the Grass10 weekly newsletter here.

We are all trying our best to manage to maximise grass utilised by stock and provide full winter fodder from inside the farm gate in order to maximise profitability within our systems.  This is set against the backdrop of reduced fertiliser allowances across many of the higher stocked systems.  Soil fertility, an on-going reseeding programme (target 10% of the farm area per year) and managing clover within our swards hugely help drive Nitrogen use efficiency within the farm gate. 

It is important that you are fully aware of your total farm N allowance for the year and manage this allowance accordingly. Your yearly purchased N allowance is based on your farm’s previous years grassland stocking rate so consult your advisor for clarification on this.

How are your clover paddocks looking – avail of the free nitrogen!

Thankfully, the spring of 2025 and weather to date have been much more favourable for good clover content in many swards. April is a key month for clover from a number of aspects. Firstly, from an establishment point of view, the April reseed rather than autumn gives the clover a really excellent start (at the ideal seeding rate of at least 2kgs per acre). 

For established swards, we encourage all farmers to walk their clover paddocks in the month of April to assess whether there is the potential to save on bag fertiliser N across the main season.  In the table below, we show the recommended levels of N use on derogation dairy farms that had varying clover contents in the month of April. As you can see, as we move up to 20% clover content, there is great potential to save on the levels of purchased chemical N we are spreading in the month if June - with up to 50% of a saving achievable or up to 100% if we can replace the N in the bag with N from dairy washings (1,500-2,000 gallons per acre).

Table 1: Nitrogen strategy for swards varying in clover content

• *Chemical N fertiliser can be increased to 230kg N/ha, in paddocks with no clover, as long as whole farm N does not exceed 212kg N/ha
• Soiled water used whenever zero chemical N application
• +25kg organic N applied

Slurry use in June

If we start by thinking about what the nutrient content of slurry is (6% dry matter cattle slurry = 9 units N, 5 units P and 32 units of K per 1,000 gals), we can maximise the return of N from slurry at this time of year by utilising dribble bar/trailing shoe technologies to reduce N losses in the form of ammonia emissions. More dilute slurry will contain less N, however, a waterier product is less of a risk in terms of grass spoilage as the N can work into the soil and then the plant more effectively. The P:K ratio in particular makes slurry an ideal product for second-cut silage or paddocks taken for surplus bales over the season as we manage grass quality. Time slurry applications carefully to avoid any extended periods without rainfall.

Second-cut silage and bales

Apply slurry (2,500 gallons dilute slurry per acre) or the equivalent of 2 bags of 0:7:30 per acre if slurry is not available (to supply enough P and K).  10 days later, top up with a protected urea +S type product (60 units N and 12 units S per acre). 

Remember to put back what you take off

Make a note of the fields that have surplus bales taken off them and ensure the required levels of N, P and K are put back.

Table 2: Units of N, P and K removed per acre depending on the number of bales per acre

Liz Duffy is a Climate Action & Sustainability Advisor based in Midleton, Co. Cork. For more information on the Signpost Advisory Programme, visit here.

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