Getting more from your nitrogen investment
As the fertiliser market continues to fluctuate because of political unrest in the Middle East the hope of prices dropping and staying down appears increasingly unlikely. Cashflow, timing of use, storage and having the time to follow markets makes it very difficult to always be on the right side of price fluctuations. If we can't control fertiliser prices, we need to ensure that every kilogram of nitrogen (N), phosphate (P) and potash (K) applied delivers the maximum return on investment.
Some of these factors come long before getting a price of fertiliser.
- Are soil pH’s at a level to ensure maximum uptake of any nutrient required?
- Are soil phosphate and potash levels sufficient to get the full growth potential of any nitrogen applied?
- What is the yield potential of the crop?
- How much N, P&K do you need to grow that crop?
- Has the N, P and K in any organic manures available been factored in?
- Are weather conditions suitable for fertiliser applications?
Grass yields drop every year after establishment due to an ingress in weeds, weed grasses and drops in soil fertility. This means silage and grazing fields will have a differing yield potential based on the age of the sward.
A ley in year five will have approximately 70% sown species compared to 98% in year one. A review of intermediate and late perennial ryegrass cultivar yields from grass trials shows that by year six the difference in yield is around 5t DM/ha less than in year one. If the yield potential of fields differs according to the age of the grass sward one way to ensure maximum return on nitrogen spend is to tailor the nitrogen rate according to yield potential.
Phosphate and Potash rates remain consistent as they are already directly related to the yield of a crop. If a typical nitrogen application for a grazing and two cut silage system is 220kgN/ha we are feeding a crop to yield approximately 11.5t DM/ha. If leys within their first three years have potential to yield 13-14t DM/ha this application rate could be limiting their yield potential. Conversely if we are applying the same rate to fields eight years plus, which are yielding between 6-7t DM/ha then we are feeding them beyond their yield potential-wasting money.
The average response to Nitrogen applications is 20kg of dry matter for every 1kg of nitrogen applied. Based on our typical application rate of 220kg Nitrogen if we apply an additional 30kg/ha of Nitrogen over the year to swards one to three years old we could yield an additional 600kg DM/ha. This is the equivalent to an extra three bales/hectare for an additional cost of £40/ha. Equally the fields with a yield potential of 9t DM/ha could be receiving 90kg/ha less N without a yield reduction. A saving of £119/ha.
Varying application rates by field does create additional work but this could be balanced by grouping fields by age, such as leys one to three years old, three to six years old etc. It will require additional planning to ensure the rate of P&K applied still matches that required for offtakes and maintenance.
In a climate where winters are predicted to be longer and wetter, there will be a greater requirement for forage reserves. Dry spells in summer become could become more common and fertiliser prices continue to be volatile targeted actions such as this can maximise forage output without adding cost.
*34.5% AN at £455/t
Top tips:
- Prepare a nutrient management plan which accounts for organic manures.
- Review field performance and grass sward compositions to identify fields with highest yield potential.
- Target Nitrogen to crops with the highest potential.
Lorna Galloway, Senior Consultant, Lorna.Galloway@sac.co.uk
Posted by SAC Consulting on 17/08/2026
