Check allowances and conditions before committing to final day fertiliser applications

With September 14 being the final day for the application of chemical nitrogen (N) and phosphorous (P) fertilisers before the closed period comes into effect, Sandra Hayes reminds farmers to check their fertiliser allowances and ground conditions before deciding to spread.

The co-ordinator of the Teagasc/Tirlán Future Farm Programme also shares key details on the expected return from fertiliser applications at this late stage of the spreading season.

Since the Minister for Agriculture, Food and the Marine announced no change in fertiliser allowances during 2024, there has been a lot of farmers contacting their advisors to review their fertiliser allowances.

Farmers that have a Nutrient Management Plan / fertiliser plan / derogation plan will know their chemical fertiliser limits in regards to nitrogen and phosphorus, along with their requirements for lime and potassium applications.

These plans use the data from soil samples taken from the farm, plus the stocking rate on the farm and the application of all slurries/FYM spread back on the farm, to work out what level of chemical fertiliser is allowed to be spread. When these plans are followed, it allows the targeting of these key nutrients to ensure soil indexes reach index 3 for P and K, along with bringing soil pH the target of 6.3. This then allows the optimum production of grass grown on the farm, while still reducing greenhouse gas emissions and the risk of losing nutrients to the water.

Table 1: Maximum chemical N (kg/ha) permitted based on the farm’s grassland stocking rate

Once you know what quantities and type of fertilisers you have already spread this year, the balance can be worked out. Where an allowance is available, applications of nitrogen and phosphorous fertiliser are permitted until September 14; however, the economic cost and response of late season fertiliser applications need to be examined, and they should only be carried out where appropriate soil temperatures and weather conditions are present to prevent any potential losses to water.

Teagasc research has been clear that nitrogen fertiliser applications in August will give a much better response in terms of grass growth than those undertaken in September, showing that for every 1kg of nitrogen applied it gave a response of 27kg DM/ha for August and 19kg in September (Figure 1 below). To put this simply, fertiliser spread in September will give you a much lower return than if spread in August; something to keep in the back of your mind for next year. Along with only spreading when conditions are suitable, if fertiliser N applications are required at this late stage of the season, only paddocks that will give a response should be selected; these are typically paddocks with a high percentage of perennial ryegrass present that are optimum for soil fertility. 

Figure 1: Grass dry matter yield response to fertiliser N

Farm focus

Potassium (K) is known as a fertiliser for the second half of the year. With this in mind, one of the Teagasc/Tirlán Future monitor farmers, Jack Kearney – who farms outside of Rathcormac, Co. Cork – is following a plan to address this deficiency on his farm.

Jack’s overall soil fertility on the farm is optimum for 55% of the farm for P, K and pH. Jack knows he has no P allowance for the farm, but after reviewing his NMP with his advisor, he knows what N, K and lime was required for the whole farm. He has looked at his NMP maps and knows what paddocks need to be targeted. Jack will spread lime on paddocks that has a pH of lower than the optimum pH of 6.3. This means 0.5 to 1 tonne of lime will be spread per acre in the next few weeks.

With having no P allowance available, the fertiliser used for the final round of applications was 19-0-15 plus Sulphur. This fertiliser is good to help build low K soils and also to optimise grass growth. Milk, meat and grass removes kilograms of P and K and it is important to replace them.

Table 2: Offtakes of P and K from milk, beef and silage production

It is also important to have your slurry tanks emptied before the end of September. Kearney’s did not get an opportunity after second cut silage to spread the remainder in the tanks. Instead, after the removal of third cut silage, the remaining slurry and farmyard manure will be applied on this ground to replace any missing P and K.

If you require any further details on what your N, P, K and lime requirements for your farm or to have a fodder budget drawn up, please contact your Teagasc or agricultural advisor.

Find out more about the Teagasc/Tirlán Future Farm Programme here.