Chemical fertiliser is a hot topic at the minute in the agricultural sector, with concern over pricing in 2022 and possibly beyond.

On the fertiliser planning webinar held by the Agri-Food and Biosciences' Institute (AFBI) and College of Agriculture, Food and Rural Enterprise (CAFRE), some research conducted by Teagasc in 2017 was highlighted.

The webinar focused on fertiliser planning on dairy farms in what is a 10-year high for fertiliser prices.

Dr. Debbie McConnell, a research scientist from AFBI, highlighted some research conducted by AFBI which showed how increasing fertiliser prices reduces the cost-benefit scenario.

Although the research showed that grass was more expensive to grow, it still remained the cheapest feed on farms.

This was based on rates of chemical fertiliser usage up to 250kg of nitrogen (N)/ha.

Chemical fertiliser

Debbie highlighted the importance of ensuring that you get the most out of your fertiliser you do spread and ensuring that it is not wasted.

This includes having good soil health, ideal weather conditions and soil temperature, to obtain the best growth rates from each kilo of N spread.

Debbie then highlighted research (Impact of soil pH on utilisation of fertiliser N, phosphorus (P) and potassium (K)) conducted by Michael Egan, a grassland researcher with Teagasc.

The research looked at how soil pH impacted on fertiliser effectiveness and in effect, how much fertiliser was wasted.

The research determined that a soil pH of 5.0-5.5 resulted in 32% of the fertiliser being wasted. This means that at a soil pH of less than 5.5, up to a third of the fertiliser is wasted.

If your soil pH is between 6.0-6.5 you waste none of the fertiliser spread.

Percentage utilisation of Percentage utilisation of Percentage utilisation of Percentage waste Potential financial loss/ha Potential financial loss/ha
Soil pH N P K Fertiliser Fertiliser at £256 or €306 Fertiliser at £600 or €718
5.0-5.5 77% 48% 77% 32% £45.06 or €53.96 £106.60 or €127.66
5.5-6.0 85% 52% 100% 21% £29.57 or €35.41 £69.99 or €83.81
6.0-6.5 100% 100% 100% 0% £0 or €0 £0 or €0
Table source: Teagasc and DAERA
Based on 150kg/ha of 27-4-4

The table above used 27-4-4 at a rate of 150kg/ha. It showed that at a price of £600 or €718/t, that £106.60 or €127.66 is lost/ha.

Meaning that on some farms, there is firstly, an improvement in N effectiveness to be had and secondly, that a large amount of money could be wasted.

The average farm size in Ireland is 33.4ha, so having soil pH at the incorrect level could potentially being costing €4,263.84 on the average farm.

That figure does not include the cost of lost grass due to reduced growth rates.

When you look at the figure it is easy to see why there has been a major focus on soil pH and fertility for the last number of years.