Farmers in NI could switch from using CAN fertiliser to protected urea when growing silage with no impact on fodder yield or quality, a new study has found.

Researchers at the Agri Food and Biosciences Institute (AFBI) conducted the study into the use of protected urea, which is also known as stabilised urea, in a three-cut silage system over two years.

“Stabilised urea was shown to be a suitable substitute for CAN in that it performs as well as CAN in terms of yield response […] and leads to no significant difference in terms of grass quality or silage quality,” the study found. The trial took place in Hillsborough, Co Down with 72 separate plots used to compare the effect of protected urea and CAN on silage production.

Both protected urea and CAN were applied at a rate equivalent to 120kg of nitrogen per hectare (ha) for first cut, then a lesser rate of 100kg/ha for both second and third cuts.

The results, which have been published in the scientific journal Grass and Forage Science, show that average annual dry matter yields stood at 15.5t/ha for CAN and 16.1t/ha for protected urea.

However, the scientists point out that data analysis found the average grass silage yields for the two fertiliser products were not significantly different.

Similarly, no significant difference was found between yield gain response, which is a measure of the grass yield that comes from every 1kg of nitrogen applied.

In the study, protected urea had an average yield gain response of 21.51kg and the response for CAN was 23.24kg.

The scientists also measured grass and silage quality throughout the experiment and again found no significant difference between the two nitrogen fertiliser products.

The researchers point out that emissions of nitrous oxide are lower when protected urea is applied to grassland instead of CAN, so wider use of protected urea on local farms will reduce greenhouse gas emissions from NI agriculture.

The only issue raised in the study were some high nitrate concentrations in grass silage from both CAN and protected urea plots, especially with third cut.

The AFBI scientists state this is likely due to reduced nitrogen use efficiency later in the growing season and suggest future studies should investigate if fertiliser recommendations for late season silage should be revised.