As part of the 58th BT Young Scientist and Technology Exhibition (BTYSTE) 2022, two students from Co. Roscommon put forward a project investigating alternatives to synthetic fertiliser using waste milk and anaerobic digestate.

The prestigious, annual exhibition – which took place virtually this year – featured an impressive array of farming- and environment-related projects. This project from Sean Allen and Dylan Treacy was just one that caught and we caught up with the boys to find out a little more.

The Roscommon Community College students wanted to find a more sustainable and cost-effective way to keep nutrients in the soil.

This is both timely and topical since synthetic fertilisers are heavily regulated by the EU, the students told Agriland:

“As animal by-products are now enabled to move freely on the single market, we want to start by testing them and using them as fertiliser.”

The students started the experiment using waste milk as it is “useless to factories”, and anaerobic digestate, which is a by-product of the methane-fermentation process.

Trial procedure

At the beginning of a six-week trial, soil samples were taken to measure nutrient levels including potassium, phosphorus, and pH levels.

The students tested four different soil treatments: waste milk; anaerobic digestate; a mixture of the two; and 10-10-20 fertiliser.

Dry matter (DM) tests on plots were conducted across the trial period to assess grass growth.

Ten grams of grass from each plot were dried for 10 minutes at 100oC to get the dry weight – the higher the percentage of dry matter, the better the quality of the grass, the students explained.

In early January, the students took the final soil samples and conducted the last DM test to judge the difference in soil nutrients and grass growth after their fertiliser alternative had been used.


Due to Covid-19, soil samples taken to the laboratory were not returned in time and are still being tested, the boys explained.

However, the DM tests and overall growth test conducted by them showed that anaerobic digestate and waste milk are an adequate alternative to artificial fertilisers, they said.

The mix of waste milk and anaerobic digestate showed best overall growth, on average. The mix was followed by the digestate on its own, which also performed better than the 10-10-20 fertiliser.

In the DM test, the waste-milk-treated soil lost the least amount of dry matter, yielding the best-quality grass

Both organic options on their own lost less DM than the artificial fertiliser, which indicates higher grass quality.

The grass growth and DM tests were sufficient in assessing that grass reacted better to the students’ natural and organic fertiliser alternative instead of artificial treatment.