“With slurry there are two very simple questions to ask: where to Spread? and when to spread?”
This was the view expressed by Teagasc’s Stan Lalor at a recent ASA technical event on the Nitrates Directive.
“If you take that slurry is worth over €20 per 1000 gallons. It is important that farmers make the most of its value. We put a lot of focus on slurry from a nitrogen application point of view. However most of the value of that slurry is in Potassium (P) and Phosphorus (K).”
He stressed: “That is why the question where to spread is so critical. Farmers need to be targeting parts of the farm that are low in P and K or that have high P and K requirements. Usually these will be the fields that have the lowest P and K soil types and are being cut for silage in a grassland situation.”
For Lalor the key point with slurry is that most of the value is P and K. He continued: “Farmers need to get that slurry out to a field where they are going to save money on P and K fertilisers. So where to spread is the first key question that farmers need to ask.”
“When to spread is when you have decided where it will go,” he noted.
“It is about putting it out when it gets best value for the nitrogen. The key issue here is in relation to ammonia volatilisation, which increases in hot and dry weather. That is why generally we would recommend spring, as opposed to summer, application as a result.”
When spreading a key factor is the weather on the day of application. Lalor explained: “A man said to me once:’ the best way to explain the optimum conditions for spreading slurry is to say Spread on a day when the farmer is wearing a t-shirt and the wiper of the tractor is on intermittent.’ And I can’t put it any better than that.”
“He is wearing a t-shirt which means it is warm and there is a bit of growth. The wiper of the tractor is on intermittent which means the day is cloudy, overcast and a bit misty. This means there is reduced ammonia volatilisation.”