The second Nitrogen application conundrum
With the month of March coming to a close. Many farmers on drier farms will be in the process of, or considering going out with their second application of nitrogen. At a recent Agricultural Science Association nitrates technical event James Humphreys of Teagasc Moorpark addressed this topic.
Humphreys outlined the results of research conducted at Moorpark which examined the effectiveness of a heavier second application of nitrogen. He said: “We would have put out Urea on grassland in January. We applied a 30kg application and followed up six weeks later with another 30kg of nitrogen. In a separate experiment we put on 30kg of nitrogen and followed up with 60kg of nitrogen. We looked at the response over a number of years.”
According to Humphreys: “We got a very good response with the first set of applications. When we moved onto the second set of applications we got a poorer response. We found the value of the response of the first application was worth around €90/tonne of DM. The value of the additional application put a value on the grass of €195/tonne of DM.”
He commented: “So if you’re a dairy farmer feeding concentrate at the moment. A lot of farms are tight for grass will be feeding 6kg of concentrates, costing €300/tonne. Putting on the additional nitrogen would obviously make sense.”
However he also said: “If you’re a beef farmer with a pit of silage in the yard maybe it would be wiser to consider going with the lighter application rate.”
Humphreys highlighted: “When looking at nitrogen response in the spring. It is very unusual not to get an economic response and there is nearly always a case for going out with nitrogen early in the spring.”
Humphreys noted: “Taking into account rainfall and evapotranspiration, there is a very high risk of loss during the spring. There are huge amounts of water entering the soil and very little coming off in evapotranspiration. “
“With an eye on this risk I would advise farmers to split the application of nitrogen at this time of the year. Going out with a light rate initially and then following up with a heavier rate as conditions improve. So we are generally talking about a farmer putting on 30 kg of nitrogen per ha between mid-January and the end of February.
He remarked: “This is depending on soil type and location. Down the south on sandier soils you can go earlier. As you move north on heavier soils it will be later and also one has to take altitude into account.”
In terms of a second application at this time of the year he advised generally the second application will be around the middle of March. With the rate somewhat dependant on the circumstances of the farm.”
He added: “As we move into the summer we switch from urea to CAN type fertilisers. To avoid the risk of volatilisation. Generally speaking nitrogen is retained reasonable well in the topsoil during the summer months. There is relatively low risk of loss once you are not using ammonia based fertilisers.”
He concluded: “We need to cease applying fertilisers from mid-September on. That’s to allow time for the nitrogen which has been applied to be taking up until such time as growth ceases at the middle of November.”