An extra kilo of spring grass is ‘5 times more valuable than a kilo in summer’

The value of grass growth in spring and autumn was hammered home to those listening to this year’s Teagasc Virtual Dairy Conference.

In the first of four webinars in this year’s conference this morning (Tuesday, November 24), which focused on making better use of nitrogen (N), the topic of nitrogen use efficiency (NUE) was centre stage.

The panel discussion featured Teagasc specialists Dr. Laurence Shalloo, Dr. Elodie Ruelle and Dr. Owen Fenton, and was moderated by Teagasc head of knowledge transfer Dr. Stan Lalor.

During the webinar, Jack Nolan, a senior inspector with the Department of Agriculture, Food and the Marine, issued listeners with the following challenge:

Can you reduce fertiliser N use next year by half a bag or urea or a bag of CAN?

Dr. Lalor asked one of the panellists, Dr. Elodie Ruelle, where farmers should start next year to cut this N.

In her response, Dr. Ruelle said: “There’s actually no magical answer on where to cut N.”

Referring to the below graph, the panellist added:

“If you look at this [graph] you could be thinking ‘OK, I need to cut my N in the spring and autumn because that’s when the response is lower and I want to grow as much grass as I can given the N I have’.

“But, what we need to remember is the extra grass you’re growing in the summer actually goes into creating silage. OK, silage is very important because you need it to feed your cows during the winter and so on, but there’s no real point in extra silage on your farm.”

She stressed: “Any additional kilo of N put in in the spring or autumn goes directly into the animal – it goes directly to feed your animal and that means you can reduce the silage you’re giving to the animal and reduce the concentrates you’re feeding to the animal, so it’s way more valuable.

Laurence [Shalloo] has done studies which have shown that an extra kilogram of grass in the spring is actually five times more valuable than one in the summer. We really need to take that into account when trying to answer this question.

Turning to another angle, Dr. Ruelle highlighted that a Teagasc study gauging the grass growth over the spring time of a number of years found that every year the grass response to N can be different depending on the weather.

In years with a bad spring – where conditions are cold and wet, with N response levels of 10-12kg DM per kilo of N spread – she said that farmers could indeed cut down on spreading N:

“There’s no point in putting out N if Met Éireann is saying there is going to be 15mm of rainfall over the next couple of days because it’s going to be leeched. You need to look at your farm and look at your weather forecast to know what’s happening.”

However, on the other hand, studies also noted that warmer springs could allow for up to 20kg of DM for kg of N applied.

“In that case, I would definitely not cut N in the spring, because that’s very valuable grass. It goes directly into your animal; that’s when you need to feed less silage or less concentrates and create less silage in summer also.

“Look what’s happening on your farm – know your farm, know your soil type, have an action plan in front of you but be flexible and see what’s happening out there,” Dr. Ruelle stressed.

Dr. Shalloo also commented, stating: What I do is start by developing a plan because I would be afraid that just ad-hoc taking out a bag of CAN or half-bag or urea going from one year to the next, you could actually end up using more fertiliser.

“So I would say that it should all be part of a plan; there’s no one saying don’t do it but you make it to be part of a plan. Part of that plan is soil fertility; understanding where your soil fertility is at and are there gaping holes here where we can use P [phosphorous], or lime or K [potassium] – some deficits to fill.

Going back to Elodie’s point about the spring or autumn, obviously we know that grass in the spring is very valuable, and grass in the autumn is valuable, so reducing N in that period may create a deficit that we don’t want to see in our systems.

“Maybe there’s scope to reduce some N but obviously we wouldn’t take out the full cycle.

“For me, the opportunities are probably going to centre around silage: what are the silage stocks like; are there big silage stock?

“If there are then there’s scope to reduce chemical N in your silage; particularly if you, over the last couple of years, have wanted to cut silage and your nitrate levels are preventing you at particular parts of the year, that’s something where maybe there’s scope here to reduce your silage.

“If we think about the mineralisation and the value that we’re going to get from clover the Elodie talked about, they’re going to be more towards the mid season and later in the year. So there is potential taking those into account for saving N.

Our competitive advantage is around grass and grazed grass, so we can’t shorten our grazing season because that’s going to add cost to our system.

“We brought out a report last week which showed that Ireland has the lowest milk price in Europe; our competitive advantage is only on cost – so we have to build on that and ensure that we don’t damage our competitive advantage by management strategies that we put in place,” Dr. Shalloo concluded.