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Spring Nitrogen, How much and where?


For a small country we have huge variation in conditions, from Wexford to Donegal, from south to north Wexford and even within our own farms. Therefore we cannot have a one fits all recommendation on fertiliser or grazing for the spring. Martina Harrington, Beef Specialist advises on Spring Nitrogen

What we can do is give recommendations and targets for different situations, then you as the person who has most knowledge of your own farm have to adopt the recommendations that best fit your farm.

We all know grass is our cheapest form of feed and therefore early grazing is essential to achieve better weight gain in growing animals, improve breeding performance, reduce greenhouse gas emissions and to save money. Teagasc figures show that for every extra day at grass in spring there is a saving of €2 per LU/day. So if you have 30 cows out 2 weeks earlier this year, that’s a saving €840.

When do I spread fertiliser?

When soil temperature are continuously above 5 oC – to see what the soil temperature is in your area get a soil thermometer or check out Met Eireann’s website on this link.  https://www.met.ie/forecasts/farming/agricultural-data-report

When ground conditions are good. This means that you can freely travel on fields with a tractor and fertiliser spreader or slurry tanker without the fear of causing damage. This point is critical.

When the forecast for the week ahead is good i.e. little to no rain and temperatures >6oC. In these conditions the fertiliser or slurry you put out today will have time to be taken up by the plant and not washed away to the nearest river, stream, lake or drain.

When you plan on letting out stock in the coming weeks                                                                                 
If you can say yes to all the questions above you should be putting out fertiliser.

If the weather is bad at the moment is there anything I can do?

Yes, you can get some fertiliser to have it ready to spread so you don’t miss opportunity when it comes. You won’t need a large amount of fertiliser a tonne of Urea will cover about 40 ac. Check your fences are ready for cattle to go out and the fencer is working. Check your water troughs and pipes are working etc.

How much fertiliser should I put out and where?

The plan is to grow 1.0-1.5 tonnes of grass from mid-February to 1st April. To achieve this, you require 30kgs of nitrogen per ha or 23 units per acre. This can be made up of a half bag of protected urea or 2,500 gallons of slurry per acre.

Medium stocked farm 140kgs N Per ha.
For most farmers stocked at 140kgs N per ha, you will looking at dividing your farm into three, 1/3 heavy covers, 1/3 medium covers and 1/3 light covers. Graze your heavy covers, apply protected urea to the medium covers and apply slurry to the lower covers. Once you have the heavier covers grazed get out with 23 units of Nitrogen on them to ensure they grow back quickly to have enough cover on them (1,200kgs DM/ha) when you come back to graze them in early April.  Plan your second round of fertiliser, this should be another 23 units of nitrogen, possibly in the form of a bag and a half of 18-6-12 per acre.

Heavily stocked farm 170kgs N/ha +
For heavier stocked farms ~ 170kgs N/ha, you will have more demand, can get around your farm quicker and will have a higher demand in April when you start your second round of grazing.  Apply half a bag of protected urea to the heavy covers you are going to graze (1/3 of the farm), this will allow then to take up the nitrogen and have a quicker response after grazing. Apply half a bag of protected urea as before to the medium covers (1/3 of the farm) and apply 2,500 gallons per acre to the low covers that will be grazed last. So two thirds of the farm will receive 23 units of protected urea per acre. The second round of fertiliser needs to be applied by mid-March, if possible use a compound like a bag and a half of 18-6-12 per acre.

Lower stocked farm <130kgsN/ha
For lighter stocked farms, apply slurry to the medium and light covers, the minute you have grazed the heavier covers, come in with 23 units of protected urea so you will have grass in April. As you graze out the second third of the farm, apply your 23 units of nitrogen to kick on grass. Your next round of fertiliser should be your compound, one to one and a half bags of 18-6-12 per acre.

Top Tip: Reseeded fields, dry fields and fields with good soil fertility will give you the best response to nitrogen early in the year, so target these for early grazing and fertiliser applications.

Start thinking about silage

In some areas animals can be housed for six months of the year being fed silage. It is therefore critical that this silage is excellent quality and there is enough of it. If you want to get top quality silage you need to have it closed up by the 1st of April at the latest, this will allow you to cut by mid to late May before the grasses start to head, the earlier you cut the better. To be closed by the first of April you have to be in grazing your silage ground by mid- March.

Silage ground also needs to have good soil fertility to ensure yield, potassium in particular plays a really important role here so you need to plan your slurry application’s to ensure you are hitting your silage fields. This leads us nicely into the spring rotation planner.

Spring Rotation Planner

If done properly the spring rotation planner will set up your grazing year. The principles are very simple:

  • Pick the date you turn out stock,
  • Pick the date your first rotation will end 
  • Have 30% of the farm grazed by the first week of March                                   For heavier
  • Have 60% grazed by St. Patrick day                                                                              farms
  • Have 100% grazed by the first week in April                                                           add 7 - 14 days
  • This gives you an area to graze per day, per week and per month  
  • On turn out, go to your grazing ground first, get at least a third of that grazed off.
  • Then go to silage ground, be out of that by the last week of March
  • Then go back and graze the rest of the grazing ground.

View a tech note on The Spring Rotation Planner

Set Targets

Once you have a target of say two acres per day or 14 acres per week, you can now manage it. You can turn out enough stock to graze 14 acres per week, you know if you are grazing enough or grazing too much and you can alter your management in accordance.

Where to go -Why must you NOT graze silage ground first?

You need to allow grass enough time to grow so the cattle have good covers of around 1,200kgs of DM/ha to come back and graze in April. If I graze a paddock on the 10th of February, and intend being back there on the 4th of April, that’s 54 days. To have a cover of 1,200kgs DM/ha it means I need an average growth rate of 22kgs DM/ha/day.

If I graze my silage fields first and only head into this paddock on the 28th of February, I only have 35 days and need a growth rate of 34kgs DM/Ha/day - this is unlikely.

This is not an exact science, and as a farmer once said to me you must write your spring rotation planner in pencil not pen and adapt as you move through the spring.  But what a spring rotation planner  does give you is a plan to work to and if you get it mostly right, you will be able to turn out stock early, keep them out, get more grass in the diet,  have better animal performance, save money and reduce greenhouse gas emissions. 

We have tools available on the links below, but if you are truly interested in grassland management talk to your advisor today about joining a grass group near you or click on this link Grass10 Grazing Courses 2021

To find out more about Grass10 click here