Nitrogen is one of the most important nutrients for growth and its application has a direct impact on dry matter yields in paddocks and fields. It will provide a timely boost to growth in early spring to help get cattle out to grass early.
It’s also an expensive input and it’s important to get the application rate and timing right. The aim of spreading nitrogen early is to get grass growing early so that stock can be turned out early and stay out. This will help to reduce costs and labour on farms.
Table 1 outlines the cost difference in feeding weanlings indoors and outdoors in spring.
The response to nitrogen in spring can be as high as 1kg N/15kg DM grass. A 50kg bag of CAN contains 13.5kg N so it has the potential to grow 202kg DM of grass.
Research work at Teagasc, Grange, Co Meath, has demonstrated that the most efficient time to spread chemical N in the spring is when soil temperatures reach a consistent 50C to 60C. There is very little benefit in spreading before this.
For the past number of years, this hasn’t taken place until the first week of March.
These will generally be the first fields closed up in autumn and therefore these should be the first fields grazed in the spring.
These fields should have accumulated good covers of grass over the winter months.
Some swards can grow up to 5kg DM/ha/week in suitable conditions.
This winter was quite mild overall, with no heavy snowfalls or prolonged frosts, so farms should see some good growth over the winter months.
If these fields were not grazed out fully in the autumn, there may be an accumulation of dead matter at the base of the sward.
While this grass may look dead in appearance, it is still very digestible with feed values of up to 70DMD which is better than a lot of grass silage being fed on beef farms. It’s important to graze this sward tight on the first grazing in spring.
If this dead matter is allowed to accumulate after the first and second grazing, it will reduce the quality of the sward in subsequent grazing. It will also reduce the growth potential of the field as this dead matter will not take in sunlight or nutrients to grow.
These fields would have been closed up in late October or the first week of November. These are the fields that will respond best to fertiliser applications in spring. If slurry can be applied via trailing shoe or dribble bar, these fields could get slurry instead of chemical N.
Trailing shoe and dribble bar application of slurry enables stock to begin grazing quicker as opposed to splash plate application.
These fields will then be ideal to graze in two to three weeks.
Grazing these swards too quickly could mean you run out of grass and finish the first rotation ahead of time, so manage carefully.
On the other hand, if you are using the spring rotation planner and are behind target on getting around the farm, it may be helpful to graze a few of these covers quickly to speed up the first round.
On dry farms, the target is to have 40% of the farm grazed by 10 to 15 March and then to have 100% of the farm grazed by 5 to 10 April.
These dates change to 40% of the farm grazed by 20 to 25 March and 100% grazed by 20 April on heavy farms. Because of the recent wet conditions many farms will now be behind in spring grazing targets so the rotation can be speeded up by grazing lighter covers until more stock are turned outdoors.
These fields would have been the last fields to be grazed last autumn/winter and probably closed from November onwards.
These fields are ideal for slurry application as no grass will be damaged in the slurry spreading process.
It’s important to aim to spread in the right conditions to maximise nutrient uptake and avoid any nitrogen losses to the atmosphere.
The right conditions are dull damp cold conditions.
You should avoid dry sunny days for slurry spreading; 2,500 gallons of slurry can contain up to 24 units of nitrogen if spread correctly.
These fields will be three to four weeks out from grazing after slurry so the time interval will be ideal.
It’s important to target early nitrogen applications to your most productive swards as they will give you the best response. These should be:
Wait for solid temperatures to reach a consistent 5°C or 6°C before spreading. In terms of application rate, 23 to 27 units of N/acre (half a bag of urea/acre) is sufficient for the first application. Higher-stocked farms may opt for more but I think it’s better to go with this application and then top up when grazing gets into full swing. Urea is cheaper than CAN. Urea needs the correct conditions for application, ie cold damp conditions. Urea is also more prone to nitrogen losses as opposed to N.
If urea costs €420/t, the cost per kilo of nitrogen is €420/460kg N = €0.91/kg N. CAN on the other hand is currently at €280/t so the cost per kilo of N of CAN is €1.03/kg N.
Use soil tests to determine what phosphorus (P) and potassium (K) status is like across the farm. Fields deficient in P, K and lime would be better served with a compound application like 18:6:12, pasture sward or, better still, target these fields for slurry application. Avoid spreading high-K compounds in spring where lactating animals are grazing. High soil K can displace magnesium and lead to the onset of grass tetany.
Leave 10 days between slurry and fertiliser applications as slurry creates anaerobic conditions and could lead to loss of fertiliser nitrogen.