Questions answered on fertiliser spreading

With air and soil temperatures recovering, and soils beginning to dry out, it’s time to focus on fertiliser to maximise grass growth and reduce the burden on purchased fodder and concentrates.

Growth rates have been very poor over the past weeks and we can expect some compensatory growth to occur as conditions improve. Planning your fertiliser programme is essential to maximise this growth and fertiliser provides an excellent return on investment.

Below, the Fertilizer Association of Ireland answers some of the questions you may have about fertiliser applications this spring. All of the advice offered is subject to soil test results, the Nutrient Management Plan and crop off-takes.

Grazing

Do I need to use a nitrogen:phosphorous:potassium (N:P:K) compound or straight nitrogen (N)?

Best practice is to use a NPK / high-N compound early in the grazing season – especially where no slurry was applied.

What level of nitrogen do I need to apply this month?

Should I consider calcium ammonium nitrate (CAN) or urea?

Both are equally effective as an N source. Urea will work well in current damp conditions. However, as soils dry out, urea can be exposed to volatilisation. Use CAN or protected urea as the N source in these conditions.

When are soil conditions suitable for fertiliser application?

If machinery is marking/tracking ground, then soil conditions are not suitable. Select dry fields to apply fertiliser. Avoid application if heavy rainfall is forecast in the next 24-48 hours.

I did not get slurry out this spring, is it too late?

Where grass has not been grazed, slurry will cause contamination of the sward. Graze these swards and then apply a light coat of slurry. Slurry is best retained for silage ground.

Slurry nitrates derogation, ammonia spreading slurry
Image source: Shane Casey

I have fertiliser out but have had heavy rain in the last two weeks, do I need to re-apply?

Monitor these swards over the next week as growth picks up. If they seem to be lacking in nutrition, an additional application may be required.

I have poached paddocks, how will I get them to recover quickly?

At soil index 1 and 2 (where permitted under nitrates) spread up to 5 units/ac to promote root development and tillering. In cases of severe poaching, consider over seeding.

Spring application of potassium?

High applications of K under current conditions should be avoided, due to the risk of grass tetany. More K can be applied later in the season, as the weather warms up and the risk will be reduced.

Is sulphur of any benefit to me this early in the season?

Yes. Sulphur will increase N efficiency, boost yields and increase grass proteins. Aim for a little and often approach for sulphur – 16 units/ac over the grazing season.

Silage

It is imperative that actions are taken not to compromise quality and quantity of next winter’s fodder. Silage ground needs to be closed by the middle of April and cut by the end of May to ensure quality.

Each week late in cutting silage after heading out date will decrease dry matter digestibility (DMD) by seven units and further delay second cuts by two weeks.

What level of nitrogen do I need for first-cut silage?

Advice is to use 80 units/ac for permanent pasture and 90 units/ac for reseeds. Generally, allow 2 units/day from application date to cutting date.

Should I delay cutting to increase volume?

For quality silage, harvest the crop in late May. Grass will seed / shoot out between May 20 and May 25.

How will I increase the quantity of silage made this summer to replenish my reserves?

Aim to increase the volume in second and subsequent cuts. Also, maximise bales taken from paddocks during the grazing season.

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Is it too late to apply slurry on silage ground?

If there is a cover of grass, slurry application will contaminate the grass unless spread with a trailing shoe or injected.

What level of P and K do I need for first-cut silage?

P requirement is 16 units/ac. K requirement is 100 units/ac. Reduce accordingly for earlier applications of slurry and/or chemical P and K applications.

If no chemical K or slurry has been applied, reduce K to 60-70 units/ac to avoid the luxury uptake of potash.

My silage ground has not been grazed, what should I do?

Leave it closed up, fertilise as soon as possible and go for an early harvest date.

Do I need sulphur?

Yes. Sulphur should be applied up to 20 units/ac for each cut. It will increase grass protein and nitrogen efficiency.

General advice

When is the best time to apply lime?

Lime can be spread at any time once ground conditions allow. However, care must be taken to avoid the contamination of grass.

Where the risk of contamination to grass occurs, use granulated lime as a short-term solution as soon as possible and plan a bulk ground limestone programme later in the season.

Lime is essential to maximise the returns from fertiliser (shown in the table below). Raising soil pH from 5.5 to 6.5 will increase the efficiency of fertiliser by >25%. Lime will deliver a return on investment of 7:1.

Can I spread urea after a bulk lime application?

Do not apply urea within three-to-six months of a bulk lime application.

Can I spread fertiliser after a slurry application?

Maintain a one week interval between slurry and fertiliser applications.