Farm Ireland

Sunday 18 February 2018

Grass grown from nitrogen is more economical than feed concentrates

Fertiliser and slurry spreading has begun for those in drier areas.
Fertiliser and slurry spreading has begun for those in drier areas.

Mary Kinston

Attention is turning to getting slurry out, and whether or not to apply nitrogen. After an extremely wet and mild winter, there are still a number of areas where soils are saturated, or haven't dried sufficiently, so patience will be required here.

However, with a somewhat drier start to the year, slurry and fertiliser spreading has commenced for those where the waters have subsided.

This mild winter has provided many farmers with good grass growth, so farms will hopefully be starting the spring with an adequate amount of pasture ahead of the cows.

Irrespective of how much pasture you open with this spring, it is still imperative to employ tools such as the spring rotation planner to ration out the available pasture until the balance date, which will hopefully be sometime in April. This is when grass growth equals grass demand.

Adequate pasture of good quality is an advantageous position to be in as it has the potential to substantially reduce concentrate feed bills in the spring - an ideal scenario when milk price is so low.

At this time of year, using nitrogen (N) fertiliser to promote grass growth is important where stocking rates on the milking platform are moderate to high. This will generally be the case where a dairy herd is calving compactly.

With urea at approximately €400/t, the grass grown from nitrogen is still more economical at around €108/t of grass dry matter than replacing such growth with concentrate - even at a response rate of 8 to 1.

However, this grass must be grown and utilised, so it's important to improve the efficiency of fertiliser use.

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Recommendations are to apply 23 units/acre (29kgN/ha) for the first application in spring from mid January until early March. Urea is more cost effective at this time than CAN.

While I concur with this advice it's still important to consider on-farm conditions. The graphic below illustrates how to apply nitrogen relative to different conditions.

Once the first fertiliser dressing has been applied, general recommendations are to apply a second application four to six weeks later.

A late first application (March) should be quickly followed by a second application (four weeks). Obviously there is the option to replace the first application of fertiliser with watery slurry.

The overall efficiency of N recovery is influenced more by site than by the form of nitrogen being applied.

However there are a few factors that can help to minimise the losses of inorganic N from ammonia gas volatilization, denitrification and leaching. These include:

Minimising other nutrient deficiencies, especially phosphorous (P), potassium (K) and sulphur (S). So consider your soil test values. The efficiency of N is maximised with regular P, K and S maintenance dressings, so aim to apply P and K with either the first or second application of nitrogen, especially on index 1 or 2 soils

Soils have a finite capacity to store N in the organic matter, so high dressings of N will inevitably result in increased losses. Make sure to target the most productive swards or reseeded fields when using higher rates

Urea can be less reliable and often has a lower efficiency due to N losses from ammonia volatilisation. Many experiments have found consistent yield losses of 6-8pc compared to ammonium nitrate, largely because urea is poorly absorbed by the soil

Cool temperatures and moist conditions often seen in spring reduce the losses of urea by moving it below the soil surface, with reduced leaching. Apply urea shortly (less than eight hours) before moderate rain (5-10mm). Rain causing run-off will carry N with it. However, when using nitrate-N, check the weather forecast and ensure that there is 48hours of good weather and less than 15mm of rain ahead

High pH soils (> 7) or recently limed areas are likely to reduce the efficiency of urea compared to CAN

Dry weather, warmer soil temperatures or high soil pH increases ammonia volatilization, making CAN fertiliser sources are more advisable.

So this spring it's a financial priority to utilise available pasture by:

* using a spring rotation planner;

* regular farm walks;

*re-adjusting your feed budget;

* fill obvious grass deficits with purchased feed;

* promote grass growth by efficiently using nitrogen fertiliser and slurry.

Mary Kinston is a discussion group facilitator and consultant, and farms with her husband in County Kerry.

Indo Farming