How farmers can cut greenhouse gas and ammonia emissions

How farmers can cut greenhouse gas and ammonia emissions
Picture: iStock

The Irish government has committed to reduce losses of both ammonia and the potent greenhouse gas (GHG) nitrous oxide, while achieving good status for all waters.

In Ireland, agriculture accounts for 33% of GHG emissions and 98% of ammonia emissions and, as a consequence, is under the spotlight to reduce emissions.

Use of protected urea nitrogen fertiliser is the largest single avenue currently open to Irish agriculture to meet the  commitments to reduce GHG and ammonia emissions.

Teagasc has issued the following information on protected urea nitrogen fertiliser.

What is protected urea?

Protected urea is urea treated with an active ingredient called a urease inhibitor. The urease inhibitor can be coated onto the outside of the fertiliser granule or incorporated into the urea granule during manufacture.

How does a urease inhibitor work?

Urease is the enzyme which catalyses the conversion of urea to ammonium.

It is during this conversion that ammonia gas is lost from untreated urea.

A urease inhibitor blocks the active site of the urease enzyme.

This moderates the rate at which urea converts to ammonium.

In so doing, ammonia loss is reduced to low levels.

Won’t slowing of the conversion from urea affect the availability of nitrogen (N) for grass?

No, because the conversion of protected urea to ammonium begins as soon as the fertiliser granule starts to melt.

The urease inhibitor moderates the rate at which the urea-N converts to ammonium.

The result is that the conversion occurs over a few days rather than a few hours, as would be the case with conventional urea.

Remember, when fertiliser N is applied to soil, its aim is to supply the grass or crop with N over a period of days to weeks, rather than hours.

Are different urease inhibitors used in protected urea?

Yes, the following products are recognised as acting effectively as urease inhibitors: NBPT, 2-NPT, NBPT+NPPT.

Teagasc has conducted research with all three inhibitor options, most extensively with NBPT and NBPT+NPPT.

Can I spread protected urea throughout the growing season?

Yes, you can spread protected urea across the growing season when you would otherwise spread calcium ammonium nitrate (CAN) or unprotected urea.

This may potentially simplify fertiliser spreading on the farm, and setting up a fertiliser spreader for only one straight-N product each year.

Will using protected urea reduce yields?

No, published Teagasc trials have shown protected urea consistently yields as well as CAN in Irish grasslands, with no difference in annual production.

How farmers can cut greenhouse gas and ammonia emissions

Is protected urea cost effective?

Analysis of costs in March 2019 showed protected urea to be less costly than CAN, while performing just as well in terms of yield and N recovery efficiency.

Bear in mind that fertiliser costs fluctuate, but always make cost comparisons on the basis of cost per kg of N for straight N-products.

Does protected urea reduce loss of the potent greenhouse gas nitrous oxide?

Yes, published Teagasc trials have shown protected urea has 71% lower nitrous oxide emissions than CAN.

Does protected urea reduce loss of ammonia?

Yes, based on published Teagasc research, protected urea has comparable ammonia loss to CAN, and ammonia loss is reduced by 79% compared to urea.

Is there potential for protected urea to reduce nitrate loss to water?

Yes, when leaching occurs, nitrate present in the soil is vulnerable to leaching loss.

Protected urea does not deliver N directly as nitrate to the soil, therefore reducing the risk of nitrate losses occurring with rainfall after fertiliser application.

Reduced ammonia loss compared to urea will also reduce the risk of ammonia N being deposited from the atmosphere onto sensitive habitats or into sensitive water bodies.

What protected urea fertiliser products will be available on the Irish fertiliser market for 2020?

While no definitive list has been approved by the Department of Agriculture, Food and the Marine (DAFM), the accompanying table shows a list of products that have shown efficacy to reduce emissions.

What are the types of protected ureas on the market?

Urea protected with the active ingredients NBPT, 2-NPT, and NBPT+NPPT have been shown to be effective in protecting urea in Irish and/ or international research.

Can phosphorous (P) be blended with protected urea?

If the inhibitor can be protected from exposure to the acidity which often comes along with P blending, then possibly yes. Ask your supplier to show you evidence that P blending has not affected the protection.

Can K be blended with protected urea?

Yes.

Can sulphur (S) be blended with protected urea?

Yes, subject to the ammonium sulphate used to deliver the S being of good quality for this use.

What is the shelf life of protected urea?

NBPT will degrade over time in storage.

However, protected urea treated and used within six to 12 months should still have very high efficacy.

Even where degradation decreases NBPT below the current regulatory minimum inclusion level, the urea will still be protected.

When NBPT has completely degraded, ammonia-N loss will be the same as unprotected urea.

Will protected urea give the same performance as CAN fertiliser in dry conditions?

Yes, Irish trial results show no significant yield or N recovery difference between CAN and urea protected with NBPT. However, if conditions are dry and remain so, response to any N fertiliser will be limited. So if you are hesitant to spread CAN, you should also be hesitant to spread protected urea. Consider waiting for rain and growth conditions to return.

Is urea more corrosive on fertiliser spreaders?

It is more hygroscopic than other fertilisers, which causes it to draw moisture, if the spreader is not washed out.

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