Urea and gaseous emissions

Greenhouse gas (GHG) emissions

➢ Urea and stabilised urea can reduce GHGemissions compared to CAN

➢ The EU has committed to reduce agriculturalGHG emissions by 30% by 2030

Ammonia gas emissions

➢ Urea will increase ammonia emissionscompared to CAN

➢ Urea can be stabilised with a ureaseinhibitor to minimise ammonia losses

➢ Ireland has committed to reduce ammoniaemission by 5% by 2030

Major fertiliser N transformations and N losspathways. Urease inhibitor (NBPT) reduces N

loss by slowing urea hydrolysis.

Relative star rating of the differentN fertilisers

Teagasc, Crops Environment, Land UseProgramme, Johnstown Castle

Wexford

Tel. 053-9171200

www.teagasc.ie/soils/

CropsEnvironment& Land UseProgramme

JohnstownCastle

Urea N Fertiliser

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Urea compared to calcium ammoniumnitrate (CAN)

➢ Urea is 46% Nitrogen (N) ➢ CAN is c. 27% N ➢ Urea is converted to ammonium and nitrate

in soil (see below)

To minimise N (ammonia) loss from Urea

➢ Rainfall: best ammonia reductions from rainshortly after application, 7-14mm gives largereductions but be cautious of leaching and Nrunoff loss

➢ Avoid applying to wet soil/grass followed bywindy, sunny conditions

➢� Urea applied into a crop canopy is moreprotected from wind and direct sun

➢� The proportion of N loss as ammonia tendsto increase with increasing N rate e.g.grazing N rates (typically <40 kg N/ha) arepotentially less risky than silage N rates(typically >80 kg/ha)

➢ Urea can be riskier on soils with pH >7.1

Urea fertiliser spreading considerations

➢ Urea is less dense than CAN making it moredifficult to spread evenly at wide boutwidths

➢ Small prilled urea (50%<2mm) is particularlydifficult to spread on bouts >10m. Largerparticle sizes (80% 2-4mm) are available andsuit wider bout widths

➢ Important to knowsize distribution,determine withhand-held sieve box

➢ Ensure the fertiliser spreader is set upcorrectly by consulting the spreadermanufacturers recommendations for thespecific product being spread

➢ Use trays to check the spread pattern

➢ Urea will have a narrower maximum boutwidth and a more wind prone spreadpattern than CAN

➢ Urea has transport and work rateadvantages over CAN because it has higherN content

➢ Plants take up mainly nitrate andammonium but can take up urea too

➢ N loss by ammonia gas volatilisation (lossto air) occurs when urea converts toammonium

YieldTeagasc trials show that CAN, Urea and Ureastabilised with the urease inhibitor NBPTfrequently give similar yields but Urea has thelowest N recovery

CAN UreaUrea +NBPT

Yiel

d re

lativ

e to C

AN (%

) 100

75

50

25

0

Average of 6 grassland sites, 5 N rates and 30 fertiliserapplications dates

➢� Apply Urea before lime application (10 days)

➢� Wait at least 3 months after liming beforeapplying Urea

➢� Wait 10 days after slurry application beforeapplying Urea and vice versa

➢� Incorporating into soil will minimiseammonia losses but risk of toxicity toseedlings increases with rate, do not placeurea with seed for this reason

➢� Use a urease inhibitor (e.g. NBPT reducedammonia N loss in Teagasc trials by c. 79%on average)

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