18 January 2002

Limitations to cheap N source has

UREA can be an attractive source of spring nitrogen fertiliser for most arable crops. But beware of choosing it on price alone, cautions ADASs Peter Dampney.

"If you compare prices on a p/kg of N basis, urea is usually significantly cheaper. As a rule, when ammonium nitrate (34.5%N) and urea (46%N) are the same price per tonne, the N from urea is about 25% cheaper.

"If the price is attractive, you should look to the quality of the product. And you must have the equipment to spread it evenly."

Mr Dampney believes quality has improved recently and suggests granular urea is of a higher standard than prills.

"Look at the prill or granule size and assess its evenness. This is especially important if you intend spinning because urea is lower density and does not throw as far.

"Spreading problems can arise if you try to spin urea on to 24m tramlines. You may be asking too much."

Growers considering switching from ammonium nitrate to urea must recalibrate their spreaders, he adds.

Moist spring conditions are best for urea and applications from mid-February to the end of April will be efficient. "Concerns about urea only arise when it is hot and dry when there is a risk of losing nitrogen as ammonia."

Provided there is moisture, urea will usually perform as well as ammonium nitrate. "The possible exception is on light chalkland soils, which can encourage ammonia formation. You may get up to 10% losses on these soils, so be prepared to compensate."

Stuart Murdock, import manager for Banks Cargill, says growers can expect granular urea to spread as well as ammonium nitrate in good conditions.

"It has the same particle size, 2-4mm, as an ammonium nitrate product with a SP rating of 5. But prilled urea, which is 1-2mm, can be spread accurately only to 12m."

Urea will work well in cold, wet conditions and the argument about relative efficiencies is immaterial when urea is always at least 20% cheaper than ammonium nitrate, he says.

"There are situations when it wont perform well – in high pH soils, in very hot, dry conditions and on spring barley."

Richard Martin of Terra Nitrogen UK adds that ureas efficiency depends on the weather at application. "But the purchase decision is often made well in advance. And with urea you need rainfall within 48 hours of application, or there will be up to 30% losses through ammonia gas."

With many cereals well forward this season, he believes N dressings may need to be delayed. "Well-tillered crops do not need early nitrogen." But delays could mean urea is less suitable.

"If you are tempted to try urea, make sure it is applied early in the season, before temperatures start to rise." &#42

Urea can be a cheap source of N, but granular and prilled urea have different physical properties which need bearing mind when spreading.