Monday, December 11, 2017

Concern grows over knock-on effect of early urea applications

August 1, 2017 by  
Filed under Crops

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Nitrogen deficiency resulting from urea applications in the dry early spring of 2017 has caused concerns for many growers this year, agronomists are warning.

Independent agronomist Sean Sparling says many crops treated with urea this year have looked ‘hungry’ and in need of extra nitrogen throughout the growing season.

“Many growers who applied urea in the middle of April had granules/prills still on the ground three weeks later – you could have put them back in the bag. These crops showed signs of nitrogen deficiency quite early on in the season.”

The problem was compounded by plants growing slowly as a result of drought combined with the relatively warm conditions that increased the volatilisation, says Mr Sparling, who is chairman of the Association of Independent Crop Consultants.

Atmosphere

“By the time the rain came and nitrogen was washed into the soil, a lot had already been lost to the atmosphere and the effects of this have lasted with the urea-treated crops looking as if they could do with an extra 30kg/ha nitrogen or so through the season.

“On the other hand, crops receiving ammonium nitrogen fared much better. A couple of days after application, all that was left of the prills was the characteristic sticky residue and you knew it had gone into the crop.”

Frontier’s crop nutrition technical manager Edward Downing says there is growing unease over the risks and effectiveness of urea as opposed to ammonium nitrate (AN) – and 2017 has brought it into sharp focus.

“Nitrogen is easily lost to the air in the form of ammonia with urea and the longer it remains on the soil without rain to wash it in, the greater this is.”

At risk

This process of volatilisation is generally greater in the dry and warm conditions characteristic of this spring, with high pH soils having been particularly at risk, he adds.

“But high losses have also been seen in trials in pH neutral, moist and cool soils meaning it is impossible to fully manage away all the problems of nitrogen lost in this way.

“In contrast, volatilisation is not a problem with AN and those crops that received their nitrogen in this way are looking in much better shape.”

CF Fertilisers’ arable agronomist Allison Grundy believes there is little point trying to calculate plant nutrient need and plan accurate applications if you risk losing a significant chunk of what you apply to the atmosphere.

“Predicting when nitrogen losses will be at a minimum with urea is near impossible and for modern finely-tuned arable business with overall margins as tight as they are, introducing an increased level of uncertainty can be the difference between financial gain or pain.

“Recent research has been very much focused on understanding plant nutrient needs and trying to match this precisely for optimum yield without wastage – physically or cost wise – and it is difficult to do this with urea.

“With AN fertiliser creating the greatest return on investment of all inputs at around 5:1 on cereals, you do wonder if it is worth taking the risk with urea any more.”

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