N prediction is still a mystery

After a quarter of a century of experiments, choosing the optimum amount of nitrogen fertiliser for sugar beet remains as tricky as ever, according to a Broom’s Barn researcher.

Given this year’s heavy summer rains, which in theory leached more N than usual, many growers felt that their yellowing crops could have done with some late N fertiliser or more than they first applied, Keith Jaggard acknowledged at last week’s trials open day.

But all work on the subject, including some as recently as 2002, suggested neither tactic would have helped improve output, he said.

The standard strategy of applying about a third of the crop’s total requirement at sowing and the balance a few weeks later was unlikely to be bettered, he believed.

What that total should be, however, was hard to determine but important in the light of consultations on revising DEFRA’s RB209 recommendations booklet.

“Agriculture has spent the past 25-30 years trying to make specific field recommendations for nitrogen,” said Dr Jaggard.

But after studying results from 160 experiments on N use on the crop since 1980 there were no clear cut answers.

“They show that in sugar beet there’s no way you can predict exactly what’s going to be needed.”

His study found no link between soil type, drilling date or any other factor which might influence individual crop’s requirements.

“There was just no relationship that we could see.With sugar beet it’s all about what happens early.”

The main demand for rapid uptake of N occurred up to mid–June, while the beet’s root system was still relatively small.

But while it might be supposed that earlier drilled crops, with their longer growing season, might need more N than later sowings, there was no evidence to support that thinking.

About 80% of the roots were in the top soil and needed rapid access to high concentrations of N, he added.

That raised the question of whether placing N fertiliser close to the seed might be justified.

“I know they’re quite keen on it in some other EU countries, but we’ve looked at the data and can’t see any justification for it.”

The cost of the specialist machinery required was something growers could ill afford given the economics of the crop, he added.


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