Farmer Focus: Surprised to see urea singled out as bad

We’ve had no rain to speak of for six weeks. My default reaction was to moan incessantly, but that didn’t seem to do any good, either with the weather or my locked down family, so I’m now trying to think of how to react in the future.

More winter crops might be one way to go, but is the opposite of what we have been doing to combat grassweeds and we have been getting on well with cover crops for soil improvement, sheep grazing and stewardship payments.

See also: Why biopesticides will play a bigger role on arable farms

I also have solid fertiliser still on the surface a month after application and scorching from liquids, so another tactic might be to use some kind of delayed release fertiliser and apply the whole lot at the start of the season, but that might not be beneficial to plant or soil microbe health.

I was surprised when completing my annual Facts scheme exam to see urea fertiliser singled out as bad. The concern is volatilisation of ammonia and, while we do have to to minimise this, ammonium nitrate was touted as a better alternative. I don’t sell either, but maybe we should recognise that both have their pros and cons.

It is said that urea may lose 20% of its nitrogen via volatilisation, but if you look at the source of this information it appears this may only happen at 32C so perhaps is not too relevant in the UK?

Also, NIAB trials over many years find the same yields from both forms of fertiliser, so ammonium nitrate must be losing an equivalent amount, and scientific work estimates that N lost by leaching ranges from 40kg to 115kg of N/ha.

Added to this, ammonium nitrate can increase crops’ susceptibility to fungal attack and reduce their ability to uptake nutrients such as magnesium, manganese and zinc, especially on my chalky soils. As ever, a balance, rather than extremes may be the answer?


Andy Barr farms 700ha in a family partnership in Kent. See his biography.

NOVEMBER
3

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