Results from a series of Scottish trials have challenged claims that the use of foliar nitrogen in grain crops is four to five times more efficient than the normal soil-based applications of fertiliser.
The research, which was carried out by the SRUC, concluded that there was little evidence of greater yield responses from soil plus foliar applications than there was from a similar level of nitrogen applied by soil application alone across two sites over two years.
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Speaking at last week’s AHDB/FAS agronomy roadshow in Perth, Professor Ian Bingham, senior researcher in crop physiology at the college, said that the trials had been designed to test claims that foliar N was taken up and used by crops with greater efficiency than standard soil applications – enabling significant reductions to be made in the total amount of N applied.
However, Professor Bingham said it was critical to know exactly where on the nitrogen response curve applications were being made, especially as, unit for unit, foliar applications tended to be between three and five times more expensive.
“Indeed, if applications are being made after the response has plateaued, it would be possible to reduce application rates by as much as 50kg per ha and not replace it with anything and still see little yield reductions,” he said.
He told growers that the trials – which had been funded by the Mains of Loirston Trust – had shown that N use efficiency was broadly similar under both application methods, with results indicating that soil-applied N had a recovery rate of around 62%, while foliar applications returned a rate of 56%.
Over the course of the trials on spring barley and winter wheat over two years, and across several sites, three different types of foliar N had been tested and all showed similar results to soil applied N when plotted on the response curve.“And this showed that foliar nitrogen is behaving pretty much the same as soil applied nitrogen,” he pointed out.
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Professor Bingham added that analysis carried out to see if foliar nitrogen offered physiological advantages within the plant had also returned similar results, with the levels of grain protein and nitrogen found in both the wheat and barley trials being broadly equivalent under similar application rates.
“While there may be situations in which foliar nitrogen is a useful tool, the take-home message from these trials at least is that there is little evidence to suggest that there is any greater level of improved nitrogen utilisation efficiency from foliar applications,” he concluded.
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