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Nitrogen uptake discussed at AHDB Potatoes Winter Forum

28 February 2012

Applying nitrogen early to potato crops and ensuring nothing restricts its uptake is a key way of boosting yield and reducing fertiliser bills, latest AHDB Potatoes funded research* has shown. 

The work, carried out by Cambridge University Farm, and presented at the AHDB Potatoes Winter Forums, show that yield potential is created very early in the season and provided enough N is available to match crop demand growers can substantially boost their bottom line.
Work over the past four years substituting grower intentions with project recommendations has shown that for some fields the N rate could be reduced by 30-40kg/ha while maintaining yield.
While the project recommendations also took account of other factors like season length and variety, earliness of application played a crucial role in the result, says project leader Marc Allison of CUF.
Further work on two crops of Saturna last season – one in Nottinghamshire and one in Yorkshire – confirmed the importance of early N uptake and availability. The Nottinghamshire crop took up 209kg N/ha (from soil and the bag) and yielded 63t/ha, while the Yorkshire crop only took up 169kg N/ha and produced about 41t/ha.
“Most of the uptake in the high-yielding crop took place in the first six or seven weeks after emergence, driving crop growth and enabling it to absorb the maximum amount of sunlight. By contrast, the Yorkshire crop took much longer to take up less nitrogen and was never able to catch up,” says Marc.
The Yorkshire crop was affected by potato cyst nematode, but compaction, drought or waterlogging could all have had a similar effect on uptake, he explains. “While it is really important to have enough nitrogen on early, anything that interferes with its uptake is likely to have a big impact on yield,” he explains.
As far as timing is concerned, the work shows biggest yields are achieved when all N is applied at planting, or split between planting and emergence. Later applications may reduce N uptake and, in turn, tuber yield he comments.
Growers should not worry too much about leaching, he adds. “The probability of enough rain falling to leach out N applied at planting is quite small. Long-term met data for Terrington shows there is less than a 1 in 10 chance of more than 25mm of rain falling in one week between April and June. When you consider that most fields will also be 15-20mm below field capacity the chances of losing much nitrogen down through the soil profile are quite remote.”
Growers in the west could ensure their second split is applied no more than 20 days after emergence. “N applied later is less likely to be taken up and you will suffer a hit on yield. The later you leave it the worse it gets.”
That holds true even for irrigated crops, Marc advises. “Trials have shown that properly scheduled irrigation where no through drainage occurs allows the crop to make much better use of N - you don’t need to apply any more.”  
Keeping fertiliser away from furrow bottoms can also improve efficiency of N use. Some 16-18kg/ha of the top dressing falls in these often compacted areas and in trials when it was removed, no yield loss was seen. “In consequence, we may be able to reduce top dressings by a similar amount, perhaps by using liquid applications to target the furrows only or by incorporating nitrogen into the furrows at planting.” 
N efficiency tips
* Match N to crop need
* Apply early
* Ensure no restrictions to uptake
* Project R405 - Improved Canopy and N management for the UK Potato Crop ran between 2008 and 2011 and aimed to develop systems that would give growers better control of canopy and nitrogen management and to provide a sound scientific basis to fertiliser recommendations.
Additional work is being carried out to develop the model and use information on variety, specific soil conditions, and other factors to determine more precisely canopy development and N applications. 
Printable Version Grower Gateway - Issue 2, 2012
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