Bitter RB209 pill is best medicine
Bitter RB209 pill is best medicine
GRAIN nitrogen at harvest rather than potential yield is a much better, albeit retrospective, aid to fine-tuning nitrogen inputs to wheat, says a leading ADAS researcher.
Peter Dampneys comment comes as growing numbers of producers say they find the latest RB209 message – yield potential is of minor importance when it comes to determining optimum N for crops – hard to accept.
"Yield is very difficult to predict, and its a brave man who does so," says Mr Dampney. "In terms of adjusting N inputs, results from 300 small plot response trials shows grain N content is a much more reliable guide. But you do need to build up a history of results on your own farm and on individual fields to be able to use it properly."
Field by field modification of nitrogen inputs according to yield potential has been dropped from the latest edition of RB209 largely because of growing evidence that first wheats use applied N more efficiently than second and subsequent crops, he explains.
"If you look over the long-term, improvements in varieties and other husbandry techniques have raised yield potential, so in that sense it is possible to justify applying higher levels of N. But on an annual basis yield potential is a poor indicator.
"We realised that the new message would be hard to swallow and it has already generated quite a bit of debate. But we are happy to stand by it after the results of trials, some for instance comparing the N requirements of wheats sown at different times from autumn to spring.
"We measured the optimum N required and it remained the same whatever the sowing date. The reason is that late sown wheats, which are inherently lower yielding, use applied nitrogen fertiliser less efficiently. So in effect they need proportionately more N to produce a ton of grain. The knock-on effect is that the residues they leave behind are likely to be higher."
Previous RB209 advice was that total N applications should be varied by plus or minus 20kg/ha/t for yields expected to be above or below 8t/ha. Previous cropping, soil type and weather are far more important drivers of N needs than potential yield, he says. *
NFORWHEAT ADVICE
NFORWHEAT ADVICE
NFORWHEAT ADVICE
• Yield potential not important.
• Output difficult to forecast.
• Efficiency of N use is key.
• Grain nitrogen better guide.