N policy provokes debate
NOT ALL our regional representatives are convinced that there are N savings on offer this season, as ADAS suggests (Arable Mar 25). However, several plan to trim inputs slightly, mainly because of higher fertiliser prices.
Among those striving to be more scientific in their approach are Troy Stuart and his UAP agronomist Howard Moore.
“I”m not against extending the Voluntary Initiative to fertilisers, says Mr Stuart. “We must be able to justify their use.”
On his Devon unit, with its particularly varied fertility and cropping history, there are two key areas of uncertainty, says Mr Moore.
“It”s especially difficult to get a handle on winter wheat requirements after grain maize because RB209 mentions only forage maize.
“Terra have done soil cores to 90cm and I”ll be basing my final N recommendations on the results fed into the UAP N Calculator, taking into account green leaf area in mid-February, target yield of 10t/ha and an optimum grain N for feed wheat of 11.4%.
“The first dressing of 133kg/ha of N has only just been applied to avoid driving too large a canopy. I”ve still got crops coming into spring visibly showing high levels of N.
“The rule of thumb here this year is that there is 20% more soil N available than usual.”
For the first time in winter oilseed rape, Mr Moore has been weighing 1sq m foliage samples to assess the N trapped by the crop over winter.
“Compared with wheat there”s a poor N to yield relationship in oilseed rape,” he says. “Best yields tend to come from open canopies fed well.
“On Troy”s farm I”ve found 100% variation in what”s already there – from 45kg/ha to 110kg/ha – which has been reflected in our applications. We”ll have to wait until summer to see if that was sensible.”
All Ben Atkinson”s decisions are RB209-based using soil analysis. “The average total N reservoir for our farm is 68kg/ha.”
But after the wet autumn much of that is in the lower (60-90cm) profile and largely unavailable, he says.
“So we”ll be using much the same as usual. In general first wheats will receive 220kg/ha and seconds 230. These figures will be reduced on some of our silt land.”
Robert Stevenson routinely uses soil mineral N testing as a guide for combinable crops. “On that basis we”ll cut back by 15-20kg/ha on cereals and oilseed rape.
“We kept up the early application to second wheats and we”ll maybe trim the balance when we see how things are going.
“We”re using fertiliser replacement costs as the basis for all our calculations.”
Although Giles Blatchford”s soil mineral N reserves are, for whatever reason, much as normal, he expects to use slightly less fertiliser this season.
“That”s partly because of the higher price, but also because our Soil Nitrogen Supply, worked out through RB209, is a bit higher than usual. We have used a lot of muck in the past and crops have grown well. Most of our cereals have growth area indices bigger than normal for this time of year.”
As a seed grower especially wary of lodging, Paul Temple”s N applications, all liquid for accuracy, are likely to remain unchanged.
“We”ve never dragged our rates too high bearing in mind our residual N from muck. I have tried leaf testing, which tended to confirm that our practices are about right.”
CONSERVATIVE APPROACH
Andrew Goodman, whose mixed farming soils are inherently quite fertile, also plans a relatively conservative approach. “We make field by field decisions based on previous cropping and RB209.
“We could perhaps push things a little harder. Last year we used a bit more than usual on a second wheat and it did very well.”
Despite the higher cost of N, John Hutcheson will not be reducing his inputs. “It”s still not at that point, though it does make the spring bean gross margin look better. We may increase the total for Robigus, but will wait to see how it looks.”
