Drill date main driver
Mixed views on the value
of soil nitrogen tests and
official RB209 advice that
yield potential is a poor
guide to N needs is evident
as top-dressing begins on
farmers weeklys barometer
farms. Andrew Blake reports
FOR Simon Porter, greener than normal winter cereals at Penn Croft Farms, Farnham, Surrey, are a sure sign there is more residual N available this spring.
"Only a few of our most forward crops are starting to yellow a bit. We dont use soil mineral N tests because we have yet to find one that gives the right answers.
Drilling date is his main top-dressing driver, especially this season, but yield potential cannot be ignored, he says. "We also consider soil type, winter rainfall, previous cropping and whether the field has had FYM or Terra-cake.
"We fertilise in the reverse order to drilling." That saw November-sown second wheats getting 50kg/ha (40 units/acre) of N at the end of February. Crops after oats received slightly more last week.
"Most of our first wheats will get their first 80kg in a couple of weeks time." Avoiding encouraging unwanted tillers is a priority. Last dressed will be winter oats to avoid low bushel weights and lodging.
"Our late-drilled wheats will have their total in three splits, but the early ones, like the oilseed rape, will get it in only two. The final amount will depend when the first dressing goes on. The later it is the less we will apply.
"We will use up to 200kg/ha on first wheats and 220 on the seconds and oilseed rape, with an extra 50-60 of urea at milky ripe stage on milling varieties."
Home-mixed liquids, with on-the-move adjustments for soil type, have helped cut costs for over a decade. "We bought ammonium nitrate for £58-75/t and urea for £95-£105 this year, but bargains are definitely getting harder to find."
Increasing trials evidence has prompted him to use sulphur on all crops, including pulses for the first time. "We have applied it as liquid on rape for four years and wheat for two. But it is difficult to adjust the mixes for different crops. So we will go with solid ammonium sulphate around the end of March." *
With Somerset wheats having up to 20 tillers, Chris Salisbury has been in no hurry to top-dress. Only backward crops and oilseed rape had had any N by last week.
"We have a phenomenal number of tillers and need to wait for some to die back," says Mr Salisbury, who has yet to try soil N tests.
"I can understand that yield potential affects P and K fertiliser requirements, but I am not sure I agree with that argument for N. The need per plant is the same, so if you have a thin crop with fewer plants you probably need less N/ha."
Ammonium sulphate liquid, applied to most of his wheats by contractor to ease workloads during potato planting, is a first for Sandy Walker in Shropshire. Despite regular use of chicken manure, he is convinced of the need for extra sulphur.
Another first is tissue testing of his most forward crops, including August-sown Claire, about a month ago.
"It showed they dont need anything for at least another week."
Soil min-N tests have previously been tried without any great confidence. "They can only act as a guide," he says.
"Never let it starve," is Peter Wombwells nitrogen strategy for his drought-prone Essex farm, where all winter crops had received 40kg/ha (50 units/acre) of N by the end of last week.
"Our rainfall averages only 21in/year, so later applications often dont work well."
Undressed breeder trials on the farm "as yellow as a guinea" and the notion that yield potential should have little influence on N input are hard to accept.
William Hemus has tried soil N tests on his Warks farm where wind recently interrupted oilseed rape top-dressing with prilled urea. "But its very difficult to translate the results from a very small area to the whole farm.
"The RB209 advice on yield potential is probably right. After all our continuous wheats get more N than our first wheats which always outyield them."
In Yorks, Catherine Thompson uses soil N tests to guide potato inputs. "But we never use them for cereals."
The main source of information where much pig muck is employed is ADASs Manner computer programme.
Late-sown wheats on light land recently had about 30kg/ha (23 units/acre) to stimulate growth. "But everything else is as green as grass and half way up my legs, so we wont do anything until GS30. We dont want to encourage any more tillers."
Mrs Thompson says she is reluctant to doubt the scientific integrity of RB209.
In Angus, Robert Ramsay is relieved to have had a weather window to get vital S and N, as ammonium sulphate, onto winter barley and oilseed rape. "Some of the waterlogged barley needed it sooner."
Soil N tests have little to offer on his thin land, he believes. "They are really only any value used deep when we tend to hit rock. We have tried chlorophyll clip tests and the N-Sensor.
"But I still think the best guide is historical data and muddy boots feel."
Variable N inputs are part of his system. "I dont disagree with RB209 thinking. But the key is to ensure N isnt a limiting factor."
• Northern Ireland
Wet weather has prevented any fieldwork in Co Londonderry. But Robert Craig is looking forward to taking part in a DARD trial of an aerial near-infra-red system to guide N treatments later in the season.
October-sown Malacca on Simon Porters southern unit gets its first 50kg/ha (40 units/acre) of nitrogen, nephew Giles applying a 33% solution of ammonium nitrate and urea.