Looks arent everything
Looks arent everything
In the quest for optimum yield without spending a packet, the A-team is employing cool scientific reasoning to determine nitrogen inputs. Tom Allen-Stevens reports.
OU would have thought the A-team would wax lyrical about the green, forward-looking crop in some of their plots at ADAS Boxworth, but looks can be deceiving.
"Some of the plots we inspected at the end of January had 700 shoots/sq m, and thats too much at this early stage," says ADAS crop physiology expert Roger Sylvester-Bradley. "Unless they start looking very yellow, we should hold off the nitrogen until April."
These were the plots drilled late with a high seed rate. Without the hammering from slugs that the early-drilled plots received, theyve established well. With only around two shoots per plant, tillering is just getting going. If fed to tiller more, the result could be a weak-stemmed crop, that might lodge easily.
But the range of crop cover in the plots is remarkable: the early-sown low seed rate plots are looking thin, with only 40 plants/sq m and about three shoots/plant. When it comes to deciding which of the plots will receive most attention early on, its not necessarily going to be the ones that look good.
"I would argue that those crops that look a bit sad now can still yield well, so will repay some management," says ADAS crop physiologist John Spink.
So whats the plan to get these plots back up to scratch? "Although there are plots out there youd weep over, re-drilling is not worth it. We have 100-200 shoots/sq m, and theres still plenty of time to encourage it to tiller out with nitrogen." The aim is for at least 600 shoots/sq m by April. The A-team accepts that these crops are unlikely to tiller out that much, but a perfectly acceptable yield is still possible. The salvage plan is 30kgN/ha in February, and again in March.
The team is much happier with the plots drilled at the same time with a higher seed rate. "The early-sown high seed rate plots have tillered well. The late-drilled low seed rate plots have also established well and are likely to reach the target shoot numbers by April," reports Dr Sylvester-Bradley.
This is where their key N weapon, soil analysis, comes into play. The results have been eagerly awaited; soil mineral N from the previous crop of oilseed rape could easily have been leached away on this heavy soil, or the rain may have just run off the surface and into the ditch. "The results show there was 140kg/ha available N still left in January, of which 60 was in the topsoil. This analysis will more than pay for itself, by cutting fertiliser bills," says Dr Sylvester-Bradley. As long as shoot production can be brought back on course, target canopies should be achieved without much further fertiliser.
While shoot numbers and canopies dictate nitrogen tactics, plant numbers dictate the growth regulator strategy. The late-sown, high seed rate plot is of greatest concern here. "With high plant and shoot numbers, we fear weak anchorage, and a weak stem base. So as well as holding off with the nitrogen, well apply some growth regulator," says Mr Spink.
Syngentas Jason Tatnell is on-hand with growth regulator advice. He believes dose rate and timing should be governed largely by variety: "Our variety profiling studies over the last four years show Consort is stem-base weak, so Id apply a Moddus (trinexapac-ethyl)/chlormequat mix at T1. With Claire the programme should be split to keep the height down. Again, Id apply a similar mix at T1 and think about applying at GS37 if lodging risk seems high later on." The combination of the two treatments will bring more height reduction than the sum of each alone, he explains.
"Well be spending more on the thick late-drilled crops, but we could have blown it already and the crop may still lodge. But a robust growth regulator programme will keep it standing for longer. The later it lodges the less you lose," says Mr Spink.