While oilseed rape PGRs grab the headlines, altering nitrogen applications may offer an important supplementary way of manipulating OSR crop growth. Martin Rickatson reports.
On the back of the development of the oilseed rape plant growth regulator market (PGR), with Toprex (paclobutrazol) this season joining Caryx (metconazole + mepiquat chloride), ADAS trials researching methods of managing OSR canopies suggest there may also be scope to influence plant architecture through other means.
The effects of PGR use, nitrogen manipulation and even defoliation early in the season have all come under scrutiny by a team led by Pete Berry, ADAS principal research scientist. The new PGRs have a definite place in canopy management, he suggests, but tailoring nitrogen use to crop density and advancement can have a significant effect, not only on yield directly, but also indirectly via reductions in lodging, which has been shown to affect both yields and oil content.
Much of the trial success in altering standard nitrogen practice has come from reducing early N, he says, resulting in a better-standing, more open canopy structure which is less prone to lodging.
Dr Berry says: “There appears to be some scope for ‘starving’ a big crop early on, without affecting its yield potential.
“In trials at ADAS Rosemaund, we compared a conventional programme of 120kg per hectare of N in mid-March before stem extension, followed by 120kg/ha at green bud in mid-April, with a ‘managed canopy’ programme. With this, the first application was eliminated, and the crop did not actually receive any N until the green bud/mid-April stage. This was increased, though, to 140kg/ha, and was followed by a second application of 100kg/ha at yellow bud/early flowering in late April.”
Both therefore received the same amount of nitrogen. However, one of the most significant visual differences between the two was the difference in crop height and, ultimately, lodging levels, says Dr Berry.
“It was clear this was caused primarily by difference in stem length, with the crop which had its first nitrogen delayed being 30cm shorter prior to harvest. Lodging levels were just 2% here, whereas the levels were 30 per cent in the crop which received the standard programme.
“At harvest, the benefit of this was shown in yield terms with the shorter, stronger-standing crop producing 0.3 tonnes/ha more than crops which received a standard nitrogen programme.”
In conjunction with use of a PGR, it is suggested such manipulation could provide OSR growers with much greater scope to influence yield and oil and protein contents. ADAS has recently been conducting trials with dedicated oilseed rape PGR Caryx and the fungicide Sunorg Pro (metconazole), with its growth-regulating side effect, both applied between the late green bud stage and mid-flowering.
“Each appeared to increase secondary branch numbers, which can contribute more than 1t/ha to yield, while there was also clear evidence of the effect Caryx has on rooting at 9-10cm, which it increased by up to a quarter,” says Dr Berry.
“This is especially important in a dry year, when good root mass at this depth can be worth 0.25-0.30/ha.”
A multi-year project funded by Innovate (formerly Technology Strategy Board) looking at the effect of foliar N timing on OSR yield and protein and oil contents has shown some strong responses and some weak, with an average which suggests there is scope for adjustment, according to Ian Matts of Yara, a partner in the research.
He says: “Over the past 10 years we have been studying the yield differences in trial crops which received foliar N at either early, mid or late flowering.
“We have seen wide-ranging responses in yield terms, from almost negligible to 0.8t/ha, producing an average of 0.3t/ha gain with both oil and protein contents also benefiting.
“But there appears to actually be little difference in which of those timings is used. In many cases it may therefore makes sense to combine a mid-flowering application with a sclerotinia spray, and save a pass.”
Research from GrowHow during the last decade suggests there is little difference in the nitrogen regime required by conventional, semi-dwarf or hybrid OSR types, says Allison Grundy, an agronomist at the fertiliser firm.
“Taking soil nitrogen samples in early February to gauge what extra is required should be part of growth management and nitrogen strategy if N use is to be optimised.
“The crop’s basic requirement is for 175kg/ha of N by green bud. It is green area index [GAI] which should drive crop management and nitrogen input planning, according to yield target – what you think the crop is capable of when measuring GAI.
“OSR with a GAI of 3.5 by the green bud stage should have 175kg/ha of N in it and potentially be capable of producing 3.5t/ha. In a crop which looks promising, each additional 30kg/ha N applied at early flowering should be worth an additional 0.5t/ha yield more than 3.5t/ha. Reining back on N at earlier timings, especially in thick crops, gives this scope.”
ADAS researchers are looking at revisiting the principle of defoliating forward crops to rein them back and encourage redevelopment of more sustainable growth. Growers may take some convincing about the idea of topping a healthy-looking OSR crop during January, says Dr Berry, but trials from the mid-1990s which are now being revisited suggests August-sown crops established at 60 seeds/sq.m benefit by 0.09t/ha, with this figure at almost 0.3t/ha in a high seed rate (120 seeds/sq.m) crop.
“This data comes from the 1995-6 season, when ADAS trials assessed topping the crop down to a height of about 5cm above the soil surface. Winter grazing by sheep of forward cereal crops has been practised before and there may be some worth in topping forward oilseed rape in this way, but we would like to research this further.”
ADAS crop physiologist Sarah Kendall says aerial surveys across 2,000 hectares in East Anglia in July 2012 and 1,000ha in North Yorks, Lincs and Cambs two years later showed all fields contained some significant element of lodging.
Trials work during the same period has allowed values to be placed on this.
She says: “While most lodging in 2014 occurred late on and was relatively mild, that observed in 2012 occurred earlier and was more severe. In all, 35 per cent of fields surveyed in 2012 showed lodged crop, and 27 per cent in 2014.
“Last season we conducted artificial lodging experiments to assess the effects of different severities of lodging. This was done simply but accurately by pressing down measured areas of the trial crop at angles of 22.5, 45 and 90 degrees, with gentle and gradual pressure used to avoid breaking stems. It was carried out at early flowering and then repeated at mid flowering and at early and mid-seed fill.”
At harvest, yield losses of up to 2.5t/ha were recorded in the lodged flat crop, while a significant drop in oil content was also noted. Crop lodged at 45-degrees also showed significant yield losses at all lodging timings and a drop in oil content at all bar the early flowering timing. It was at the early and mid-seed fill timings when the crop lodged at 22.5 degrees showed significant yield loss.
“Across the whole trial, oil losses of up to 8% were recorded, with yield losses of up to 62%. The greatest effect was on the number of seeds produced per sq.m, rather than thousand seed weight, suggesting seed and pod abortion were significant here.
“Putting a value to the yield loss figures across the trial, they translate to £170/ha for a flat crop, but even a leaning crop will lose £70/ha. And then, of course, there are the other effects of lodging on crop quality and harvest efficiency – uneven ripening and slower combining speeds.”