Spring vigour in oilseed rape
Spring vigour is a key criterion scored in the field-scale oilseed rape studies Agrii trials manager, Jim Carswell runs each year with up to 20 of the most popular and promising varieties on iFarms across northern England and Scotland.He sees consistent differences between varieties in both the earliness with which they grow away in the spring and the speed with which they develop – DK Exsteel and DK Exstar invariably being some of the earliest and fastest respectively.
These differences were underlined in the series of 14 field-scale strip trials run by Bayer with growers under their own farm regimes across the country last season. DK Extremus was the earliest into regrowth in February followed by DK Exstar and DK Exsteel.
DK Expectation showed a particular turn of stem extension speed to match DK Exstar in its earliness of flowering in April, while DK Excited also picked-up its pace of development to flower ahead of DK Exsteel and DK Exposé.
While the earliest-developing varieties also tend to be the earliest to flower in the experience of both researchers, this isn’t always the case. And while many growers favour those that develop the fastest and flower the earliest, they find that initially slower or later developing hybrids with the right genetics can perform every bit as well at harvest.
“A good 30% of our DK Exstar plants at Bishop Burton were flowering when we scored the iFarm plots on April 5 last year compared to just 0.5% of the DK Exposé ones,” reports Mr Carswell. “Yet both varieties gave us a very impressive 5.8t/ha gross output at harvest on July 29.”
“We found little to choose between our top Dekalb hybrids performance-wise too,” Mr Williams notes. “Despite an inevitably earlier harvest than ideal for the later flowerers, variety seed yields were in a very tight 4.8-5.1t/ha range.
“What’s more, the latest flowerer, DK Exposé underlined its developmental flexibility with an above average 5.0t/ha. And when harvested a week later than the main strips on one site to to better match combining to its maturity, the variety delivered 5.65t/ha – 15% up on the average.
“All our work with OSR emphasises the importance of choosing hybrids with the most appropriate spring as well as autumn development for a farm’s particular conditions then matching their agronomy to the varieties’ specific strengths,” he stresses.
“In some cases, rapid spring growth can be a great help in enabling crops to grow away from winter or pest damage. But on cold, wet ground the earliest crops can start growing before the soil warms-up enough to meet their nutrient needs. And the more vigorous a variety is in the spring the more important it is to be stiff in the stem.
Early flowering
“Earlier flowering can also mean a longer pod fill period for higher yields,” he adds.” Having said that, though, the risk of frost damage is higher. This means early flowering varieties need to be particularly strongly branching, so they can compensate as well as possible for any early pod loss.”For the best results, Mr Carswell urges growers to match their spring management to the particular characteristics of the varieties they are growing, stressing the importance of being especially ‘on-the-ball’ with the earliest and fastest developers.
“Early nutrition is even more crucial than normal for the earliest starters,” he stresses. “You need to get your first nitrogen and sulphur on as soon as you can travel so they have something there to support their growth as soon as they need it. Then you can tailor your N to GAI with the second split.
“Fresh available phosphate in the spring can be particularly valuable on higher pH soils to combat their tendency to lock up these and other nutrients too. And spring applications of the phosphate availability enhancer, Release have given us the most cost-effective responses on high vigour varieties like DK Exsteel in our trials.
“It’s worth considering early foliar nutritional support for varieties with the greatest spring vigour if your soils remain cold and wet too,” Mr Carswell advises. “As it may also be if the weather turns very dry – with boron especially important to combat stem cracking.
“Good plant growth regulation should be another priority with any particularly vigorous varieties that don’t have the stiffest of stems. They can go into stem extension surprisingly early and the best stem strengthening always comes from early PGR application.”
