On first look this year’s yields may seem disappointing, but for many it is close to the five-year average. Last year just happened to be a bonanza harvest for OSR growers.
Sowing the ideal seed rate for autumn establishment is always a balancing act. Growers make assumptions regarding the winter weather as well as predicting losses to slug and pigeon grazing.
“Last autumn was good for oilseed rape establishment with favourable seed-beds and despite the dry conditions many crops were well established,” says Clare Tucker, BASF agronomy manager. “Even in November when normally temperatures begin to drop and growth slows that didn’t happen. This led to very forward crops coming into early spring.
“This year’s OSR crops following winter barley have established themselves well. Therefore, care will be needed to avoid compaction issues where a quick turnaround is required following late harvested wheat crops.
“We still tend to be over-generous with seed rates since we need no more than 40 plants per sq m by early spring with 25-30 plants being optimum to produce potentially high yielding flower canopies.
Green area index (GAI) is a useful management tool in pinpointing nitrogen and PGR timings. This is how growers can manipulate growth in the spring to produce the optimum canopy size, linked with high yields.
“In spring 2011 canopies were small (many thought frighteningly small) due to dry weather, but this was key to the larger yields. This led to good light penetration and, consequently, excellent pod set and seed numbers throughout the canopy. That year demonstrated that we need to be bolder in reducing the canopy size of our crops when the winter weather doesn’t do it for us.
“In 2012 there was low light intensity in May and June for good pod set. The canopies were too big and started to lodge. When you have got big canopies it is very difficult for light to penetrate them. Even when a crop just starts to lean it can seriously affect the amount of light penetrating,” adds Ms Tucker.
Summer 2012 was one of the dullest on record with just 399 hours of sunshine (up to 31 August) and has been the worst since 1980, according to the Met Office. Not surprising then that OSR crops were a little disappointing.
“So assessing the crop GAI will enable growers to manage nitrogen applications and decide whether or not to use a fungicide that has plant growth regulatory (PGR) properties,” says Ms Tucker.
GAI should be measured before the start of stem extension in the spring. This will enable you to make the most efficient use your nitrogen and fungicide applications while developing a canopy that can utilise the maximum amount of light. Good light penetration leads to an enhanced pod set and fill, creating better yields of seed with higher oil contents.
However, canopy management can start in the autumn by using fungicides that have a growth regulatory effect. These are more common place in Europe, but can have a role to play in the UK.
“For forward crops (those with 4-6 leaves by mid October or before) consider using metconazole in the autumn. Metconazole is a protectant fungicide spray with growth regulatory properties so will need to be applied before phoma thresholds of 10% are reached. It will give the standard four weeks protection against Phoma so monitor the crop for a potential repeat phoma spray after that,” says Ms Tucker.
The metconazole reduces the height of the growing point while thickening the stem. This has several distinct advantages. Firstly, by reducing the height of the growing point it can make the crop safer from harsh winter weather and pigeon grazing, and can prevent early stem extension. It also increases rooting, as good rooting is important for yield potential and reducing the lodging risk.
However, Tony John, technical director at Procam, believes that later planted crops might not benefit from a growth regulatory fungicide this autumn.
“Phoma control this autumn will be really important, so consider using a flusilazole or a flusilazole carbendazim mix,” he says.
“Every field is different so good agronomy is vital. Slugs are taking crops at will and much of the N has been leached away so monitor crops on an individual basis,” adds Dr John.
Oilseed rape performance
This season’s oilseed rape yield was only 5% down on last year for Strutt and Parker managed farms with the specialist high erucic acid rape (HEAR) crop delivering strong margins.
Data from managed farms and agronomy averaged 3.9t/ha compared with 4.05t/ha last season.
Strutt and Parker’s Richard Means explains that the crop definitely had as much potential as 2011 if not more. “But poor pod fill due to low sunlight levels led to smaller seed size this year and there was a higher incidence of lodging.”
Looking in more detail, conventional varieties out yielded their hybrid counterparts achieving 4t/ha against a hybrid average of 3.85t/ha. He puts the lower hybrid yield down to bigger crops with a greater incidence of lodging compared to conventional types.
Lodging will reduce yields by around 15% and this poorer hybrid performance this season has been borne out in the NIAB TAG and HGCA variety trials.
The top four varieties in order of area were DK Cabernet, Vision, PR46W21 and the HEAR variety Palmedor.
Conventional variety Sesame has been the highlight putting in a very strong overall performance. Alienor and Camelot crops have both been pleasing but were grown by fewer farmers.
Interestingly, while the HEAR yielded less at 3.5t/ha, it still gave the highest gross margin at £1,025/ha against DK Cabernet at £978/ha primarily because of the oil premium.
How much nitrogen is left in soil this autumn?
After such a challenging growing season and harvest, a key question for growers this autumn is how much mineralised nitrogen will be left in soils, vital for successful establishment of winter cereals and oilseed rape.
“Heavy rain will have caused some nitrate to be taken down the soil profile especially on lighter soils,” said Mike Slater, fertiliser technical development manager for Frontier. “With yields below what was hoped for, it is true that less nitrogen than expected will have been removed from the field by the grain.
“However, growers should not take this for granted as monitoring in late June 2012 indicated that crops, (although looking well to the naked eye) actually had low levels of dry matter accumulation and total nitrogen uptake. This indicated that yield potential was already under threat back then, which raises questions about what is actually happening to the mineralised nitrogen in our soil.”
Mineralised nitrogen test results already conducted this autumn from heavy soils in the eastern counties indicate that soil nitrogen levels are 25 to 30 kg/ha above the long term average for those following cereal and oilseed rape crops. However, it is highly likely that on the lighter soils more nitrogen will have been lost through leaching. Growers with concerns over nitrogen levels in their own soils, are advised to test soils.
Steps to dealing with problem weeds
With resistant blackgrass becoming more widespread on farms throughout the UK, growers should seize the opportunity to control problem weeds throughout the rotation.
There is no known blackgrass resistance to propyzamide and carbetamide so there is a great opportunity to reduce the weed burden in the OSR crop.
Control may seem expensive at the time but over the course of the rotation it can represent good value. So for growers who have a broad-leaved and grassweed problem could consider a targeted approach.
Apply metazachlor, growers can add dimenthenamid-p and or a quinmerac-based product depending on weed spectrum. This can remove 75-80% of blackgrass populations where seed-beds are good and the surface trash has been spread evenly and shallowly incorporated.
Apply Cycloxydim/tepraloxydim at 1-3 leaves of the blackgrass. This will remove cereal volunteers and other grassweeds. It helps to reduce the population further and ensures survivors grow more slowly ahead of Step 3.
Residual graminicides propyzamide or carbetamide once soil temperatures have cooled down.