The Cost of Lodging in Oilseed Rape
24 Aug 2017
Lodging in oilseed rape is a significant problem and can have a considerable impact on yield. Even what may look like a fairly minor ‘lean’ can prove costly as Dr Sarah Kendall, Crop Physiologist with ADAS explained.
She said, “We have done aerial surveys in 2012 and 2014 where we determined the area of a field that has lodged. Across these two years, we found that the average area of a field that lodges is 31%. Therefore, there are considerable areas of the crop where lodging occurs and this can have a significant effect on yield. In 2012, the percentage of fields where we were seeing no lodging was rather small. By looking at the average from these surveys, it helps us to extrapolate what the impact will be for the industry.”
Dr Kendall added, “Quite often in oilseed rape, the majority of lodging takes place in the middle of the field, so often it is not until the farmer is combining that they become aware that there has been some lodging.”
Using aerial surveys to determine the extent of lodging, did however, have drawbacks, as Dr Kendall explained, “From the aerial survey we found it difficult to ascertain the severity of the lodging, hence it is likely that we picked up more of the severe lodging and less of the leaning OSR. This is because you need quite a change in angle to pick up lodging from the aerial photos.”
To enhance the results from the aerial surveys, researchers devised trials using crops which had been lodged artificially. Dr Kendall said, “This work is really important because it will help us start to determine the impact of the angle to which the plant lodges.”
In these experiments crops were lodged to an angle, from the vertical of 22.5°, 45°, and 90° which is where the crop is completely flat.
Dr Kendall said, “We were particularly interested in the 22.5° angle. Sometimes growers believe that if the crop is leaning slightly, this can have a beneficial effect on yield and make the crop easier to combine. However, this was not seen in the results of our experiments.
“In one experiment that we did, when the crop was artificially lodged, leaning at 22.5°, the yield was actually reduced by 27%. So even lodging that doesn’t look particularly severe can still have a significant impact on yield.”
There are two types of lodging which can occur in oilseed rape: root lodging which occurs when the strength of the anchorage system fails, and stem lodging when the stem will buckle. Lodging can be influenced by a number of factors, such as extreme isolated rain fall or isolated high winds, but it can also happen in the absence of these weather conditions.
Dr Kendall said, “Lodging is really driven by the size of the canopy, if the canopy is too large it is much more likely to lodge. Obviously, a multitude of factors contribute to how big the canopy is.
“Variety wise, height is a contributing factor, so taller varieties need to be managed in a more risk averse way than shorter ones but there is still potential for semi- dwarf varieties to lodge,” she cautioned.
“High seed rate, high plant populations and high amounts of nitrogen applied early to the crop will give a dense canopy making the crop more likely to lodge. However, a lot of growers are aware of, and now use, canopy management principles.”
In order to work out the economic impact of different angles of lodging for growers, researchers tried to work out a costing depending on the degree to which the crops were artificially lodged.
Dr Kendall said, “We found that leaning, where the crop might not look completely flat but there has been a change in the canopy structure, can reduce yield by 27%, which if you work on an area basis would cost the grower £ 75/ha. In contrast, if the crop is lodged to 90° at early flowering, we found that this would reduce yield by 50% and so you are looking at a cost of £ 150/ha.
“Our experiments showed that lodging which occurred early in the season, at early flowering, is likely to have the biggest effect on yield because this is the point where the number of seeds per metre square is being determined. However, we have also seen significant yield losses, up to 60%, from lodging which has occurred late in the season during seed filling.
“I would say generally, there is no good news with a lodged crop. If your crop lodges, there is going to be a yield reduction, whether it occurs early or late in the season and whether the crop is completely flat or just leaning.”