Dr Pete Berry
The winter oilseed rape variety Es Astrid has produced outstanding and consistent yields across many geographic locations, not just in HGCA trials but also in commercial crops over a number of very different years. Grainseed in conjunction with ADAS have been investigating how to manage the crop to best effect and a series of trials has been looking at the impact of seed rate on yields at three different locations.
Neil Groom, Technical Manager of Grainseed, explains that the three replicated trials of Es Astrid were laid down at High Mowthorpe in Yorkshire, Boxworth in Cambridgeshire and Rosemaund in Herefordshire where three seed rates of 67, 80 and 100 seeds/metreĀ² were compared. "The best yields usually result from a well rooted crop which produces an optimum plant population and an optimum canopy structure that can intercept and use light efficiently. To do this you need to achieve the optimum number of plants. There is much debate about what the optimum plant population is and how many seeds should be sown to achieve it. 40-50 plants/mĀ² is generally regarded as optimum. In practice over 100 plants/mĀ² are often established when high seed rates are used and high yields have been recorded with plant populations as low as 10 plants/mĀ². The seed rate, used in official trials for conventional varieties has been around 110 seeds/metreĀ² and has recently been reduced to 100 seeds/mĀ²."
Dr. Peter Berry, ADAS Plant Physiologist, reports that at two sites, Boxworth and High Mowthorpe, the 100 seeds/metreĀ²seed rate produced more and stronger plants that survived the winter and went on to produce the best yields. "At Boxworth 67 seeds/metreĀ² produced 3.97 t/ha, 80 seeds/metreĀ² produced 3.98 t/ha and 100 seeds/metreĀ² produced 4.16 t/ha. At High Mowthorpe 67 seeds/metreĀ² produced 4.45 t/ha, 80 and 100 seeds/metreĀ² produced 4.65 t/ha."
Dr Berry points out that at these sites the dry spring resulted in much shorter crops than usual and it is likely that the canopy size at the lower seed rates was below the optimum required to intercept light and form yield.
"At Rosemaund, on the more moisture-retentive silt clay loam, the shortening effect was much less severe and a larger canopy was produced. Here the highest seed rate had high levels of brackling due to an over-large canopy, which resulted in the lowest yield. Here in the West the 67 seeds/metreĀ² seed rate produced 4.49 t/ha, 80 seeds/metreĀ² produced 4.65 t/ha and 100 seeds/metreĀ² produced 4.14 t/ha," reports Dr. Berry.
The trials also looked at plant populations in the spring. "The plant populations for the seed rates with the highest yields were 51 to 60 plants per mĀ² at Boxworth and High Mowthorpe where the dry spring caused crop shortening. At Rosemaund, where larger canopies were produced, the highest yield came from a plant population of 42 plants/mĀ²."
The trials also looked at the effect of growth regulating fungicides applied in early spring to Es Astrid. "Although Astrid is the shortest variety on the HGCA list and has very stiff straw, the use of a growth regulating fungicide can help reduce the risk of lodging, manipulate the canopy structure so that light is used more efficiently, and also improve rooting. At Boxworth the use of Caramba (metconazole) resulted in yields of 4.29 t/ha, which was over 0.5 t/ha extra compared to the untreated. The lower seed rate yielded an extra 0.57 t/ha and the mid rate 80 seeds/metreĀ² an extra 0.55 t/ha when treated with Caramba. These effects may have resulted from improved rooting. At Rosemaund Folicur (tebuconazole) gave an extra yield benefit of 0.31 t/ha at the high seed rate and reduced brackling down from 71% to 27% and lodging down to from 6% to nil. Its effect was less in the lower seed rate plots where there was little lodging anyway," outlines Pete Berry.
Neil Groom concludes that sowing rates of oilseed rape are critical to final yields, but growers need to make the decision based on their specific field and weather conditions. "Last year, even with a good autumn, the highest seed rate (100seeds/mĀ²) gave the highest yields at two of the sites. The influence of the unusually dry spring must be recognised when interpreting these results. Where the dry spring had less impact 100 seeds/mĀ² was too high, too many plants survived, the canopy structure at the seed-filling stage was too thick and yields impacted. This autumn, however being so dry could be one where the higher seed rates should have been used," points out Neil.
Neil points out that despite the very difficult conditions in 2006/2007 season with a very dry March and April and a wet June and July, Es Astrid produced excellent yields across the board. "On average at Boxworth Astrid yielded 4.03 t/ha, at High Mowthorpe 4.58 t/ha and at Rosemaund 4.47 t/ha. This reflects Astrid's excellent performance in the HGCA trials this year where it was the top yielding variety, with a seed yield of 107%."