Spring-sown winter canola performs
GroundCover™ Issue: 110 | Author: Annieka Paridaen - Southern Farming Systems
Grazing cereals have developed into a proven opportunity for mixed-farm growers. If managed correctly, these crops can provide a source of forage over winter and go on to produce grain with minimum yield penalty.
With an increase in canola plantings in the high-rainfall zone (HRZ), recent research has focused on finding the best fit for canola in mixed farming systems.
During the past four years, Southern Farming Systems (SFS) trials have shown that autumn-sown canola has not supplied as much early season feed as was initially hoped, and that feed still had a negative impact on yields.
However, with the release of new varieties such as CB™ Taurus and Hyola® 971 CL, an opportunity now exists to sow canola in spring and graze the crop in summer and autumn with little impact on subsequent grain yield.
In spring 2011, SFS sowed CB™ Taurus canola into a fallow at Dunkeld, 264 kilometres west of Melbourne, to test the performance of winter canola varieties and to answer some questions about grazing management, including:
- how many times can winter canola be grazed before a yield penalty is suffered?
- should I graze the canola lightly or can I graze it as heavily as my cereals? and
- does nitrogen application following grazing enable better recovery?
In spring 2012, a further five winter canola varieties were sown at Inverleigh, 30km west of Geelong, Victoria, into a paddock with a 30-year history of poor pasture production.
The summer and autumn of 2013 tested the resilience of this crop rotation because next to no rainfall was received between sowing in November 2012 and the seasonal break in May 2013.
Grazing started on 31 January 2012 after summer rainfall allowed the crop to establish. At that stage, three tonnes per hectare of good-quality dry matter became available when most of the area was lacking feed. Dry ewes grazed the canola at 13 dry sheep equivalents (DSE) per hectare. The crop was subsequently grazed three times (Table 1). In total, more than 4000 kilograms/ha of dry matter was removed after 55 days of grazing.
The quality of the feed on offer was high, with the metabolisable energy (ME) averaging 13.5 megajoules/kg of dry matter and the protein 22 per cent.
In 2012, nitrate poisoning was not of concern, with levels well under the toxic threshold of 1000 micrograms/kg for lambs.
Nonetheless, growers introducing livestock onto forage brassicas need to do so gradually. Avoid putting animals on canola with empty stomachs and ensure a source of roughage is available when canola is grazed.
Observations suggest animals can take a few days to develop a taste for canola. In the trial area almost every other plant was eaten before they started eating the canola.
Also, take care to monitor feed levels when livestock are grazing. The third and final grazing (Table 1) was heavier than planned because the sheep defoliated the crop more quickly than anticipated.
The experiment demonstrated the capacity of spring-sown canola to recover from the stress of complete defoliation and go on to produce a high grain yield.
The final grazing was severe, with most plants eaten back to the ground with almost no leaf present. However, after about a week, the heavily grazed canola started to reshoot and grow back rapidly, catching up with the plants that were grazed lightly.
After the grazing treatments were completed, the gate was closed and the trial was left to grow into a grain-producing crop.
The spectacular recovery and compensatory nature of canola following the stress of grazing meant it was difficult to visually identify any difference between treatments.
In 2012, allowing animals to graze the canola over summer increased grain yield compared with the ungrazed spring-sown treatment (Table 1).
The spring-sown and ungrazed canola yielded 1.9t/ha while the grazed canola yielded 2.7t/ha. CB™ Taurus sown at the conventional time (April) yielded 2.3t/ha.
The grazed plants produced a denser canopy with more branches and grain pods.
The number of times the crop was grazed had a small effect on yield. Grazing twice produced the best result, yielding 0.1t/ha more than grazing once and 0.2t/ha more than grazing three times.
Although there was a yield penalty by grazing three times, the third grazing meant there was an additional 1t/ha of high-quality feed available for sheep at the beginning of May.
Heavy grazing reduced yield compared to light grazing irrespective of the actual number of times it was grazed.
However, the yield reduction was small and the heavy grazing produced 4t/ha of feed compared with 1.4t/ha when lightly grazed.
When deciding on stocking rate and grazing intensity, there will always be a trade-off between the value of the feed over summer and autumn, and final grain yield.
Applying nitrogen over summer produced no yield benefit, except when the site was grazed heavily three times. In this case, grain yield increased from 2.0 to 2.7t/ha.
A well-prepared seedbed is paramount. Sowing into dry, cloddy soil has the potential to slow the production of fodder and grain.
For successful seed germination, plenty of seed-to-soil contact is needed so aim for a loose, friable soil that is free of lumps and clods.
Despite heavy grazing in 2012, plant numbers did not suffer under grazing. In fact, the heavily grazed spring-sown canola looked better than April-sown canola, which appeared to be struggling with the cool, wet weather and pressure from slugs and redlegged earth mites.
The summer of 2013 was hard on the crop, resulting in a 30 to 40 per cent plant loss; however, plant loss was similar between the grazed and ungrazed treatments so can probably be attributed to the dry, hot conditions.
Conditions in 2013 were almost the opposite to what was experienced in 2012, with extremely dry and hot weather from sowing in spring 2012 at Inverleigh until the break in May 2013. Dry matter production in 2013 was about 1t/ha less than 2012.
The resilience of the canola was severely tested, with three very heavy grazing events between 31 January and 30 April 2013.
The plants were so heavily defoliated research team members were unsure they would grow back. However, the thick starchy stem and root system of the established canola allowed the plants to survive, and they started growing leaves when the seasonal break arrived.
Everyone who saw the site in winter 2013 was astounded by how well the grazed canola plants had recovered after it was so heavily grazed in summer and autumn.
Although this means it is impossible to compare yields between 2012 and 2013, comparisons can be made between varieties and spring versus autumn sowing for the 2013 Inverleigh trials.
The results showed no significant differences between varieties when looking at yield under spring and autumn sowing except for CB™ Taurus, which came from a seed source with a low germination rate.
In the spring sowing treatments, grazing had no impact on final grain yield. Considering the sheep had access to almost 3t/ha of high-quality green feed in an extremely dry summer and autumn, there was plenty of advantage in grazing.
In 2012, there was no difference in weed numbers between the grazed and ungrazed treatments. There was also no difference in weed numbers between the spring and autumn sown treatments.
In 2012 and 2013, the rapid closure of the canopy following grazing appears to have allowed the crops to outcompete any early developing weeds.
The release of winter canola that can be used as a part of the Clearfield® Production System has provided more weed-control options, particularly when sowing in spring or early autumn.
As the trial crops matured, there were noticeable differences in canopy development.
Grazing appears to have removed the main stem, causing the growth of secondary stems or tillers, all of which went on to produce pods and grain.
Additional grazing led to more stems, but grazing did not alter plant height.
Putting it together
One of the benefits of sowing in spring is the crop can make the most of summer rainfall and establish at a time when there are fewer threats to plant growth.
In 2012, heavy rainfall in May (80 millimetres) and June (75mm) left a lot of the site and surrounding area either under water or very close to it, making access for sowing and subsequent management difficult.
By then, the spring-sown and grazed plants were well established with 300mm taproots to support healthy, vigorous growth at a time when the autumn-sown canola was struggling to cope with the wet and cold conditions.
A concern for many growers is the ability for the canola to survive a dry summer and autumn, recover from grazing and then go on to produce viable quantities of grain.
Following 40mm of rainfall two weeks after sowing in November 2012, the spring-sown crop was virtually deprived of rain until the break in May 2013.
Although the researchers doubted the plants would bounce back from three grazing events on top of the dry and hot conditions, they came back with flair.
At the time we were sowing the autumn crop, the spring sown and grazed plants were well on their way to being a viable commercial canola crop, without the threats caused by slugs, redlegged earth mites and cold, wet conditions during winter.
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