Improving harvest management decisions in canola – implications of seed colour change and windrow timing on seed yield and oil concentration
Author: Rick Graham (NSW DPI, Tamworth), Leigh Jenkins (NSW DPI, Trangie), Kathi Hertel (NSW DPI, Narrabri), Rohan Brill (NSW DPI, Narrabri), Rod Bombach (NSW DPI, Tamworth), Don McCaffery (NSW DPI, Wagga Wagga) and Neroli Brennan (NSW DPI, Orange) | Date: 28 Feb 2018
Take home messages
- Seed colour change occurs later on the branches of canola plants compared to the primary stem.
- Research examining the partitioning of yield between the primary stem and branches found that branches can contribute up to 80% of total yield.
- Relying solely on seed colour change from the primary stem to determine windrow timing could result in overall seed development being underestimated, potentially impacting seed size, yield potential and oil concentration.
- Results highlight the potential for significant yield and quality penalties associated with early windrow timings, before 40% seed colour change on the primary stem.
- There is potential for yield and oil concentration benefits to be obtained with delayed windrow timings at the upper end of current industry guidelines ≥ 60% seed colour change.
- Given the significance of the proportion of yield contributed by the branches as opposed to the primary stem there appears to be a need to reconsider how windrow timing is determined.
Windrowing is a widely adopted harvest management practice of canola (Brassica napus L) in Australia. Its timing has traditionally been based on the seed colour change of seeds taken from pods (siliques) in the middle third of the primary stem (primary racemes). Current industry guidelines based on research undertaken in the 1980s and early 1990s recommend that canola is ready to windrow when 40–60% of seeds on the primary stem change colour from green to red, brown or black (Hocking and Mason, 1993). Over the past decade however, with the introduction of hybrid varieties, improvements in germplasm and developments in farming practices and machinery, there has been increased discussion about what is considered the optimum windrow timing and how best to determine seed colour change (Street, 2014).
The main issues of concern relate to the proportion of yield contained on the branches (secondary racemes) versus the primary stem and the effect of the differential rate of seed maturity on yield and seed quality parameters. This is further accentuated when you consider that canola seeds mature progressively up the primary stem and from the lower branches to the upper branches, with changes in seed colour indicative of declining metabolic activity and increasing seed maturity (Hertel, 2012). Based on these observations, there is an obvious need to consider in detail the partitioning of yield (stem vs. branches) and rate of seed development when looking at recommendations around seed colour change and optimum windrow timing, particularly in the hotter finishing environments of northern NSW (Hertel 2013).
In 2015, research commenced as a component of the GRDC co-funded ‘Optimised Canola Profitability’ project (CSP00187) to examine the relationship between seed colour change, seed yield and quality parameters. The objective was to assist growers to make more informed decisions around canola harvest management in northern NSW and potentially across Australia. Preliminary results outlined, looking at the partitioning of seed from pods on the primary stem and branches of two hybrid canola varieties, that seed colour change occurred later on branches compared to stems (Graham et al. 2016). Importantly, it was observed that ≥ 70% of total seed yield was coming from the branches with this percentage increasing with decreasing plant density (Figure 1). The results indicated that by relying solely on the primary stem to estimate seed colour change and hence windrow timing, that overall seed development is being underestimated, potentially adversely affecting overall yield and quality parameters.
Based on these preliminary findings a comprehensive set of experiments were conducted across a range of environments in the northern grains region of NSW in 2016 and 2017. Findings from these experiments are reported in this paper.
Figure 1. Mean yield contribution (%) of primary stem vs. branches for two target plant densities (15 and 45 plants/m2) at Trangie in 2015.
Research in 2016
Replicated field experiments were conducted at three sites; ‘Tarlee’ near Edgeroi on the north-west plains of NSW, Tamworth Agricultural Institute on the north-west slopes of NSW and Trangie Agricultural Research Centre on the central-west plains of NSW.
Experiments were sown on 6 May at Tamworth and Trangie, and 10 May at Edgeroi, and were managed using best management practices to limit biotic stresses and nutritional constraints. Two hybrid canola varieties, Pioneer® 44Y89 (CL) and Hyola® 575CL with similar flowering times but different maturity ratings, were sown in small plot experiments at Tamworth and Trangie, however only one variety Pioneer® 44Y87 (CL) was sown at the Edgeroi site, which was overlaid in a commercial crop. Windrow timings were conducted at 2 day intervals from the start of seed colour change on the primary stem up until 100% seed colour change on branches, alleviating difficulties associated with trying to target seed colour change and hence simulated windrow timings.
Actual seed colour change was determined from a representative 200 seed sub-sample, taken from the middle third of the primary stem and randomly from across the branches of individual plants at each windrow timing. Yield and seed quality components were determined by threshing 3 x 1 m hand-cuts taken from the three middle rows at either end of experimental plots, giving 6 m of total cut area. Six plants sampled from the middle rows, three from each end of a plot, were threshed to determine the proportion of yield from branches and the primary stem, with seed moisture percentage and thousand seed weight at actual seed colour change and its contribution to yield (primary stem vs. branches) recorded. Seed quality parameters measured included oil concentration (adjusted to 6% moisture), determined by near-infrared spectroscopy (NIR) with an Infratec® 1241 Grain Analyser.
The following results focus on overall effects of windrow timing and seed colour change on canola yield and oil concentration, rather than on varietal differences.
Seed colour change
Seed colour change and windrow timing treatments commenced on 4 October at Edgeroi, 7 October at Trangie and 14 October at Tamworth. Consistent with the 2015 Trangie findings, seed colour change occurred earlier on the primary stem compared to the branches (data not shown). Windrow timing averaged across the two varieties at Tamworth showed that when seed colour change on the stem was at 61%, branches were only at 20% seed colour change (windrow timing 7, Figure 2). Similarly, at Edgeroi and Trangie where seed colour change occurred earlier than Tamworth, the primary stem was more advanced compared to branches at key windrow timings. At Trangie for instance, when the primary stem was at 84% seed colour change (windrow timing 7), branches were only at 43% seed colour change, likewise at Edgeroi when the primary stem was at 80% seed colour change, branches were at 52% seed colour change (data not shown). The results from Tamworth also illustrated how rapidly seed colour change can occur, with seed colour change on the primary stem progressing in a five-day period from 18% to 61% seed colour change (windrow timing 5 to timing 7) (Figure 2).
Figure 2. Seed colour change (%) primary stem vs. branches over time as determined by windrow timings at Tamworth in 2016. (Vertical line approximates 60% seed colour change on the primary stem ~ windrow timing 7).
Changes in seed size (thousand seed weight) across windrow timing can be used as an indicator of both reaching physiological maturity and yield potential over time. At Tamworth (Figure 3a) and Trangie (Figure 3b) differences in thousand seed weight on the primary stem vs. branches was greatest during the earlier windrow timings, reflecting differences in seed colour change and maturity. This would be expected given that seeds mature progressively up the primary stem and from the lower branches to the upper branches, with changes in seed colour indicating declining metabolic activity and increasing seed maturity (Hertel, 2012).
Importantly, the optimum thousand seed weight for branches occurred at a later windrow timing than current industry recommendations which are based solely on seed colour change on the primary stem. This is of relevance given that branches contributed 63% and 78% of potential yield at Trangie and Tamworth respectively. A similar pattern of thousand seed weight development on branches vs. the primary stem was also observed at Edgeroi (data not shown).
Figure 3. Changes in seed size (thousand seed weight) on primary stem vs. branches over time as determined by windrow timing for Tamworth (a) and Trangie (b) in 2016.
Windrowing at the start of seed colour change of 6% on the primary stem at Trangie resulted in a 1.34 t/ha decline in yield compared to windrowing at ~60% seed colour change, a yield loss of 48% (1.47 t/ha vs. 2.81 t/ha) as outlined in Graham et al (2017). When looking at the breakdown of yield contribution of the primary stem vs. branches, it was observed that stems only contributed 37% of the total yield at Trangie, averaged across windrow timings (data not shown). At Edgeroi, yield based on 40─60% seed colour change on the primary stem ranged from 1.70─2.35 t/ha, with yield peaking at 2.42 t/ha when seed colour change on primary stem was 89% and branches 65%. A yield penalty of 0.6─1.3 t/ha was observed at Edgeroi when windrowing occurred at ~6% seed colour change on the primary stem vs. industry guidelines when 40─60% seed colour change on the primary stem, 8-10 days later, resulting in a yield loss of up to 55% (Figure 4). At Tamworth, the penalty for early windrowing at the start of seed colour change versus industry recommendations was 1.20 t/ha, a potential yield loss of 32% (data not shown). In all three experiments delaying windrow timing to where seed colour change on the primary stem was >60% either resulted in significant (P<0.001) increases in yield at Edgeroi and Trangie, or trended towards a yield increase at Tamworth.
Figure 4. Effect of windrow timing and seed colour change on canola seed yield (t/ha) at Edgeroi 2016
There were significant (P< 0.001) oil concentration penalties for windrowing at early stages of seed colour change. At Tamworth, there was a 14% decline or a 6.3% unit reduction in oil concentration (38.9% vs. 45.2%) when windrowing at the start of seed colour change versus at ~60% seed colour change on the primary stem (Figure 5). There was also an increase in oil concentration at Tamworth where seed colour change was >60% on the primary stem, with increases in oil concentration of 0.6─2.0% units. At Edgeroi there was a significant (P = 0.001) decrease in oil concentration with early versus >40% seed colour change on the primary stem, with oil concentration declining by 3.9% units (Figure 6). Similarly at Trangie, there was a significant (P<0.001) decline in oil concentration of 4% units, whilst there was an increase of 1.1─1.9% units in oil concentration, with delayed windrow timings of >60% seed colour change (data not shown).
Figure 5. Effect of windrow timing (seed colour change) on oil concentration (%) at Tamworth in 2016 (Vertical line approximates ~60% seed colour change on the primary stem – windrow timing 7)
Figure 6. Effect of windrow timing (seed colour change) on oil concentration (%) at Edgeroi in 2016 (Vertical line approximates ~40% seed colour change on the primary stem – windrow timing 6)
Research in 2017
In 2017, experiments were conducted at Tamworth and Trangie. Results from the Tamworth experiment only are outlined in this paper. In keeping with previous years, the Tamworth experiment was sown in the first week of May. In contrast to 2016, which received 543 mm (decile 9) growing season rainfall (April to October), in 2017 the site only received 203 mm (decile 2).
The methodology for the 2017 experiments was as per 2016, the only variation, being the two varieties that were compared. Unlike in 2015 and 2016, where two hybrid canola varieties Pioneer® 44Y89 (CL) and Hyola® 575CL were assessed, in 2017, a hybrid variety Pioneer® 44Y90 (CL) and an open pollinated variety ATR-Bonito were evaluated. This change was made to see if there were any differences in yield components (Stem vs Branches), SCC and seed development, between a hybrid CL variety and an open pollinated triazine tolerant (TT) variety.
Seed colour change
The two varieties evaluated had comparable 50% flowering dates but differed in terms of maturity, with Pioneer® 44Y90 (CL) 4 days faster to the end of flowering compared to ATR-Bonito. Windrow timing commencing on the 18 October for both varieties and concluded on the 30 October and 6 November respectively for Pioneer® 44Y90 (CL) (windrow timing 6) and ATR-Bonito (windrow timing 9), reflecting the difference in maturity. Consequently, at any given windrow timing, seed colour change was more advanced for Pioneer® 44Y90 (CL) compared to ATR-Bonito. For example at windrow timing 1, Pioneer® 44Y90 (CL) was at 71% seed colour change on the primary stem, ATR-Bonito was only around 29% seed colour change.
Consistent with previous findings, seed colour change occurred earlier on the primary stem compared to the branches. In the case of ATR-Bonito when the primary stem was at 29% seed colour change, the branches were only at 6% seed colour change (windrow timing 1) likewise, when the stems were at 99% seed colour change, the branches were only at 65% seed colour change (windrow timing 5). Results from 2017, again reinforced how rapid seed colour change can occur, with seed colour change on the primary stem progressing from 29% to 90% seed colour change in a 5 day period.
Seed size expressed as thousand seed weight, is considered an indicator of physiological maturity and yield potential. When looking at changes in thousand seed weight over time as it relates to windrow timing for ATR-Bonito it can be seen that differences in thousand seed weight stem vs. branches are greatest during earlier windrow timing’s, reflecting differences in seed colour change and overall maturity (Figure 7). This trend was also observed for Pioneer® 44Y90 (CL) (data not shown). This is of significance given that the branches contributed ~85% and ~87% of potential yield for ATR-Bonito and Pioneer® 44Y90 (CL) respectively, also indicating that yield partitioning did not differ greatly between an open pollinated and a hybrid variety in this case.
Figure 7. Changes in seed size (TSW - thousand seed weight) on primary stem vs. branches over time for ATR-Bonito as determined by windrow timing at Tamworth 2017
Figure 8. Effect of windrow timing on ATR-Bonito seed yield (t/ha) at Tamworth in 2017
Early windrow timings before 40% seed colour change on the primary stem, resulted in the potential for a significant yield penalty. When looking at the results for ATR-Bonito it was shown that there was a 13% yield penalty (Figure 8) windrow timing 1 vs windrow timing 3 (3.11 t/ha vs 3.56 t/ha) and stems were at 29% seed colour change vs 90% seed colour change respectively. Importantly when looking at the breakdown of yield, stem vs branches only ~ 15% of yield was attributed to the stem and that at windrow timing 1 and windrow timing 3, the branches were only at 6% and 38% seed colour change respectively. These results would indicate both a need to consider the breakdown of yield, stem vs branches and how rapid seed colour change can occur both of which may be influenced by seasonal conditions.
Results from these experiments clearly show that seed colour change occurs later on the branches of canola plants compared to the primary stem. This is important when you consider that branches can contribute in excess of 80% of canola yield potential. Relying solely on seed colour change from the primary stem could result in the plants seed development being underestimated, potentially impacting seed size, yield potential and oil concentration.
Findings from this research highlight the potential for significant yield and quality penalties due to early windrow timings (i.e. before 40% seed colour change on the primary stem), with yield losses of up to 55% and decreases in oil concentration of up to 7.7% units observed. This study indicates that seed colour change should ideally be measured on a whole plant basis and not based solely on the assessment of seed from the primary stem when determining windrow timing operations. Furthermore, results demonstrated the potential benefit of delayed windrow timings related to seed colour change, with yields optimised at the upper end of current industry guidelines of ≥60% seed colour change .
This project is a component of the collaborative ‘Optimised Canola Profitability’ project (CSP00187) between GRDC, NSW DPI and CSIRO in partnership with SARDI, CSU, MSF and BCG. We gratefully acknowledge the assistance of NSW DPI technical staff with this work including Stephen Morphett, Jan Hosking, Jim Perfrement, Michael Dal Santo, Peter Formann (Tamworth); Jayne Jenkins, Scott Richards, Liz Jenkins, Joanna Wallace (Trangie); Leah Rood-England, Mitch Whitten, Joe Morphew, and Brooke McAlister (Narrabri). The research undertaken as part of this project is made possible by the significant contributions of growers through both trial cooperation and the support of the GRDC. The authors would like to thank them for their continued support and in particular Paul White and Alex Murray, ‘Tarlee’, Edgeroi.
Graham R, Jenkins L, Brill R, Hertel K and McCaffery D (2016). Assessing seed colour change for improved harvest decisions in canola: include branches in the main stem. In: Proceedings of Brassica 2016, 3 – 6 October 2016. Melbourne, Victoria, Australia.
Graham R, Jenkins L, Hertel K, Brill R, McCaffery D, and Graham N (2017). Re-evaluating seed colour change in canola to improve harvest management decisions. Proceedings 18th Australian Agronomy Conference, Ballarat 24-28 Sep 2017.
Hocking PJ and Mason L (1993) Accumulation, distribution and redistribution of dry matter and mineral nutrients in fruits of canola (oilseed rape), and effects of nitrogen fertilizer and windrowing. Aust. J. Agric. Res. 44, 1377-88
Hertel K (2012) Better canola technology update, Module 7: Harvest management.
Hertel K (2013) Canola: the economics and physiology of the timing of windrowing
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