During the soybean webinar, Kristen P. MacMillan provided a summary of the applied pulse and soybean lab’s results, discussing seven research projects in just under four minutes a piece. She returned during the pulses webinar to provide an overview of three on-going dry bean research projects.
Dr. Syama Chatterton provided a summary of her most current research on root rots in peas. Specifically, the yield robbers Aphanomyces and Fusarium avenaceum.
Putting Soybeans to Work on Your Farm was presented by Kristen P. MacMillan and covered the applied pulse and soybean lab’s recent research on soybean agronomy topics in Manitoba.
The soybean seeding window is flexible in Manitoba. There was no difference in soybean yield when planting throughout May 1 to 24. Yield was reduced by 15%, on average, when delaying seeding until May 31 to June 4.
On the flip side, seeding can be too early in western Canada. Soybeans are susceptible to frost and cool soils. Check the average date of the last spring frost in your area, avoid cool soils below 8°C and make sure there is no cold rain in the forecast for the first 24–48 hours after planting.
Seeding during the second week of May maximized yield potential while avoiding cold soil and the risk of late spring frost.
LATE SEEDING OF SOYBEANS
Can 80% yield potential be maintained with June seeding? In short, yes, in southern Manitoba at the Portage and Morden sites, but not in shorter and cooler growing areas of the province like Arborg. At Arborg, as seeding was delayed, yield was reduced by up to 35% and the risk of a fall frost was just too great.
These results may mean extending seedling deadlines in southern areas like Portage and Morden to the first week of June, but not in other growing areas, due to the risk of early fall frost.
Is there a yield penalty if we seed soybeans deeper, seeking moisture in dry conditions? Even under dry soil conditions like those experienced from 2017–2019, it was not beneficial to seed deep. According to this research, the optimal seed depth range was .75 to 1.75 inches, where yield was maximized at 1.25 inch seed depth. Precipitation at Arborg and Carman over the three years of this study was 40 to 70% of normal during May and June, but the rains always came.
This research found a 20% yield loss from shallow seeding (< .75 inch) and a 10% yield loss from seeding too deep (> 1.75 inches). At shallow depths (< .75 inch), seeds imbibed water and then dehydrated and desiccated. Yield loss from deep seeding can likely be attributed to the loss of cotyledons, hypocotyl swelling, chlorosis and delayed emergence. Measure your seed depth while seeding and post-emergence when doing plant counts to make adjustments for next time.
IRON DEFICIENCY CHLOROSIS (IDC)
How much is yield affected by IDC in Manitoba? In this study, each 0.1 unit increase in IDC reduced yield by two to three bu/ac. As a next step, Kristen’s lab is investigating if there is a trade-off between IDC score and yield, and working to identify varieties that perform well in both IDC and non-IDC areas of the field, to manage it more precisely in the future.
On average, from 2009–2018, the majority of hail events occurred from July 1 to August 31. Specifically, in soybeans, the greatest losses from hail claims occurred from V7 to V10, which coincides with flowering and pod fill.
Previous estimates for assessing hail damage in soybeans have underestimated yield loss by as much as 30%, especially when high levels of leaf defoliation occur from V3 through R4. For example, no yield loss is currently attributed to defoliation during soybean vegetative stages, but this new Manitoba research found significant yield loss during V3 with 100% leaf loss.
Results of this study will be made available to farmers, agronomists and crop insurance adjusters to more accurately estimate the impact of hail damage on soybean yield and maturity.
There have been no significant yield responses to foliar fungicide in soybeans over three years of testing (2017–2019) at Carman. This is consistent with the findings from MPSG’s On-Farm Network. The foliar diseases we commonly see in Manitoba are not yield robbers. n
DRY BEAN AGRONOMY UPDATE
Three research projects have been underway in the soybean and pulse agronomy lab to support dry bean production in Manitoba. This is a summary of the findings from all three projects to date. Full details can be found in the annual report available at manitobapulse.ca.
PRECEDING CROP AND RESIDUE MANAGEMENT
Pinto bean production can be successful following a range of crops (wheat, corn, canola or dry beans) and under direct seed conditions in Manitoba with no penalties to plant stand or yield. But there were important and clear agronomic effects on weed density and root rot in this study that should be considered in crop rotation planning.
For example, pinto beans grown on wheat stubble had grassy weed pressure that was 4x greater than beans grown on corn stubble. This suggests that the herbicide program in the preceding crop can influence the following year’s crop. Beans grown after beans had higher root rot pressure — something that will depend on each field’s history and soil moisture conditions. And it should be noted that white mould was not present in any of these trials, but past white mould pressure is an important consideration when selecting bean fields.
OPTIMIZING NITROGEN RATES
Dry beans are an N-fixing legume, but nitrogen (N) has traditionally been supplied by fertilizer rather than N-fixation. This is because the N-fixing capability of beans is relatively low compared to other pulse crops. N-rates are being revisited in Manitoba to update old research and to investigate the relationship between N-fertilization and root nodulation, due to the common, yet peculiar, presence of root nodules in fertilized bean crops around the province. Rates of 0, 35, 70, 105 and 140 lbs N/ac were tested from 2017 to 2019 in both small-plot and on-farm trials.
Emerging N fertility guidelines for dry beans from this study:
- No supplemental N and no inoculation — The most economical practice so far from five site-years. Expect 86–93% of maximum yield.
- Supplemental N at 35 lbs N/ac or ~70 lbs total N — If skipping fertilizer is too risky, you can achieve maximum yield without reducing nodulation with this practice.
- Inoculation — Not a viable option yet but will become a good option as product availability and testing increases.
- Inoculation and supplemental N? — Has not been tested yet.
EVALUATION OF DRY BEAN INOCULANTS
Preliminary findings show that dry bean nodulation and yield response to inoculant depend foremost on the environment. A statistically significant response was found at one of the three site-years in this study, in which Primo GX2 boosted nodulation and yield. All bean market classes behaved similarly. Recent testing in Saskatchewan from five site-years has shown no response to inoculant in CDC Blackstrap black beans.
There is still much to learn on this subject, including how much N is being acquired by modern bean varieties through N-fixation in our Manitoba environment.
THE COMPLEX TALE BEHIND ROOT ROT IN PEAS
Dr. Chatterton leads a research program at AAFC Lethbridge, focusing on root rots in pulse crops across western Canada. Here are the main take-aways from her presentation.
The two main root rot players in peas are Aphanomyces euteiches and Fusarium avenaceum that act together in infecting roots. F. avenaceum is the most common, but there are several other Fusarium species that can be found in peas.
One main driver for Aphanomyces infection is soil moisture. In Manitoba, Aphanomyces was present in more fields and at higher incidence in the wetter years of 2016 and 2019, compared to lower levels in the dry years of 2017 and 2018.
The other main driver is crop history. The threshold for Aphanomyces to develop is 100 oospores/g of soil. At a starting population of 1,000 oospores/g of soil, it takes at least five to six years to drop below the threshold and seven to eight years at a starting population of 10,000 oospores/g of soil. This is where the current recommendation comes from to wait six to eight years before growing peas again on a field with Aphanomyces pressure. Starving the pathogen of its hosts will reduce soil inoculum.
However, there is still more to learn on the impact of pea or lentil frequency in rotation, with research currently underway (2020 was year three of a five-plus year study). So far, soybeans, faba beans and chickpeas appear to be alternate crops that do not increase disease inoculum in the soil. Dry bean susceptibility to Aphanomyces varies by variety and market class.
Other ongoing research is focused on intercropping peas with brassicas like canola and mustard. Early results have shown a yield boost from intercrops but no reduction in disease severity.
For 2021, choose your pea fields very carefully, considering crop frequency, performance, weather (e.g., was it a wet year the last time you had peas on a certain field?) and field conditions. Get your soil tested, consider seed treatment for low risk or patchy fields and test your roots in-season.