An update from the soybean and pulse agronomy lab
Kristen P. MacMillan, MSc, PAg, Research Agronomist, Department of Plant Science, University of Manitoba
THIS WAS THE second growing season for the soybean and pulse agronomy lab – what have we been up to? It was a warm, dry season with the lack of rain days that increased our own productivity but limited soybean yields. Crops advanced three weeks ahead of normal, soybean leaves started turning over July 9, and on August 14, I predicted soybean harvest would be in full effect by the end of that month. Harvest did start early but as I write today in early October, I’m thinking of the crops that received snow and I hope harvest finishes before you are reading this.
In this second year of operation, we had 17 field trials spread across seven locations in Manitoba and we grew 12 different crops. Soybeans and dry beans comprise 95% of the program but we also grow peas, canola, corn, spring and winter wheat, fall rye, flax, chickpeas and winter camelina either as preceding crops to dry beans or as relay and intercrop combinations. This diversity is an important reminder following the past two dry growing seasons, which have created disparity among crop performance in Manitoba. Soybeans have been below average for many and cereals have captured a few well-deserved wins. Some are re-evaluating their soybean acreage for 2019, particularly those who went all in following the bumper years of 2015 and 2016. I’m curious if this affects how a diverse and balanced rotation is perceived as a risk management tool?
Growing season results are typically not available until November at best, but February is more realistic. After harvest, samples get cleaned, tested for moisture and seed quality, followed by data entry, summary, analysis and interpretation. It’s a long process to produce good quality data and the story is best told with multiple sites and years of data. For now, here are a few project highlights.
PROJECTS IN A POD
1. Soybean seeding windows
With dry spring conditions since 2015, opportunities are arising to seed soybeans earlier. Previous research by Cassandra Tkachuk demonstrated that earlier seeding produced modestly higher yields in Carman and Morden, regardless of soil temperature. This project expands that work to Dauphin, Arborg, Melita and Carman. Soybeans were seeded in four windows: very early (April 28–May 5), early (May 6–14), normal (May 15–25) and late (May 30–June 5). In 2017, soybean yields were statistically similar among the first three seeding windows followed by a 15–20% yield decline with late seeding. In both studies, seeding early hasn’t shown a yield penalty but does come with the risk of soybeans being up during frost. My advice for now is to know your typical last spring frost date (May 20–June 7 in Manitoba) and if conditions are suitable, you can seed ahead of it within two weeks, which is the average time it takes for soybeans to emerge.
2. Soybean seeding depth
Do you adjust and measure seed depth in each field? I’m afraid I might know the answer. Seed depth is typically an overlooked or last-minute decision. Yet it’s a cultural practice that can improve yield without investment. This project compares soybean seed depth from 0.25 to 2.25 inches in a tilled sandy clay loam (Carman) and clay soil (Arborg). The dry spring conditions as of late have also put a spotlight on seed depth and chasing moisture. In 2017, soybean yield was in fact reduced with deep seeding (2.25 inches) at Carman and in 2018, sub-optimal plant stands at 0.25 inches and >1.75 inches at both locations are not expected to optimize yield. Preliminary results have surprised the audiences who have heard this. Stay tuned for the combined results of 2017 and 2018 this winter, before you need to make your next seed depth decision.
3. Relay and intercropping with pulses
I can honestly say that I grew intercrops before they were cool! Pulse-cereal intercrops were part of my graduate research program and we’ve used them as green manures on the farm. They’ve long been part of organic and low input cropping systems and have now become a more realistic option for large commercial acres. I’m testing a combination of relay crops and intercrops to evaluate agronomic, ecological, practical and economic considerations. What are relay crops? A relay crop system is where you start growing one crop and plant the second crop directly into it before harvest – so you have both crops growing together for some time. Examples are winter wheat-soybean and fall rye-dry bean. The crops are seeded and harvested separately but share the same space in alternating rows. Intercrops, on the other hand, are two or more crops that are seeded, grown and harvested together (e.g. pea-canola). It’s somewhat of an art and science to determine which crops can and should be grown together.
L–R: Soybean-flax intercrop, soybean monocrop, fall rye-soybean relay crop and winter camelina-soybean intercrop are some of the cropping systems being tested at Carman. Fall rye and winter camelina were harvested July 24 and pictures were taken after harvest on August 14.
4. Dry bean nitrogen (N) fertility
Nitrogen fertilization practices vary among dry bean farmers in Manitoba. This parallels the reality that dry bean N-fixation varies by variety and environment. The aim of this study is to identify the “right rate” of nitrogen for Windbreaker pinto beans and T9905 navy beans. In 2017, there was no response to added nitrogen at Carman – the zero N control produced 2800 lbs/ac navy beans and 3500 lbs/ac pinto beans with spring soil tests of 40 lbs N/ac. In 2018, however, yellowing of the zero N control in Carman and Portage is likely to yield a response, no pun intended. This study has quickly become one of my favourites (okay, I say that a lot). It started out as a basic question and has quickly become complex, which is a good transition into my next thought – expanding the data we collect to further understand the variability in response and improve dry bean production systems.
GOING BEYOND YIELD DATA
Crop biomass, development, nodulation, root rot, height, yield components, maturity, seed quality – these are some of the key variables measured in agronomy research, in addition to yield. This type of data is important to help explain the outcome – why did one treatment yield higher than another? And to make observations that develop new questions to advance our knowledge of the system. For example, previously I’ve reported on how late soybeans can be seeded in Manitoba. The practical outcomes are to guide management decisions and crop insurance, but yield component, crop development, oil and protein data is providing the scientific community a first characterization of how environment, variety and seeding date influence soybeans in western Canada.
Now back to dry beans – N response has varied and so has nodulation (without inoculation!). In the spring, I was invited to speak at the North American Symbiotic Nitrogen Fixation conference. I presented my agronomy work on dry bean nitrogen fertility, soybean iron chlorosis and intercropping. Why did I choose those three projects? They are related to the soil-plant rhizosphere and could benefit from conversations with scientists who specialize in the physiology and genetics of the bacteria responsible for nitrogen fixation and their plant hosts. I gained an appreciation for the complexity of the N fixation process, and how unique and particular dry beans are. They heard from me about fertilization practices, the widespread occurrence of iron chlorosis and the growing interest in intercropping – and I suggested that each of these systems may be improved with multidisciplinary conversations and approaches. I’m optimistic about how projects evolve and continue to provide tangible benefits to Manitoba farmers.
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