A behind-the-scenes look at interdisciplinary soybean crop-rotation research during the 2020 pandemic

Dr. Yvonne Lawley, Assistant Professor of Agronomy and Cropping Systems, University of Manitoba – Fall/Winter (December) Pulse Beat 2020

Crop rotation studies require a long-term commitment to research. The COVID-19 pandemic in 2020 was a new test for our commitment to long-term research at the University of Manitoba (U of M). Our study looking at the frequency of soybeans in Manitoba crop rotations was initiated in 2014 and has become a field laboratory for interdisciplinary research. With a team of graduate students and postdoctoral fellows relying on this experiment, we had to find creative ways to keep the study going within the health protocols established to keep staff and students safe. At the best of times, collaboration takes good communication and that was never more true than for the summer of 2020 when we had to work and collaborate together while being apart.

Our rotation study compares four different crop sequences: 1. continuous soybeans 2. soybeans grown every second year with canola, 3. soybeans grown every second year with corn, and 4. soybeans grown once every four years in rotation with wheat, canola and corn. Every year, technicians Codi Hennan and Stephanie Dheilly plant, manage and harvest these crops and take key measurements like yield, plant establishment, crop residue biomass and weather data that are the foundation of the experiment. This year, they coordinated these activities over the phone from separate vehicles instead of face-to-face, met up in the field with their dedicated personal sampling equipment, and practiced social distancing while collecting samples in the field. Daily observations that technicians were able to make about progress of the field trials located at the U of M Carman research farm and Richardson’s Kelburn Farm were communicated to the rest of our team through online meetings, emails and text messages. This allowed collaborators to make targeted trips on their own out to the field to collect samples for each of their objectives within the larger project.

Pathology

With a high frequency of soybeans in rotation, pathology is an important focus in the rotation study. Dr. Fouad Daayf and postdoctoral fellow Dr. Ahmed Abdelmagid have been following the development of pathogens in our rotation study since 2017. Root rots continued to be the most prevalent and damaging disease in the study, especially Fusarium spp. In 2019, when three of the four rotations had soybeans present, they found the highest severity of root rot occurred in the continuous soybean treatment followed by the canola-soybean, and lastly, the corn-soybean treatment at both the Carman and Kelburn locations. The continuous soybean treatment in this study has been running for seven years and it has not been disappointing our pathology team. They identified and published the two first reports for Fusarium cerealis causing root rot in soybeans and Northern Stem Canker caused by Diaporthe caulivora on soybeans in western Canada in the journal Plant Disease. A cautionary tale for soybean growers across Manitoba.

Soil microbiome

Soil populations of Bradyrhizobia bacteria that fix nitrogen when nodulated within soybean roots have been an important focus in the rotation study for Dr. Ivan Oresnik and his new PhD student Ambihai Shayanthan. Their current project builds on the completed MSc thesis of Patricia Ordonez, who followed the change in Bradyrhizobia populations within a growing season and between seasons. Patricia confirmed that Bradyrhizobia can persist in Manitoba soils from year to year. Ambihai will take this project to the next step by studying rotation effects on the biome of microbes surrounding the soybean root in the rhizosphere. She is very interested in understanding which soil microbes are enriched by the presence of soybean plants and those positively correlated with increased productivity and plant health.

Soil health

We know that crop rotation can improve both plant and soil health. Graduate student Chathuri Weerasekara is working with Dr. Lawley and Dr. Oresnik to measure the impact of the frequency of soybeans in rotation on new measures of soil health. Soybeans are a low-residue crop that don’t return as much carbon to the soil as cereal crops like wheat or corn. This experiment allows us to track carbon inputs from crop residues over time and to follow resulting changes in soil carbon. Chathuri is looking at both the traditional stable pools of soil carbon as well as a new method called active carbon that focuses on the carbon pool that can easily feed and be decomposed by soil microbes. Chathuri has also been following the concentration of soil enzymes released by microbes as an index of microbial activity for processes involving the cycling of carbon, nitrogen and phosphorus in the soil. After analyzing archived samples from 2017 and 2019 (four and six years into the study, respectively), Chathuri has not found any differences between rotation treatments in total or active carbon pools at both the Carman and Kelburn sites. However, soil enzyme activity has consistently been lowest in the continuous soybean treatments at both sites. All of the interdisciplinary layers in this rotation study connect with the soil microbial community — both good and bad. These layers are going to help us to integrate the possible outcomes that farmers can expect as soybeans continue to be an important crop in Manitoba rotations.

Focusing on the agronomic funda­mentals for our rotation study in 2020 has set us up for an important year in 2021, where all treatments align to grow soybeans and we have a test crop year where we are planning to make many important measurements. Each member of the team will have the best opportunity to compare treatments in the coming soybean test crop year after maturing over the past eight years. Postdoctoral fellow, Dr. Navneet Brar, will also join our team in 2021 to take an in-depth look at soybean performance and integrate the impact of our crop-rotation treatments on mycorrhizal colonization, nodulation and biological nitrogen fixation.

Like many, we were tested by the conditions of the 2020 pandemic. Being able to work outside helped many of us to feel a sense of normalcy at a time when accessing indoor lab spaces has been much more limiting. Following health guidelines and keeping to the fundamentals through­out each step of the 2020 growing season made even simple tasks more complicated time and time again. This forced us to find efficiencies and focus on the essentials. The sense of community that comes with collaborating together while being apart has helped us to make it through this crazy year and we are looking forward to a future where life — and our research — can return to normal.