| Crop | Soybean |
|---|---|
| Start Date | 2012 |
| End Date | 2015 |
| Principal Investigator | Lawley, Yvonne , University of Manitoba |
| MPSG Financial Support | $134,225 |
| Total Project Funding | $134,225 |
| Report | Final Report – Lawley – Soybean crop rotation |
Research Objectives
- Determine the effects of crop sequence on soybean yield, mycorrhizal colonization, and biological nitrogen fixation
- Quantify the nitrogen benefit of soybean to a subsequent wheat crop relative to a canola crop
Project Description
Limited research has been conducted on the crop rotation benefits of soybean or their nitrogen contribution to subsequent crops in Manitoba. Crop rotation trials were set up at two locations (Carman, Kelburn) in 2012-2013 and at three locations (Carman, Kelburn, Portage) in 2013-2014. Significant crop sequence treatment effects in the soybean test crop were observed in three of the five site years of the experiment. Wheat-Soybean and Corn-Soybean crop sequences were good rotational choices in all site years. Surprisingly, the soybean-soybean treatment was both the highest (Carman 2013) and lowest (Kelburn 2014) yielding treatment depending on site and year . Using samples collected from the field experiments, the relationship between crop sequence and biological nitrogen fixation by Bradyrhizobium bacteria as well as interactions with mycorrhizal fungi colonization of soybean roots was studied. Soybean plants that had been grown on soybean or corn stubble had significantly higher mycorrhizal colonization than plants growing on wheat or canola stubble. Results from the 2013 soybean crop indicate that crop rotation did have a significant effect on biological nitrogen fixation: as expected, the canola-soybean rotation always had significantly lower nitrogen fixation, but the soybean-soybean crop sequence always had significantly higher amounts of nitrogen derived from biological nitrogen fixation.
A second field trial was set up at Carman and Glenlea in the 2012-2013 and 2013-2014 years. Rotational crops of soybean and canola were grown prior to wheat; wheat plots were then subdivided to incorporate a range of nitrogen fertilizer treatments to produce a nitrogen response curve. In three of the four site years, yields of the wheat test crop following soybeans was the same or lower compared to the wheat test crop following the canola reference crop. In the one site year of the study where the wheat test crop following both soybeans and canola responded to nitrogen fertilizer treatments (Carman 2013) the yield of wheat following canola was always higher than following soybeans across the range of fertilizer rates tested. Soil nitrate N concentrations were lowest following soybean in all site years when compared to canola. In addition, the C:N ratio of soybean residues were higher than expected. Soybean did not provide a nitrogen credit to the wheat test crops in this study; rather soybean showed negative nitrogen balance.