Field pennycress (Thlaspi arvense) is a winter annual oilseed crop that is being domesticated to fit into Minnesota’s cash cropping system. Research at the University of Minnesota envisions pennycress as a crop that can provide all the ecosystem services of a cover crop, such as reducing erosion and nitrogen loss, while also being harvestable for profit.
The UMN pennycress breeding program began in 2013 with goals to develop high yielding, non-shattering, winter hardy varieties. These varieties show potential for fitting into our cropping systems, and a recent UMN study investigated the role pennycress could play in conjunction with a particularly common crop in Minnesota: sweet corn.
Sweet corn and pennycress should work well together for several reasons. First off, the timing lines up. Sweet corn is typically harvested in August, much earlier than grain corn, and pennycress seeds are planted in late August-early September. The seeds germinate and develop into a rosette in the fall. It over winters in this rosette stage, flowers and develops seeds in late April-early May, and is ready to harvest in early June. Additionally, to meet quality standards, sweet corn requires high nitrogen fertilization. It is also harvested as a fresh vegetable rather than a grain, meaning there is a large quantity of nitrogen in the residue that is left on the field after harvest. As a result, sweet corn systems are particularly susceptible to nitrogen loss. Planting a cover crop after sweet corn can help keep this nitrogen in the field and out of waterways.
UMN researchers wanted to address three main questions about pennycress in a sweet corn system: Can pennycress sequester nitrogen after sweet corn? Does the amount of fertilizer applied to sweet corn affect pennycress yields? Will pennycress planting method impact pennycress yield or the ability of pennycress to sequester nitrogen?
In this study, the researchers planted sweet corn in June with fertilizer applied pre-plant as urea, then harvested in August and chopped sweet corn stalks which were then left in the field. Pennycress was planted directly into the sweet corn stover in September using two seeding methods – broadcast and drilled – and then harvested at maturity the following June. They also collected soil samples and pennycress biomass samples to calculate sequestered nitrogen.
Pennycress sequestered approximately 17 pounds/acre of nitrogen following sweet corn and reduced residual soil nitrogen by 27-42% when compared to fallow check plots. This finding was true regardless of pennycress planting method or the nitrogen rate applied to sweet corn. This shows that pennycress can successfully provide ecosystem services similar to traditional cover crops.
Pennycress grain yields were not influenced by the nitrogen rate applied to sweet corn, demonstrating that pennycress can scavenge enough nitrogen (left by the previous sweet corn crop) to produce an adequate stand. Planting methods did not affect pennycress yields, indicating that simple, cost-effective broadcast planting can be employed without reducing yields.