By Dr. Kim Schneider, Assistant Professor in Forage and Service crops, University of Guelph, and Connor Goodwin (MSc student)

Consistent cover cropping has proven to help improve both long-term productivity and environmental outcomes. Cover crops can help farmers increase organic matter content, add soil N through legume fixation, help supress weeds, and increase the water holding capacity of a field. However, there are some challenges in making it a consistent practice within a rotation. Growers are understandably concerned with the short-term economics of regular cover cropping given the costs of seed, termination, equipment, and potential cash crop complications. Research addressing specific short-term economic solutions for implementing cover crops can help reduce the associated risk that farmers face. Ontario’s most popular cash crop rotation of corn-soybean-winter wheat is sometimes paired with red clover following winter wheat. Currently, the standard practice is to frost seed the red clover into winter wheat stands when the snow melts in early spring. This can help give red clover a head start and improve coverage in the fall after wheat harvest. However, despite the benefits of frost seeding, establishment of red clover can still be variable year to year potentially leading to inconsistent field coverage and unreliable benefits such as providing an N credit.  As a result, this study compares red clover to some alternative fall annual legume monocultures (planted post-winter wheat), as well as legumes planted in oat-based mixtures. Our objective is to support farmer decision making and potentially increase cover crop adoption by a) determining if harvesting cover crop biomass can generate a profitable forage and b) determining which cover crop monocultures/mixtures contributes the largest savings in fertilizer nitrogen replacement value (FNRV) to a subsequent corn crop. Through this research we hope to help farmers find a potential blueprint to reduce or eliminate the financial barrier of making cover crops a consistent part of their rotation.

About The Project

This project is in its final year of a 3-year trial that was based at the Ontario Crops Research Station in Elora.  This project is evaluating different fall cover crop treatments planted after winter wheat harvest and followed by a corn crop. The treatments include monocultures of oat, winter pea, berseem clover, balansa clover, red clover (frost seeded) and mixtures of oat/winter pea/radish, oat/berseem clover/radish, and oat/balansa clover/radish. The experiment compared the different cover crop monocultures and mixtures and the effect of harvesting a fall forage from the cover crop. An economic analysis was conducted on potential N credit savings related to cover crop species and additional forage income to determine the best short-term economic practices.

Cover Crop Fall Forage Harvest

All three years of cover crop yield data has been collected and analyzed (Fig. 1). In 2021, 2022, and 2023 cover crop biomass averaged 1.12, 0.76, and 1.02 Mg DM ha^-1 respectively. Balansa clover failed to produce a harvestable yield in all three seasons, while berseem and red clover failed to produce a harvestable yield during the drought-like 2022 growing season. In 2021, red clover produced the largest yield at 1.76 Mg DM ha^-1, which was statistically greater than all treatments except for the oat monoculture, oat/winter pea/radish mixture, and oat/berseem/radish mixture. In 2022, the oat monoculture produced the greatest yield at 1.49 Mg DM ha^-1, which was significantly greater than all other treatments except the oat/winter pea/radish mixture. During the 2023 season, the oat treatment produced the largest yield at 1.47 Mg DM ha^-1 which was significantly greater than the legume monocultures, but statistically similar to all three mixtures. When it establishes well, red clover can provide the largest forage yield. Oat-based treatments showed to be the most resilient regardless of growing conditions, whereas legume monocultures struggled in dry conditions. This is evident in the consistent production of oat and poor production of legume treatments during the drought conditions of the 2022 cover crop season.

N Credit provided by legume-based cover crops

In the first cover crop season (2021), N credits to the subsequent corn crop peaked in the red clover treatment with 82.80 kg N ha^-1 more than the no cover crop control. All other annual legume treatments produced a smaller N credit than the frost-seeded red clover. Of the annual legumes, only the monoculture winter pea treatment was significantly larger than the no cover crop control by 32.62 kg N ha^-1. In 2023, the winter pea cover crop treatment produced the largest N credit at 27.40 kg ha^-1 greater than the no cover crop control. N credits were generally lower than the first year as a dry season resulted in no harvestable biomass from any legume monoculture outside of winter pea.

In both years, harvesting the aboveground cover crop biomass in the fall reduced the N credit provided to the next year’s corn crop. For the 2022 corn year, harvesting the cover crop in fall 2021 reduced the N credit by 10.43 kg N ha^-1 on average. Whereas harvesting the cover crop in fall of the 2022 season reduced the subsequent 2023 corn N credit by 8 kg N ha^-1 on average (Table 1). Although this represents a statistically significant difference in N credit, it is still a relatively minor agronomic difference.   

Economic Findings

Not planting a cover crop was still the most profitable short-term option in most cases, however, there are promising results in three of the cover crop treatments. In the first season, the combination of a substantial harvestable yield and the N savings in corn resulted in red clover being significantly more profitable at $127 ha^-1 more than no cover crop. Additionally, the oat monoculture and oat/winter pea/radish mixture generated enough harvestable biomass in both years to offset any short-term cost of cover cropping.

It is important to note that these results don’t encapsulate any of the long-term benefits of cover crops.  We also see that profits are frequently higher when harvesting the cover crop compared to not harvesting (especially for 2022), however, when cover crop yields were lower the following year, this is not always the case (Table 2).

Conclusions and Significance

When red clover establishes well and is able to produce a good amount of biomass, it seems superior at providing an N credit and harvestable forage than any other cover crop tested. This is illustrated in the first season with red clover producing a more profitable system than the no cover crop control. Thus, farmers should consider frost-seeding red clover into winter wheat if possible.  However, if harvesting a fall forage is possible and a more stable cover crop is desired, oat monoculture or oat/winter pea/radish mixture appear to be a reliable economic option regardless of growing conditions.  This trial compared harvesting vs. non-harvesting cover crops, but grazing a cover crop might have greater economic benefits due to the avoidance of harvest costs and the return of most of the nutrients to the soil when grazing.  This should be explored in future research.  More research is also needed to continue to improve red clover establishment to make it a more reliable option year to year. Finally, longer trials are needed to account for economic effects of consistent cover cropping over the long-term.

Ontario Forage Council would like to thank Dr. Kim Schneider and Connor Goodwin (MSc student) for providing this article.