Improving cover crop management: Cover crop mixtures with different termination methods

Objectives:

• To assess cover crop growth and residues remaining after termination in terms of quantity of aboveground biomass and nitrogen (N) content in the fall (before freeze-up) and the following spring.
• To quantify the impact of various cover crop systems (species, mixture, tillage, and termination methods) on grain corn emergence, growth, yield, and select soil parameters at corn planting.

Impacts:

• By developing a better understanding of the complex interactions within the agroecosystems, this research program facilitated development of effective and cost-efficient cover crop recommendations based on mixtures and tillage practices, which will allow growers to be more confident in cover cropping management and predicting the potential outcomes.
• Beyond advancing scientific knowledge, the proposed research program had an  impact on the general public by providing agronomic recommendations for best management practices (i.e., cover crops and reduced tillage) that are recommended to improve soil organic matter and soil health with more stable agroecosystem resiliency and increased biodiversity (including microbes, insects, birds), which is of benefit for all Canadians.
• The development of new regionally-specific production recommendations will provide farmers with information to be more economically and environmentally sustainable by adopting cover crops and reduced tillage practices, which is in alignment with agricultural policies.
• Application of results from optimization of cover crop mixtures and termination methods in various locations will help meet farmer demand for local information about optimal cover crop strategies. By quantifying value to farmers in terms of improvements into their corn crop, this research provided strong incentives for integration of cover crops under various environmental conditions within a large regional scale.
• Identification of well-adapted cover crop mixtures may spur development and marketing of cover crop seed mixes tailored to specific Ontario locales, enhancing cover cropping adoption rate, and boosting business interest in selling cover crops as a farm input.

Project Overview:

Integration and management of cover crops is challenging due to the immediate time and cost constraints, while potential benefits may be long-term. Adjusting cover crop production methods may balance these challenges while meeting producer goals. But there are many cover crop species and mixtures to choose from, especially with winter wheat in the rotation. Moreover, there are many different cover crop termination methods, such as winter kill, herbicides or tillage, and various tillage approaches (no-till, strip/zone tillage, bio-till, etc.). With the complex interactions of cover crop planting and termination options, research was needed to identify effective strategies. This research project evaluated, in terms of grain corn yield, various cover crop termination methods.

This research identified cover crop management strategies (i.e., mixtures, termination, tillage) that are a benefit or detriment to grain corn yield. While many farmers intuitively realize that there are soil and environmental benefits to cover cropping, there are barriers to adoption. Improper management of cover crops can lead to substantial yield losses. With the knowledge gained from the project, we have sound management recommendations from cover crop planting to termination relevant to the south (Ridgetown), east (Winchester) and north (New Liskeard), under various environmental conditions (e.g., soil types, precipitation, temperature, etc.).

Results:

With the complex interactions of cover crop species and mixes along with multiple termination options, this research evaluated, in terms of cover crop performance and the following grain corn yield, the following various cover crop approaches after winter wheat:

• 1-way: winter cereal rye, hairy vetch, oats, peas, radish, red clover (frost seeded in wheat)
• 2-way: cereal rye plus hairy vetch compared to oats+peas
• 4-way: cereal rye + hairy vetch + kale + sunflower vs. oat + peas + sunflower + radish
• 8-way: mix included both 4-way mixes plus sunflower + flax
• 12-way: 8-way mix plus sorghum-sudan grass + Austrian winter peas + crimson clover + winter barley
• Controls were treatments without cover crops, where corn was grown with the same N rate as in the other plots (total of 150 or 100 lbs N/ac) or starter N only (30 lb/ac).

Also compared was planting corn into cover crop residues: no-till, fall strip-till, and two biostrip treatments (radish alone or a 4-way mix of radish + oat + faba bean + buckwheat). Biostrip tillage is precision planting of cover crops where wheel-traffic areas have over wintering cover crop species but the area where corn will be planted has winter-terminated cover crops with little crop residues that are used to prepare the seedbed for the following crop.

COVER CROP SEASON:

• Data were collected on cover crop establishment and fall and spring growth (dry biomass) at all 9 site-years.
• All cover crop treatments established well. The majority of cover crop treatments had at least 1000 kg of dry biomass per hectare by the end of October at all locations
• In the fall, biostrips had equivalent growth (dry biomass) similar to full coverage cover crop treatments.
• Hard frost in September 2020 terminated the most sensitive species (buckwheat and sorghum-sudangrass) and sunflower in New Liskeard, but these species were in mix (4 or more species) so there was little impact on overall cover crop growth.
• In 2022 at Ridgetown, cover crop growth was quite low relative to other years (e.g., winter cereal rye and other treatments were about 800 kg ha^-1 dry matter), which was attributed to dry soil conditions in summer and fall. Cover crops were planted into moisture but received very little appreciable rainfall and conditions were dry into colder weather.
• Overwintering cover crops had variable growth in the spring, but it was typically over 1000 kg/ha. Hairy vetch did not overwinter well in New Liskeard but did in the other locations.

CORN SEASON:

Biostrip cover cropping provincial recommendations (9 site-years):

• Corn yield and test weight was not influenced by tillage system. Biostrips of radish or biostrips of radish, oats, faba bean and buckwheat mixed were equivalent to direct sowing into cover crop residues (no-till) or into soil that was strip-tilled in the previous fall. Therefore, farmers do not need to modify their tillage system to accommodate specific cover crops and vice versa.
• Corn populations (measured 3 weeks post emergence) were greater or equivalent with biostrips (particularly radish only) to fall strip-till and no-till, suggesting equivalent planting conditions. This effect was particularly evident in the rye cover crop, where perhaps biostrips protected corn stands from the negative impact of rye.
• Thus, biostrip cover cropping appears to lower the risk of cover crops and would save fuel, labor, and equipment depreciation relative to strip-tillage.

Provincial recommendations of cover crops (CC) before corn (9 site-years):

• Forage pea or oat cover crop grown after winter wheat going into corn are recommended. Corn yield (167 and 162 bu/ac) was equivalent to the No CC+N control (168 bu/ac).
• Winter cereal rye (144 bu/ac) is not recommended before corn, especially in fields with limited plant available N.
• All cover crops increased corn yield relative to the No CC + 0N control (i.e., when only starter N was applied = 119 bu/ac).
• Corn populations (measured 3 weeks post emergence) were reduced with those CC treatments dominated with rye, improperly controlled red clover, and the 12 species mix.
• Corn test weight was greatest in the No CC + N, while winter cereal rye and the No CC + 0N control were among the lowest (1.5% difference).
• We are exploring the aforementioned effects with corn emergence date to better understand the link between grain corn yield.

Eastern Ontario recommendations (Winchester 2019-2022):

• In terms of fall cover crop growth, many cover crop species performed well as single-species or in mixes, including widely available species such as oats, peas, cereal rye, and radish. Winter survival of cereal rye and hairy vetch was challenged with complete winterkill in one year of the trial.
• In both years, in the No CC control, N deficiency was observed when only starter N was applied. This lowered grain yield by 34% to 43% compared to the No CC control with nitrogen fertilizer.
• In all 3 years, all cover crops tested were statistically equivalent to the No CC control (183 to 219 bu/ac) when N fertilizer was applied, with the exception of improperly terminated red clover in 2020. Corn yields after all cover crops were very close to 201 bu/ac with the exception of peas (210 bu/ac) that were numerically but not statistically higher.
• Tillage (no-till versus fall strip-tillage) did not affect yield at Winchester, nor were any tillage by cover crop interactions found.

Northern Ontario recommendations (New Liskeard 2021-2023):

• In terms of fall cover crop growth, the most consistent species was radish (in mixture or as single-species), which achieved at least 1 t/ha of biomass each fall before winterkill. Highest cover crop biomass achieved was in 2022, when the oat-pea mixture achieved over 3 t/ha of dry biomass. This shows that in a warmer-than-average fall and when planted by late August, northern Ontario farms can get very high biomass yields.
• Nitrogen availability does not seem to explain treatment differences in corn yield as yields were equivalent regardless of fertilizer application.
• Corn yields were affected by both tillage and cover cop treatments. Yields were slightly but significantly greater with fall strip-tillage versus no-till (114 bu/ac vs. 111 bu/ac). There was no significant tillage by cover crop interaction, meaning the effect of a cover crop on corn yield was the same regardless of tillage type.
• Cover crops tended to reduce yield compared to the no cover crop control. Statistically speaking, only cereal rye, red clover (spring-terminated), and the 12-species mix significantly reduced yield compared to the no-cover crop control. Otherwise, cover crops yielded statistically similar to the no-cover crop control. But numerically, yields were reduced. This yield loss was partially due to the fact that the corn planter at New Liskeard did not have any trash whippers. Thus, surface residue from even winter-killed cover crops likely interfered with corn planting. This may also be a climate or location effect, as corn was planted at the end of May/early June, so any emergence delay may have reduced yield.

Southern Ontario recommendations (Ridgetown 2020-2023):

• All cover crops tested grew well, accumulating over 2000 kg/ha dry biomass, except in 2022 when dry conditions limited growth.
• Across all 3 site years, corn grown after cover crops of hairy vetch (182 bu/ac) or peas (178 bu/ac) yielded similarly to the no-cover crop control (187 bu/ac) as all plots received in-season fertilizer N.
• Nitrogen availability seems to explain treatment differences in corn yield. Despite N mineralization from legume cover crops (forage pea and hairy vetch) and immobilization with grass cover crops (cereal rye and oats), all cover crops tested were greater than the starter-only treatment control (No CC + 0N) by at least 17 to 43%.
• There was no effect of tillage and no cover crop by treatment interaction, which we attribute to the planter that had trash whippers to deal with plant residues.

Cover crop recommendations for the province and regions were not as complicated as initially expected. It was expected that there would be a cover crop by termination interaction on corn yield, but this interaction was not observed at all – not at the provincial level (all 9 site-years together), regionally (3 sites), or in the vast majority of individual site years. This was surprising as it is known that cover crop management is a barrier to adoption. The lack of observed interaction was attributed to planting when soil conditions were ideal and setting up the planter for good seed to soil contact while removing crop residues out of the seed slot and off the soil surface. Overall, good logistics and good agronomy are recommended when cover cropping.

Corn yield was as good as or better with cover crops than without. Improper termination of overwintering cover crops can cause corn yield losses. Biostrips may reduce that risk. Biostrips were equivalent to strip tillage, suggesting an opportunity to reduce passes through the field with biostrips compared to strip tillage. The lack of advantage of fall strip tillage may be due to over wintering cover crops encroaching on the tilled area, leaving some plots with about 2” of bare ground. Farmers should target strip tillage as late into the fall as possible and recognize that they may want to freshen up strips in the spring. At Ridgetown, the lack of tillage effect was attributed to using a no-till planter with trash whippers that removed residues (6” wide) from the corn row.

Cover crop treatments tended to establish and grow well at all sites. In Winchester and Ridgetown, many cover crop treatments established 2 t/ha or more dry biomass by the sampling date, meaning many possible mixes and species are viable options for growers in these regions (i.e., surpass the minimum threshold of 1 t/ha). In extremely dry fall conditions (Ridgetown 2022) cover crop growth was less than 1 t/ha for winter cereal rye, hairy vetch, red clover, and the oat+pea mix. The successful establishment and growth of some cover crop treatments after winter wheat at New Liskeard was most notable, including the oat, radish, and cereal rye, which were living in November.

External Funding Partners:

Cribit Seeds

This research was funded in part by the Ontario Agri-Food Innovation Alliance, a collaboration between the Government of Ontario and the University of Guelph.

Project Related Publications:

None.