Original report by: Peter Johnson (Agronomist, Real Agriculture) & Shane McClure (Research Lead), condensed by Cathy Dibble, Thames Valley Regional Communication Coordinator

Considerable enthusiasm still exists for the concept of having living roots in the soil at all times, but very little data was available to show either long or short term impacts when the Thames Valley/Heartland Regional Tier Two project was initiated in 2015. 

Three replicate field scale trials were established to assess the Roots Not Iron concept. The treatments continued in the same location at established sites over the length of the project. Minor adjustments were made to the original protocol. The seeding rate of the multi-species cover crop after wheat was reduced from 110 lbs/acre to 50 lbs/acre, and spring strip-till was performed before corn planting to address slot closure and soil contact issues. Cereal rye after corn harvest replaced annual ryegrass interseeded at V6. Three strips were replicated three times across each plot. 

1 – Cooperator’s current conventional best management practices with no cover crop. Tillage following co-operator’s normal practice. 

2 – Standard best management of cover crops including clover in wheat (reseeded with oat/pea mix if poor establishment), burned down in fall. Tillage following co-operator’s normal practice.  

3 – #RootsNotIron; multi-species (minimum 8 species) cover crop containing a mixture of oats, radish, clover, cereal rye, sunflower, peas, phacelia, and sun hemp planted after wheat harvest and left to over winter, terminated in the spring and strip tilled prior to corn planting. Cereal rye following corn harvest and terminated in the spring, prior to no-till soybeans. 

Applications of manure as desired by individual cooperators applied consistently across all treatments and repetitions, with manure nutrient values taken into consideration.

The first Tier 2 project of 2015-2018 showed significant negative impacts on yield in both corn and soybeans in the “plant green” plots compared to other treatments. These losses appeared to be associated with poor slot closure, and inconsistent seed to soil and soil to plant contact. After 3 years, no increase in soil health could be measured. Adjustments were made to the “plant green” treatment with strip tillage used to overcome the challenges in the original project. The majority of the sites continued through to fall 2022. 

Annual ryegrass had a negative impact on stand establishment over the course of the first stage of the project and at the Lucan site in 2018. Except for 2020 at the Elmira location, cereal rye showed little impact on stand counts. 

Soil samples were regularly collected from each treatment. Thirty soil cores were taken at 6 inches from each 1-acre plot. The soil samples were air dried and sent to Cornell University for testing. The soil health results for each plot are available in the full report. There is still a lot of debate about what constitutes a healthy soil and which tests are the best indicators. Organic matter has always been the gold standard for indicating how healthy a soil is, but the current thinking is that active carbon and potentially mineralizable nitrogen are two other tests that may be a good indicator of if a soil is healthy or not. 

Year	2022 – 8 Years of Treatments
Treatment	No Cover	BMP	Plant Green
water capacity	0.24	0.24	0.24
aggregate stability	32.5	31.1	30.6
organic matter	3.7	3.6	3.6
soc	2.5	2.4	2.4
Total C	3.2	3.2	3.3
Total N	0.22	0.21	0.21
Ace soil protein index	6.3	6.3	6.3
respiration	0.80	0.80	0.83
active carbon	704.4	701.7	691.8
Overall Rating	79	79	79

After 8 years of the Roots Not Iron project there is essentially no difference between the soil health measurements. The variability in results between sampling years shows how much variability there is within a field and how much variability there can be from year to year.

There was little difference in wheat yields across treatments over the length of the project. On average there was very little difference in corn yield across treatments in later years, which is a drastic improvement from the results seen in the first stage of this project where yields were reduced by 16.6 bu/ac in the plant green treatment. It was hypothesized that emerging corn plants sensing the presence of other green plants nearby caused the corn plant to alter its growth pattern, along with difficulty in getting sufficient seed/soil contact through masses of living roots. It is still unclear if the improved results are due to the introduction of strip-till in year 4, reduced greenness in the cover crop at corn emergence, improved soil health, or a combination of many factors.

From yield numbers in this project, it appears soybeans may be able to handle the stress of plant green better than corn. Soybeans suffered only minor yield loss when planted into a green cover crop. Beginning in 2019 soybeans were seeded into cereal rye instead of annual ryegrass. Results may indicate that cereal rye has less of an impact on soybean establishment compared to annual ryegrass although spring cereal rye growth was limited due to late fall establishment.

After 8 years, there was no noticeable difference in soil health overall. A few sites appear to potentially show some soil health improvement but there is a lot of variability between repetitions, sites, and even years.   

Huge thanks to our co-operators. Thanks to administrator Marian Desjardine. Special thanks to Cathy Dibble for helping to coordinate sites and data. This project would not be possible without the support and funding of the Ontario Soil and Crop Improvement Association. The full report is available here https://www.ontariosoilcrop.org/crop-advances/

This project was funded in part by the governments of Canada and Ontario through the Canadian Agricultural Partnership (the Partnership), a five-year, federal-provincial-territorial initiative.