Four wheat, three corn, and two soybean fields (9 total) carried through from 2015 across the Thames Valley and Heartland Regional Soil and Crop Improvement Association regions into the 2016 & 2017 growing seasons. Each field followed a corn, soybean, wheat rotation for the duration of this project. Plots were field scale with three replications. The treatments are:
1. Conventional Management (No cover crops)
2. Conventional Management (Clover after wheat, oat + peas if clover fails to establish)
3. RootsNotIron (Continuous cover crop, multi species if possible, strip till or notill)
The RootsNotIron cover crop treatment interseeded into the growing corn crop was changed from a cereal rye/annual ryegrass/crimson clover blend (2015) to an annual ryegrass/crimson clover blend (2016/2017), which was not be terminated until spring. The rye mixture was planted at a rate of 46 lbs/ac (40 lbs cereal rye, 4 lbs ryegrass, and 2 lbs crimson clover) in 2015. However, the cereal rye simply did not withstand the competition, so in 2016 and 2017 6 pounds/ac annual ryegrass plus 2 pounds/ac crimson clover was seeded at 6 leaf corn. Soybeans were planted no-till directly into the cover crop. Wheat was no-tilled into the soybean stubble. After wheat harvest a multi-species cover crop was planted in treatment 3. The multi-species cover crop was planted at 110lbs/ac (30 lbs oats, 30 cereal rye, 20 sunflower, 20 peas, 4 ryegrass, 2 radish, 2 clover, 2 phacelia). The multispecies cover crop was left till spring then corn will be planted directly into the cover crop or following a single strip till pass.
Tillage done on treatments 1 and 2 followed the co-operators normal practice but treatment 3 did not receive any tillage for the duration of this project. All other variables (i.e. starter, nitrogen, manure) were the same for all three treatments following the cooperators normal production practice.
Table 1: Number of Plants to Emerge Each Day (plants/5.3 meters of row)
In the initial year no treatments had been established prior to the corn being planted, thus the corn was planted following the co-operators normal practice. The “plant green” treatment was then interseeded into the corn at the 6 leaf stage in the continuous cover plots. At four of the 6 sites there was no significant difference in yield whether a cover crop was interseeded or not. Two locations stand out in Table 1. There was an 8 bu/ac yield increase at the Glencoe site when cover crop was inter-seeded, while Strathroy #2 lost 18 bu/ac by inter-seeding. More research will need to be done to determine what conditions lead to an increase in corn yields at Glencoe, while there was a significant reduction in yield at Strathroy #2, or if this was just a random outcome.
All three corn sites had good to excellent annual ryegrass establishment during the 2015 and 2016 growing seasons. Unlike the first 2 years of this project ryegrass establishment was poor during 2017 growing season.
In the second and third year of the project corn was planted directly into the multi species cover crop. At the 2016 Bornholm and 2017 Lucan sites the corn was no-tilled into the living cover crop while the other 2 conventional treatments received tillage prior to planting. At the 2016 Elmira and 2017 Embro locations all treatments received a single pass with a strip till unit prior to planting. At the 2016 Lucan, and 2017 Dungannon sites all strips were planted no-till.
Corn emergence was tracked at each location. To do this 5.3 meter row length (1/10th acre) was marked off across several rows in each treatment after planting. Each day a different coloured flag was used to mark each plant that had emerged that day. These results are summarized in Table 1. Any corn plant that emerged after day 5 was recorded as a “late emerging”. The emergence data is fairly similar from the no cover and BMP treatments while emergence from the plant green treatment was slightly slower, and about 1000 plants/acre less in total.
Table 2: Leaf Tip and Plant Height
|Day||No Cover||BMP (Clover)||Plant Green|
|Leaf Tip||Height||Leaf Tip||Height||Leaf Tip||Height|
These plants were followed through the growing season to determine differences in growth. Leaf tips were counted around the 10- leaf stage and are summarized in Table 2 along with the plant height measurements. Again, there is little difference in leaf tip counts between the no cover and BMP treatments. However, one surprising outcome was that the corn plants in the plant green treatment continued to fall further behind the other 2 treatments. The plants emerged a little slower, but then continued to fall further behind plants that emerged on the same day in the other 2 treatments. This slowed development could still be seen at tassel timing, with the plant green treatments lagging. Plant height differences were unexpected. The plants in the BMP treatment have separated from the no cover treatment, while the plant green heights are similar or slightly taller than the plants in the no cover treatment. The corn yield results from these locations are six sites are summarized in table 3. Substantial yield loss occurred at 4 of the 6 locations with the plant green treatment (Roots Not Iron). At these 4 sites yield loss ranged from 18 to 25 bu/ac. There was little yield difference between the no cover crop treatment and the BMP treatment except for the Elmira, and Embro locations.
Table 3: 2016-17 Corn Yields (bu/ac)
|Year||Location||No Cover||Clover||Plant Green|
Table 4: Greenness Ratings
|Year||Location||No Cover||BMP (Clover)||Plant Green|
At the Elmira location, red clover was not terminated in the fall as planned, and control was not able to be applied until 3 days prior to planting. The yield loss in the red clover treatment at this location can be explained by looking at the greenness ratings (Table 4). The greenness ratings were taken on the same day as the corn first emerged using the Canopeo app, developed by the Soil Physics Research Group at Oklahoma State University.. The greenness ratings show that the clover was still green at Elmira when the corn emerged. Image 1 shows visually how much green cover remained in the clover strips at emergence. This shows that any green material has the same impact on the corn crop, whether red clover or some other species. Table 3 shows that the yield impact of green clover at Elmira was exactly the same as the impact of the green multi species mix
The Embro site had variable treatment results between reps. Some of the variability can be explained by looking at the stand count and greenness results from each rep (Table 5). Yield results are quite consistent across the reps except for Plant Green rep 2
Table 5: Embro Corn Plot Results
and BMP rep 3 which are highlighted. Both of the strips had substantial yield loss compared the rest of the treatments and the reason may be explained by looking at the stand count data and greenness ratings for the reps in question. A strip till unit was used at this location and the planter got off line with the strip till row in a few spots in both plant green rep 2 and BMP rep 3. This resulted in some of the seeds being left on the soil surface, and a substantially lower population in the 2nd rep of the plant green treatment which could explain the low yield result. The 3rd rep of the BMP treatment had a slightly lower stand count but when combined with the higher greenness rating may explain the yield loss for the BMP strip. The high greenness rating is due to a sprayer miss in the fall of 2017. The spring herbicide application did kill the wheat and clover but did not manage to brown all the clover off before the corn emerged (Image 2).
The Greenness ratings also indicate why there wasn’t a substantial yield loss at the Dungannon location. There was very little green material left in any of the treatments when the corn plants emerged. This site was planted late and sprayed two days before planting. The combination of warm temperatures and spraying before planting resulted in the ryegrass and any crimson clover that overwintered being brown and dead before the corn emerged. Due to this impact, yield results from Elmira, Embro, and Dungannon should really be viewed separately from the other locations
In 2016 and 2017 the soybeans were also planted into a living cover crop in the Roots Not Iron treatment.
Difficulties maintaining good seed to soil contact plagued the plant green treatments wherever no tillage was done. Soybean stands were reduced by 10% (Table 6) in the plant green strips. While this did not reduce yields by 10%, it does indicate the problems associated with living roots holding tightly to soil, and the difficulties that this can present when attempting to get good seed to soil contact and close the slot. On average across all sites there was a 2 bu/ac yield loss to the plant green treatments (Table 7).
Table 6: Soybean Stand Counts
|Year||# of sites||No Cover||BMP||Plant Green|
Table 7: Soybean Yield Results
|Year||# of sites||No Cover||BMP||Plant Green|
At one location in 2017 the plant green strips started to turn yellow during July showing symptoms similar to nitrogen deficiency (image 3). A tissue analysis was done to determine if there was a difference in nitrogen concentration between the plant green and BMP treatments. The plant tissue results are shown in table 8
The nitrogen content in the BMP treatment is quite a bit higher than the plant green treatment. Plants were dug up in each treatment to confirm that plants had nodulated and the nodules were active, which they were in all treatments. The only conclusion is that there must be lower soil nitrogen levels in the plant green treatment. The probable cause of the lower soil nitrate levels is that the nitrogen is being tied up as the annual ryegrass cover crop is being broken down. The higher phosphorus and potassium levels in the plant green tissue analysis is likely due to nutrient build-up in the plant as low nitrogen levels stunt plant growth. Calcium, magnesium, sodium, iron, manganese, copper, zinc, and boron are all at sufficient concentrations.
Table 8: Plant Tissue Results
|Nutrient||BMP||Plant Green||BMP||Plant Green|
Table 9: Wheat Yields (bu/acre)
|Year||No Cover||BMP||Plant Green|
The wheat results are shown in Table 9. Numerically the BMP treatment yielded slightly less than the other 2 treatments but overall there was no statistical difference in yield across treatments.
Summary: Inter-seeding annual ryegrass/crimson clover into an existing corn crop had no significant impact on corn yield. Major yield loss was found when corn was planted into a green cover crop. Hypothesized reasoning is twofold: emerging corn plants sensing the presence of other green plants nearby which causes the corn plant to alter its growth pattern, and the difficulty in getting the sufficient required seed/soil contact through masses of living roots. The research showing that plants are able to sense other plants nearby has been well documented by Dr. Clarence Swanton at the University of Guelph. A reduction in rate of development of the corn plant was also found in the plant green treatments. This may add to the reasons for reduced yield.
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 (2 bu/ac) when planted into a green cover crop, however this yield loss was quite consistent across sites. Nitrogen deficiency in the soybean crop was identified at one location and could be another issue that growers need to be aware of. More research is needed study the effect that planting green has on a soybean plant.
There was no significant difference in wheat yields across treatments.
This trial is now complete. The trials will be continued next year at a few locations which had a multi-species cover crop planted after the wheat or ryegrass planted into corn during the 2017 growing season.
A continuation of this study with a modified “plant green” treatment would be of great value. This modification would include some form of strip till (bio-strip till, mechanical strip-till) to avoid the seed to soil impacts that where experienced.
Huge thanks to our co-operators. Thanks to technician Shane McClure, and 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 and OMAFRA.
Peter Johnson, Agronomist, Real Agriculture, firstname.lastname@example.org
Shane McClure, Research Lead, email@example.com
Cathy Dibble, Thames Valley SCIA firstname.lastname@example.org