Recent Project Work: Winter Cover Crop Termination Demonstration - Funded by the On-Farm Climate Action Fund Program
Our March madness of winter work continues! The second demonstration that I'd like to talk about this month is funded by the On-Farm Climate Action Fund (OFCAF) program. For this work, I wanted to focus on the efficacy of different termination methods for winter cover crops.
Why Cover Crop?
Before I dive in to the demo itself, I wanted to talk a little bit about why we might want to cover crop our protected spaces through the winter. This list is specifically geared to folks who are not producing winter greens, and have empty tunnels during the winter months. For those who are growing cash crops through the winter, cover cropping may be better suited to other times of year where cash crops are not being produced.
1) Support soil structure in intensively cropped soils
High tunnel soils are the most intensively used on the farm, so the growth of low-feeding, low maintenance crops through the winter can help to support aggregate stability in our soils and prepare them for the next round of summer cash crops. Where erosion is less of a concern in high tunnel spaces, plant roots work wonders on soil structure and their ability to hold water for the following year.
2) Support microbial communities following our summer cash crops
Our soil microbial communities require a food source in order to maintain their populations. While metabolic activity will slow in the winter, it doesn't stop completely in a protected space. Growing cover crops in the greenhouse through the off-season provides a steady flow of root exudates into the soil, which are a great food source to support our microbes. This means that come time for transplant, our microbial population is going to be much stronger and much more active right from day one, compared to a fallow greenhouse which will 'wake up' in response to the introduction of plant roots. For more information, check out this article from Penn State.
3) Weed suppression before we come in with our spring transplants
Once February and March roll around, it is fair game for any and all plant life that could be surviving in the high tunnel. Having a well-established cover crop in place provides competition for weeds that are trying to establish in late winter/early spring.
4) Help to generate organic matter in the greenhouse
For those who do not grow winter greens, protected spaces are usually left fallow for the winter. Why not take this opportunity to grow plant material that can help to build organic matter in your greenhouse? Where our best management practices (BMP) surrounding nitrogen use are leaning towards pointed nitrogen application and less towards regular bulk additions of compost in high tunnels, we can look to other practices to support organic matter generation.
5) Soak up residual fertility left over from our summer cash crops and turn it into biomass that will hold the nutrients in a more stable form
Certain nutrients, like plant-available nitrogen for example, are quite prone to loss if there are no plant roots around to take it up. Planting a cover crop following your summer cash crop is a great way to take advantage of residual fertility hanging out in the soil, and convert it into plant tissue...a much more stable form! Once it comes time to terminate the crops, we can return those nutrients back into the soil to feed our next round of cash crops, making sure none of our valuable added fertility goes to waste.
Figure 1. The soil observed in our cover crop termination demonstration in December. Photo credit: Talia Plaskett
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Through the OFCAF program, we have already demonstrated the impact of planting dates, as well as the impact of row cover for supporting winter cover crops. For this winter, I wanted to talk a bit about how we manage this winter cover crop in the transition to spring cash crops.
Winter cover cropping requires specific selection of species that are going to withstand winter conditions in a high tunnel. Combining these winter-hardy species with row cover to help buffer the lower temperatures of the off-season leaves us looking for other methods to terminate cover crops in time for our spring plantings. Organic and regeneratively-minded farms do not have the reliability of spraying out cover crops, meaning they are more prone to survivorship in cover crops once they have been terminated.
For this demonstration, we are showcasing the efficacy of flaming, mow + flaming, mow + incorporate, tarping, and winter kill on their abilities to terminate a winter cover crop of oats and peas. Due to the variable nature of high tunnel production across the province, we will terminate on three key dates - December, end of January, and end of March. These are representative of times where we may be transitioning over to new crops, and I wanted to showcase any headaches or differences in efficacy of these termination methods as a result of termination date.
The full list that can be found on site includes:
December termination
-flame
-mow + flame
-mow + incorporate
late Jan/early Feb termination
-flame
-mow + flame
-mow + incorporate
mid-late March termination
-flame
-mow + flame
-mow + incorporate
-tarping
-(assess) winter kill
There's another piece to this however...how does winter cover cropping termination method impact our cash crop success? Having a high degree of residue left over from our termination methods is going to impact what we can plant in that soil...a direct-seeded green is going to have a much harder time at establishing compared to a tomato transplant in a high-residue bed. The timing of our termination, as well as the method, is going to impact the success of establishing our cash crops, and that was the basis for this conversation on cover crops.
Once May rolls around, I will be going on farm and documenting weed pressure and cover crop survival in each of our terminated blocks/dates, as well as the amount of residue left on each block, and report back on what we see! I will also be linking each method to a rough cost so that we can be better prepared to adopt this BMP on farm.
We are also going to show the impact that each termination type/time has on our soil microbial health - how does an early termination of a winter cover crop impact our microbial communities compared to one done in March? These results are going to take more time to generate, but I will share them with you as soon as the lab gets back to us with results.
So...what have we seen so far?
Cover crops were maintained under row cover through the duration of the winter to maintain them through the significantly colder temperatures experienced in '25/'26 compared to the last few years! When we pulled back the row cover, the cover crop was quite moist, raising some concerns on the efficacy of flaming, as well as the amount of propane we would need to burn through in order to terminate them. This is where the mow + flame treatment came into play - if we are able to cut up the tissue a bit, will the cover crop terminate better?
Looking at our three termination methods for December, we can see the mow and incorporate treatment on the left hand side of figure 3. In the middle is our mow + flame treatment, and on the right hand side we have our flame only treatment. We have a visible difference in the amount of biomass left between the middle and the right hand side, so I'm curious to see what spring will bring in terms of termination success and ease of planting.
Figure 4 was taken at the end of January, 5-6 weeks following our first round of termination. It was hard to feel confident that flaming was a successful termination method in the crop because of how wet it was, and how much biomass had been generated at the time. Looking at the photos after a few weeks, however, shows that both methods of flame treatment appear to have been successful at terminating the crop.
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Did you notice the white stakes in each block in Figure 3 and 4? We decided to track soil temperature and soil moisture to show how it is impacted by the different termination methods. Why do we care about temperature and water content? The associations of both variables on microbial activity, diversity and nutrient cycling are too important to ignore!
Figures 5 and 6 depict the sensor data we collected from our first termination (December) to our second termination (end of January). As we would expect, a soil with a living cover crop is going to be much more buffered against changes to temperature compared to a soil that is exposed. The flame treatment, represented by the orange line in figure 5, left a significant amount of residue behind on the soil. This provides some buffer against temperature changes in the high tunnel but not as much as a living cover crop does.
From a moisture content perspective, the bare soil where the cover crop was mowed and then incorporated into the soil, has the lowest recorded moisture. Treatments with residue, either living or terminated, retain a higher degree of moisture by comparison. The living cover crop showed a much more consistent level of soil moisture over time, whereas the plot where the cover crop was terminated and left on the soil surface is still prone to fluctuation.
I'm hopeful that the soil health samples that were sent off to PEI are going to link nicely to our temperature and moisture data...so stay tuned! I'm also very curious to see how these temperature trends hold up from our first round of termination to our second round of termination over the last few weeks. We will be doing our final termination in the next few weeks here and then start to look at some of our other metrics of interest- cover crop survivability, weed pressure, and cash crop success based on leftover residue. I will be updating you all on the work as we wrap up the demonstration, so keep those eyes peeled!
