The Cover Crop Disconnect: Ignoring what the data says
Scott Gillespie
Author: "Practical Regeneration" | Podcaster: "Plants Dig Soil" | Monthly Newsletter: #RealisticRegenAg
Welcome to the final newsletter of the year!
As mentioned previously, I’ll be taking a break over the holiday season but will return in early February. If you’re in southern Alberta and would like to connect before then, I’ll be at the Irrigated Crop Production Update on January 23rd in Lethbridge. You’ll find the registration link included in this email.
This month, I’m diving deeper into the topic of #RealisticRegenAg with just four articles that explore it in greater detail. Along with summaries and my own thoughts, I encourage you to save these articles in your favourite reading app and take the time to explore them fully.
Speaking of reading—if you haven’t had a chance to pick up my book yet, now’s the perfect time! Winter is ideal for catching up on the reading you meant to do over the summer. Scroll to the bottom of this email for a link to all the ways you can get a copy—locally, online, or as an e-reader version for your favourite app.
Wishing you a wonderful holiday season. See you in the new year!
Scott
In case you’re new here, let me introduce myself. I’m an author and independent agronomist from the Western Canadian Prairies specializing in Climate-Smart Agriculture. I focus on scientifically proven practices that benefit the planet and, just as importantly, farmers' economic sustainability. Be sure to visit my website, www.plantsdigsoil.com, to learn about my book “Practical Regeneration” and for services I that I offer for farmers and agribusiness.
Promising practices: Cover cropping for potato nutrient needs
This article inspired the title of this month’s newsletter. At first glance, the headline might lead you to believe that cover crops were beneficial for potato nutrient needs. A closer look at the article reinforces that impression—initially at least. The researchers attempted to integrate cover crops into a Saskatchewan crop rotation after observing successes in other regions where nitrogen-use efficiency was improved. The bottom line: it wasn’t. The data showed no evidence of changes to in-season nitrogen dynamics when cover crops were added. The only notable impact occurred in the fall, where cover crops tied up some of the nitrogen.
The silver lining is that cover crops did not negatively impact yield. This suggests they could be integrated if there are other benefits, such as disease suppression. However, without clear benefits, they represent an additional cost with a negative return on investment (ROI). It’s worth noting that this was only a three-year study, so the researchers are correct in stating that longer-term rotations are needed to observe potential differences.
One concern I have is the potential for cover crops of similar species to increase disease pressure. For example, a brassica species (tillage radish) was introduced midway between a canola crop. Could this increase the risk of clubroot or other canola diseases? In a recent episode of The Agronomists, I asked Lana Shaw about the frequency of intercrops, and her response highlighted the importance of maintaining proper break periods. In other words, you can’t grow a chickpea/flax intercrop every two years between cereal crops as a substitute for a four-year rotation with separate chickpea and flax crops.
Phosphorus on organic farms - from struvite to peecycling
This is an example of data being acknowledged and addressed. “Organic farming has a phosphorus problem,” says Dr. Joanne Thiessen Martens from the University of Manitoba. “This problem is especially common in long-term organic systems if livestock manure is scarce and the soil is alkaline.” The article continues, stating, “...incorporating cover crops in the crop rotation can help make more P available to crops. However, more P may still be needed as a soil amendment.” Joanne further explains, “...in most cases more P is removed with the products than applied as fertilizer, leading to reductions in plant-available soil P, which threatens the long-term sustainability of organic farming systems.”
The article dives deep into the sources of phosphorus available to organic farmers, outlining the pros and cons of each. Some challenges are ethical, such as the carbon impact of long-distance shipping, environmental degradation from mining the amendment, and worker safety concerns during recovery. Another significant issue is product safety. Without the processing methods that are prohibited in organic systems, materials can contain high levels of metals that are toxic to plants. Additionally, these products may harbour human, plant, or animal pathogens.
One proposed solution is “peecycling”—recovering phosphorus in the form of struvite from waste treatment systems. Organic standards allow this when sourced from animals but not from humans. Because struvite is a precipitated mineral, the risks of contamination—whether organic or inorganic—are minimal to nonexistent. Dr. Joanne Thiessen Martens focused on this approach during her PhD research and has achieved significant success with it on the Prairies. Allowing this would be one step towards a circular economy.
The weeds are winning
This article was brought to my attention in the Future Ecologies Discord server. If you’re not familiar with either, Future Ecologies is a podcast I love and the Discord server is a place for fans to discuss the show and other topics of ecology. A couple years ago I was fortunate to be able to produce an episode for the show about the agricultural potential of carbon sequestration.
MIT Technology Review isn’t a place I’d expect an article about herbicide resistance but it turned out to be a great overview of the issue. Sometimes an outside voice can see the issue clearly. The article covers the early days of herbicides and traces their evolution through the decades. Being technology magazine it covers many of the advances in non-chemical controls, many of them things I teach in my Precision Agriculture courses.
The Buzz About Native Pollinators
To finish off the year, get to know all the native pollinators that exist in southern Alberta! I’m not great at species identification but I can say I recognize many of the critters profiled in the article. I keep a messy yard. I love seeing all the insects that show up. For most of the year I have flowers available for at least someone. Right now many of them are overwintering in the mulch, leaves, and stems I’ve left in place.
“To begin evaluating an agricultural system, you’ll need to get to the core ideas and features that actually drive the system to ensure that you have a grounding for best methods and practices.”
In his consulting career as an agronomist, and as a lifelong gardener, Scott Gillespie has learned to critically evaluate information before jumping into something new. Particularly in these days of climate-change anxiety, he has seen people choose agricultural systems that seem right on the surface but aren’t actually making a difference.
Many times, a new idea is simply a good hypothesis. Early success can mean things get picked up quickly and are applied before they are fully tested.