Cover Crops: The Most Complicated Blanket in the World
I love plants. Anybody who has read this blog should suspect that by now, but I thought I would clarify for the uninitiated so I don’t scare them off with my unbridled enthusiasm for the wonderful practice that is using a cover crop. Ground cover is the first tenet of syntropic agriculture, and it typically covers two main sources of cover: organic ground cover, often abbreviated as OGC, and cover crops. The key difference between OGC and cover crops is that cover crops are planted in the ground, while OGC is not. Think about OGC as a mulch or bed of leaves, and cover crops as a bed of wildflowers. See the difference?
Both OGC and cover crops work together to help the soil fertility on farms, but for the majority of this blog post, I will be focusing on cover crops, because quite frankly, cover crops are way more interesting than OGC. Also, I spent many, many, hours spreading mulch this summer, and if I have to think about it any more than absolutely necessary, I may throw up.
Organic Ground Cover:
OGC is fantastic, primarily for the protectionist element that it brings to an area. When you lay down a thick blanket of leaves or woodchips or other types of ground cover, the soil is being protected. OGC traps water, helps prevent wind erosion and wildlife interference, and attracts decomposers (things that eat dead things), all of which support soil fertility and crop production.[1] The best part about OGC is that once it’s on the ground, you are done with it! No additional labor required. The worst part about OGC is that it sits on top of the soil rather than mixing with it, so the effects can be limited. Nevertheless, OGC is a simple, easy technique to improve the soil. Now for the complicated stuff.
Cover Crops:
YAY! I could not be more excited to write this blog post. Cover crops are confusing, contradictory, and an absolute joy to figure out. Because it can be so confusing, I am going to structure this section on cover crops in two sections. First, I am going to explain why cover crops are used by farmers in the United States. Second, I am going to explain how cover crops are used by farmers in the United States, and the barriers that stand in the way.
1. Why Cover Crops?
Technically, the answer to this question is simple: farmers use cover crops because it improves the quality of the soil. But that’s pretty much the reason for everything that farmers do because good soil leads to a good crop, so let’s get a little more specific.
Cover crops support and improve irrigation practices by increasing the absorption of water into the soil.[2] How does this happen? In soil, there are two types of pores, called macropores and micropores. Macropores are the space in between the soil particles, and micropores are the spaces within the soil particles. I like to think about soil as a house. In the house, there are hallways (macropores) and air vents (micropores). In this house, Ms. Water Particle just got home from work in the clouds and needs to rest in the bedroom. It would be far easier for Ms. Water Particle to go through the hallways to get to her bed than it would be for her to go through the air vents. In the same way, water finds it much easier to navigate through the soil through macropores as opposed to micropores. Cover crops increase the presence of macropores in the soil through the decay of their roots. As the roots decay, they leave behind macropores, increasing the ease of water flow through the soil, and therefore also improving irrigation practices.[3] This can also improve “free water” in the soil, which in turn encourages microbial growth in a damp environment.
In addition to supporting irrigation by encouraging the development of macropores, cover crops result in more hydraulic roughness in a field.[4] I love the term hydraulic roughness because it sounds really intense and hardcore, but it’s actually very simple. Hydraulic roughness is the amount of friction water experiences when passing over land. The more hydraulic roughness, the more friction. More friction means that water takes longer to move over the surface, and more time spent on the surface of soil means more absorbance into the soil. Picture trying to spread butter on the outer crust of a lovely French baguette. Your knife may slip around the hard outer crust, and the butter will rest on top, not sink into the bread. This is a bit like how water flows over hard-packed soil surfaces with low hydraulic roughness. It is more likely to run over and off the surface without getting absorbed, just like butter on bread crust. Now picture ripping apart the baguette and spreading butter on the soft, rough, pliable inner surface of the bread. This is like soil with cover crops and therefore a high hydraulic roughness. Just as the pockets of warm fluffy bread capture and holds the butter, the friction of the soil captures and holds water, affording it a greater opportunity to absorb.
Cover crops give a lot to the soil. They help support the soil fertility and help water absorption. So why, then, do only a marginal number of farmers use them?[5] Let’s take a closer look at how farmers use cover crops, and the barriers surrounding cover crop use in the United States.
2. How do farmers use cover crops? And why don’t more farmers use them?
When in use, farmers will plant cover crops in rotation with harvestable crops as a way to restore the soil. This is sometimes called “crop rotation”, but I don’t like to use that terminology because it implies that the crops being rotated are harvestable crops, which cover crops generally are not. Cover crops are most often planted overwinter in fields that would be otherwise unused, in hopes of increasing crop yield (the amount of profitable crop harvested) in the spring.[6] However, the planting of cover crops costs both time and money, something that is in short supply for most farmers. Now, you might say “If cover crops increase soil quality, and therefore crop yield, then wouldn’t that make up for the extra seed costs?”
And I would say yes…in theory. You see, the fun thing about cover crops is that the effectiveness varies extensively by plant and region, so in order to maximize the benefit of cover crops, a farmer has to pick the right one.[7] If a farmer picks the wrong cover crop, it may actually cause negative interactions with the soil, and decrease soil fertility. One small choice could ruin or severely decrease a harvest. Would you like to hear something even more fun? There is very limited data about what cover crops provide the best benefit for specific regions and crops, so not only do farmers have to make what could be an incredibly costly decision, they have to make it blind.[8] They could make the best guess after reading a few studies, but these would be generalizations. Generalizations are the enemy of productive farming. Each aspect is so specific — the region, the climate, the crops planted, the previous land use — everything affects how cover crops impact the soil. In order to make cover crops a viable option for farmers, we have to gather more information about how they function. This costs money, which always seems to be in limited supply. Especially if you are working toward sustainability and not profit.
I must confess, after writing that last paragraph I feel a little like a 13-year-old who just waved a lollypop in a child’s face and then ripped it away. “Do you want this amazing thing that has the potential to revolutionizes our farming system? Well, that’s a huge bummer for you, because it can’t translate to wide-spread use. Sorry!”
It is, however, a welcome reminder that many farmers do wish to incorporate sustainable practices into their business. They merely lack the resources and support to do so, both from a pure academic and informational standpoint and from a governmental standpoint. We are failing our farmers, not the other way around.
To recap: Cover crops=good! The fact that farmers can’t reliably use them=bad! ☹.
There won’t be a blog post next week, so I will see you in two weeks to talk about the second tenet of syntropic agriculture: maximizing photosynthesis.
With a wild desire to go plant some hairy vetch (a common cover crop),
Ajah
[1] Zhang, Yichuan, Lifang Qiao, Chaoping Chen, and Jian Zhou. “Water Absorption Features of Organic Ground Cover under Artificial Rainfall.” Alexandria Engineering Journal, January 1, 2020. doi:10.1016/j.aej.2020.08.010
[2] Bryant, Corey, Martin Locke, Larry Krutz, Bobby Golden, Robert Steinriede, G. Spencer, Trent Irby, and Daniel Reynolds. “Furrow-Irrigation Application Efficiency in Mid-Southern USA Conservation Tillage Systems.” Agronomy Journal (2020). In Press.
[3] Bryant, Corey, Martin Locke, Larry Krutz, Bobby Golden, Robert Steinriede, G. Spencer, Trent Irby, and Daniel Reynolds. “Furrow-Irrigation Application Efficiency in Mid-Southern USA Conservation Tillage Systems.” Agronomy Journal (2020). In Press.
[4] Bryant, Corey, Martin Locke, Larry Krutz, Bobby Golden, Robert Steinriede, G. Spencer, Trent Irby, and Daniel Reynolds. “Furrow-Irrigation Application Efficiency in Mid-Southern USA Conservation Tillage Systems.” Agronomy Journal (2020). In Press.
[5] Singh, Gurbir, Thilakarathne, Ashani D. G. M., Karl W. J. Williard, Jon E. Schoonover, Rachel L. Cook, Karla L. Gage, and Randy McElroy. “Tillage and Legume Non-Legume Cover Cropping Effects on Corn–soybean Production.” Agronomy Journal 112, no. 4 (2020): 2636–2648. doi:10.1002/agj2.20221. https://doi-org.holycross.idm.oclc.org/10.1002/agj2.20221.
[6]Bibliography
Singh, Gurbir, Thilakarathne, Ashani D. G. M., Karl W. J. Williard, Jon E. Schoonover, Rachel L. Cook, Karla L. Gage, and Randy McElroy. “Tillage and Legume Non-Legume Cover Cropping Effects on Corn–soybean Production.” Agronomy Journal 112, no. 4 (2020): 2636–2648. doi:10.1002/agj2.20221. https://doi-org.holycross.idm.oclc.org/10.1002/agj2.20221.
[7] Ruis, Sabrina J., Humberto Blanco-Canqui, Roger W. Elmore, Christopher Proctor, Katja Koehler-Cole, Richard B. Ferguson, Charles A. Francis, and Charles A. Shapiro. “Impacts of Cover Crop Planting Dates on Soils After Four Years.” Agronomy Journal 112, no. 3 (2020): 1649–1665. doi:10.1002/agj2.20143. https://doi-org.holycross.idm.oclc.org/10.1002/agj2.20143.
[8] Singh, Gurbir, Thilakarathne, Ashani D. G. M., Karl W. J. Williard, Jon E. Schoonover, Rachel L. Cook, Karla L. Gage, and Randy McElroy. “Tillage and Legume Non-Legume Cover Cropping Effects on Corn–soybean Production.” Agronomy Journal 112, no. 4 (2020): 2636–2648. doi:10.1002/agj2.20221. https://doi-org.holycross.idm.oclc.org/10.1002/agj2.20221.
