Cover Cropping | Part 2
September 9, 2022
What’s Your Type?
Part 1 | Part 2
The plant species you use in your cover crop mix is a crucial decision. We always start at square one– and you can too. Square one is: What is it exactly you are trying to accomplish? Planting stuff to feed the soil because April said it was a good idea isn’t an appropriate answer!
You need to be very clear about your goals.
Our motive is always “a healthier, more resilient soil system.” But what specifically does that mean?
Past soil tests results indicate that nitrogen is a limiting factor in our cropping system. That means our vegetables take a lot of nitrogen to grow, which can deplete our soil reserves. Legumes (peans, peas, vetch, clovers, etc.) work in symbiotic relationship with bacteria to pull atmospheric nitrogen out of the sky and deposit it in nodules affixed to the roots of the legumes. This ‘free’ fertilizer becomes available for other plants to use after the legume completes its lifecycle. That’s nothing short of magic! So, we focus on including at least one legume in our cover crop mix.
We also know that winter rains leach nutrients out of our soils and can cause compaction on bare soil. So we need a cover crop plant that specializes in capturing and holding nutrients and has a large aerial portion to slow down the force of heavy rains. The bigger the root system of a plant, the higher the nutrient storage capacity. So we look to the grains and grasses that cover the bare soil quickly and have a lot of biomass.
Sometimes, in parts of our field, there is a compacted layer. In these places, we know we need to include a cover crop plant species that has a strong taproot to break up the hardpan and restore healthy water and nutrient cycle within the entire soil profile. Crops like alfalfa and clovers, as well as and many brassica species have tenacious roots that work to aerate the soil.
Finally, we know that organic matter, i.e. plant material (stems, leaves, roots, etc.) is what fuels the entire soil ecosystem. Without organic matter, the soil starves. One more goal of ours with respect to cover crops, is that we want living roots growing in our soil as much as possible for as long as possible. That means we want to minimize the acreage and the length of time any of our soil is bare. For this scenario, we need plants that have short life cycles- meaning they germinate and grow really quickly. Some examples are buckwheat and phacelia. In this way, cover crops help us fill in the gaps of time between the crops we grow for market, keeping the soil nourished with living roots and organic matter.
Respectable seed suppliers and university extension programs have a lot of good information on specific benefits of different types of cover crops. Here’s a few examples from Johnny’s Seeds and OSU. I frequently learn a lot from reading seed catalogs too. For example, Territorial Seed, Fedco Seeds both have pictures and descriptions available. Companies marketing toward commercial growers sometimes refer to Cover Crops as Farm Seed. They are one and the same.
After you’ve thought about what your soil needs, think about how your cover crops will be integrated into your current system. As a grower, what are your needs? This gets us thinking about what is or isn’t working right now. Your own observations are very important here– don’t discount them because you don’t have scientific proof. You know your garden and your goals better than anyone else.
In our case, we want to make sure we have a cover crop plant that blooms as early as possible to support hungry pollinators that don’t have a lot else to eat when it’s cold and grey. That means we focus on cover crops we can plant in the fall that will protect our soil during the rainy months and be blooming as soon as possible in the spring.
And in our spring planted fields, where we need to be transplanting crops ideally in May, we need cover crops that do not have really fibrous stems because we are transplanting literally between rainstorms and have only small windows of time to be working in the field. That means we have to have a fast transition time to move from cover crop to market crop. We need our cover crops to be completing their life cycle in early spring, or that break down quickly when cut. For example, oats have a much less fibrous stem than rye grain, and peas sometimes winterkill, meaning lower temperatures kill the plants so we don’t have to.
It’s important to know that some cover crops grow better in the cooler months, and some thrive in the warmer summer season. When you intend to plant your cover crops so you can also help determine the type to utilize.
These are a few examples of a grower's needs. What would you like to accomplish through the use of your cover crops? What problems are you needing to solve? Jot down a few notes to identify what you want to achieve.
Now– stop and notice something. At this point, do you see how we haven’t decided specifically what exact cover crops seeds to sow? We’ve focused on identifying the needs of our soil, our own needs, and thus the characteristics (aka superpowers) our cover crops must possess. That’s because we still have decisions to make about timing and technique.
Coming up with a good cover cropping plan is an iterative process. We’ll come back to refine the types of crops we want to use after we think through the preliminary decisions on timing and techniques.
If you want an even more structured approach to cover crop planning, take a look at my in-depth article about cover cropping that I wrote as part of my Soil Health Roadmap (SHR) project. ~AJ
“Reality is made up of circles but we see straight lines.”