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Homestead Reflections: Feed the Soil With Cover Crops

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This article comes from the NOFA/Massachusetts 2018 May Issue Newsletter

By Sharon Gensler, Soil Carbon Outreach Coordinator

Cover Crop Cocktail

Here it is, another wild-weather day here at the homestead. I realize that it is still early spring and the weather is unpredictable, but somehow in recent years, the swings in daily weather patterns seem more extreme. Another good reason to be glad that I am a “Carbon Farmer”, co-creating a more healthy and resilient soil, which can roll with the punches, tolerating swings between mild, 60-degree days and those like today, with high wind, snow, sleet and rain. 

This time of year (most times really) I like to take regular garden walk-throughs, inspecting and observing the conditions of the soil, growing beds and mulch. Earlier this week (in mid-April) I determined it was time to plant those early cover crops (discussed in the April issue of this newsletter). For the most part, the beds were still covered in mulch, with just a few bare spots of unprotected soil. The depth of all of the mulch is much thinner now than it was in the fall, an indication that throughout the winter, there has been a slow process of healthy decomposition. The worms, macro and microorganisms have been doing their jobs, integrating organic material into the soil and simultaneously receiving nutrients for their winter survival.

However, as the soil warms up, many more soil organisms will break dormancy and the rate of decomposition will speed up. So, in the interests of healthy soil, it’s imperative to not only keep these creatures alive but also thriving, by having additional food available.  Keeping the soil covered at all times is paramount. During the winter that thick mulch was essential. Now it’s time to use a GREEN, growing, cover crop, so that as much photosynthesis as possible will take place. Through photosynthesis, liquid carbon will be exuded through the plant roots to feed these important soil microorganisms. For this reason, as discussed last month, I plant cold tolerant cover crops (CC) as soon as possible in in the spring. Usually this means early April.

Yesterday was cold and raw, but despite my reluctance to go out, it was a good day to plant my cocktail mix of oats, field peas and forage radish through the thinning mulch. I won’t be planting many of my vegetables for a month or two, so most of my beds are now planted in CC. Knowing that today was predicted to have mixed precipitation, it seemed like perfect timing to get the seeds in. This morning the beds were covered in over two inches of snow, which protected the seeds as it then turned into slush from the heavy rain.  Depending upon the weather in the next couple of weeks, the seeds will germinate, sprout and start to photosynthesize –beginning another year of soil building.

One of the qualities of healthy, carbon rich soil is water absorption and retention. This is not only important for growth of our vegetables and fruit but also for the protection of our planetary store of fresh water.  Carbon is the basic building block of all life on earth, including soil structure. Glomalin, a glycoprotein produced by mycorrhizal fungi, is a highly stable form of soil carbon, and is the glue that holds soil particles together to form aggregates. These aggregates give soil its texture and are crucial to the water-holding capacity of soil. There is more water held within an aggregate than outside of it. Aggregates are also safe-houses for biological activity in the soil, protecting tiny microorganisms from larger ones.

Sandy soil allows water to pour through it with little moisture retained. A heavy clay or compacted soil is almost impenetrable and sheds water, often causing erosion. A healthy soil is like a rich moist chocolate cake, with the aggregate allowing water and air penetration and retention. Plant roots can easily grow within the light, moist crumb between aggregates. The longer the soil retains the rain and makes it available for plants and soil organisms, the less erosion occurs and the less dependent plants are on unpredictable rains and/or watering that we have to do.

soil aggregate “glued” to rootsI know that I’ve told you to not pull out plants, but to cut them leaving the roots in the undisturbed soil, however, occasionally, for hands-on research, it’s OK.  So, if you do pull up a healthy plant, you should see soil clinging to the roots in the form of tiny clumps. This shows that you have good texture and aggregate.

Another test is to squeeze a handful of soil, then, upon opening your fingers, observe if it is a rock-hard clump, if it falls through your fingers like sand at the beach, or if it gently fall apart in small clumps. Yes, the small clumps are what we are after, indicating good aggregate.

I recently heard someone describe healthy water retention capacity with this analogy: poor soil is like a mound of flour, which sheds water poured on top rather than absorbing it. On the other hand, water poured over a stack of sliced bread is easily and quickly absorbed. The bread has crumb and texture, with many pours available to absorb and retain the moisture, while the flour is dense with very little porous space for absorption of air or water.

Well, now that we’ve added another reason to improve our soil texture, let’s look at some considerations for our May gardening.

Depending on where you garden and the temperatures there in early May, I’d stick with planting cold-tolerant CC (oats, field peas & radish). But, as the soil and air warm up and stabilize, it’s time to add more variety to your CC mix. Research is indicating that the more types of CC seeds we mix together, the greater the benefits to our soil. Remember, diversity is beneficial, whether in our soil, our plants, our garden habitat, our diet, or our society!

If you have growing beds, which haven’t yet been planted to CC, do so now, adding more cold-sensitive plants to the CC mix. Buckwheat, sunflowers, sorghum/Sudan grass, and barley are all good soil builders that will be killed by late frost and by 20-degree temperatures, come winter. This year, I am also going to experiment with adding any outdated vegetable seeds I happen to have on hand. I have corn, beans, peas, and some brassicas that may or may not germinate but hopefully some will grow and be beneficial to the soil.

I will use some of this mix on beds, which I want for veggies a bit later in the season. For example, a bed that will have second plantings of summer squash or my late/storage carrots will get two months of CC photosynthesis first and many benefits, before I cut it back.

Pepper PlantsBy mid-May, the mid-April-planted CC will be up and probably 12” tall. Whenever a bed is needed to plant a veggie crop, I will cut the CC back at or below the soil level, thus killing them back. The tops can stay on the bed as mulch, while the roots remain undisturbed, decomposing and feeding soil organisms. Seeds or transplants can be planted through the stubble.

On those beds designated to remain in CC for the full-year, I just let them grow, or I may cut them back to about four inches in height and sow some of the more cold sensitive CC to mix in with them. By allowing CC to grow throughout the season, soils will reap the benefit of a long-term fertility boost while they are sequestering more atmospheric carbon, deeper into the soil.

lettuce plants protected by buckwheat During late May, it is also good to sparsely sow some buckwheat around your lettuce plants, once they are at least 6 inches tall. I’ve found that the broad leaves of the buckwheat prolong my lettuce harvest, by shading both the plant and the soil, thus retaining moisture and cooling the soil. 

Before I end, I do want to remind everyone that the benefits of CC are fantastic, BUT they must go hand-in-hand with the practice of NO-TILL. No-till will exponentially compound these benefits! So, remember to implement these techniques discussed last month: solarization, occultation, lasagna method, and mulching.

It is so exciting to observe all of the new spring life returning. The bluebirds, tree swallows and phoebes are back, twittering and eating garden insects; the daffodils are pushing through the snow; and the sun is growing stronger every day. Breathe deep, give thanks and love this earth.

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