Healthy Soil = Healthy Plants: Peter Callen
Healthy Soil = Healthy Plants
Peter Callen
How do you feed your plants? What do you feed your plants?
There are 3 basic ways plants take in nutrition through their roots, and one way through their leaves.
Through their roots:
These 3 ways usually all take place under good growing conditions, but sometimes one or more is favored than another.
Plants can feed Hydroponically, which doesn’t mean the plant necessarily has to be floating in water, just that their nutrition is water soluble, along with other factors that make it possible for the plant to “drink their food”. This is how most commercial agriculture operations feed their plants - water delivery. The soil is basically just holding the plant upright. Unfortunately, this method has led to a lot of dead soils.
Plants can feed through a method (ingenious plants) called mineral exchange, or technically, “Cation exchange” where the plant exchanges a positively charged Hydrogen atom for a positively charged Calcium, Magnesium, Potassium or Sodium atom. The cations are positively charged whereas the anions, like Nitrogen, Sulfur, and Phosphorus, are negatively charged. Those anions are water soluble, so the plant can drink them up, if they are available in the soil. In acidic soils, the cations can get washed away or leached out of the soil, but here in the alkaline soils of the Southwest, our cations get bound to the rock and clay in the soil, making “cation exchange” difficult and costly for the plant.
Then there is plant feeding through the active biology in the soil, or SOM feeding. SOM is Soil Organic Matter, and that doesn’t mean chunks of wood in the soil. SOM consists of 3 parts, the food, the living biology, and the waste products. The living biology part of SOM consists of bacteria, fungi, nematodes, rotifers, and many other denizens of the deep. To keep all this biota alive requires the proper food, water, temperature and shelter, just like any other farm animals. So not letting the soil dry out too much, or become waterlogged, is a good way to keep the soil life well hydrated, but not suffocated. The soil life breathes in oxygen and exhales CO2, just like other animals do. All of this soil life needs to be fed a proper diet as well, and there is a standard recipe for this diet, which is 25 parts of Carbon to one part of Nitrogen (the standard compost making ratio).
If you are planning on feeding your plants through the percent of SOM in the soil, you can figure your plants will receive about 100 lbs. of nitrogen per acre per one percent of SOM. This is adequate for medium to low nitrogen requirements. A couple of caveats though.
First one: In the history of the Earth, which came first, land plants or the soil life? The soil life of course, made it possible for land plants to exist, so which one feeds first? Again, it may be obvious, but seldom do people think of feeding their soil, they think of feeding their plants. But the soil always eats first.
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| Sheet mulch beds “composting in place” in the field, building soil organic matter in a “no-till” field. |
Second one: Soils in the arid SW United States seldom have SOM percentages above 2 or 3%. Several reasons for this, the first being that hydration requirement; if the soil dries out too much, the soil life dies back and has to start over again instead of growing all spring/summer and fall. The second being the temperature. Biological activity in the soil doubles with every 10°F. rise in temperature. But this happens within a temperature range of about 40 to 80°F. Below or above that, soil biologic activity slows way down or stops altogether. So if soil temps. are getting into the 90’s in the summertime, the process of building SOM is going to slow down or stop. The ideal soil temps. are in the 70’s for soil biology to thrive and grow - if the food and water is adequate. The third reason that it’s so hard to maintain soil life in the arid SW is shelter for the soil life. Without adequate carbon stores (humates) in the soil, or mulch/cover on top of the soil, the soil life is exposed to wild temperature and moisture swings, as well as damaging UV rays from the sun.
With all of these challenges however, it’s still worth it to maintain soil life and help it grow. One of the big reasons you might not think of (is) that one of the major benefits of all that life in the ground are the waste products they produce.
Cookies and cake: Plant roots not only exude H+ ions, they also exude whole molecules of H, C, O combinations, like carbohydrates, proteins, and sugars. Lots of sugars. This attracts the real arbiters of health, the real conveyors of nutrients, the beneficial bacteria and fungi - yea team! "Life is short, eat dessert first", says the bacto-fun team. All that binging on carbs and sugar leads to a short life for those little gluttons, but their dead bodies pile up into a massive storehouse of broken-down carbon humates. These humates are a joy for plant roots to live in, as they store both water and nutrients like a bank that the plant can draw upon when it needs to. The living part of the soil is important for plants too, as many bacteria and fungi mediate the transport and chemical availability of plant nutrients, even living within the plant roots themselves.
The waste products however accumulate over time and not only build up in the soil, but persist in the soil for many hundreds, even thousands of years, if not eroded away by wind and water. Hence the very deep, black soils in the Mid-West which were formed under prairie grasses and wildflowers for millennia. These waste products are specially formed biological carbon molecules called humates, humic acids, and other compounds that will break down no further. These stable structures then provide safe homes for the living part of the soil, as well as providing an easy way for plant roots to penetrate further into the soil. Another spectacular benefit is the water holding capacity of these carbon structures. So as you can see, it’s not only the life in the soil, but their waste products that provide the conditions for what we call healthy soil.
So with all the benefits described, it’s worth doing everything we can to protect the living soil and encourage its growth. It's challenging to build SOM and provide food for your plants in this way and challenging in different ways to feed your plants through the other pathways described earlier; cation exchange and hydroponically. Taken all together, these 3 ways that plant roots can feed are all useful to organic gardeners and farmers. The first 2 feeding methods described can be employed by organic growers as well, there are soluble organic minerals that can be used for hydroponic feeding, as well as a naturally occurring mineral (gypsum) also organically approved, that can be used to help buffer our alkaline soils and increase cation exchange capacity.
Plants also absorb nutrition through their leaves (foliar feeding) and this is a good way to provide extra nitrogen at critical times, but there is so much to cover with that method, it’s probably best left to another article.
So now how do you feed your plants?
Healthy soil = Healthy plants = Healthy seed = Healthy people
Peter Callen has been working with Cameron Weber on rejuvenating this public field at the ABQ City Open Space Visitor Center for the past 2 years. Monthly workshops and volunteer days will be held again this year on soil building, soil testing, planting native pollinator plants and harvesting their seeds for other restoration projects. Check the visitor center for details.