Soil Fertility and Fertilizers
There is difference between dirt and soil. Dirt is sand, silt, and clay - void of life. Which commonly means a lack of capacity to retain Hydrogen or Oxygen - water. Soil is millions of microorganisms living in and amongst sand, silt, clay and carbon. We want to raise our plants in soil that is rich with microorganisms. Much like in the body, it is these microorganisms that make all of the micro/macro-nutrients available. And in some cases they are byproducts of these organisms consumption. We want to have a natural balance of commensal (beneficial) microorganisms and pathogenic (opportunistic) microorganisms. Nature has a balance and that balance is not 50/50, it fluctuates.
It is common when we speak of soil fertility to think about adding fertilizer. I mean, it has the word fertile in the word “fertilizer”. To our soils dismay, these products rarely benefit the soil itself. When I think of fertile soil, I think of the forest, a wide variety of species living together within Nature’s balance. This is what I strive for in my garden. Fertilizers are like salt, they are mostly commonly and naturally occurring Earth elements, isolated and concentrated, which have been intelligently formulated to provide micro/macro-nutrients to our plants at different stages of plant development. A similar statement could be made about salt. Salt is a concentration of naturally occurring Earth elements. However I am not certain about adding salt my garden soil. That doesn’t seem good for the overall conditions. Here is why…
When Earth elements become isolated from their natural source they become volatile. When we take volatile elements and concentrate them, what do we have? Concentrated volatility. While volatility can be great in the stock market, not so in the soil. For every action there is an equal or opposite reaction. While there is certainly an apparent benefit to seeing our plants vibrantly green, equally there is an opposite action taking place within the soil biology. The fertilizer alters the balance (pH) of the soil making in uninhabitable for the microorganism residents.…converting the soil in to D-I-R-T. Dirt is an unspeakable four-letter word in my garden. These microorganisms play a large role in symbiotically working with plant roots to provide the necessary elements which the plants need. In trade, the plant will provide sugars and other desired chemicals to the microorganisms. This is the cycle that has been taking place for eons.
It never hurts to get annual soil tests to know what is going on in the soil and there are many things that one can test for. This testing will allow for a more specific approach for your soil amendment application. You can find a simple at-home soil pH kit at your local garden supply retailer. If nothing else, it is certainly good to be aware of the pH of the soil. The soil pH is the primary factor that will determine if the nutrients which are present in the soil will be available to the plants! On average, most plants will thrive within a pH of 6.5. This also means that the microorganisms in the soil, which symbiotically relate with the plants root system are looking for these conditions as well. Things like blueberries and azaleas prefer more acidic soil in the 5.5 range. By looking at the following chart you can see that blueberries would then benefit by more elements like iron, manganese, boron, copper, and zinc available to them. Just because we put these elements in the soil it does not mean that they are available to be used by the plants and relating microorganisms.
While it is good to test your soil, if you need to take the pH up, the natural answer is to add organic matter. And if you need to bring the pH down, the natural answer is to add organic matter. I know it sounds too easy to be true but the truth is simple. Organic matter is generally plant matter, or animal manures that have been decomposed or will soon be decomposed. Most commonly referred to as compost (decomposed), or mulch (soon to be decomposed, providing shade and holding water in the mean time). We can get specific with our choices of organic material, but most simply put, know that if you continually feed organic matter to the soil the natural balance will ensue.
Most plants, trees, and all soil systems appreciate shade. Things like mulch, a shady tree or shade cloth, will be appreciated by the plants and soil. They will show their appreciation with large green leaves and commonly more flowers than those outside of the shade. The soil will hold water longer creating the conditions for microorganisms to do what they do, which is digest the mulch. I like to keep a 2” - 4” base of mulch on the soil and around the plants when possible. Being sure to keep the mulch a couple of inches off of the trunks of trees and bushes. Many are aware of the soil frost line that occurs in regions which have a freezing winter. There is also an evaporation line that occurs in regions that have a greater amount of evaporation than precipitation. In my region of Southern California we can experience upwards of a 4” evaporation line. This is a primary factor as to why we add “so much” mulch. Thus, when increasing the soil profile by 4” with mulch, we now have 4” of material that will evaporate the water that is held within. This will allow the soil to maintain its stored water, creating the conditions for living organisms to thrive.
Keep in mind it is critical to keep feeding the soil organisms in order to keep them around. This is all a part of creating the conditions for the right things to occur. I think of it as a party, if I make sure there is always punch, some chips and salsa available, most folks will be hang out and mingle at the party. In the garden, we put out wood chips and leaf salsa for the organisms to stay fed and mingling amongst the garden. I like to plant things like Daikon radish, vetch, rye grass, or peas for the soil. The root systems exude certain sugars and chemicals that microorganisms love. I am always seeking to increase the amount of carbon (sponge factor) in the soil. Because of this, I will leave all of the non-edible plants and a majority of the edibles i.e. daikon radish, peas to rot in place, only harvesting a small amount for myself. This will provide shade, feed microorganisms and provide a carbon carcass, which acts as a home for microorganisms. It will also aid in holding the soil together, reducing the possibility of soil erosion. All good things!
Lastly in this section, I would like to share a method referred to as “Chop n’ Drop.” When we prune our trees, bushes, and vines we have the opportunity to feed all of that material back into the soil. Simply chop it, and drop it. Let the microorganisms do the rest. If you have a need for uniformity you can shove it through a mulching device, then scattered through the garden. The microorganisms will appreciate it being chopped up smaller anyway, they have really small mouths.
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