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Complete Mineral Balanced Fertilizer! 
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Soil Minerals for Organic Gardeners
Compost and Minerals or
Why Does My Garden Need a Soil Test?
By Agricola
March 23, 2008
We all know that a fertile soil grows better crops, just as we all know that nutritious food grows a healthier body, and the same minerals that make the soil fertile are the minerals that make food more nutritious. The lack of essential minerals in the soil will have the same sort of detrimental effect on crops that the lack of minerals in our diet has on our health. The analogy goes even further: It is largely the presence of healthy soil microorganisms that make the minerals available to the plant, and it is largely the same sort of microorganisms in our digestive systems that make the minerals in our food available to our bodies. Neither the plants nor our bodies can do much with simple ground-up rocks; the minerals first need to be changed into a form that can be absorbed. That is what a healthy, biologically active soil does for the plants, and what a healthy population of probiotic organisms does in one's digestive system.
Now we begin to get into something interesting and controversial: The organic and biologique (Euro-speak for organic) gardening movements are all about creating that healthy population of soil organisms by increasing the organic matter content of the soil. Great effort is put into making biologically active compost and applying it to the garden and croplands, but little or no effort is put into supplying the microorganisms in that compost with minerals. Organic matter is vitally important to a fertile soil, but it is only one-third of the whole equation, or, one could say, one leg of a three legged stool that supports the whole food chain for life on Earth. Those three legs are biology (the living and formerly living parts of the soil), minerals, and energy (as in energy flow like a current of water or electricity). In most cases, if one gets the minerals right, the biology and energy flow will fall into line automatically; one cannot prevent life from growing in an environment that has all of the essential minerals it needs; the soil and plant life will find those spots and thrive there. This essay will address the biology and mineral aspects; we'll save the energy leg of the stool for another time.
As noted, life will find those places that have all of the mineral nutrients needed for growth and reproduction, but on the other hand, one can have a highly organic soil and still not have healthy crops if the minerals are missing or out of balance. Any grower who has tried growing plants in pure, sterile organic matter, such as unfertilized potting mix, will know that doesn't work too well. The plants need more than just water, air, light, and an organic medium to send their roots through: They need mineral nutrients too. Standard chemical fertilizers supply three of those nutrients: Nitrogen, Phosphorus, and Potassium, the familiar NPK listed on the fertilizer package as, for instance 5-10-10. In addition, air supplies the nutrients Oxygen and Carbon (from Carbon dioxide) while water (H 2 O) supplies Hydrogen and Oxygen. With these six nutrient elements, Nitrogen, Phosphorus, Potassium, Carbon, Hydrogen, and Oxygen, just about any plant can be grown, but it won't necessarily be a healthy plant and it surely won't make very nutritious food.
We noted above that soil microorganisms are necessary to make soil minerals available to plants, so how do the plants manage to grow when fed only a chemical mixture of N, P, K, and water? Commercial chemical fertilizers are made with highly soluble salts of NPK that the plants are able to absorb through their roots and use much as a person unable to eat can get nutrients from an intravenous IV drip. Plants are simpler in their nutrient requirements than higher animals, and able to use elements in simpler forms, so it is easier to grow large and healthy-looking plants on an IV drip than it is to keep humans healthy on one. In nature these simple forms of soluble salts are seldom plentiful in the soil.
Moving to the next step in organic-matter based fertility, what happens when a plant is grown in pure, rich compost, without any mineral soil? Often it will do well, or at least appear to do well, growing large and quickly, but it also may be susceptible to fungal diseases and blights, and the food grown will often lack flavor. Compost, of course, does contain some minerals, the amount and range of minerals depending on the source of the compost. Leaf compost will contain the minerals that the leaves contained, compost made from garden waste will have the minerals that the garden crops absorbed while growing, compost made from animal manure will contain the minerals that were in the feed the animals ate, perhaps including grain imported from other areas with different soil minerals, and often including mineral supplements that the animals were fed. Chicken manure is known as the manure with the most fertilizing power, and that is largely due to the very high grain content that the chickens are fed, as well as the insects that the chickens eat whenever available. However, chicken manure is also usually a good source of Calcium, Boron, Copper, and Zinc; not because the grains in the chicken feed are high in those elements but because the chicken feed is fortified with those elements. Similarly, cattle and horses are generally given a "salt block" both in the pasture and in the barn or paddock and many times are given a powdered mineral mix "free choice" at their feeding stations. Hog feed is also fortified with minerals. Interestingly, the salt blocks given to horses and cattle are different in different areas of the USA, so that whatever minerals are usually missing in the local pastures can be supplied. The veterinarians, veterinary researchers, and farmers are all well aware that the animals need far more minerals than are normally found in their hay or grain rations alone.
Think of how strange this is: Even the smallest farmers make sure that their cows and horses have a salt block, even the person with only a small flock of laying hens in the yard supplements the birds' diet with at least oyster shell grit to make the eggshells strong, yet they give little or no thought to mineralizing the pastures where their animals graze, the hay and grain fields where the feed is grown, or their gardens where they raise the food to feed their families or to sell. Nor do they give much thought to how many of these essential minerals they or their families are getting.
The claim is often made that "organically grown food has more minerals", but seldom is it backed up with factual evidence, so let's take a look at that claim. Obviously if the minerals are not in the soil, they cannot be in the crops grown. What quantity of minerals are available form compost, for instance?
Completely dry plant matter consists mostly of compounds made from the air elements Carbon, Hydrogen, Oxygen, and Nitrogen. The Nitrogen originally comes from the air, but is made available to the plants by soil microorganisms, or today by synthesized Nitrogen fertilizers. If this dry plant matter is burned, perhaps 95% of it will return to the air as some combination of these four elements. The remaining 4 or 5% is unburnable ash, and that is where the soil minerals reside. The minerals in that ash will naturally vary depending on the species of plant and the soil in which it is grown. The ash from wheat straw will be high in Silica, an essential nutrient but not one in short supply in our croplands. Silica is the most abundant of all Earth elements. The ash from the wheat kernels themselves will be much richer in essential minerals, as the plants concentrate them there to feed the seeds for the next generation. If one starts with 100 lbs of fresh compost, which will likely be around 75% moisture, and then dries it to leave 25 lbs of dry organic matter, and then burns that to ash, one will end up with about 1 1/4 lbs of mineral ash total, perhaps a double handful. One can see that there is really not a whole lot of minerals in that 100 lbs of compost, and we haven't looked yet at just which minerals are to be found in that ash.
Of course, there are many beneficial plant nutrients to be found in the 98 3/4 lbs of compost that we are not measuring as ash, such as humus and fulvic and humic acids, ammonia and nitrate Nitrogen, natural growth stimulants, beneficial fungi and bacteria, perhaps earthworms and arthropods, but we are talking here about the actual mineral content of the compost; there are thousands of books and articles written about that organic portion but very, very few about soil minerals.
Let's look at another factor in using compost or organic matter as a mineral source: How much would we need to use to add significant amounts of needed minerals to the soil? This gets a little difficult to quantify, but going back to research done by Davidson and LeClerc in the 1930s, we find that the amount of Potassium found in ash from commercial vegetables was around 7%, the amount of Calcium averaged about 2% (they also measured 95%+ moisture content and 20% ash from dry matter, which leaves only 1% total ash, but let's be generous and stick with that 1 1/4 lbs we came up with above).
1 1/4 lbs= 566 grams
566 grams x 2%= 11.3 grams Calcium per 100 lbs compost
566 grams x 7%= 39.6 grams Potassium per 100 lbs compost
Even a sandy loam requires at least 2,000 lbs of Calcium per acre for best growth. What if we measured the minerals and found that we needed to add 1,000 lbs of Calcium? How much compost would that take, at 11 grams per 100 lbs? I'll spare you the arithmetic: It would take about 4,000,000 lbs: Four million pounds of that 75% moisture content compost per acre to add 1,000 lbs of Calcium. Wait, it gets worse: While we were adding that 1,000 lbs of Calcium we were also adding almost 4,000 lbs of Potassium, far too much. Well balanced soils need about 1/7th as much Potassium as Calcium, so this soil would call for about 280 lbs of Potassium per acre; we would be adding over 3,700 lbs too much, assuming that we were crazy enough to try adding four million pounds of compost anyway.
Putting that in terms a backyard gardener could relate to, one would need 90,000 lbs of compost per 1,000 square feet of garden just to bring the Calcium level up to par.
It's easy to see from the example above that although compost might be a reasonable source for Potassium, if we knew the Potassium needs of that soil in the first place, it isn't going to work for most of the other minerals. Just to add 140 lbs per acre of Potassium would require 80 tons of this particular compost per acre.
Note that we haven't even considered the other fifteen or so other essential plant minerals, nor the other thirty or so essential minerals needed by humans and animals. As essential and marvelous as compost and organic matter are, we are not going to be able to depend on them to provide a balanced supply of minerals to the soil.
The only way to know what the mineral content of the soil is, is to measure it. That's what a soil test does. Further, the only practical way to add the minerals that are needed, and to bring them into balance, is to add them in the mineral form, not as some minuscule portion of the organic matter. Agricultural "sweet" lime, which is simply ground up limestone, is about 40% pure Calcium. To add 1,000 lbs of Calcium using sweet lime would require 2,500 lbs of sweet lime per acre. That is do-able. That is 56 lbs of sweet lime for a 20' x 50' garden. To add 140 lbs of Potassium one would only need to use 280 lbs of naturally mined sulfate of potash per acre, or 6 lbs per 1000 square feet.
Your garden also probably needs a few ounces of Copper, Zinc, and Boron. It may or may not need Phosphorus or Magnesium or Sulfur. How are you going to know? By getting an inexpensive laboratory soil test, and either learning how to interpret it yourself (not hard to do) or paying someone who does know how a few dollars to interpret it and make recommendations for your particular soil. Then, for the first time, you can quit guessing and know exactly what your soil needs to grow the most flavorful, healthy, mineral and nutrient rich crops you have ever had.
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WHY MINERALS? 
The difference between rich, fertile soil and poor, infertile soil is essentially this: the mineral composition of the soil. The flavor and nutrition in fruit, grains, and vegetables are based on the soil minerals available, not the amount or type of organic matter. If a needed mineral is missing, it is just that, missing, and no amount of organic matter will make up for it. No amount or combination of the air elements Carbon, Oxygen, and Hydrogen will add Zinc to your soil, and all plants and animals need Zinc. Plants also need Copper and Iron and Manganese, Calcium and Magnesium and Phosphorus, and at least seven other essential minerals (animals need at least fourteen more), and they need them in an available and balanced form. Rotting organic matter may release growth stimulants like Nitrogen and Potassium, but the other minerals are what create sweetness and flavor and nutrition in food. Without these other minerals you may achieve high production, but you will not achieve the highest quality.
We are Organic, Biodynamic, Biologique, and Sustainable gardeners, and we strongly support the idea of a living, energetic, biologically active soil. We have learned that the absolute best cannot be achieved without a full complement of minerals available and in balance. Welcome to SoilMinerals.com!
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