Earth is the only place in the universe we know with certainty that life resides. Our lives and the lives of the animals, plants and insects we depend on, depend in turn on more fundamental forms of life. The microbiology of the soil is the support and intimate partner of the growing plants that feed us. The soil microbiology is in turn supported by the air, water and minerals that compose the soil structure. With a well balanced support, biology and life may thrive; without it, there is danger of decline and collapse. Optimization of the soil, the foundation of human health, is our concern here. We are interested in practical ways to build and maintain a solid foundation of life and health.
What constitutes a balanced soil? The Soil Pyramid illustrates the relative amount of each of these four basic elements present in the top six inches of a balanced soil: about 25% air, 25% moisture, 45% minerals and 5% organic matter. Without air, the soil medium breeds stinky anaerobic microbes and most food plants die. Without water plants die. Hydroponic growing works without mineral soil, but it is an unnatural system and not our concern here. The growing creatures in and on the soil (including soil microbes, earthworms, plants, cattle and people) constitute just a few percent of the overall soil volume.
All of the parts are critical if the system is to effectively transfer nutrients up the food chain and grow healthy, vibrant people and animals. Many organic gardeners concentrate on getting their soil’s organic matter percentage as high as possible, without really understanding the need for balanced minerals, but few working farmers make this mistake for long. High organic matter is great — it increases the soil life and increases the capacity of the soil to hold nutrients — but organic matter alone does not supply the minerals plants need to grow.
Organic matter is mainly composed of three elements, carbon (C), hydrogen (H) and oxygen (O). However, plants need significant amounts of other mineral elements to grow, just as humans need essential vitamins and minerals to sustain life. Some minerals are needed in fairly large quantities while some are needed only in very small quantities, but they are all equally essential for life.
Gardening and farming are intensive and fundamentally unnatural processes. In a natural system like an old growth forest for example, plants grow in exactly the environment they have evolved to grow in and they recycle nutrients in place. In cultivated systems, non-natives are generally introduced and the nutrients in the food usually leave the farm or garden, even if the residue is composted and returned. “Sustainable agriculture” sounds good but how can it be achieved in practice? A truly sustainable system would require recycling of all nutrients, including human manure. And if the fundamental fertility was not available in the system, it would need to be brought in from outside or else the consequences of deficiency would be felt.
Soil nutrient deficiencies are common throughout the world. In 1990 the Food and Agriculture Organization of the United Nations reported on 190 agricultural soils worldwide (note that your soil may not even be considered “agricultural”). They found that 73% of these soils are deficient in phosphorus, 55% are deficient in potassium, 31% are deficient in boron and 49% are deficient in zinc. These are deficiencies by conventional standards, not the higher standards required for nutrient density. Most, if not all soils need additional minerals in order to optimize nutritional balance of the food grown on them.
Nutrient deficiencies in the soil translate into nutritional deficiencies in the animal that eats the food grown on that soil. Although we now tend to eat food grown in diverse places, the nutritional content of most food, even organically grown food, is marginal at best. See the book we contributed to, “The Intelligent Gardener: Growing Nutrient Dense Food”, by Steve Solomon, with Erica Reinheimer, for a great discussion of the evidence linking soil fertility to human health.
This means balancing the soil mineral reserves, building the capacity of the soil to hold and distribute nutrients and enhancing the means with which plants take up nutrients, both biologically and directly.
Home gardens can be a great source of nutrient dense food. They are usually fairly small in area, and so do not require truckloads of mineral nutrients. There are many, many benefits to the gardener and the local community. And if you are going to be growing your own food, why not grow the best?
The cost of external inputs is a major concern for farmers who need to make a living from their crops. It pays to make sure that any mineral amendments applied are of benefit and take the soil in the direction of balance. If you are going to be adding amendments, why not make sure they are “just the right ones”?
Some people (like us) are fascinated by soil chemistry and biology and how it all works together. For these people we have put together a short discussion of the major mineral nutrients. Click here to follow the nutrient trail.
Besides carbon (C), hydrogen (H) and oxygen (O), plants need these macronutrient elements:
and these micronutrients:
and with traces of these other elements:
and these other elements:
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