In the organic gardening and farming world, one of the key ideals, if not dogmas, is that healthy soils create healthy plants and healthy plants provide better nutrition to people and animals that consume them. Anecdotal evidence suggests that this is generally true. Washington State University has studied nutrient content of a variety of foods grown conventionally and organically, and finds with some level of regularity and consitency that organically grown foods have higher vitamin, mineral, and protein content than conventionally raised foods, but not always. There are a lot of reasons why the generality is true and a lot of reasons why the specifics don't concur with the generalization.
From Acres USA and related publications, I have learned several things. The soil is made from weathered rock and organic matter. The rock is different from region to region, which leads to different nutrient profiles for soils in different areas. Generally food and forage crops perform best with a good profile and ratios of various soil minerals, which originate with the native rock material. Oganic matter in the soil promotes and sustains soil life (bacteria, fungi, and higher order life like earthworms). The soil life, in conjunction with plant life work on decomposing the rock materials, making it available to other plants through a slow weathering and then infinitely recycling process of growth and decay. If the native rock material in a specific region does not provide the optimal mineral profile, the food quality and quantity produced can be improved by supplementing with materials, preferably naturally occurring materials. We generally think of that as fertilization.
I had heard about farmers farming a plot of land and then "farming it out," or depleting the nutrient levels of the land, then abandoning it and moving on. This still happens today in the Amazon rain forests, where indigenous people slash and burn and area, farm it, then let it grow back to forest. The interesting thing is that there is a cycle of farm, recovery (long recovery), farm, recovery. The trees pull up minerals from the soil far below the soil surface, and deposit them on the surface through leaf fall, or the death of trees and surface decay. The land naturally provides a mechanism to heal the soil. Man's interference in otherwise natural processes should mimic that, perhaps at an accelerated rate.
As a basic example, one of the minerals that is considered a micro-nutrient is selenium. It does a lot of good things for people and animals. Here is the Willamette Valley, low selenium levels lead to white muscle disease in cattle. The native rock material is low in selenium and the relatively high winter rain levels disolve and leach away much of the small amount that is there. For optimum human and animal health, selenium needs to be supplemented. Given that it is a micro nutrient, the levels required are minimal. Selenium complexed in carbon as a food source is much more readily available than taking a mineral selenium supplment. This is why I eat brazil nuts as a source of selenium. The top six inches of an acre of soil is about two million pounds. The amount of selenium per acre required is between one and two pounds. That seems like such a trivial amount that one would wonder why it matters. It does matter. However, too much is toxic. The holding capacity of the soil (CEC or TEC) and the total amount of a nutrient and the ratio of each nutrient to other nutrients all play important roles in the growth of healthy plants and animals, leading to optimally healthy foods for people.
The fact that since WWII, that farmers have been told to focus on three or four, maybe five soil nutrients is leading to a steady decline in the vitamin, mineral, and protein levels in the foods. This is very well documented. Farmers are told to focus on nitrogen, phosphorous, and potassium. Separately, they accidentally focus to a degree on calcium through liming to correct soil pH. Some farmers pay a little attention to sulfur, a precursor to the development of most proteins. In effect farmers have not considered other nutrients because the focus on these things do create lots of pounds produced - but in decreasing nutrient density.
My goal is to grow food that is ever moving towards more optimal levels of nutrient density. This is a key foundational element of my drive to have a farm. The idea, ideal, and goal is to grow the best food possible for my family. This can only be done if you pay attention to the soil and treat it appropriately.
Soil testing and understanding nutrient and mineral provides a foundation for understanding the first phase of soil treatment. The soil needs to be optimally mineralized. Once that is done, the foundation is set for increased soil biology and sustainable nutrient cycling, which when combined with plant selection and other food raising techniques, leads to the best possible food. The starting point is soil mineralization.
I have taken soil samples of our property and determined a few important things. The soil is lacking in calcium in a fairly significant, but not unexpected way. Magnesium is close, but a little short. Potassium and phosphorous are both fairly abundant, perhaps to the point where I don't know that I will ever need to add these two elements, at least in the next several years. Iron is high, sulfur is sufficient. Zinc is low, selenium is low as well, as I suspected. There are many other aspects to consideration, but these are foundational. This is where I will start, along with the addition of a modest amount of compost. The soil already has pretty good organic matter, but it could still be improved. Making these soil corrections will set the foundation for the growth of fantastical foods.
While I did not learn all I know from Acres USA, the publication set me on the right path to understanding the soil and how to grow the best food possible within certain natural constraints and the very human constraint of imperfect knowledge.
