From Ecology Action
Question: There are a number of publications done in the 1930s and 1940s, particularly those by Sir Albert Howard, a noted agricultural researcher, that observed a strong correlation between healthy soils and healthy people, and between healthy soils and disease resistance in plants, animals, and people. While according to standard nutritional assays organic foods are similar to conventional foods in nutrient content, if the anecdotal observations have merit, the health /disease prevention benefits are likely due to other factors, perhaps plant phenols that are produced in response to attacks by bugs and pathogens. Foods grown in healthy soils would therefore be "functional" foods. Unfortunately, neither Sir Howard or his followers followed through with research studies that could verify his observations. Are you aware of any studies that have proved the connection?
Answer: Thanks for the good question!
First of all it might be useful to be more specific about nutritional comparisons of organic vs. conventional produce. I have highlighted standard nutritional assays and similar in the following statement from your question, “. . . according to standard nutritional assays organic foods are similar to conventional foods in nutrient content . . .” It would be good to know what a standard nutritional assay looks at, and similar is definitely not “the same.” Critical trace elements could be missing that are essential to how the body can use a food, and it can be said to be similar.
The second element not being addressed here is how healthy the soil is after having conventional crops grown in it, and how quickly the available nutrients are stripped from it?
Let’s approach this from the standpoint of what the difference is between healthy or fertile soil and depleted soil. Fertile soil that is stable over time has soil organic matter of 4% to 6% in temperate zones and 3% in the tropics. What is soil organic matter? Basically it is compost or plant materials that are decomposing and returning the elements needed for life back to the soil.
Here are the benefits of Fertile soil, rich in organic matter (well-cured compost):
Improved Structure – Compost breaks up clay and clods and binds together sandy soil. It helps make proper aeration in clayey and sandy soil possible.
Moisture Retention – Compost holds up to 6 times its own weight in water. A soil with good organic matter content soaks up rain like a sponge and regulates the supply to plants. A soil stripped of organic matter resists water penetration, thus leading to crusting, erosion and flooding.
Aeration – Plants can obtain 96% of the nutrients they need from the air, sun, and water. A loose, healthy soil assists in diffusing air and moisture into the soil and in exchanging nutrients. Carbon dioxide released by organic matter decomposition diffuses out of the soil and is absorbed by the canopy of leaves above in a raised bed mini-climate created by closely spaced plants.
Fertilization – Compost contains some nitrogen, phosphorus, potassium, magnesium, and sulfur but is especially important for trace elements. The important principle is to return the soil, by the use of plant residues and manures, all that has been taken out of it.
Nitrogen Storage – The compost pile is a storehouse for nitrogen. Because it is tied up in the compost-breakdown process, water-soluble nitrogen does not leach out or oxidize into the air for a period of 3 to 6 months or more—depending on how the pile is built and maintained.
pH Buffer – A good percentage of compost in the soil allows plants to grow better in less-than-optimal pH situations.
Soil Toxin Neutralizer – Important recent studies show that plants grown in organically composted soils take up less lead, heavy metals, and other urban pollutants.
Nutrient Release – Organic acids dissolve soil minerals and make them available to plants. As organic matter decomposes, it releases nutrients for plant uptake and for the soil microbial population.
Food for Microbial Life – Good compost creates healthy conditions for organisms that live in the soil. Compost harbors earthworms and beneficial fungi that fight nematodes and other soil pests.
The Ultimate in Recycling – The Earth provides us with food, clothing, and shelter, and we close the cycle in offering fertility, health, and life through the shepherding of materials.
There can be plenty of fertilizer applied to a soil to help provide nutrients, but this is far different from soil fertility,and plants still may not grow well. When you add compost, the organic acids it contains will release the hidden nutrients in a form available to the plants. In many cases, a nutrient deficiency is really only a compost deficiency. However, in some cases, a soil simply does not contain major and/or minor nutrients in sufficient quantity for optimal productivity, and building compost with crops raised in those soils will not resolve the nutrient deficiency. In these cases, the nutrients must be added to the soil in the form of fertilizers derived from minerals, plants or animals containing the missing nutrients.
Optimally, every year you will be able to add up to 4 cubic feet of compost (that is 50% soil by volume) that you have produced yourself to every 100 square feet in your garden or farm. This quantity of compost typically contains enough nitrogen for good production of all crops, assuming the soil has good structure and a high content of organic matter that will hold the nutrients contained in the compost. Furthermore, 4 cubic feet of compost will sufficiently maintain the soil’s supply of organic matter and will help prevent the soil’s nutrients from leaching. Poor soil often results from production of high-yielding crops that pull nutrients from the soil without adequate replenishment of those nutrients. Additionally, application of chemical inputs of fertilizers, herbicides and pesticides kill the microorganisms that help to make nutrients
In the end your decision about whether you want to eat organic or conventional produce may just come down to the fact that organic generally tastes better! Do a comparison for yourself and see.
Note: The image of Albert Howard was taken from http://www.journeytoforever.org/farm_library/howard.html