By Charles Walters
This is an excerpt from Eco-Farm: An Acres U.S.A. Primer by Charles Walters, founder of Acres U.S.A.. Excerpt from Lesson 12. Reprinted with permission from the publisher.
pH measures soil acidity, and the pH figure merely expresses negative logarithms of active hydrogen concentration. All soil audits hand out a pH figure and designate the soil as acid, neutral or alkaline. Early agronomists discovered that low pH soils produced poorly, and thus was born the idea of liming to the neutral point. Soil acidity was blamed for poor crop performance.
The old triple A program of the New Deal seized upon this half-truth and inaugurated a liming program nationwide. “Lime to the neutral point,” ran the advice. “You can’t overdo it. And we’ll pay you to do it.” This position was unscientific simply because it ignored the services of soil acidity in mobilizing nutrients in the rocks and minerals of the soil.
I. Fertility Depletion
Excess acidity is nothing more than the reciprocal of fertility depletion. Nature simply puts acidity into the soil from plant roots so that this acid action can break nutrients out of locked-up position and feed the several life forms. In liming an acid soil to correct pH, the farmer is merely providing rock that can react with the acid clay of the soil system. Acid goes from the clay to the lime, and lime being calcium breaks down to give carbonic add while the calcium is absorbed by the clay. Held on the clay it is available for plant use, and it corrects or adjusts the pH in the colloidal domain where plant roots expect their energy exchange. In the meantime the carboiric add decomposes into water and carbon dioxide. Carbon dioxide escapes from the soil, taking acidity with it.
There is a benefit here, but it has all too little to do with making the soil neutral. The benefit is derived by trading calcium off for hydrogen, and hydrogen is of no direct nutritional service to plants.
Adjusting pH, then, has to do with loading nutrients back into the soil system, and not removing acidity. In fact it is bad business to remove all the acidity. Since time began, soil acidity has been breaking potassium out of potash feldspars. It has been taking magnesium from dolomitic limestone much the same as it has taken calcium. Acid soil uses the same mechanism to make phosphate rock available for plant uptake as factories do to convert mineral rocks into soluble fertilizer.
In other words, add soil is beneficial. It is also a free source of virgin plant nutrients. The pH measure is of great value—^if we pause to understand what it means. Yet it should stand to reason that adjusting pH with one nutrient alone has got to result in shortages or marked imbalances of some fertility elements. As a matter of fact, it would be well to consider pCa, pMg, pNa and pK in addition to pH.
Lime to the neutral point is a breath-taking error. It may well be a self-serving error proposed and furbished by those interested in selling water soluble salt fertilizers. A farmer with neutral soil cannot possibly grow crops without having a factory acidulate the nutrients indicated for crop production. Without an add soil, or a good colloidal humus energy exchange system, it is no longer possible to rely on phosphate in the rock, potassium from green sand, magnesium from dolomite, or any of the trace nutrients available in the gravels that nature has provided. Soil without a measure of acidity condemns crops to simplistic fertilization, and when essential nutrients are restricted, plants exhibit their stress in the customary way: lodging, fungal diseases, bacterial debilitation, and insect attack.
2. The Demands of Most Commercial Crops
The conventional wisdom has it that pH of 6.2 either in the soil or in its colloidal pantry meets the demands of most commercial crops. This wisdom permits exceptions, the reasons for these exceptions often being subtle. In legend there are the lime-loving legumes. The foundations of thought expressed by the simple statistical array of pH variables shown in the chart on page 157, must now be challenged and corrected. We can no longer permit the usual lip service that chemistry agronomists use to ignore away or skip over the responsibilities that molecular biologists or biological agronomists are tending to. Moreover, continued ignorance by the chemical agronomists is quietly sustained and perpetuated by the chart that expresses the tolerance of our usual farm crops. Inversely it covers up and gives integrity to those who wish to ignore the power of the soil and the factors that permit degeneration of the biological potential of soil nutrition.
For more information on pH in ecological farming, as well as the charts and the remaining 3 sections in this Lesson (3. The pH Process; 4. Character of the Lime; 5. The Task of Acidulation) – then find Charles Walters’ book Eco-Farm: An Acres U.S.A. Primer at the Acres U.S.A. Bookstore.
About the Author
Charles Walters was the founder and executive editor of Acres U.S.A. He penned thousands of articles on the technologies of organic and sustainable agriculture and authored many books on the subject. You can find a full list of books written by Charles Walters here.