Soil Acidity Is Beneficial Not Detrimental

Only recently have we come to appreciate the services by soil acidity in mobilizing, making available, many of the nutrients in the rocks and minerals of the soil. When we learned that soils are less productive in giving us legumes and other protein-rich forages, according as they become more acid either naturally or under our cultivation, we came to the conclusion that soil acidity is the cause of this trouble. We now know that a plant puts acid into the soil in exchange for the nutrients it gets. It is that same acid held on the clay that weathers the rock fragments, and serves to pass their nutrients on to the clay, and from there on to the plant.

The coming into the soil of excessive acidity is merely the reciprocal of the going out of the fertility. Nature’s process of feeding the plants, and thereby the animals and us, is one of putting acidity into the soil from the plant roots in order to break out of the rocks what nutrients they contain for nourishment of all the different life forms. Soil acidity always has been the agency in the soil to keep the assembly lines providing the available fertility for crop nutrition, which in turn is nutrition for all higher life.

Limestone Becomes a Calcium Fertilizer on Acid Soil

When we put lime rock on the soil as a fertilizer supplying calcium to our legume crops, we know full well that this rock reacts with the acid-clay of the soil. The acid goes from the clay to the lime rock which, being calcium carbonate, breaks down to give carbonic acid, while the calcium is absorbed, or taken over, by the clay. While the calcium goes on to the clay, to be available there for the plants, the carbonic acid decomposes into water and carbon dioxide as gas. Since this gas escapes from the soil, this escape takes away the acid, or, as we say, “it makes the soil neutral.” The benefit to the legume crop from the application of this lime rock to the soil, does not rest in the removal of this soil acidity. Rather, it rests in the exchanging of calcium, as a nutrient to the clay which was holding the acidity or hydrogen, a chemical element that is not of direct nutritional service.

Various Other Rocks as Well as Lime Rock Are Fertilizers on Acid Soil

Soil acidity has been breaking potash rocks down chemically, too. During all these past years the potash feldspars have been undergoing weathering attacks by soil acidity. On this rock the acid clay carries out its weathering effects in the same way as it does for lime rock, except that it trades acid to the feldspar, and takes potassium unto itself in exchange. Magnesium rock, as we have it in dolomitic limestone, is also broken down by the acid clay. By this same process the clay becomes stocked with magnesium. This is then more readily exchangeable and available to the plant from the clay than it would be if the plant root were in direct contact with the rock fragment itself. By exactly the same mechanism we can expect phosphate rock to be made available for the plant’s use.

It is in these processes by which the acidity of the soil is beneficial. If the soil contains the two colloids, clay and humus, which can hold acidity, and then if that soil has scattered through it fragments of lime rock, magnesium rock, potassium rock, phosphate rock, or in fact any rock with nutrients, it is the soil acidity that mobilizes to the clay the calcium, magnesium, potassium, phosphorus, or all the other nutrients respectively, for rapid use by the plants. This is nature’s process of providing plant nutrients on the clay of the soil in available form. By it, nature has stocked our moderately acid soils with fertility. It was that condition of our virgin soils that spelled our prosperity. We need to go back and study the soil in order to learn how we can gear the lime rock into our acid soils so it will stock our soils with calcium, and still not remove all the acidity needed to make the other nutrients available in other rocks, of which some are giving phosphorus, some giving potassium, and some giving one or more of all the other nutrients in whatever rock form nature has them.

Acidity is a Slow Mobilizer of Nutrients Contained in the Minerals

Of course, nature’s processes do not demonstrate high speed. It takes six months or more for limestone to stock the clay with enough calcium to feed our legumes. It takes longer for others. Consequently, if phosphate rock is slow in demonstrating its effects on the crop, we need not be alarmed. It certainly will not be very active in soils that are not acid. In our western soils that have considerable free lime rock mixed throughout them, the plants suffer from phosphate deficiencies. Rock phosphate may not be so efficient there.

Dr. Hutton, of South Dakota, pointed out that phosphorus delivery to the crop was the major problem on these highly calcareous, or these distinctly neutral soils. It is on soils of that reaction that cattle have been bone-chewers. Apparently they are going to that extreme behavior in order to get their phosphorus, which the forages as feeds on the soils there fail to provide. So, when the soils are not acid, we may expect shortages of some fertility elements like phosphorus, for example, in the plants, and even in the animals. It is on the acid soils where most of our population has always fed itself, suggesting that it is on those acid soils where there is much more speed in making the fertility active and available from out of the reserve minerals.

Phosphorus Deficiencies in the Soil Suggest Possible Health Troubles

That human health may be related to the deficiencies in the soil, has come to be more than mere speculation when animal troubles are localizing themselves more and more according to soil fertility deficiencies. If one looks at the map of poliomyelitis in 1946, for example, it is significant that this health trouble was most severe in those same states where the less acid soils give deficiencies in phosphorus for the plants and animals. It is all the more significant when we remind ourselves of the fact that the brain and nerve tissues–most seriously affected by “polio”–represent high concentrations of phosphorus. Whether there is any causal connection between this human affliction and these non-acid soils, because phosphorus availability there is low, is a question that remains for research to answer.

There are also other nutrients, in addition to phosphorus, that are not mobilized effectively unless the soils are acid. These include iron, manganese and boron. Perhaps these, or some others not yet appreciated, are causally connected with this baffling disease. Other diseases may be in a similar category. When we see the inroads by brucellosis on our herds of cattle and hogs, and when undulant fever, passed seemingly from these, is becoming more common, there is decided encouragement to theorize and do some research on the belief that we need acid soils, and need to gear more mineral fertility through the acid assembly lines of our soils.

Understanding Soil Acidity Means Appreciating the Deficiency of Soil Fertility

We have used lime rock, phosphate (rock, and green sand as potassium rock, in both the experimental work and in the field trials, to convince ourselves that the plant nutrients within these are made available to plants by the acidity of the soils. Possibly as we come to appreciate the benefits of soil acidity we shall no longer fight it with carbonates, but shall guard it and use it to treat our lime rock as calcium fertilizer, our phosphate rock as phosphorus fertilizer, and possibly many other rocks whose fertilizer values we still do not appreciate. In the future more of these mineral, or rock, types of soil builders will very probably go into the soil to build up a reserve of minerals there when it becomes more common knowledge that soil acidity is beneficial and not detrimental.