IT USED TO BE THAT A GOOD FARMER COULD TELL a lot about his soil by rolling a lump of it around in his mouth. I once spent a week trying to find somebody who still did that. Not a prayer. Not in Texas, nor Vermont, nor Kentucky, nor California, nor western New York. Everybody knew somebody who once did it, but nobody could quite remember the name of the fellow.
Finally, I found Bill Wolf, president of a company called Necessary Organics. Wolf had chewed soil himself up to a few years previously, when his doctor had strictly forbidden him. Soil contains bad bugs as well as good ones, and the physician did not want to have to sort them out in Wolf’s guts.
But in the days when he chawed, Bill could tell acid from alkaline by the fizz of the soil in his mouth. A very acid soil would crackle like those sour candies that kids eat, and it had the sharp taste of a citrus drink. A neutral soil didn’t fizz and it had the odor and flavor of the soil’s humus, caused by little creatures called “actinomycetes.” An alkaline soil tasted chalky and coated the tongue.
For most plants, neither of the extremes is palatable, any more than the fizz or the chalk was to Wolf. Here is the graphic and immediate reason that pH actually is important.
If you mention the word “soil” to a gardener, the first question is liable to be, “What is its pH?” In answer, you give a number between 0 and 14. Whatever the figure, it has the force of a talisman.
The pH value is one of the few instances in daily life where moderation is graphically praised. In almost any sporting event, one seeks the highest (football, baseball) or the lowest (golf, track) number. But if you tell a gardener that his soil’s pH is 14 or 0, he will keel over in a faint. Even 3 or 8 is very unpleasant to hear. No, a gardener cannot be pleased unless the number is greater than 5 and less than 7.5. The middle terms are where fertility lie.
In the microcosm, this principle is represented in the play of acids and bases, by means of which rocks are broken, foods mobilized, digestion accomplished, excretion stimulated, growth catalyzed, destruction indicated, and new life spawned. pH is simply a way to talk about this game.
pH measures the activity or concentration of hydrogen ions in a substance. Scientists being devious creatures, however, they arranged the scale that measures pH so that a small number means lots of hydrogen, while a large one means little hydrogen. The scale runs from 0 to 14, and each whole number change is equivalent to a tenfold decrease or increase.
An acid has a greater concentration of hydrogen ions (which are the same as a single proton), a base has less. Acids and bases react together to make salts. It might be said that hydrogen has two personalities. In the sun it is the source of the incandescence that makes all life possible. In the sublunary world, it is the chief substance that regulates the exchange of mineral substances. Ecologists say that Earth has a surprisingly high pH. What does this mean?
A cell full of saltwater or my coursing salt blood or the plasma in a plant are all media for the exchange of the bases calcium, magnesium, and potassium. It is these elements whose circulation balances the chemistry of the Earth, raising the pH. Their dance with the acid ions of hydrogen regulates most of the processes by which cells make exchanges.
Consider their interaction in the soil. When the rains come, the rainwater brings hydrogen to the particles of clays and humus. The highly charged hydrogen ions muscle onto the surfaces, pushing the bases calcium, potassium, and magnesium into the soil solution. From there, either the bases will leach down and out of the soil or plants will take them up.
The bases bloom into solution, while the soil particles themselves turn acid. The roots of the plants sweat a mucus that captures clays and ions. Releasing a stream of hydrogen ions themselves, the roots make Space on their electrical edges to receive still more bases. The opposite of what is happening to the soil particles happens to the roots, so that they dance like a man and woman in the play of action and reaction, forward step to backward step, backward step to forward step. An alternating current of ions flows into roots’ cells along these infinitesimal, reciprocating channels; a channel of hydrogen flows out, making the surrounding soil medium more acid still.
The soil and a tree transform each other, through the medium of the exchange that happens in the roots. A forty-five-year-old shore pine growing in isolation on a hill of shelly sand causes the pH of the soil under its canopy to fall by 1.5 points (that is, the hydrogen ion concentration was raised 150-fold) in comparison with the fresh sand around it. At the same time, however, the soil doubled its ability to exchange bases, and developed a black litterfall horizon rich in nitrogen.
All this depends upon the life-giving osmotic gradient, the difference in salt concentration that allows bases to flow from a place of lesser concentration (the soil) to greater concentration (the inside of the cell). When the flow is reversed by an excess of salts, mineral-laden water flows out of the root cells, and they die of dehydration. This is precisely what happens when a dog pees on the lawn.
You have only to remember how sick and cramped you felt when after vigorous exercise in the hot sun, you failed to replace the salts you had sweated out. Drinking water only increased your nausea, because the salt was still on the wrong side of the cell walls.
The agricultural cure for both acid and salted soils is to apply natural materials that are rich in bases. Limes (calcium carbonate) and gypsum (calcium sulfate) react with the hydrogen of acid clays and the sodium of salt-clays, respectively, sending the hydrogen and sodium into the soil solution, improving the soil’s structure, and capturing the nutritious calcium. Some of our lesser-known heroes, the eighteenth-century statesman Edmund Ruffin and the twentieth-century soil scientist E. W. Hilgard, were responsible for the development of these all-important soil cures.
In the autumn, the tide of bases climbs into the finest pores of plants—the tissues of flowers, leaves, and fruits—whence it falls to the ground. Within a day, almost half the fallen tissue has been digested by the microbes and invertebrates dwelling on the ground. The acidity of the soil recedes, and it prepares for its slow, neutral winter life, making an equilibrated medium to protect the roots until the spring.