Lime the Soil to Correct its Major Fertility Deficiencies
LIMING THE SOIL, so that this practice can build up the fertility reserve of calcium (and magnesium), has gone unappreciated all too long. Instead, we have persisted in the erroneous belief that the benefits to crops from liming result from the reduction of soil acidity by the applied carbonate. We are gradually realizing that our productive soils, under annual rainfalls abundant enough to give larger crop yields, must contain more of calcium (and of magnesium) in the exchangeable (available) form than any other fertility element. The laboratory gadgets for measuring soil acidity in degree—and in total—have absorbed our interest so completely, and for all too long a time, that they kept us from recognizing the services by limestone in the nutrition of the crops in the field. We failed to connect the activities and ratios of the fertility elements, exchangeable and active, in the soil with the nutrition of the plant. We were oblivious to the facts (a) that calcium is one of the elements which the growing plants must find in the soil very early, and (b) that it seems to serve in setting up the conditions by which the other nutrient elements and compounds are mobilized into the roots for crop growth. We are gradually coming around, however, to see that by liming the soil we are fertilizing it with the two major nutrient elements; namely, calcium and magnesium. Accordingly, this practice is taking on a new classification and a greater significance.
Now that we view most of the plant nutrition processes as a case of the positively charged elements held on the clay exchanging from there for the non-nutrient hydrogen, or acid, coming from the plant root, the extensive soil testing is pointing out that crop production requires larger amounts of the exchangeable calcium in the humid soils than of any other fertility element. Calcium is especially important in the production of proteins. These are the only compounds capable (a) of giving cell multiplication or growth, (b) of protecting the plants against disease, etc., and (c) of reproducing them by seeds. It is required by legumes for this reason more than for the “suitable degree of soil acidity” of which the carbonate of calcium might have been the producer. Lime is important because its calcium (and magnesium) nourish the crops.
In order to appreciate just how much exchangeable calcium a productive soil contains, let us consider the soil test results from a good silt loam, a corn-belt soil like the Marshall of north Missouri or Iowa. This has a total exchange capacity of near 18 milligram equivalents. This figure tells us that such a soil could hold by adsorption, and for possible exchange, 18 milligrams of active hydrogen—a non-nutrient and acid—per 100 grams of soil, or the equivalent in other positively charged ions. This would be 18 pounds of hydrogen per 100,000 of soil or 360 pounds of hydrogen per plowed acre of 2,000,000 pounds. For good crop production, it is considered well that about 75% of the soil’s exchange capacity should be taken by calcium, and from 7 to 10% by magnesium. These make up the maximum two of all the nutrient elements held by the adsorptive and exchange capacity of the soil, or nearly 85% of the total capacity. For potassium, the next item in order, the figure is 2 to 5%. This leaves but 10 to 16% of the soil’s exchange capacity for all the other necessary positive ions of nutrient services to the crops.
In terms of pounds per acre of soil of plow depth, or 6 to 7 inches deep, these percentage saturation values as replacements in equivalents for hydrogen or acidity represent (a) 5400 pounds of calcium, (b) 302 to 432 of magnesium, and (c) 280 to 700 pounds of potassium. Even with these amounts occupying the soil’s absorbing power, it would have capacity remaining to hold the other nutrients in ample amounts, especially the trace elements, and then also some capacity for hydrogen, or acidity, as the favorable soil condition. Plants are nourished better in the presence of some soil acidity. Let us note that the amount of exchangeable calcium in this series is more than ten times the maximum of the nearest amount of any one of the others. By finding such calcium values in terms of the requirements for plant nutrition, we begin to get some basic concept of the importance of liming for the calcium supplied to feed the crop rather than for the carbonate incorporated to fight the soil acidity.
All of this may well serve to classify the liming of our humid soils into the category of farm operations more technical than those of merely dumping any kind of limestone on the land, and of proceeding under the belief that “If a little is good, more will be better.” It puts liming into the group of skilled operations calling for a clear-cut diagnosis of the soil’s condition before treatment is undertaken. Testing the particular soil for its shortages in calcium and magnesium in order to build up its supplies of these by either a calcic or dolomitic stone, or both, makes liming a prescribed nourishment of the crops. This is a treatment different from one of using the carbonate of any stone, regardless of whether calcic or dolomitic, merely to reduce the degree, or the total, of soil acidity.
Viewed from the vantage point of plant nutrition, liming the soil becomes the application of fertility elements of quantities nearly ten to twenty times as large as any of the other elements commonly used in commercial fertilizers. It becomes then a major fertilizing performance. Surely under such large amount applied according to soil test, and under the concept of lime as our foremost fertilizer, the business of limestone production and distribution should feel itself playing the major role in maintaining the fertility and productivity of our soils. Unfortunately for the liming of the soils, as for the other fertility restorative treatments, its services in food production for all of us, rather than for profit only to the farmer, are not yet recognized nor appreciated. The 85% of us in the urban portion of our population do not yet feel any obligation to help resources coming to us gratis from out of the rural area. We are set up in urban commercial businesses and industries of which the laws, economics and taxation procedures are so formulated under carefully lobbied legislation that our capital investments in them are self-perpetuating. Even for the minerals or rocks taken out of the limestone quarry, for example, the owner-investor may be allowed a depreciation, or depletion, figure as high as 15% of the income. For the owner-investor in an oil well, it may be a larger amount. The capital investment in these mineral businesses is soon recovered.
But for the mineral fertility taken out of the soil and delivered in the crops to the urban population without charge for it, there is as yet no economist or authority on taxation suggesting the justice of a depletion allowance to the landowner, or investor in that kind of real estate, for the perpetuation of his capital in his farming business. His investment in the minerals in the soils for the food production for all of us is being liquidated gradually under an economic thinking (or the lack of it) which contends that the farmer is thereby taking a profit. On the contrary, he is compelled to throw his financial, and our national, security by installments into the bargain every time he makes a sale of his products. Those of us on the urban receiving end of that transaction get those installments gratis and flush them into the sea. We are parties to the crime of soil fertility exploitation, but yet are crying against the rising costs of living. We are slow to see that such short sightedness (or absence of any sightedness) in our economic, agricultural, and other policies toward the fertility resources in the soil are undermining seriously our national security. All this is the more serious with a growing pressure on the soil’s production potential by our own increasing population to say nothing of that by the rest of the world calling on us to share that potential with them.
Liming our soils deserves consideration as an operation undergirding our future security in food, and particularly those foods of high protein content. We have long known that lime is needed for legumes. We are slow to see that need as one for the production of protein, rather than the tonnage, yield of the crop. It is lime via that route that gets us our meat, milk and eggs. Viewed in this light, one cannot escape the question whether we dare expect the farmer to continue liquidating his fertility assets under the false concept of taking a profit and at the same time ask him to purchase large amounts of calcium and magnesium to aggravate his rate of liquidation all the more. Isn’t it about time that as a basic agricultural policy we design the required machinery of economics and taxation to guarantee the self-perpetuation of the farmer’s fertility capital which must feed all of us, both urban and rural?
Perhaps now that the fertility restoration by liming the soil is moving itself into the more exact category of soil chemistry for the nutrition of our plants, our animals and ourselves, should not the maintenance of the soil fertility and thereby of agricultural industry be interpreted by the same views in economics and taxation as those prevailing in other industries?
Perhaps we can bring about self-perpetuation of our soil fertility capital under the agricultural business in the rural areas in the same manner as perpetuation prevails for monetary capital under all businesses in our urban centers. If that situation is consummated, then liming the soil for calcium’s sake will become big business by meeting the major needs in our soils; namely, lime and other fertility-restorating helps through which there can be guaranteed greater national food security for the future of all of us.
How shall we get lime or calcium into the plant and how much will it take? If all that we needed to use were that which gets into the crop, the figure would be less than 150 pounds of limestone a ton of clover hay produced, or less than two-thirds of this figure for a ton of soybean hay. We still can’t get the lime into the plants by external application. We can’t rub it on. It must come through the roots and they must take it from the soil. Delivery to the plant by this soil route is far more effective when a little of the soil is heavily loaded with lime, than if all of the surface soil has the limestone thinly scattered through it. Non-legumes such as bluegrass and redtop, as well as legumes, get their lime or calcium much more effectively if the upper two inches of soil are heavily dosed than if this same amount of limestone is mixed into the soil to a depth four times as great. Soil that has become sour has a tremendous power to hold lime. Plants can’t take from it all the calcium it has. Studies to date give a low efficiency in lime recovery by plants unless the lime is used so as to saturate the soil in the root feeding zone. We are then forced to think of the practice that loads a little of the soil completely rather than all of the soil only partially, if the investment in limestone is to give us maximum return.
Studies of the practice of drilling limestone as a fertilizer have demonstrated that as little as 600 pounds on a soil needing more than 2 tons to sweeten it can establish sweet clover regularly in a rotation, though more limestone is better. The stand of sweet clover from drilled limestone holds out against winter-killing when that sown without limestone fails. The composition of the crop in terms of forage feed, and its effects as a soil-improver on the corn crop following, are all evidence that giving the crop its calcium without neutralizing the acidity is coming to be the real function of liming, and that economical and effective use of limestone means that it may well become a fertilizer in our thinking and in its use.
The art of liming is old. The science of it is new. Our science has led us astray and we are just now getting back. Nature always has been consistent in demonstrating the effects on plants by liming, but we have not been so consistent in explaining how these effects came about. We have looked to the wrong one of two things going on at the same time, as the real cause. When we use limestone we put on calcium combined as a carbonate. The carbonate neutralizes the soil acid. We have misconstrued this phenomenon as the cause of plant improvement when we should have been thinking of the addition of the calcium to the soil as the causative factor. Since sodium carbonate which removes the acid doesn’t help the plants, while calcium chloride helps the plants but doesn’t correct the acidity, we know now that liming is not a matter of fighting soil acidity but one of giving the plants calcium, their much-needed nutrient on our humid soils.
Thus, we can put liming into the fertilizer category and look to lesser applications per acre to serve its fertilizing function. But we must remember that nature has been taking the lime out of our soils for many years and a teaspoon dosage now won’t do the work completely. We need to give many of our soils a heavy liming to offset this neglect and then we can go to regular lighter applications of 1,000 pounds an acre by drill in place of tons by spreader. As we go to using lime to feed plants so they can feed and protect our animals against starvation fevers, we see prospects of making this operation economical enough in money and labor costs so we will adopt it for use as regularly as we scatter a legume seeding.