Soil Fertility and Alfalfa Production

The fact that alfalfa, ground or chopped, is so widely used in the manufacture of mixed feeds, shows that the high value of this crop in terms of animal nutrition is highly appreciated by both the manufacturer and purchaser. Alfalfa has long headed the list of desirable hays. But that desire, strong and universal as it may be, has not made alfalfa a universal farm crop. Its small acreage in Missouri, for example, is due, not necessarily to a lack of appreciation of it, but rather to the fact, as the farmer puts it, that “alfalfa is a difficult crop to grow.” Now that soil science has helped us to a better understanding of the soil-plant interactions, it may be well to recognize in this difficulty of growing alfalfa the homely but inescapable fact that even plants–like seals on the stage and humans too–will not perform unless they are well fed. Alfalfa is no exception to this rule. It will not be difficult to grow if the soil feeds it amply.

Soil Conditions Point to Fertility, the Common Deficiency for Growing Alfalfa

If one examines most any set of instructions for alfalfa production, there will be listed the following,as common demands by this seemingly fastidious crop concerning the soil conditions for it. “The soil must be deep and well drained. The soil should not be seriously acid in reaction. The soil must not be foul with, but free of, weeds or grass lest these ‘take’ the alfalfa.”

These seem to be simple requisites. They seem far removed from the nutritional needs of the crop in terms of the fertility of the soil. Yet the effects of these conditions so commonly prescribed are in control, not so forcefully by way of the soil’s physical condition. They become decidedly important, however, by way of the mineral nutrients that are delivered or denied by each of these regularly listed requisites.

Shallow surface soils resting on compact, acid clay subsoils that reach well down in the soil profile have long been considered unfavorable for alfalfa. The reasons given have been “(a) impossible deep rooting required by this crop, and (b) poor soil aeration and drainage with winter heaving.” While the physical aspects of the soil that keep out air and that hold water are associated with the troubles, the same chemical conditions are responsible for these physical properties that are responsible for the crop failure. It is the absence of the fertility rather than the so-called “bad physical conditions” accompanying it that spells the trouble.

Deeper Soils Mean More Nourishment for the Crop

Heavy subsoils and claypans are impervious to plant roots more because the clay offers no nutritional service than because it is a mechanical obstruction. Roots stay away because it offers so little to feed them. Mechanical shattering of the claypan by dynamite, by subsoil plows and other types of deep tilling machinery has too many past years of failure in bringing deeper root penetration for us to grant that the physical condition alone of the soil is responsible.

Experiments on the Soil Conservation Experimental Farm, operating in cooperation with the College of Agriculture, University of Missouri, where the claypan was shattered and lime and other fertilizers put into the subsoil, show clearly that sweet clover, for example, is shallow rooted, poorly developed, and heaved out by freezing where shattering only is practiced. But this forerunner crop for alfalfa is deeply rooted, well established, and not heaved out if the fertility of the subsoil is increased to serve as inducement for the roots to grow rather than only go down into the subsoil.

It is more than the compact condition of the subsoil that hinders alfalfa production. It is the insufficient supply of fertility, limited to a shallow surface soil of which the upper four or five inches are dry during much of the growing season. Sufficiency of fertility for a crop like alfalfa calls for more depth as means of offering more root contact with soil that is both fertile and moist. When we say “alfalfa needs a deep soil,” we are only saying that alfalfa needs more fertility than can be found in the shallower depths of fertile soil represented by most surface layers.

Fertile Soils Have Good Structure and Good Drainage

When soils are deep and well-loaded with the fertility constituents demanded by alfalfa, they will also take on a more granular form. Subsoil clays are compact because they are usually highly acid. Their saturation with hydrogen or acidity disperses their fine particles. This generous hydrogen presence means fertility absence, especially of calcium, the presence of which would have brought about flocculation and granulation of the clay through help of the humus it encouraged to be grown there.

It is by virtue of their fertility contents that productive soils also provide the favorable physical conditions, including good aeration, and good drainage. The reputedly bad physical conditions are merely symptoms of the real trouble, namely insufficient calcium and other fertility elements. If these are present the favorable physical conditions accompany them. Mechanical shattering only of the claypan is a case of treating the symptoms and not removing the cause. Like the aspirin for a headache, it may remove the symptoms but does not remove the cause of the trouble.

Soil Acidity, a Deficiency of Fertility

Unfortunately, our understanding of soil acidity was one of confusion too long. Only recently have we discovered that natural soil acidity hinders plant growth because of the nutrient deficiencies rather than because of the presence of hydrogen, or acidity. In saying that “alfalfa does not grow well on acid soils” we were only saying that soils made acid by high rainfall have had most of the plant nutrients replaced by the ionized or acid hydrogen which does not serve as a plant nutrient in that form. Soils, which we say are failing to grow alfalfa because they are acid, should properly be listed as failing to grow alfalfa because they do not provide enough nutrients to let this crop survive. The starvation of the alfalfa may not mean the starvation of grasses or weeds needing less fertility and thereby doing what the farmer is describing when he says “the grass and weeds took my alfalfa.”

Unfortunately, also for better alfalfa production, we have emphasized liming as a soil treatment because the carbonate of limestone (calcium carbonate) neutralizes soil acidity. It has been, however, the application of the calcium as a plant nutrient, and not the removal of the acidity, that was the benefit to alfalfa from liming. Lime is a fertilizer for alfalfa on the soil we say is acid, because lime makes up the foremost deficiency of nutrients in that soil. It does so not only for alfalfa, but for other crops as well. Because alfalfa needs more calcium; because it uses more of this in its internal synthetic performances than most other crops; and because in our liming the soils to correct acidity we have unwittingly been fertilizing with calcium, we have believed alfalfa does poorly because soils are acids. Back of this so-called “bad environment for alfalfa roots”, was a fertility deficiency in one respect, namely calcium. Acid soils are bad for alfalfa because they starve the crop with respect to its great need for calcium in its production of mineral-rich, protein-rich makeup as highly nutritious feed.

Other Nutrients, Beside Calcium, Deficient for Alfalfa in Acid Soils

While soil acidity represents an excessive removal of calcium as nutrient for alfalfa, it also represents the dangerous exhaustion from the soil of all the other essential elements needed by the alfalfa in serving itself and in serving as feed for animals. All others, of the essential cationic nutrients, are more easily washed out of the soil than is calcium. Since they are present in such small amounts, but since those lesser amounts make them no less essential for the crop, we must recognize the serious shortages in all the other fertility elements than calcium long before this constituent of limestone records its own shortage in the.form of the poorer alfalfa crop.

Experiences, all too numerous and disturbing, are now telling of poor alfalfa crops because it was just lately learned that potassium was needed as well as lime on many soils. In the New England States, dairy cattle taking alfalfa grown on heavily limed soils are having troubles during calving with symptoms suggesting milk fever. But instead of responding to injections of calcium gluconate they require magnesium gluconate to restore them to normal health.

Heavy treatments by calcium limestone on the soil invite not only shortages of potassium and magnesium for the alfalfa crop, but also shortages in those elements taken in minor rather than major quantities as we think of them as fertilizer. Manganese, recognized as causing perosis when deficient in the diet for chickens, is not supplied amply to plants on heavily limed and neutral soils. Boron has suggested itself as eligible for the list of deficiencies in Missouri soils if they are to grow good crops of alfalfa.

When zinc, copper, and molybdenum, not commonly appreciated as plant nutrients, are deficient in Missouri soils for good alfalfa has not yet been determined. Then, too, we have been using phosphates liberally, which carry generous amounts of sulfur, without appreciating the services the sulfur, as a constituent of certain amino acids, plays in protein-building by plants. It, too, may be deficient in many soils. Then, too, plants have been carriers of iodine and cobalt, both essential for good animal health, which come via the crop from the soil to the digestive tract in possible organic combinations still unknown. They may be contributing to deficiencies.

When we speak then of soils for alfalfa production and say that acid soils fail to produce this fine feed crop successively, we are including more than the troubles that can be remedied by so simple a manipulation as the spreading of a few tons of crushed limestone per acre. We are including troubles more numerous and deep seated than those detected by a simple test for the degree of acidity of the soil. We are including possible need for the entire list of nutrients needed by both plants and animals. These needs call for the finest of chemical tests of both soil and alfalfa, and the best of animal assays as well of the crop, if the soil is to be the efficient provider of the chemical elements needed to let alfalfa exert its potentialities as a nutritious feed provider.

Alfalfa Is More Than a Hauler of Minerals

In thinking of the soil as the provider of the fertility for the alfalfa crop, the essentials for alfalfa are listed of necessity as mineral chemical elements. We think of them and make chemical analyses of them, in these elemental forms in the ash or after the plant has been burned. Because of this mental habit that was given us by inorganic chemical analyses, we are prone to think of alfalfa as a provider for animals also only in terms of the percentages of these mineral elements the alfalfa supplies. We are apt to judge the crop by its ash content, or by its services as a hauler of minerals to the manger more than by its services in using the soil fertility to synthesize the myriads of organo-mineral complexes that nourish animals.

The soil fertility is the potent force in making alfalfa the excellent feed that it is for growing young animals rather than one for laying fat on older ones. Biochemical assays have added to our former list of dietary requisites many compounds, like vitamins, hormones, and others now recognized as essential, finding their origin in the synthetic performances by the plant, and closely regulated by the soil fertility. We are slowly coming to recognize the soil fertility as the contributor by the help of which forage plants serve many of our body functions rather than only the one of supplying energy. We are thinking more about alfalfa as a desirable crop because it is a synthesizer of essential compounds rather than only a hauler of minerals.

Carbohydrates Synthesized More Commonly Than Proteins Because of Soil Deficiencies

Alfalfa is of different feed values according as it is grown on different soils. Here is the evidence that fertility differences in the soil make for different nutritive values in the crop. One of the controlling forces in making legume crops like alfalfa highly proteinaceous or more nearly only carbonaceous, is the ratio of calcium to potassium in the soil. This ratio becomes narrower as one goes from the soils of the west growing alfalfa naturally to those soils in eastern United States where alfalfa is grown with difficulty. Correspondingly the proteinaceousness of not only legume crops but crops in general goes down in this traverse from west to east. Their mineral contents in calcium, phosphorus, and potassium also go down but that of calcium declines the more rapidly. Here is a suggestion why forages serve more effectively as “grow” foods when grown in the western United States. Here are some differences in alfalfa quality that escape attention when our measure of alfalfa specifies its value only in tons.

“Soils Fertile Enough for Alfalfa,” a Good Ideal for Soil Management

Fortunately for our soils in terms of their higher productivity and for more of such nutritious crops like alfalfa, there is a growing appreciation of the productive power of our soils. Not only the national activity in forming soil districts under guidance of the Soil Conservation Service, but the many other recently formed voluntary organizations given to concern about our declining soil fertility are testimony. that not only better feeds like alfalfa for better animal nutrition, but also better foods for better humans, all demand attention to the better maintenance of the fertility stores of our soils.

But when many of the life processes of the plant are still chemical mysteries, and when numerous diseases of animals, like many of those of man, result from nutritional deficiencies, there is encouragement in thinking about their prevention in terms of better feeds and foods via better soils. Then, too, when, even for a crop like alfalfa, less than 10 per cent of the crop as ash comes from the soil, it would not seem fanciful to believe that putting these ash constituents on the soil might be the logical way of making our soils better. Through such treatments, then may we not lay the foundation for the maximum production by any crop? As long as we are no more able in diagnosing and curing diseases, surely it is wise to think of eliminating deficiencies by preventing them at the source of all life, namely, the soil. In a crop, like alfalfa, so sensitive to its unbalanced or deficient nutrition, we have a good biochemical indicator of the higher levels of soil fertility toward which we might well work. For want of better chemical laboratory guidance in proper soil-building, small seedings of alfalfa may well serve as soil fertility testers. It would be no small improvement for our soils even if we did no more than build them under the simple slogan of “Soils fertile enough for alfalfa.”