In the United States as well, the ancient prejudices have now gradually given way before the urgent call for more definite information than could otherwise possibly be given to farmers by the experiment stations, most of whose cultural experiments, made without any definite knowledge of the nature of the soil under trial, were found to be of little value outside of their own experimental fields. Even the multiplication of culture stations in several states, unaccompanied by soil research, is found to be a delusive repetition of the same inconclusive, random experimenting, since it takes into consideration only the climatic differences, but leaves out of consideration the potent factors of soil quality and soil variations. At most these were usually mentioned by them in such indefinite terms as “a clay loam,” “a coarse sandy soil,” “gray sediment land,” and the like; frequently not even with a statement of the depth and character of the subsoil and substrata, much less of their geological derivation or correlations. Thus any one not happening to be personally acquainted with the land in question would be wholly without definite data to correlate the results with his own case. It is quite obvious that even if only to make possible the identification of new lands with others that have already fallen under cultural experience, and can therefore afford useful indications to the new settler, a close physical and chemical characterization of lands should be made the special object of study by the experiment stations and public surveys, particularly in the newer states.
Advantages for Soil Study offered by Virgin Lands.—Among the special advantages, then, offered by virgin soils for the study of the correlations of soils and crops, the usual existence of a native flora, representing the results of secular adaptation, is of fundamental importance. As it is at this time still historically known of most lands west of the Alleghenies what was their original timber growth, it is clear that their original condition can still be ascertained by comparison with uncultivated lands of similar growth, usually not very far away; and as their cultural history also is largely within the memory of the living generation, the behavior of such lands under cultivation is known or verifiable. Foremost among the data thus ascertainable is the duration of satisfactory crop production, and its average amount. To ascertain these surviving data by inquiry among the farming population should be among the foremost duties of those connected with soil surveys; and persons temperamentally unable to enlist the farmer’s sympathy and interest in such inquiries must be considered seriously handicapped, no matter what their scientific qualifications may be. In no quest is it more literally true that there is no one from whom the earnest inquirer may not learn something worth knowing.
Practical Utility of Chemical Soil-Analysis; Permanent Value vs. Immediate Productiveness.—In many existing treatises so much emphasis is given to the alleged proofs of the inutility of chemical soil examination in particular, that a special controversion of these arguments seems necessary, in connection with a detailed statement of what can, and in part has been, done in that direction. Hence the often-repeated allusion, in the sequel, to points bearing on this question. Hence, also, the detailed discussion of many points which in most agricultural publications are given only passing notice.
In all these discussions the difference between the ascertainment of the permanent-productive value of soils, as against that of their immediate producing capacity, must be strictly kept in view. The former interests vitally the permanent settler or farmer; the latter concerns the immediate outlook for crop production, the “Düngerzustand” of the Germans. The methods for the ascertainment of these two factors are wholly distinct, even though the results and their causes are in most cases intimately correlated. The failure to observe this distinction accounts for a great deal of the obloquy and reproach that has in the past so often been heaped upon chemical soil-analysis and its advocates.
PHYSICAL AND CHEMICAL CONDITIONS
OF PLANT GROWTH.
While it is true that plants cannot form their substance or develop healthy growth in the absence or scarcity of the chemical ingredients mentioned on page xxxi of this volume, it is also true that they cannot use these unless the physical conditions of normal vegetation are first fulfilled. Both sets of conditions are intrinsically equally important and exacting as to their fulfilment; and the farmers’ task is to bring about this concurrence to the utmost extent possible. The chemical ingredients of plant-food can, however, be artificially supplied in the form of fertilizers, should they be deficient in the soil; but as has been shown in the preceding pages, it is not always possible to correct, within the limits of farm economy, physical defects existing in the land. Hence, however important is the natural richness of the soil in plant-food, the first care should always be given to the ascertainment of the proper physical conditions in the soil, subsoil and substrata. Without these, oftentimes, no amount of cultivation, fertilization and irrigation is effective in assuring profitable cultural results.
Condition of the Plant-food Ingredients in the Soil.—But even the abundant presence of the plant-food ingredients, as shown by analysis, will not avail, unless at least an adequate portion of the same exists in a form or forms accessible to plants. Of course this condition would seem to be best fulfilled by the ingredients in question being in the water-soluble condition. But in the first place, plants are quite sensitive to an over-supply of soluble mineral salts, as is evidenced by the injurious effects produced by the latter in saline and alkali lands. Furthermore, substances in that form would be very liable to be washed or leached out of the soil by heavy rains or irrigation, and would be lost in the country drainage. It is therefore clearly desirable that only a relatively small proportion of the useful soil-ingredients should be in the water-soluble or physically absorbed condition, but that a larger supply should be present in forms not so easily soluble, yet accessible to the solvent action which the acids of the soil and of the roots of plants are capable of exercising. This virtually available supply we may designate as the reserve food-store.
Finally, there is practically in all soils a certain proportion of the soil-minerals in their original form, as they existed in the rock-materials from which the soil was formed. These minerals being usually in a more or less finely divided or pulverulent condition, they are attacked much more rapidly by the chemically-acting “weathering” agencies, viz., water, oxygen, carbonic and humus acids, than when in solid masses; and thus, transformation of the inert rock-powder into the other two classes of mineral soil-ingredients progresses in naturally fertile soils with sufficient rapidity to produce, in a single season, sensible and practically important results, known as the effects of fallowing.
The Reserve.—The nature of these processes has been discussed in chapters 1 to 4; and it will be remembered that two of their most prominent results are the formation of clay, and of zeolitic-compounds, the latter being, as heretofore stated ([pp. 36 ff]) hydrous silicates of earths and alkalies, easily decomposable by acids, and also capable of exchanging part or the whole of such basic ingredients with solutions of others that may enter the soil. These zeolitic compounds therefore fulfil two important functions in the premises, viz.: a ready yielding-up of part of their ingredients to acid solvents, and a tendency to fix, by exchange, a portion or the whole of the soluble compounds that may be set free in, or brought upon the land. The first-mentioned property is of direct avail in that the soil-humus forms, and the roots of plants exude, acid solvents on their surface, and can thus draw upon the reserve store of food; the second tells in the direction of preventing the waste of water-soluble manurial ingredients supplied to, or formed in the soil. ([See above, chapter 3, page 38]).
The reserve food-store may then be placed under the following heads: