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Several experts in agricultural science having stated to me their need of a systematic summary of the present state of our knowledge with regard to the specific influence of climate in agriculture and its relation to or absolute effect on the percentages of the resulting harvest, and the subject being one in which I had long been interested, I therefore presented the matter to the Chief Signal Officer, who thereupon issued an instruction, dated February 25, 1891, authorizing me to prepare this work, completing it before June 30 of that year. The present report is a rapid compilation from a wide range of sources, and presents a preliminary view of the condition of our knowledge at that time as to the effect of climate upon the growth and distribution of our staple crops. As far as practicable I have presented, in the words of the respective authors, the results of their own investigations on the points at issue, my own duty being not to undertake any extensive original study, but to merely connect their results together in a logical manner, to collect data for future general use, and to suggest, or stimulate, further inquiry on the points here presented. I regret that the report could not have been published in 1891, as many of the ideas presented therein have by delay thus been withheld from their practical applications to the benefit of agriculture.
As the study of phenology and agriculture, in the modern spirit, has been cultivated for over a century in Europe, much of our knowledge must be drawn from European literature, which is really far too extensive to be satisfactorily summarized in the time and space at my disposal. Originally it was my hope to introduce into this report a summary of the large and sadly scattered literature of American phenology, including the dates of blossoming and ripening both of native and cultivated plants, enlarging the work already done in this line by F. B. Hough for the State of New York; but I did not succeed in completing this part of the work, and reserve it for a future occasion. Requests for phenological observations in the United States have been frequently made since 1800, and large collections of data exist in manuscript and print sufficiently extensive to justify the hope that they may prove worthy of a study as elaborate as that which European observations have received at the hands of the lamented Linsser.
The very extensive problem suggested by the title of this report involves, first, a general study of meteorology in its relations to vegetable and animal life; second, the determination of the effect of climate upon the growth and distribution of staple crops; third, the determination of the climatic conditions and the localities best suited to the growth of special varieties of plants and seeds; fourth, the statistics of the extent of the areas best adapted to each of the more important crops; fifth, the separate and the combined effects of temperature, rainfall, and sunshine, both in their normal and abnormal proportions, upon the annual yields of the staple crops. But such study necessitates great labor and much time, and as the first step in any such investigation consists in the critical examination of the work already done by others, in order to prevent unnecessary duplication and avoid the troubles that others have experienced, therefore the reader must consider this first report as only a brief introduction to our knowledge of the relations between climates and crops.
Three ways are generally recognized as affording our only methods of advancing our knowledge of our subject, viz, physiological, experimental, and statistical. I shall therefore endeavor to present the question of climates and crops from these three points of view.
1. The physiological studies of many botanical physiologists, under the leadership of Prof. Julius von Sachs, of the Botanical Institute at Würzburg, Germany, have given us an insight into the method of growth of plants and the conditions upon which successful agriculture must depend. Their conclusions, based upon microscopic examination, delicate measurements, and detailed study of all the minutiæ in the life of a plant, have given occasion to the development of what may be called a theory of vegetable life, which, however, is still far from having reached a perfect stage of development. Under this head I have collected observations relative to the germination of seeds, the flow of the sap, the action of sunlight on the leaves, the absorption of moisture by the roots, the transpiration from the leaves, the ripening of the seeds, the nutritious value of the crop, and the acclimatization of plants.
2. The experimental method of determining the relations of crops and climates is that practiced at agricultural experiment stations and also in the botanical or biological laboratories that are so plentiful in the United States and in Europe. In these institutions special seeds are sown with special care, either in the open air in small plats of ground or in culture pots in rooms where the temperature, moisture, and other conditions are under control. The numerous abstracts that I have presented in this report tend to show the effect of varying conditions upon the resulting crops, and I must agree heartily
with De Candolle in his plea for a climatic laboratory. It is evident that in such an institution one may reproduce to perfection the climatic conditions under which a given seed was grown, and thus insure a maximum crop; or, on the other hand, by successive cultivations, under successive slight changes in the artificial climate, may so modify the seed as to produce a new variety with a fixed habit of growth adapted to any natural climate that the farmer has to deal with. The laws of acclimatization that naturally follow from Linsser's investigations, and, in fact, from general experience in all parts of the world, point to this as a most important field of future usefulness. It is thus that we may hope to accelerate the natural course, which, on the one hand, has already produced grains adapted to the Russian steppes, and, on the other, will eventually evolve those adapted to the vicissitudes of our own arid regions and possibly our severe Alaskan climate.
3. The statistical method of ascertaining the effect of a climate on the resulting crop consists in comparing the statistics of the successive annual harvests in the country at large with the statistics of the prevailing climatic conditions. At the close of this report I have given a large collection of data of this kind, sufficient, I think, to show that this method is very unsatisfactory because of our ignorance of the many details that must be considered in discussing the statistical figures. I have compiled these elaborate tables for the United States from the data given by the former Statistician of the Department of Agriculture, Mr. J. R. Dodge, and his able assistant, Mr. Snow, and have indicated a method of treating these figures which will, I think, eventually give us the best results that they are capable of affording, and will be, perhaps, sufficiently accurate for the needs of the farmer, the merchant, and the statesman, but which can scarcely respond to the exact demands of agricultural physics. The great collection of data given in the reports of the Tenth and Eleventh censuses of the United States for the crop years 1879 and 1889 will, I hope, tempt some one to an extended study for those years.
I shall not devote much space to the question of the relative influence of forests and cultivated fields on the temperature and moisture of the local air. This has become a special study on the part of those devoted to forestry, and the papers of Professor Ebermayer (1873), Muttrich (1880), Nordlinger (1885), and others a teem with figures to show that in the heart of an extensive forest the mean daily variations of temperature or the range from minimum to maximum is, on the average, from 2° to 5° C. less than in the open air just outside the forest, while a similar difference of only 1° to 2° C. exists for the annual ranges of temperature. Some attempts have also been made to show that in a forest region more rain falls than in adjacent open fields; but this I shall not further consider, as I have elsewhere shown that the measured differences are all due to the influence of the wind on the catch of the rain gage and have nothing to do with rainfall itself. All reliable observations show that the percentage of moisture in the soil is larger under the forest than in the open air, and all investigations show that the temperature of the soil is far more uniform under the forest than in the full sunshine.
a The full titles of the works referred to in this report will be found in section on “ Bibliography," Part IV.
The proper conclusion to draw from these forest studies, in so far as they relate to the question of the influence of climate on crops, is simply that plants growing within the influence of a forest have a somewhat different climate from those growing in the open field. The amount of this influence will become a proper study when any important crop is cultivated within a forest or under its influence, which, however, is not now generally the case.
The inverse question as to the influence upon general atmospheric phenomena of the temperature and moisture of the thin layer of quiet air within a region covered with a forest is one that may be relegated to the future as being of minor importance in dynamic meteorology and of still less importance in agricultural climatology.
On the other hand, the distribution and quality of forest trees affords a very important illustration of climatic influence. Indeed, the forests themselves furnish a most important crop of lumber and firewood, perhaps the most valuable crop recorded in the statistics of the country, and one whose relation to climate must be important, but, unfortunately, the statistics of annual forest growth are not yet available for this study. I have, therefore, deferred the consideration of this branch of our subject to a future date, when perhaps American forestry will be more fully developed.
I shall omit the consideration of theories and experiments as to the artificial improvement of the weather, especially the production of rainfall, protection from hail and lightning, and the amelioration of our hot winds. Although this subject is alluring, I hope the common sense of the agricultural community will eventually indorse my conviction that, for the present, our wisest plan is to confine our study closely to, first, the influence of sunshine, heat, moisture, and atmosphere on the growth of plants, on the nature of the seed, and on the character of the crops; second, the influence of the quality of the seed itself and of the richness of the soil on the crop; third, how to choose our seed, cultivate the ground, and protect the plant from frost, birds, insects, fungi, etc., so as to secure a good crop in spite of adverse natural climatic conditions,
In general, I have labored to put my data and conclusions before the reader so fully that, if a student, he may utilize this report as a