Professor Moore is one of those who have pointed out that the forecasts based upon the actual condition of the growing crops can be vastly improved by a mathematical analysis of the weather reports from the various regions in which the crops are grown. In fact, he goes so far as to assert that much better forecasts can be made from the weather reports alone than from reports on the condition of the crops. Whether or not this view is unduly optimistic, it goes without saying that the precise data which agricultural meteorology is now acquiring cannot fail to enhance greatly the accuracy of crop forecasts.
Of course, the weather has always been watched with keen interest by everybody concerned with the purchase or sale of agricultural products and has been one of the chief factors determining the rise and fall of prices. At produce exchanges throughout the United States daily weather bulletins are received from the agricultural districts, and at many of them a large weather map is drawn every morning by an employee of the Weather Bureau detailed for this purpose. The Bureau has made various other arrangements for supplying the information that is so eagerly desired concerning the weather as it affects crops, as well as the animal industries. During the “growing season” in the cotton, corn, wheat, sugar, rice, broom-corn and cattle-producing areas, designated centers receive telegraphic reports of rainfall and the daily extremes of temperature from substations in the regions concerned, and these are distributed in bulletin form. Each local center, besides publishing detailed reports from its own area, issues condensed reports from all the others. The Bureau also issues every week during the agricultural season a “National Weather and Crop Bulletin,” with text and charts setting forth the current conditions of moisture, temperature, etc., and the state of the crops in all parts of the country.
The use which dealers and farmers make of these weather reports is, however, very far from having been reduced to science. Some of these persons, it is true, are frequently able, by a purely instinctive process of deduction, to make successful forecasts of crop yields from a close study of the weather, and others have worked out crude rules of their own for the same purpose; but the agricultural meteorologist approaches the problem in a different way. Immense progress has been made in the past decade in applying the mathematical theory of correlation to this problem. This branch of mathematics, originally developed chiefly for statistical studies in biology by Galton, Pearson, and others, is now extensively used by meteorologists not only for studying the effects of weather on crops, but also for finding out what correspondences or relationships exist between variations of weather in different parts of the world, as well as between weather and sun spots, weather and vital statistics, etc.
Sometimes, when the farmers do not disagree on the subject of favorable and unfavorable weather for the crops, they hold opinions in common that agricultural meteorology is unable to substantiate. An illustration is found in the idea that a good covering of snow during the winter is favorable to the yield of winter wheat. Apparently this is one of the host of popular ideas that are based merely on the delusive foundation of “everybody says so.” Smith has investigated the statistics of wheat for Ohio and C. J. Root those for Illinois. In both cases their results negative the prevailing opinion. Professor Smith finds “some evidence to indicate that wheat has a better prospect if it is not covered by snow during the month of January,” while Mr. Root states that, in general, “the winters of light snowfall are followed by good wheat yields and the winters of heavy snowfall by light yields.”
The study of the relations between weather and crops is really a branch of a science of broader scope, known as phenology. This science is devoted to the investigation of all periodic phenomena of plant and animal life that are controlled by the weather. There are, in some parts of the world, large corps of phenological observers, who maintain records year after year of the leafing, flowering, and fruiting of both wild and cultivated plants, the migrations and first songs of birds, and various other events of a biological character that recur with the seasons. In the course of time it becomes possible to compute from such records the normal dates of these events; and then, in any particular year, a comparison between the actual dates and the normal shows whether the season is early or late, and by how many days. Phenological observations on plants also make it possible to draw charts showing the normal march of the seasons over a country, expressed in terms of plant life, and such charts are often more valuable to the agriculturist or horticulturist as a guide in selecting varieties for cultivation and in timing his operations, than any charts that can be compiled from ordinary climatic data. Some admirable charts of this kind have been drawn for parts of Europe.
There are many practical applications of phenology to agriculture, and there would be more if phenological observations had been made more extensively throughout the world. Good phenological charts of different regions would, for example, greatly facilitate the work of foreign plant introduction carried on by the United States Bureau of Plant Industry. In the United States phenological observations were made systematically between 1850 and 1863, but only desultory work has been done in this line subsequently. The most comprehensive individual record is that maintained by Thomas Mikesell from 1873 to 1912, at Wauseon, Ohio, and published in full by the Weather Bureau in 1915.
The old rule of American farmers, inherited from the Indians, that the time to plant corn is when the leaf of the white oak is “the size of a mouse’s ear,” illustrates the use that can be made of so-called “index plants” of the native flora as guides for farming operations. Professor A. D. Hopkins writes on this subject:
“If such guide plants do not occur on the farm, they can be found among the ornamental trees and shrubs and hardy flowering plants of other localities or countries and transplanted. The periodical event of the falling of the flower catkins of the Carolina poplar has been found to be one of the best guides to the general early or late character of one season as compared with the average, while the opening of the leaf buds and unfolding of the leaves serve as reliable guides to the progress of spring. The various magnolias in their succession of flowering events serve as excellent guides to the rate of progress of spring and the time to do various kinds of work. The ornamental Spiræas, Deutzias, Diervillas, climbing roses, and Clematis among the ornamentals, and the dogwood, service tree, redbud, and oaks among the native trees of the middle and eastern regions of the United States are more or less constant in their response to prevailing local influences which are indicative of the time to plant certain field and garden crops. The opening of the leaf and flower buds and the flowering of the common fruit trees and shrubs of almost every farm serve as more or less reliable guides to the time to spray for certain insect and plant diseases.”
Dr. Hopkins has worked out an interesting rule known as the “bioclimatic law,” according to which the periodical events of plant and animal life advance over the United States at the rate of 1 degree of latitude, 5 degrees of longitude, and 400 feet of altitude every four days—northward, eastward, and upward in spring, and southward, westward, and downward in autumn. Thus, when the date of any phenological occurrence is known for one locality, it may be approximately determined for any other. This law has enabled the Department of Agriculture to publish rules of general application concerning the best time to plant winter wheat in order to escape the ravages of the Hessian fly, thus saving many millions of dollars to American farmers. The same law is susceptible of various other profitable uses.
