Day after day, and year after year, the principal atmospheric conditions are observed and measured at a great number of points scattered over the State of Ohio, as they are elsewhere throughout the Union, and the records thus obtained are carefully compiled, summed up, averaged and otherwise discussed by officials of the Weather Bureau. Thus a great fund of detailed statistical information about the weather is available for comparison with the statistics gathered by other agencies concerning the yield of crops and their condition at different stages of growth.
Professor Smith’s analysis of the Ohio records revealed a fact of so much practical importance that this discovery alone suffices to place agricultural meteorology among the most fruitful branches of knowledge cultivated by mankind. He discovered that the success of the Ohio corn crop depends chiefly upon the amount of rain that falls during the month of July. The normal rainfall of that month for the State is 4 inches, while the average yield of corn during the past sixty years has been 34.5 bushels per acre. Comparing the values for individual years, it is found that the yield is strikingly sensitive to variations from the normal July rainfall, and especially so when the rainfall is a little more or less than 3 inches. Near this critical rainfall point, a variation of one-fourth inch of rain in July means a variation in the value of the corn crop of Ohio of nearly $3,000,000, and a variation of one-half inch makes an average variation in the value of the crop of more than $7,500,000. When the rainfall for July averages over 5 inches the probable yield of corn will be more than 27,000,000 bushels greater than it will be if the rainfall averages less than 3 inches. In other words, this difference of 2 inches in the rainfall for the month of July adds $13,650,000 to the income derived by Ohio farmers from corn alone.
Variations of the temperature in July, in Ohio, have been compared with variations in the yield of corn, with the result that the temperature of the month appears to have little effect upon the crop. Thus we find Farmer A to have been right and Farmer B wrong; but both were merely expressing personal opinions based upon an insignificant sum-total of experience. Science rests upon a surer foundation.
Although the case of the Ohio corn crop is probably simpler than most of those that agricultural meteorology has to deal with, for the reason that a single meteorological element is, in this case, of decisive importance, it illustrates a rule of quite general application that has recently come to light; viz., that in the growth of any particular crop there is usually a rather brief “critical period,” when it is most sensitive to the influence of weather. For corn, in a considerable area of the northern United States, this period is July, or more specifically, in Ohio, the interval from July 11 to August 10. The rainfall and temperature of other months have, however, definite though minor influences, which can be evaluated for the same regions.
With respect to the American “corn belt” in general, it is not certain how far the rules deduced for Ohio are applicable. Professor Smith has been inclined to look upon July rainfall as the dominating factor for the whole of that region; so that, for example, a difference of 1 inch in the rainfall (viz., a total for July of 4.4 inches or more, as compared with 3.4 inches or less) has been held responsible for an increase of 500,000,000 bushels of corn in the eight principal corn-growing States. It has also been stated that in the four States of Indiana, Illinois, Iowa and Missouri an increase of half an inch of rain in July meant an increase of $150,000,000 in the value of the crop. These figures have, however, been challenged, and the subject is still under discussion.
The study of the critical periods of different crops, and the determination of the amounts of heat and moisture most favorable to the success of the crop at such periods, may be regarded as the leading task of the agricultural meteorologist. The most elaborate researches of this character have been made in Russia by Professor P. Brounov, who founded in 1896 a meteorological bureau, attached to the Ministry of Agriculture, with an extensive network of stations scattered over the Russian Empire. This bureau was quite distinct from the ordinary meteorological service, under the direction of the Central Physical Observatory in St. Petersburg. Just before the war Professor Brounov had 150 stations in operation; most of them for observing the effects of weather on the leading cereal crops, though some studied the corresponding relations of horticulture or the animal industries. Each agricultural station comprised a small plot of land, on which a certain sequence of crops was grown year after year under conditions of cultivation as nearly uniform as possible, the only variable factor being the weather. Meteorological instruments were installed in the immediate proximity of the plants under investigation. Prior to 1914 Brounov had determined the critical periods of most of the crops grown in Russia, and had published a great deal of information on this subject that could be turned to practical account by Russian farmers.
It will perhaps not be immediately apparent to the reader just how such information can be utilized. Its practical applications vary, in fact, according to circumstances. First of all, a knowledge of critical periods and of the weather requirements of crops at these periods enables the farmer to select his crops and time his farming operations on the basis of climatic statistics. Brounov published a series of charts showing the probability of dry weather, as deduced from many years of observations, for each ten-day period throughout the agricultural year for every part of European Russia. With such charts at our disposal, and knowing how long after planting each crop arrives at its critical period with respect to moisture, we can readily estimate the probable success of a given crop planted at a given time and place; at least, so far as this is determined by rainfall. If temperature or other meteorological conditions are of special importance at the critical periods, we shall need additional climatic charts. Of course, the weather in any particular year may differ widely from the climatic averages; but in the long run crops will prosper in proportion as their critical periods coincide with the occurrence of favorable weather as shown by the climatic record. It will be seen that this is quite a different idea from the traditional one that a certain crop needs a “moist climate,” another a “hot climate,” etc. The agriculturist now asks the man of science to tell him when, between planting and harvesting, heat or moisture is of vital importance to the crop, and how much of each will produce the biggest yield.
In regions where irrigation is practiced it is obviously advantageous to the farmer to know at what stage of its growth a crop becomes sensitive to the amount of moisture received. During the greater part of its life the plant may be quite indifferent to moisture, and at such times irrigation would be wasteful. The farmer needs to know not only when the critical period has arrived, but also what the water requirements are at that period. Too much water may be as bad as too little.
Even when agricultural practice ignores the rules laid down by the agricultural meteorologist, a knowledge of these rules may be applied with great advantage to the prediction of crop yields. It is hardly necessary to tell any farmer or business man that accurate crop forecasts are an economic desideratum of the utmost importance. The United States Government maintains an army of more than 200,000 volunteer crop reporters, supervised by a staff of experts, for the purpose of determining month by month the condition of every agricultural crop and its prospective yield. With regard to the monthly announcements of the Bureau of Crop Estimates, Professor H. L. Moore, of Columbia University, says:
“The commodity markets are in a state of nervous expectancy as the time approaches for the official forecasts, because great values are at stake. It has been estimated that in the case of the cotton crop alone an error in the forecasts which should lead to a depression of one cent a pound in the price of cotton-lint would—assuming a crop equal to that of 1914—entail a loss of eighty million dollars to the farmers. The vast values at stake and the dangers when no official estimate is available of the manipulation of the markets in the interest of speculators are held to justify the large recurrent annual cost of the employment of the numerous correspondents, clerks, and experts.”