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PART III. STATISTICAL FARM WORK.

Chapter XIII.

THE CROPS AND CLIMATES OF THE UNITED STATES.

The ultimate object of our inquiry is to determine the exact percentage of the effect of normal and abnormal climates upon special crops in special regions of this country and the relation to the whole crop of the United States. To this end we must first ascertain the climatic effect on the yield per acre, and this is our present special problem, leaving it to the statistician and census taker to ascertain how many acres are under cultivation and what the actual effect will be in bushels or pounds. The climatologist, or Weather Bureau, has only to determine numerically the climatic effect upon a given unit area.

The tables of yield per acre for ten important crops and for all years will be given in a subsequent portion of this section, but the study of these must be preceded by several studies into matters that are not strictly climatic, but which nevertheless enter into the statistics of actual harvests and obscure the strictly climatic influences. Thus the statistics must be corrected in some way for the effect of the customary modes of cultivation and the quantity of seed that is sown, on which point I give statistics appropriate to the United States.

Again, before comparing our climatic data with the phenomena of vegetation we must know something of the average date of seeding, with respect to which I have given the dates for seeding of winter wheat.

The corresponding dates for rye will not differ very much. The dates for maize, potatoes, tobacco, and cotton have already been given for special localities, but still require to be tabulated in a general way. The necessary climatic data are given in my next section for twenty Signal Service stations, and I regret that the shortness of time has not allowed me to give more complete data for these and for all other stations, but the tables here presented will serve to show the form in which such data should be presented for the greatest convenience in phenological studies.

But before entering upon so extensive a system of numerical comparisons it is necessary to bear in mind certain principles which I would illustrate in the following remarks.

VARIABILITY OF RESULTS FROM PLAT EXPERIMENTS.

The reliability of the data obtained from experiments on small plats of ground, and on which we should naturally place much reliance in discussing the relation between climates and crops, is a matter of the first importance, and we must begin our study with an attempt to obtain a clear idea as to the extent to which such data are fit to be used as a basis for our studies. In the light of all that has thus far been ascertained with reference to the nature of the influences at work to increase or diminish the resulting crop, we may safely say that the results obtained from two different plats will not be comparable with each other and still less be applicable to the larger fields harvested by the farmers, unless we know for each plat or field the absolute or relative conditions as to the following matters:

(1) The mechanical condition of the soil as affecting aeration, percolation, and temperature.

(2) The chemical nature of the original soil.

(3) The character, proportion, and uniformity of distribution of the fertilizers and the history of the previous rotations of crops on these plats; the influence of climate, rain, and drainage on the available nutrition in the soil.

(4) The dates of cultivation and application of the fertilizers. (5) The exact area of the plats.

(6) The distance apart of the hills or stalks.

(7) The number and quality of seeds sown per acre.

(8) The moisture in the soil at the beginning and the quantity and times of rain or irrigation.

(9) The chemical and biological quality of the rain or irrigation water-i. e., rain or snow water; rain with much or little nitrogenous compounds and biological germs.

(10) The injury by insects and animals.

(11) The temperature of the soil.

(12) The remaining climatic details as to heat, sunshine, dryness, and velocity of the wind.

(13) The sterility of the soil as to the microbic life that seems. indispensable to the success of certain crops or to the growth of the plants.

(14) The nature of the climate in which the seed and its immediate ancestor was grown.

In the total absence of knowledge as to many of these points and fragmentary knowledge on others, a simple direct comparison between the results of two plats lying side by side and that have in some few respects been treated alike must be entirely misleading. But the extent to which such comparisons are deceptive, or rather the

extent to which we can rely upon them for further instruction, can only be estimated by a study of such exact experiments as have been made at the experiment stations throughout this country and Europe. Some illustrations of this matter are given by C. S. Plumb, under the title of the "Fallacies of plat experimentation" (Agr. Sci., Vol. II, p. 4), to which I will add the following remarks. Two sets of measures are taken from the results of the year 1887 at Geneva, N. Y. The plats were arranged in two series, or two fields, but were in every respect as much alike as possible and supposed to be identical. The harvests from the respective plats were as follows:

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The individual differences between these 36 plats simply show that the conditions were not so uniform as the author supposed; in fact, the regular gradations from the high numbers at the top of the column to the low ones at the bottom show that there was a slight systematic difference among the plats in each series. On the other hand, the decided apparent differences between the two series, as well as between the plats, is very largely of the nature of those differences that are called accidental in the theory of exact measurements. Similar diferences in a long series of observations of the temperature or the rainfall of any locality are spoken of not as accidental error but as the variability of the climate, and these differences in the present case may properly be treated as variability in the productive power of any plat compared with the neighboring plat without for the moment inquiring as to the cause of this variability. But the mathematical theory of probabilities, or chance, or errors of observation, is equally applicable to this question of variability due to unknown influences. According to that theory we obtain the index of variability if we take the difference between the average of a series and the individual num2667-05 M- -23

bers in the series and treat these departures according to the following formula:

Index of variability of the plats equals

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which formula may be interpreted as meaning that from the squares of the departures added together and divided by the number of plats less 1 we derive an index called the "probable uncertainty of 1 measure," or "the probable variability of 1 plat as compared with all the plats of the series." Again, knowing this uncertainty of any one measure, we find the "probable uncertainty of the average of n measures" by the following formula:

Probable uncertainty of the average = ±

Index

√n

This latter formula is to be interpreted as meaning that there is an even chance that the computed average is too large or too small by this probable uncertainty. Applying these principles to the measures of plats C and E, I obtain the figures 34.3 and 22.9 as the indices of variability and 8.33 and 5.26 as the probable errors of the two averages. That is to say, so far as any internal evidence is given by the discrepancies between the measurements of the plats themselves, there is an even chance that the crop from a plat in series C is between the limits 212.9 and 196.3 or outside of these limits; similarly, for series E there is an even chance that the crop from any plat is within the limits 188.9 and 177.4 or outside of these limits. But the numbers within each of these two series overlap each other so much that it is perfectly possible that if we could increase the number of plats in each series sufficiently, all other conditions remaining the same, we should eventually arrive at very nearly the same average value for each. In other words, the mere difference of the two averages 204.6 and 182.7 is no evidence that in this particular case there was any important constant difference between the plats of series C and those of series E, but that, on the contrary, unknown sources of influence are at work in each series and in all the plats that are more important than any that were thought of when the experimenter endeavored to make these 36 plats perfect duplicates of each other.

Professor Plumb shows that this difference did not depend upon the previous crops or treatment of the plats during the previous five years. It certainly did not depend on the meteorological climate, the mechanical condition of the soil, nor on the seeds, nor on injury by insects and animals. We may possibly find a partial explanation in the irregular distribution of microbic life in the soil, but it is more likely that it depended upon the inherent variability of the

vitality of the seed, due to unknown causes, and which we have no means of measuring except by just such experiments as these. The elaborate measurements made by Lawes and Gilbert at Rothamsted, England, since 1850, furnish innumerable illustrations of this same principle; so, also, do those of W. R. Lazenby, at Columbus, Ohio, and many others.

We shall therefore hope to derive more reliable results from the study of farming operations on a large scale, taking the averages by counties and States where the crops have been carefully measured. We may possibly eliminate irregularities in many disturbing elements, and be able to clearly set forth that small percentage by which the crops of the United States as a whole are influenced by purely climatic conditions. Such influences may in extreme cases be very large, but, on the average, they are not so large as those which depend upon seed, cultivation, rotation, and fertilizers.

EFFECT OF VARIATIONS IN METHOD OF CULTIVATION AND IN QUALITY OF SEED FOR DIFFERENT REGIONS AND YEARS.

Among the modes of cultivation that materially affect the development of the plant and the quantity of the harvest must be considered the practice of sowing seed broadcast with the hand as contrasted with that of putting it in with the drilling machine. The drilling requires less seed, the saving being about one-half bushel per acre; the grain is buried more evenly, starts more uniformly, and stands the droughts better. Moreover, the drilled wheat fields are considered to yield more per acre, although it is difficult to state how much is due to the drilling independent of the character of the soil, because in general the fields that are drilled are most apt to be those free from stumps, stones, and steep slopes, while the broadcast sowing is especially adapted to this latter character of field. The census of 1879 shows that the drilled fields of winter wheat in Ohio yielded 50 per cent more than the broadcast fields of summer wheat in the Northwest; but it is not plain what proportion of this is respectively due to the drilling and to the soil.

In the report for 1875 of the Department of Agriculture (p. 42) the following statistics are given as to the percentage of area drilled, the quantity of seed per acre, and the increase of harvest in drilled fields over that in broadcasted fields:

The following table omits the New England States, which produce little wheat, nearly all of which is sown broadcast. The wheat area of New York is divided equally between the two methods. In New Jersey, Pennsylvania, Delaware, and Maryland the drill greatly predominates. In the Southern States the area is small, particularly in the cotton States, and the drill is comparatively unknown. North of the Ohio River, in the winter-wheat States, the drill is very

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