TABLE III.-Barbados sugar crop and rainfall of preceding year. NOTE. In calculating the average crop and the respective annual excesses or deficits given in Tables I and III Governor Rawson says that "he has made an arbitrary division of the whole period into two sections marked by the introduction of the use of guano as a fertilizer." For the first section, 1847-1856, inclusive, he considers 38,795 hogsheads as the average, but for the second section, 1857-1872, inclusive, he takes 45,036 hogsheads as the average. He states that this is virtually assuming that during the whole period climatic and other conditions were nearly constant and that the principal difference was in the introduction of the use of guano and the great increase of crops was due to that. During the first interval an inch of rain corresponded to 642 hogsheads of sugar in the crop of the next year, but during the second interval it corresponded to 800 hogsheads. 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: 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 num 2667-05 M-23 |