Geographical Distribution of Variability in the Yields of Cereal Crops in South Dakota

Abstract

In a recent paper (Klages, '30) the difference in the degrees of variability in the yields of various field crops for the states of the Mississippi valley were discussed. It was found that the seasonal fluctuations in the yields of all crops, except wheat in the states producing hard red winter wheat, were greater in the Great Plains states than in the more humid states to the east. Marked differences were also pointed out in the trends of the yields of these crops over a 37 year period, as well as in the degrees of correlation existing between the yields of separate crops of the respective states in the two sections. The data presented indicated that the geographical localization of the lowest degrees of variability in the seasonal yields of a crop, or a series of crops, corresponds well to the section to which that particular crop or group of crops is best adapted. The facts brought out in the investigation referred to above have general application only. The specific effects of climatic factors are, as is commonly known, modified to a considerable extent by other factors of the environment, especially by variations in local soil conditions. Furthermore, the climatic conditions of as large an area as the confines of a state are far from uniform. This is especially true for the Great Plains states, with their eastern portions in a type of climate entirely different from that of their central and western parts. As may be observed from the maps of natural vegetations given by Shantz and Zon ('24), and from the various root studies of native plants by Weaver ('20) and by Weaver and Crist ('22), entirely different types of vegetation, which reflect directly the prevailing climatic conditions, are encountered in the eastern and western portions of these states. Consequently the values given on yields, variability of yields, etc., of such large units have all the shortcomings of average values. The justification for the employment of such large units as the areas of individual states was found in that they offered the only available source of information. With these points in mind it was thought worth while to take up the study for the confines of one state only, and in that state from only well defined locations. The distribution of the main station and the various substations of the South Dakota Agricultural Experiment Station was found favorable for a more definite, and in some respects a more detailed, investigation on variability of crop yields. Figure i shows the distribution of these stations over the state. The main station at Brookings is located in the east-central part