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COMPOSITION OF CORN IN THE UNITED STATES 1946-1947* INTRODUCTION The chemical composition of crops varies in relation to a number of factors, many of which are not clearly understood. Climate, species or variety, soil type, management prac- tices including fertilization, and the storage or processing of the crop comprise the most im- portant considerations. In launching a survey of the nutrient contents of corn in the United States, there were limitations to the number of factors that could be studied. For example, it was unpractical in a nation-wide survey to attempt a detailed study of all of the varieties of corn, because several hundred varieties may be grown in any one state. The decision was made to ignore variety in the selection of samples but to record it at the time of sam- pling. Similar problems were encountered with regard to soil type and management practices, but no attempt was made to record data on these factors. The number of samples collected in this survey was limited to the facilities that were available for analyses. It was estimated for 1946 that a maximum of 200 samples could be processed through the commercial, institu- tional, and state feed control chemical labora- tories that might cooperate in the study. It was judged that this number of samples would give an average for the nation accurate to 1 per cent for proximate nutrients and certain min- eral elements and 3 per cent for most of the micro-elements and vitamins. PROCEDURE Selection of Samples The sampling plan was based primarily on climatic regions and on corn production data. * Initial funds for this work were provided by Swift and Company. Later grants were made by the American Feed Manufacturers Association, the Gould Research Foundation, Merck and Company, Inc. and the Ralston Purina Company. The United States was divided into ten regions. These were so delineated that the climatic conditions of rainfall and temperature were somewhat similar throughout each region, and the effect of these factors on composition was assumed to be fairly uniform. A map showing the regions is given in Figure I. The percentage of the nation's total corn production contrib- uted by each region, state, and county was computed and used as a basis for allocating samples. Within a state the counties were stratified according to production. The number of strata was equal to the number of samples to be taken in the state and the total produc- tion in all strata was equal. One county was then selected at random from each stratum. Two hundred counties were designated to be sampled in each year, and one farm was sam- pled in each county in 1946. In 1947 an extra farm was designated in each of 50 counties, dis- tributed among states and regions at a rate proportional to production. Sixteen states were not granted any samples because they did not produce enough corn. Two states that were allotted samples did not cooperate. In regions 9 and 10, no single state could be selected for a sample, but one state was chosen at random to represent each of these regions. Within states, the county corn production was the basis for allotting the samples. Where one county alone did not rate a sample by virtue of its own pro- duction, a county was chosen at random from a group of counties with sufficient corn produc- tion. Selection of the sampling site within a county: County agents and extension personnel in the various states were enlisted to procure the samples. In those states from which five sam- ples or less were taken, the Extension Agrono- mist was requested to collect all samples. In the more heavily sampled states, however, the help of the County Agents was enlisted. In the selection of actual farms in the coun-
