Laboratory Data as an Aid in Interpreting the Results of Cotton and Corn Fertilizer Experiments in Georgia

THE need of supplementary data for use as an aid in interpreting the results of fertilizer experiments is one generally acknowledged by field agronomists. Fields designated as the same soil type may respond differently to fertilizer or lime. These differences in response may be the result of previous treatments, inaccurate designation of soil type, or a number of other factors. Consequently, in making fertilizer recommendations based on the results from experimental plots alone, the field for which the recommendations are being made often differs in response to those used in formulating the recommendations. Discussing agronomic problems of the South, Funchess (5) states, "In practically all cases field plot experiments are located on land that is very much more productive than the average land in the area represented". Moreover, because of difficulties envolved, many fields in the South, as well as fields in other sections of the United States, may be considered unsuitable for conducting fertilizer experiments. It is . necessary, therefore, to resort to methods of bridging the gap between the fields on which experiments are conducted and those for which recommendations must be made. Laboratory methods, while not adequate in themselves as a means of determining the fertilizer requirements of soils, should be included in any well-balanced study of soil fertility along with experimental fields and possibly pot culture studies. It is the purpose of this report to show some of the results where laboratory data have been used in the interpretation of data from field fertilizer experiments with cotton and corn in Georgia. The laboratory determinations reported for the soil consist of reaction, clay content, available potash, base-exchange capacity, and exchangeable bases. Plant tissue tests were made for nitrate nitrogen, phosphate, and potash. Modifications of existing analytical methods were used in most of this work. Soil reaction was determined by means of a glass electrode; clay content, by the method of Bouyoucos (I) ; base-exchange capacity by the method of Olson and Bray (6) ; total exchangeable bases, according to Bray; and the available potash, the sum of the exchangeable and water-soluble potash, by a modification of the method of Bray (2). Tests on plant tissue were made according to the technic suggested by the Purdue Agricultural Experiment Station (8). Field tests reported were conducted on a cooperative basis with individual farmers in the state and were short-time, Iand 2-year tests. At the beginning of each experiment, the fertilizer and cropping history of the land was obtained from the cooperator. In most cases, six replications of i/2oacre plots were used.