ANALYSIS OF THE EFFECTS OF SOIL COMPACTION ON COTTON YIELD TRENDS

Cotton (Gossypium hirsutum L.), yields in the U.S. Cotton Belt decline d from 1960 to 1980 despite improvements in technology and introductio ns of higher yielding cultivars. As part of the effort to examine poss ible causes for the yield reduction, the cotton crop simulation model, GOSSYM, was used to analyze the effects of soil compaction on cotton yield trends, Weather, soil and cultural input data from six locations over 20 years were acquired and used or this study. There were no con sistent trends over all locations. Prior to 1974, compaction had some negative effect at Florence, South Carolina, but due to annual in-row subsoiling, had no effect after that time. At Stoneville, Mississippi, the effects of compactions were generally detrimental but they were o ften masked by weather. In years of abundant moisture, wheel traffic c ompaction had little negative effect on yields, since shallow root sys tems could extract sufficient moisture for plant growth and yield. In extremely dry years, predicted yields were low for both compacted and uncompacted crops. The effect of wheel compaction on yield was general ly favorable at College Station, Texas. The lower yielding crop, howev er, generally put more of its photosynthate into roots during the boll filling period. This was also true at Phoenix, Arizona, where the res ults were erratic. At Lubbock, Texas, on a clay soil the effects of si mulated compaction were negligible.