Davis R. Clark and M. Wayne Ebelhar. Delta Research and Extension Center, Mississippi State University, P. O. Box 197, Stoneville, MS 38776-0197
Long-term crop rotations systems involving cotton, corn, and soybean were initiated in 2004 at the Delta Research and Extension Center to examine the long-term effects of crop rotations utilizing the most up-to-date technology available. This includes bio-technology in cultivars, high fertility management, and irrigation. Six rotation systems have been included with each component of each system included in every growing season. The six systems are 1) continuous cotton, 2) cotton/corn [2-yr system], 3) corn/cotton/cotton [3-yr system], 4) corn/soybean [2-yr system], 5) soybean/corn/cotton [3-yr system], and 6) soybean/corn/cotton/cotton [4-yr system]. It will take a total of 12 years for all systems to be at the same point as the initial year of the study. Of the system being evaluated, continuous cotton has removed the least nutrients as expected. Corn and soybean yields have been good throughout the study especially since shifting to twin-row production and ESPS (early soybean production system) philosophy. Glyphosate-resistant cultivars are being used for all crops along with insect resistance. To date corn yield increase has been measured following soybean production and cotton lint yield increases are 10-12% following corn in the system. The second year of cotton following corn has not shown the same increase as observed for first year cotton behind corn. Economic considerations will be included in the study as the data set is built. Weed shifts have not been evident, late season weed control problems have surfaced, especially as the corn and soybean mature and the canopy opens.