Cullars Rotation : The South ’ s Oldest Continuous Soil Fertility Experiment

on this site led to the discovery of K deficiency in cotton, which had been referred to earlier as “cotton rust” (Atkinson, 1891, 1892). Today, the experiment is a 3-year rotation of: 1) cotton followed by crimson clover, 2) corn harvested for grain and followed by winter wheat, and 3) soybeans double-cropped after the small grain is harvested. The soil is a Marvyn loamy sand (fine-loamy, siliceous, thermic Typic Kanhapludults) in the Coastal Plain physiographic region. Treatments and plot layout . The study included 11 soil treatments with three crops in the 3-year rotation. In 1914, an additional three treatments (designated A, B, and C) were added to include the effect of winter legumes in the rotation. Plot size is 20 x 99 ft., with a 2-ft. border between each plot and 20 ft. between each tier (block). Alabama’s “Cullars Rotation” experiment (established in 1911) was placed on the National Register of Historical Places in 2003 as the oldest continuous soil fertility experiment in the South. Along with its nearby predecessor on the National Register, “The Old Rotation,” which started in 1896, these experiments contain the oldest cotton research plots in the world. Both are located on the campus of Auburn University in east-central Alabama. Treatments on the Cullars Rotation dramatically demonstrate the long-term effects of fertilization and the lack of specific nutrients on non-irrigated crop yields over a 95-year period. The Cullars Rotation is one of the few sites where controlled nutrient deficiencies can be observed on five different crops during the course of a year (cotton, crimson clover, corn, wheat, and soybean). The experiment preserves a site for monitoring nutrient accumulation and loss and soil quality changes and their effects on long-term sustainability of an intensive crop rotation system.