In 1911, Alabama Agricultural and Experiment Station at Alabama Polytechnic Institute (now Auburn University) received state funding to conduct fertilizer experiments on farmers' fields throughout Alabama. One of those fields was near Auburn on the farm of J.A. Cullars. Today, the “Cullars Rotation” (circa 1911) is the only one of more than 200 original on-farm experiments that has been maintained. It continues to demonstrate the effect of N, P, K, Mg, S, ground limestone and winter legumes on long-term yields of a three-year rotation of (1) cotton followed by a winter legume (e.g. crimson clover), (2) corn harvested for grain followed by winter wheat harvested for grain, and double cropped with (3) soybean. There are 14 soil fertility variables replicated 3 times, one replicate for each crop in the 3-yr rotation. Each plot is 30 m long by 6.1 m wide with 0.75 m between each plot. Dramatic yield responses to P and K variables have been recorded on this sandy, Coastal Plain soil (fine-loamy, siliceous, thermic Typic Kanhapludults). Since 1997, all crops have been produced using high residue management and conservation tillage. Today, this experiment provides a teaching and demonstration laboratory for sustainable, soil fertility management. It is on the National Register of Historical Places.