Nutrient Movement in a 104-Year Old Soil Fertility Experiment.

Alabama’s “Cullars Rotation” experiment (circa 1911) is the oldest, continuous soil fertility experiment in the southern U.S. Treatments include 5 K variables, P variables, S variables, soil pH variables and micronutrient variables in 14 treatments involving a 3-yr rotation of (1) cotton-winter legumes, (2) corn-wheat, and (3) soybean.  Each fertility treatment is replicated 3 times.  The soil is a Marvyn loamy sand (Fine-loamy, kaolinitic, thermic Typic Kanhapludults) typical of the Gulf and Atlantic Coastal Plain region.  Core samples were taken to 100 cm in 1986 and again in 2013 to monitor nutrient (primarily K)  accumulation and movement under long-term cropping and fertilization. Potassium application rates ranged from 0 to 335 kg K ha^-1 per 3-yr rotation.  Although maximum K accumulation in the surface horizon of these low CEC soils (CEC~3.5 cmol kg^-1) was only about 50 mg exchangeable K kg^-1,  exchangeable K accumulation decreased with depth in all treatments.  Where no sulfate-S has been applied, K accumulation was significantly higher at all soil depths to 100 cm.  Extractable P, Ca, Mg, and soil pH have also been monitored with depth.