Ever since land-grant agricultural research began in Alabama, soil fertility has been of primary interest to producers and researchers. The first research plots established on research stations throughout the state addressed soil fertility issues on different soil types. Many of these sites remain in use today and continue to provide invaluable information. The long-term results of these studies allow researchers and producers to map the past, but also plan for the future. These long-term experiments are the basis for Alabama’s research-based soil test interpretations and recommendations. The following articles look at modern nitrogen, phosphorus, and potassium issues as seen through the lens of long-term studies.

    Information for this study was obtained from Alabama’s Two-year Rotation (circa 1929) and Rates of N-P-K experiments (circa 1954). The Two-year-Rotation tests are located at six sites in the state and have always involved cotton, corn, sorghum, soybean, or peanut rotations. Five of these have included cotton since 1992. The Two-year Rotation experiments involve: five nitrogen (N) rates, three phosphorus (P) rates prior to 1982, four potassium (K) rates, a fertilized control (annual rate of 90-60-60 pounds per acre N-P2O5-K2O), a no-lime treatment; low Mg, no fertilizer plus lime, plus micronutrients; and nontreated since 1928.

     To maintain a sound research basis for its soil testing services, the AAES established additional soil test calibration experiments in 1954 known as the Rates of N-P-K experiments. These have been continued at seven locations since their establishment. Cotton has been planted on these experiments more than any other crop (Table 1). Five of the seven experiments have been planted in cotton every year since 1992. The Rates of N-P-K tests involve: six N rates; four phosphorus rates prior to 1982; five K rates; fertilized control (annual rate of 90-100-100 pounds per acre N-P2O5-K2O); no lime; and nontreated control.


Map showing soil types and locations of AAES study sites for this study.

    The locations of these experiments are shown on the map. They continue to exist because of the support of the AAES and the dedication and hard work of the superintendents and staff of Alabama’s outlying research units: Randy Akridge, Brewton and Monroeville Experiment Fields; Don Moore, Prattville Experiment Field; Larry Wells, Wiregrass Research and Extension Center in Headland; Randall Rawls, Upper Coastal Plain Station in Winfield; Chet Norris, Tennessee Valley Research and Extension Center in Belle Mina; and Tony Dawkins, Sand Mountain Research and Extension Center in Crossville. The experiments at Sand Mountain Research and Extension Center and at the Upper Coastal Plain Station have been converted to forage crops while the others remain in cotton production. In recent years, producer checkoff funds have also helped support these experiments.

     These papers are dedicated to the memory of Dr. Tom Cope, Jr. (1921-1998), professor emeritus of Agronomy and Soils, who passed away on October 11, 1998. Cope was a mentor to the senior author and was responsible for the Two-Year Rotation and Rates of N-P-K experiments from the 1950s until his retirement in 1984. His publications from these experiments provided the basis for Alabama’s current soil test calibration and fertilizer recommendations, and his interest in long-term research helped to assure their continuation.

Mitchell is a Professor of Agronomy and Soils.

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