M. Wayne Ebelhar and Davis R. Clark, Delta Research and Extension Center, Mississippi State University, Stoneville, MS
Crop rotation has continued to return to the Midsouth following many years of continuous cotton production as irrigated corn has risen in the region. A long-term rotation study was established at Stoneville, MS and designed to utilize the latest technology available. Crops included are cotton, corn, and soybean, with cotton as the only continuous crop. In the beginning, cotton was the dominant crop even though more soybean was grown. For several years, cotton acreage has declined and corn acreage has increased to more than 365,000 ha. The study features five rotation systems and continuous cotton. The rotations include 1) continuous cotton, 2) cotton/corn [1:1], 3) cotton/cotton/corn [2:1], 4) corn/soybean [1:1], 5) soybean/corn/cotton [1:1:1], and 6) soybean/corn/cotton/cotton [1:1:2]. Each crop is grown each year in order for direct comparisons of the systems with respect to price. In many years, producers make their decision on crop mix based on prices. Grain prices are at all-time highs and this coupled with irrigation, early planting, and early harvest place the Mississippi producer with a distinct advantage. Shifting to grain crops within a rotational system can also alter total nutrient uptake and removal compared to cotton. With comparable yields in the Midsouth, nitrogen (N), phosphorus (P) and potassium (K) removal by grain crops (corn and soybean) could be two to three times more than cotton. Thus nutrient replacement would be much more critical for maintaining high yields. After eight years, continuous cotton has removed an estimated 567, 106, and 293 kg N, P, K ha-1, respectively compared to a corn/soybean rotation (4 years of each crop) that has removed an average of 1900, 265, and 541 kg N, P, K ha-1, respectively. The more grain crops in a rotational system, the greater the N, P, and K removal and subsequent need for replacement.