The Centennial Rotation - Effects of Crop Rotation On Yield, Nutrient Uptake, and Nutrient Removal.

Long-term crop rotation continues return to the Midsouth following years of continuous cotton production as irrigated corn and soybean have become more profitable.  A long-term rotation study was initiated on the Delta Research and Extension Center and designed to utilize the latest technology available for crop production.  Crops included in the rotations are cotton, corn, and soybean, with cotton as the only continuous crop.  Cotton acreage has declined and corn production has increased to more than 300,000 ha.  The study features five rotation systems along with 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 have been at all-time highs and this coupled with irrigation, early planting, and early harvest place the Mississippi producer with a distinct advantage.  However, shifting to grain crops can also increase total nutrient uptake and removal compared to cotton.  With comparable yields, nitrogen (N), phosphorus (P) and potassium (K) removal by grain crops could be two to three times higher than cotton.  This would require additional nutrient replacement 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.   As these rotations continue the difference in nutrient removal will also continue to grow.