FACTORS AFFECTING ROTATIONAL BENEFITS FROM COTTON/CORN ROTATIONS IN THE MISSISSIPPI DELTA.

Research studies were setup at the Delta Research and Extension Center (DREC, Bosket very fine sandy loam [Mollic Hapludalfs]) and at the Tribbett Satellite Farm (TSF, Forestdale/Dundee silty clay loam [Typic Ochraqualfs/Aeric Ochraqualfs]) beginning in 2000 to investigate the interaction of nitrogen (N) rates and potassium (K) rates in cotton/corn rotation systems. The studies were designed to evaluate rotation effects on both poorly drained to somewhat-poorly drained silty clay loam soils (Forestdale/Dundee) as well as better drained sandy loam soils (Bosket) typically used for optimum cotton and corn production. The studies were established to examine both the benefits and problems associated with corn/cotton rotations in the Mississippi Delta. In the last decade changes in farm legislation has allowed mid-south producers the flexibility to shift from continuous mono-crop cotton to alternative crops and cropping sequences. Replacement of traditional cotton acres, in certain years, while using rotation to improve soil productivity, offers potential for profitability not available with mono-crop systems. This series of studies were intended to examine the impact of cotton/corn rotations on the whole farm enterprise. The objectives included a) determining the effects of N and K nutrition on cotton lint yields and corn grain yields for different soil types, and b) determining rotational effects of corn on cotton production and the implications of these rotations on whole farm economics. Factors that influence the degree of increase or decrease in lint yield associated with rotation have also been examined. Areas were setup on each research farm that could be rotated over a 3-year period with one year planted to corn and the two subsequent years planted to cotton. Each of the three sections at each location had a factorial arrangement of nitrogen (N) and potassium (K) rates. The corn and cotton sections consisted of 4-row (40-in spacing) plots, 90 to 100 feet in length, with either four (TSF) or five (DREC) replications. Nitrogen rates were 60, 90, 120, 150, and 180 lb N/acre for cotton and 120, 160, 200, 240, and 280 lb N/acre for corn with the fertilizer N applied as urea-ammonium nitrate solution (32% N). Potassium rates for all rotations were 0, 40, 80, and 120 lb K/acre. Nitrogen was applied at a uniform rate (60 lb N/acre for cotton, 120 lb N/acre for corn) prior to or near planting with the various N rates established as a sidedress application. Potassium applications were made after planting utilizing a 0-0-16 solution (1.3 lb K/gal) applied with the same equipment used for N applications. Corn and cotton cultivars having high yield potential were planted at each location and maintained throughout the growing season. Soil moisture sensors were installed to measure soil water tension and the data used to initiate, schedule, and terminate irrigations for both corn and cotton whenever possible. Crops were harvested by use of commercial harvesters modified for plot harvest with grab-samples taken for laboratory analyses and ginning. Stand counts were taken in the corn studies by counting the stalks in one of the two remaining border rows. The seedcotton grab-samples taken at harvest were later ginned through a 10-saw micro-gin for calculation of lint percent. Data were summarized and statistically analyzed using SAS (Statistical Analysis Systems) with mean separations by Waller Duncan K-ratio t-tests and Fisher=s Protected Least Significant Difference (LSD). Means across both N rates and Krates were used to measure the benefits from corn in the production systems. Comparisons were made of cotton following cotton and cotton following corn with the latter used to measure the actual benefits from corn in the system. There was no significant interaction between N rates and K rates at either location over the years.… [ABSTRACT FROM AUTHOR]