ABSTRACT

Soil fertility research with cotton has not been conducted on the fine-textured, often calcareous soils of the Alabama Black Belt Prairie region in several decades although as much as 30,000 acres are being planted on these soils. Cotton producers on these soils regularly express concern about N rates and potential K deficiencies. An on-farm experiment in 2002 and 2003 on a Houston clay in Dallas County included N, P, K, S, and B variables. Very high soil K levels at this site precluded any expected response to added K. Leaf blade K levels suggested the need for growers to pay very close attention to the time of sampling when using leaf analyses to diagnose K sufficiency levels in cotton. Excessive K application appeared to suppress leaf-blade Mg concentrations and yields in 2002. Although soil test P was near the critical value used for Lancaster extractable P on Black Belt soils, there was no yield response to added P. This suggests that the current critical value is certainly not too high. There was no yield response to B or S. Leaf blade B and S were within the established sufficiency ranges for mid bloom. Most of the total N application should be applied as a sidedress even if it is applied as late as early bloom. This is to avoid denitrification losses from extremely wet springs such as 2003. In moderately dry years as in 2002, the A.U. standard recommendation of 90 pounds N per acre appeared sufficient for maximum yields. However, in extremely wet years as in 2003, rates as high or higher than 120 pounds N per acre as a sidedress may be warranted.