Conservation-tillage practices have renewed interest in research evaluating fertilization responses of cotton. Research was conducted to evaluate the cotton-yield response to P and K fertilization under two tillage systems. Field research was established in 1994 and continued through 1999 on a Loring silt loam having Mehlich-I extractable P and K levels of 4 and 50 mg kg-1, respectively. The experimental design was a split-plot, main plots were tillage (disk-till and no-till), and subplots were a factorial arrangement of 0, 20, 39, and 59 kg P ha-1 rates and 0, 28, and 56 kg K ha-1 rates. Disk-till yields were higher than no-till yields. Broadcast P and K rates increased yields of both tillage systems. The P and K rate producing highest yields varied with year and tillage system. The calculated P rates producing the highest yields were 50 and 41 kg P ha-1 for the disk-till and no-till systems, respectively. The calculated critical P rates were 47 and 39 kg P ha-1 for the disk-till and no-till systems, respectively.Yields of both tillage systems were increased with K rates increased to 56 kg ha-1. Petiole and leaf P concentrations increased with P fertilization, but K concentrations were reduced by P fertilization. Petiole P and K concentrations were higher for the no-till system. Mehlich-I extractable P was increased with P fertilization, and was greater for surface broadcasting 39 and 59 kg P ha-1, compared with soil incorporation. The critical extractable P levels were 20 mg kg-1 for both tillage systems.
