Influence of Potassium Rates on the Late-Season, Leaf Spot Complex under No-Till and Conventional Tillage Systems

M. A. Newman, D. D. Howard


In an attempt to reduce the incidence of late-season leaf spot complex in cotton (mainly caused by Alternaria spp.), muriate of potash (KC1) was broadcast before planting at 0, 30, 60, 120 lbs./acre. In sub-plots, foliar applications of 10 lbs./acre of potassium nitrate (KNO3) were made four times on a two-week interval starting at blooming stage. Both methods of application were tested on no-till as well as conventional tillage systems at the Ames Plantation Experiment Station in 1993 on low K testing soil. The cultivar Deltapine 50 was planted in 30 foot plots, four rows wide in a split-plot design with the main plot as soil applied K2O rates.

Significantly less fungal leaf spots and higher yield were noted as K2O rates were increased in both conventional as well as no-till plots. No-till plots had significantly more leaf spot and higher yield at each K2O rate compared to the conventional tillage system.

Foliar KNO3 applications also reduced the leaf spot complex and increased yield. Again, no-till plots had significantly more leaf spots and higher yield than conventional plots.

The data from 1993 agrees favorably with the previous year's data except the conventionally tilled plots out-yielded the no-till plots in 1992. This is mainly because the 1993 growing season was very dry and the 1992 season was much wetter. In many situations no-till cotton may out-yield conventional cotton under dry conditions, however the leaf-spot complex may still be more severe.

Reprinted from Proceedings of the 1994 Beltwide Cotton Conferences pg. 273
©National Cotton Council, Memphis TN

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Document last modified Sunday, Dec 6 1998