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Selected Chemical and Physical Properties of Soils Manifesting Cotton Root Rot¹

Some soils that produce cotton (Gossypium spp.) that is free of Phymatotrichum omnivorum are physically adjacent to similar soils on which cotton annually succumbs to the fungus. This study evaluated relationships of soil properties to incidence of cotton root rot (CRR) at 26 sites. Complete pedon descriptions were made, and horizons were sampled and analyzed to determine selected physical and chemical soil properties. Means of soil analyses for non-root rot (NRR) and root rot (RR) soil groups were compared by t-test using the weighted averages for the surface horizons, upper 0.50-m and 1.0-m sections. Physical properties were not suitable indicators of disease incidence; however, extractable Mg²⁺ within land resource areas was found to be significantly greater in NRR-affected rather than RR-affected soils. Furthermore, the ratio of extractable Ca²⁺ to Mg²⁺ was found to be greater in RR soils than NRR soils. X-ray analysis of the soil carbonates did not indicate that the differences were the result of differential Mg contents of the soil carbonates. In addition to Mg²⁺, mean extractable Fe²⁺, Zn²⁺, and Cu²⁺ were found to be greater in NRR soils in some cases. The soluble bicarbonate ion content of surface horizons was also found to be higher in RR soils than NRR soils. Results suggest that cotton grown in RR soil is more stressed than that grown in adjacent NRR soil.

Key Words: Vertisols • Disease-suppressive soils • Phymatotrichum • Gossypium spp.

² Former graduate research assistant and associate professor of Pedology, respectively, Soil and Crop Sciences Dep., Texas A&M University, College Station. Senior author is now manager of Education and Technical Services, National Fertilizer Solutions Assoc., St. Louis, MO.

Received for publication November 12, 1985.