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Take-All of Wheat as Influenced by Organic Amendments and Nitrogen Fertilizers. R. W. Smiley, Former Research Assistant, Department of Plant Pathology, Washington State University, Pullman 99163, Presently Turf Pathologist, Cornell University Nematode Research Laboratory, State University, Farmingdale, New York 11735; Phytopathology 64:822-825. Accepted for publication 4 January 1974. DOI: 10.1094/Phyto-64-822.

Take-all of wheat, caused by Ophiobolus graminis was suppressed by maintaining a substantial proportion of rhizosphere N in the NH4 -N form. The result was the same regardless of whether NH4 -N was supplied by fertilizers or by mixing alfalfa meal with soil shortly before seeding wheat into Ophiobolus-infested soil. Disease suppression was highly correlated with the magnitude of reduction in rhizosphere pH and with the concn of NH4 -N in the rhizosphere. Take-all was not suppressed at low absolute concns of NH4 -N, or at any concn of NO3-N.

Additional keywords: Ophiobolus graminis, rhizosphere, pH, ammonium.