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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.