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Anhydrous Ammonia as a Soil Fungicide Against Fusarium and Fungicidal Activity in the Ammonia Retention Zone. R. W. Smiley, Soil Scientist Research Assistant, Soil and Water Conservation Research Division, ARS, USDA, Pullman, Washington 99163, Senior author is now Research Assistant, Department of Plant Pathology, Washington State University; R. J. Cook(2), and R. I. Papendick(3). (2)(3)Pathologist, Crops Research Division, and Soil Scientist, Soil and Water Conservation Research Division, respectively, ARS, USDA, Pullman, Washington 99163. Phytopathology 60:1227-1232. Accepted for publication 20 March 1970. DOI: 10.1094/Phyto-60-1227.

Populations of Fusarium roseum f. sp. cerealis ‘Culmorum’, F. solani f. sp. pisi, and total fusaria (including saprophytes) declined to zero, or nearly so, within the ammonia retention zone in both Palouse silt loam (PSL) and Ritzville silt loam (RSL) in the laboratory following injection with liquid anhydrous ammonia (NH3). In soil 0-2 cm from the site of injection, the Fusarium populations began to drop within 1 day after injection and reached zero by 14 days. In soil 4-5 cm from the site of injection, the respective Fusarium populations declined less rapidly, but approached and in some cases reached zero by 49 days after injection. Fusaria outside the NH3 retention zone were not significantly affected, whereas inside the zone no recovery had occurred by 225 days after injection. Initially, and particularly in the centermost portions of the retention zone, NH3 apparently caused most of the destruction of the fusaria. Nitrite (NO2–) accumulated with time, and probably constituted an additional source of fungicidal action. In PSL incubated at 24 C, more than 30 to 35 ppm NO2– was detected within 4 days in soil 0-2 cm and 2-4 cm from the NH3 injection site and within 14 days in the 4-5 cm zone. Concentrations exceeding 100 ppm NO2– were measured in PSL incubated at 6 C. Additions of 35 ppm NO2– (KNO2) to PSL reduced populations of all fusaria to undetectable numbers within 1 week. High pH in the absence of NH3 and 100 ppm N as nitrate (NO3–) (KNO3) had no significant effect on the Fusarium populations. When soil “sterilized” by gamma-irradiation (9.8 megarads) and later aseptically reinfested with Culmorum was injected with liquid anhydrous NH3, reductions in populations of Culmorum were less marked by comparison with those in nonsterile field soil. The reduced fungitoxicity of injected NH3 in sterile soil was attributed largely to the lack of NO2– accumulation.