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Soil Urease: Paucity in the Presence of the Fairy Ring Fungus Marasmius oreades (Bolt.) Fr.¹

ABSTRACT

Turf infection by Marasmius oreades (Bolt.) Fr. produced concentric rings of affected soil or fairy ring phenomena. Urease activity of soil invaded by the fungus ranged from 0.86 to 15.4 mg NH₄⁺-N/100 g per 3 hours, or about 10 to 40% that in unaffected soil. Normal soil from outside the fairy rings had activity ranging from 8.9 to 36.2 mg NH₄⁺-N/100 g per 3 hours. Urease activity of soil was determined by distillation of NH₄⁺, radioactivity of ¹⁴CO₂, and respirometry of CO₂. In determining urease activity, the quantity of NH₄⁺-N produced by hydrolysis of added urea was correlated (r = 0.84) with released ¹⁴CO₂, but was twice as large. The results from respirometry of CO₂ agreed with that from distillation of NH₄⁺-N. The numbers of microbes and urease activity were correlated for fresh soil with coefficients (r) ranging from 0.62 to 0.77. Extractable NH₄⁺-N was about 40 times larger in affected than in normal soil, although NO₃^--N was unchanged. Soil pH was reduced about one unit. Urease activity was restored in affected soil by three successive incubations. The decrease in soil urease caused by the fungus likely was concomitant with humus destruction.

¹ Contribution from the Western Region, Agr. Res. Ser., USDA, in cooperation with Colorado State Univ. Exp. Sta., Ft. Collins, Colo., Scientific Jour. Ser. Paper no. 1841.

² Soil Scientist and Research Technician, respectively, USDA, P. O. Box E, Ft. Collins, Colorado 80521. Third author is presently employed as a Seed Plant Manager by Great Western Sugar Co., Longmont, Colorado.

Received for publication May 5, 1973. Accepted for publication August 3, 1973.