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

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 NH 4 + ‐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 NH 4 + ‐N/100 g per 3 hours. Urease activity of soil was determined by distillation of NH 4 + , radioactivity of 14 CO 2 , and respirometry of CO 2 . In determining urease activity, the quantity of NH 4 + ‐N produced by hydrolysis of added urea was correlated ( r = 0.84) with released 14 CO 2 , but was twice as large. The results from respirometry of CO 2 agreed with that from distillation of NH 4 + ‐N. The numbers of microbes and urease activity were correlated for fresh soil with coefficients ( r ) ranging from 0.62 to 0.77. Extractable NH 4 + ‐N was about 40 times larger in affected than in normal soil, although NO 3 ‐ ‐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.