Generation of volatile ammonia from urea fungicidal to Phellinus noxius in infested wood in soil under controlled conditions

Abstract

Phellinus noxius was not recovered from pieces of artificially infested wood placed in or on soil amended with urea (NH4)2CO3 or aqueous ammonia. High concentrations of volatile NH3 were detected in these treatments, indicating that NH3 generated from these chemicals was fungicidal to P. noxius. A high concentration of volatile NH3 was detected from nonautoclaved soil amended with urea, but not from amended autoclaved soil, indicating that soil microorganisms were involved in NH3 generation. To kill P. noxius completely required 3000 p.p.m, urea in soil. Volatile NH3 was generated from urea in alkaline soil, but not in acidic soil. In acidic soil 1 month after urea amendment, populations of both fungi and bacteria, and the concentration of NH4+ (but not of NH3 in the air), were significantly greater than in the no urea treatment and in the urea treatment 3 d after amendment, indicating that NH4+, generated from urea in the soil enhanced the activity of soil microorganisms. In contrast, 1 month after amendment of alkaline soil, the concentration of NH4+ in the soil and NH3 in the air increased significantly and the populations of both fungi and bacteria decreased, indicating that NH3 in the air inhibited activity of soil microorganisms. Similar quantities of volatile NH3 were generated at temperatures ranging from 12 to 32°C. A large quantity of NH3 was generated at low soil matric potentials (-0.75 to -0.15 MPa) while high potentials (>-0.025 MPa) and flooded soil hindered production of volatile NH3. Ammonia was more effective at killing P. noxius growing in smaller pieces of wood than in larger pieces. The fungus was not recovered from wood pieces less than 3 cm in diameter. Volatile NH3 was also lethal to six other root rotting fungi (Ganoderma australe, G. lucidum, G. tropicum, Rigidoporus vinctus, Heterobasidion annosum, and Rosellinia necatrix) in addition to P. noxius.