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

Phellinus noxius was not recovered from pieces of artificially infested woo d placed in or on soil amended with urea (NH4)(2)CO3 or aqueous ammonia. Hi gh concentrations of volatile NH3 were detected in these treatments, indica ting that NH3 generated from these chemicals was fungicidal to P. noxius. A high concentration of volatile NH3 was detected from nonautoclaved soil am ended with urea, but not from amended autoclaved soil, indicating that soil microorganisms were involved in NH3 generation. To kill P. noxius complete ly 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 o f 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 m icroorganisms. In contrast, 1 month after amendment of alkaline soil, the c oncentration 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 quantitie s of volatile NH3 were generated at temperatures ranging from 12 to 32 degr ees 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 fun gus 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 Ro sellinia necatrix) in addition to P. noxius.