EFFECTS OF INHIBITORS OF MICROBIAL ACTIVITY ON UREA HYDROLYSIS AND NITRIFICATION IN A SOILLESS POTTING MEDIUM

George C. Elliott
The objective of this research was to determine the effect of fungicides, and other treatments which might be expected to inhibit microbial activity, on urea hydrolysis and nitrification in soilless potting media. Effects of gamma irradiation, autoclaving and toluene were examined. Fifteen cm-3 samples of medium were scooped into 50 ml tubes, treated, and urea (2.5 mol m-3) and ammonium (0.5 mol m-3) were added. The potting medium used was composed of sphagnum moss peat, vermiculite and perlite, and had been cropped. Samples were incubated for up to 7 days, and soluble nitrogen compounds were extracted with 1.0 M KCl. Autoclaving completely inhibited urea hydrolysis and nitrite accumulation. Gamma irradiation and toluene had no effect on urea hydrolysis. Toluene inhibited nitrite accumulation about 80%. In a separate experiment, fungicides were applied to samples 12 hr prior to addition of urea and ammonium and incubation as above. Fungicide treatments slightly delayed urea hydrolysis between day 1 and day 3. Accumulation of nitrite was inhibited by propamocarb and ethazol but stimulated by benomyl. In a third experiment, fungicides were applied to fresh medium in which Iris siberica crowns had been potted. Samples were obtained during cropping up to 9 weeks after fungicide application. Nitrification and urea hydrolytic activity were determined in short-term assays. Effects of fungicides on urea hydrolysis were inconsistent and generally not significant. Nitrification was inhibited by fungicides containing ethazol, up to 4 weeks after application. Fungicides applied to soilless potting media can have effects on nitrogen transformations which might be important for plant nitrogen nutrition. Urea hydrolysis in soilless potting media apparently involves the activity of both living microbes and cell-free urease. Nitrification may involve both chemoautotrophic and heterotrophic microbes.
Elliott, George C. (1989). EFFECTS OF INHIBITORS OF MICROBIAL ACTIVITY ON UREA HYDROLYSIS AND NITRIFICATION IN A SOILLESS POTTING MEDIUM. Acta Hortic. 238, 173-180
DOI: 10.17660/ActaHortic.1989.238.20
https://doi.org/10.17660/ActaHortic.1989.238.20

Acta Horticulturae