Abstract

Pollution caused by animal wastes has become a great problem in many countries. The objective of this study was to test the effects of water potential on survival of fecal coliforms in a soil treated with 3 manures. A semiarid soil was treated with raw cow and poultry manures (CM and PM) and sewage sludge (SS) at a rate of 20 g kg^-1 (dry weight basis). Three water potentials established for soil incubation were: Saturation (SAT, 0 bars), field capacity (FC, -0.3 bars), and permanent wilting point (PWP, -15 bars). Fourth irrigation treatment was drying-rewetting cycle (DWC) between -0.3 to -15 bars. Colony forming units of Escherichia coli and fecal coliforms on EMBA (eosin methylene blue agar) were counted during soil incubation. The population of E. coli was higher in the soils treated with CM but the populations of lactose positive and negative coliforms were higher in the soils treated with PM. The populations of E. coli and other fecal coliforms were significantly higher in the soils incubated in SAT compared to those in soils incubated in other water potentials especially in the early stages of soil incubation. The populations of fecal coliforms were decreased significantly with increasing time of incubation. Survival ofE. coli were near 40 days in the soils treated with PM and SS. E. coli could survive in the soils treated with CM and incubated in SAT and PWP for more than 90 days may be due to low level of negative interactions in these unsuitable water conditions.

Key words: Organic wastes, soil water potential, Escherichia coli, fecal coliforms, survival, incubation.