The interrelationship between microbial numbers, application rate and biodegradation products of two organic manures in a sandy soil

The relationship between microbial numbers and rate of application and biodegradation products (mainly CO2 and NH3 evolution) of chicken manure (C.M.) and municipal refuse (M.R.) was determined using the data obtained during field incubation studies under centre-pivot sprinkler irrigation in Central Saudi Arabia. Microbial numbers increased with increasing rate of manure application and with incubation time. Maximum microbial proliferation coincided with the optimum (feasible) rates of application of both manures with respect to CO2 evolution previously reported by Abdel Magid et nl. (1993). In microbial growth rate terms the effect of the optimum rate of application was more pronounced with C.M. than with M.R. at the 16th week of incubation. After 16 weeks, highly significant correlations were obtained between microbial numbers and rates of treatment application, cumulative CO2 and cumulative NH3. The highest rates of CO2 and NH3 evolution coincided with the optimum rates of application of both manures. A laboratory study of the effect of temperature on NH3 evolution during the biodegradation of C.M. revealed that at high rates of application the magnitude of the temperature coefficient (Q(10)) Of NH3 evolution is affected by the rate of application irrespective of temperature. At application rates higher than the optimum biodegradation was insensitive to temperature. The results obtained confirm our previous findings that the optimum economic rates of application of C.M. and M.R. occur between 8.25 to 16.5 and between 16.5 to 33.0 tonnes/ha, respectively.