THE INTERRELATIONSHIP BETWEEN MICROBIAL NUMBERS, APPLICATION RATE ANDBIODEGRADATION PRODUCTS OF 2 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 man ure (C.M.) and municipal refuse (M.R.) was determined using the data o btained during field incubation studies under centre-pivot sprinkler i rrigation in Central Saudi Arabia. Microbial numbers increased with in creasing 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, h ighly 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 optimu m rates of application of both manures. A laboratory study of the effe ct of temperature on NH3 evolution during the biodegradation of C.M. r evealed that at high rates of application the magnitude of the tempera ture coefficient (Q(10)) Of NH3 evolution is affected by the rate of a pplication irrespective of temperature. At application rates higher th an the optimum biodegradation was insensitive to temperature. The resu lts obtained confirm our previous findings that the optimum economic r ates of application of C.M. and M.R. occur between 8.25 to 16.5 and be tween 16.5 to 33.0 tonnes/ha, respectively.