Organic Residues and Their Effect on Selected General of Autotrophic and Heterotrophic Soil Bacteria

Abstract

The population of total soil bacteria increased in response to added organic amendments. Results obtained reflect the impact of C:N ratio of the residue on the degree of its influence. An/hun- dred-fold increase in total soil bacteria after one week of observed incubation in samples received wheat-straw or dry- manure. Alfalfameal amended samples showed a mush higher values and reached ten thousands-fold after two weeks of incubation. The heterotrophic, non-symbiotic ni- trogen-fixing bacterium of the genus Azotobacter responded effeciently to wheat-straw. An increase in their num bers by ten-thousands-fold was observed throughtout the incubation period. No response was detected with alfalfa-meal or dry-manure except after four days of incubation where the numbers increased by a hundred-fold, afterwhich a draw- back to the original values was seen. This could be due to the inhibition ac- tion of mineralized nitrogen (ammonium + nitrite + nitrate) which reached val- ues in excess of 200ppm in alfalfa-meal amended samples and by the antagones- tic effect of protein-decomposing bacte- ria that proliferate successfully in sam- ples recieved drymanure. The autotrophic nitrifiers (Nitrosomonas, Nitrobacter), behaved just-like the total soil bacteria in re- sponse to all organic amendments. The numbers increaed by ten-fold in wheat- straw or drymanure amended samples and reached a hundred-fold in al-falfa- meal treatment.