Fluctuation patterns of microbial numbers in soil applied with compost

Abstract

Abstract Plate- and direct-counts of bacteria as well as hyphal length were determined in fields applied annually for 10 years with definite amounts of artificial compost made from rice straw. The succession of microbial groups was observed after application of the compost. The direct-count of bacteria increased immediately and reached its highest level just after the compost application in October. The plate-counts of bacteria on conventional media such as albumen and nutrient broth agars fluctuated in a similar manner to the direct-count. However, the plate-counts of bacteria on 10- or 100-fold diluted albumen or nutrient broth agar fluctuated in a different manner: they began to increase from April and attained a maximum level in June. The hyphal length reached maximum in March. These microbial successions are assessed in relation to the decomposition process of the compost in the soil and the importance of oligotrophs, which can grow only under poor nutrient conditions, is noted.