SEASONAL-VARIATION OF SOIL PROTEASE ACTIVITIES AND THEIR RELATION TO PROTEOLYTIC BACTERIA AND BACILLUS SPP IN PADDY FIELD SOIL

Hydrolytic activities toward benzyloxycarbonyl-L-phenylalanyl-L-leucin e (z-FLase) and caesin (caseinase) in soil were measured during rice c ultivation, before irrigation, before and after midsummer drainage, an d before and after the final drainage. The activities were maintained at a high level in three paddy fields, an organic-manure field (z-FLas e, 191-684 pKat g-1 dry wt soil; caseinase, 220-652 pKat g-1 dry wt so il), a chemical-fertilizer field (z-FLase, 368-472 pKat g-1 dry wt soi l; caseinase, 319-773 pKat g-1 dry wt soil) and a no-fertilizer field (z-FLase, 358-702 pKat g-1 dry wt soil; caseinase, 424-758 pKat g-1 dr y wt soil). The total numbers of bacteria did not correlate with soil protease activities. Numbers of proteolytic bacterial groups, counted on azocoll agar plates and with a MPN method, correlated well with the soil z-FLase activity (r = 0.625 to 0.767). Numbers of vegetative cel ls and total cells of Bacillus spp decreased after irrigation and cont inued to decrease until after the final drainage, with only a weak neg ative correlation between their number and soil water content (r = -0. 488 and -0.555). The ratio of spores-to-total cell numbers of Bacillus spp increased after irrigation and reached a maximum after 1-2 months , when 43-100% of Bacillus cells existed as spores. The number of spor es of Bacillus spp was weakly correlated with the soil caseinase activ ity (r = 0.459).