Thesis (M.Sc.)--Chulalongkorn University, 2009

Phospholipid fatty acid (PLFA) patterns and cellulase activities of microbial communities in rice field soils were investigated after chemical fertilizer grade 16-20-0 at 25 kgrai-1 as the recommended dose by Department of Agriculture was amended. The fertilizer amended (FA) soils were tested against the rice soils without chemical fertilizer amendment (control; C) for 50 days of the experiment and the samples were collected on Day 0, 1, 3, 7, 14, 21, 28, 35, 42, and 49. PLFA data showed that saturated fatty acids, especially 16:0 and 18:0, and i15:0 and a15:0 which are signature PLFA of Gram-positive bacteria, were predominant throughout the experiment period in both C and FA treatment sets. Principle component analysis (PCA) data showed that there was also no significant difference between the total PLFA patterns of C and FA sets. The study of cellulase activity indicated that the cellulase activities of FA set were similar to C set and there was also no significant difference, and the highest cellulase activities were occurred on Day 21 in both FA and C sets (170.21±19.21 and 194.46±12.44 g GEg-1dm24h-1, respectively). The soil microbial community activity was also measured by the determination of carbon dioxide (CO2) evolution from soil respiration over a 50 day-period. The results showed that the CO2 evolution trend in FA set was higher than that of C set and the 50-day of CO2 accumulation of FA set was higher than C set (3,339.79 and 2,663.84 g CO2g-1 dm, respectively). The soil physico-chemical properties were analyzed on Day 0, 18, and 49 of the experiment. The results showed that soil pH was the only parameter in this study that was affected by chemical fertilizer amendment which decreased significantly at the 95% of confidence level. The decreasing trend of soil pH was correlated to the detected CO2 amount which declined through the experiment period.