Growth and activity of N2
-fixing bacteria can be affected by N fertilizer application. A study was conducted at Universiti
Putra Malaysia, Malaysia, to determine the effect of urea-N on the growth and indoleacetic acid (IAA) production of
strain Sb16 (accession number, JQ820255), previously isolated from rice
( Oryza sativa
L.) growing soils of Malaysia. Five rates of N from urea fertilizer were applied (0, 50, 100, 150, and 200 kg
) to the flooded rice soil and incubated in the control environment for 6 wk. Results showed that the population growth
increased with increased N rates and highest population (8.2 log10
) recorded in soil-standing water at the second
week of incubation. The population decreased with the reduction of total N. Soil and soil water pH increased from 7.1 to
8.4 at the first week of incubation. Production of indoleacetic acid was significantly reduced with N fertilizer application.
The highest indoleacetic acid (2.6 mg mL-1
) was produced in the control treatment. Application of high rates of N fertilizer
increased the population of diazotrophic strain Sb16 but significantly reduced indoleacetic acid production.