Published online by Cambridge University Press: 03 October 2008
The effects of phosphorus fertilizer and the insecticide carbofuran on the growth and N2-fixation of Azolla pinnata and on the growth, grain yield and nitrogen uptake of intercropped rice were examined in a wet and a dry season. Treatment with phosphorus or carbofuran increased the biomass of Azolla and the amount of nitrogen fixed (nitrogen yield) in both seasons, but the response was much better in the dry season. Azolla inoculation at 1.0 t ha−1 resulted in a greater bio mass and nitrogen yield than inoculation at 0.5 t ha−1. In the dry season, a combination of phosphorus and carbofuran enhanced the growth and N2-fixation of Azolla more than either treatment alone. Carbofuran treatment slowed the rate of decomposition of Azolla, particularly in the dry season. The plant height, leaf area index and dry matter production of rice at flowering time were increased in the plots treated with phosphorus or carbofuran in the wet season and these treatments increased rice grain yield and nitrogen uptake in both the wet and dry seasons.