The Influenec of Azolla pinnata on Floodwater Chemistry, Grain Yield and Nitrogen Uptake of Rice in Dano, Southwestern Burkina Faso

Nitrogen fertilizer recovery by lowland rice can be as low as 10% and rarely exceeds 60%. Azolla contributes to the nitrogen (N) nutrition of rice plant through biological N fixation (BNF). This study aimed at assessing the influence of Azolla pinatta on floodwater chemistry, rice yield, total dry matter and N uptake of rice. The study was carried out at the Dreyer Research Station in South Western Burkina Faso in 2005 using a split urea application method called Experiment 1 (E1) which was compared with what the farmer’s practice (E2), which is basal application of NPK (16 16 16) and one top-dress of urea. Four levels of nitrogen was used in the experiments (0, 40, 80, 120 kg N ha-1). The full Azolla cover on the floodwater surface by the time of urea application prevented rapid increase in floodwater pH in the range of 0.52 to 0.68. The presence of Azolla lowered floodwater temperature by 1.9 to 2.0 oC. There was a significant increased (p < 0.01) in total dry matter yield of rice by 7.8% in E1 and 9.8% in E2 as a results of the presence of Azolla on floodwater surface. Similarly, Azolla significantly (p < 0.01) increased grain yields in both experiments. Apparent N-recovery of rice increased between 13.3 and 16.8% in grain and 39.1 and 42.6% in straw. There was however no significant interaction (p > 0.05) between Azolla and nitrogen. It is concluded that Azolla brought about an additive effect and could be an efficient fertilizer alternative or supplement in flooded rice cropping system in Dano.