Prospects of using Azotobacter, Azospirillum and cyanobacteria as supplements of urea nitrogen for rice production in Bangladesh

摘要

The responses to inoculation with (ⅰ) Azotobacter and Azospirillum of boro rice under five levels of nitrogen (N) fertiliser (0,60, 80,100 and 120 kg N/ha from urea) and (ⅱ) blue-green algae (BGA) of transplanted aman rice under four levels of N fertiliser (0, 20, 30 and 40 kg N/ha from urea) were examined in two field experiments in Bangladesh. Maximum grain yield (8.43 t/ha) was recorded with Azospirillum at 100 kg N/ha, 1.34 t/ha higher than the yield obtained with 120 kg N/ha applied alone, suggesting the benefit of reducing N application by 20 kg/ha with extra yield. Similarly, Azotobacter showed the potential to save 20 kg N/ha with additional yield of 1.24 t/ha. Mixed cultures (Azospirillum + Azotobacter) were statistically similar to individual cultures at all the N rates, showing that single species inoculation suffices to increase grain yield and suggesting a common mechanism of the effect. In the case of aman rice, grain yield increased significantly from N fertilisation at 20 kg N/ha without inoculation, but increasing N rates above this rate only gave a nonsignificant trend in increasing grain yield. With inoculation treatments, grain yield responses to added N were significant up to 40 kg N/ha, indicating that BGA increases the rice plants' capacity to use more fertiliser-N for grain production. The grain yield obtained by the local isolates at 30 kg N/ha were higher than the yield obtained at 40 kg N/ha without inoculation, indicating the prospect of reducing urea by 25%, although the yields were lower than those obtained at 40 kg N/ha with these inoculants.