The effect of Azolla on nitrogen balance in paddy field

The effect of Azolla on N balance in paddy field was studied by 15N tracer technique. Using 15N labelled Azolla as basal dressing, 27.8% and 5.38% of 15N were utilized by early and late rice respectively, while 36.10% of 15N were remained in the soil. Azolla dressed were reduced 15N loss by 9.1% as comparing with an equal of N from urea. 12% of total N of Azolla was excreted through its root system. In addition, inoculation with Azolla could inhibit the growth of blue-green algae in the field and decrease the pH value, amount of NH4+-N in water of paddy field, ammonia volatilization and denitrification caused by the algae. Inoculation with Azolla in paddy field increased 4.25% of recovery from urea-15N as basal dressing and 8.35% and 25.11% 15N recovery from urea-15N as top dressing, compared with the treatments without Azolla inoculation. These results suggested that inoculation with Azolla into rice field may be not only beneficial to rice production but favorable to N balance in the field