Study of utilization of azolla in paddy fields in Beijing [China].

The paddy yield and effect of soil on Azolla imbricata (Fongshan) and Azolla filiculoides were studied under Beijing ecological conditions in 1983-84. The trials were carried out at three transplanting patterns, (1) wide-narrow row (46.7 + 13.3) x 10 cm, (2) wide row (30 x 20 cm), and (3) traditional pattern (20 x 15 cm), and at three levels of N application, 0, 45, and 90 kg/ha. The optimum amounts and application methods were selected. Biomass and paddy yield showed significant differences among treatments. Incorporating 45 t azolla fresh wt/ha increased paddy yield by 35% in the first crop, equivalent to that obtained from 90 kg N/ha applied as ammonium sulfate. An additional yield increase of 5-10% was realized from the second crop. A. imbricata gave the higher yield increase. The highest yield was obtained from the wide row transplanting pattern. The effect of azolla on rice growth and development may be divided into three stages: (1) transplanting to tillering (15 d). The greening and tillering of seedlings were slightly inhibited due to absence of nutrients and presence of toxic materials where only azolla was applied basally; (2) beginning normal seedling growth (7-10 d), (3) beneficial effect of azolla gradually appears: azolla incorporated into the soil decomposed and mineralized rapidly. Seedlings developed dark green leaves and grew much more vigorously than seedlings in plots that received no azolla. Rice growth was promoted during stages 2 and 3. Plants in plots fertilized with mineral N were yellowish and grew slowly. Azolla promoted rice growth mainly in the mid and late stages during young panicle development. The effects of azolla were seen in the increased number of panicles, greater panicle size, and increased number of grains. Higher yields of rice and azolla were achieved with wide row transplanting azolla combined with N fertilizer gave the highest yields. The best way to utilize azolla in rice fields is with a mixed culture of A. filiculoides and A. imbricata supplemented with 67.5 kg N/ha, and wide row spacing.