Azolla (Azalla filiculoides) compost improves grain yield of rice (Oryza sativa L.) under different irrigation regimes

The effect of azolla (Azolla filict doides) compost application on the mitigation of the effect of water deficit stress on rice (Oryza sativa L.; cv. Hashemi) growth and yield was studied for two growing seasons. Azolla compost was applied in the soil at the rates: 0% (control), 2.5%, 5.0%, and 7.5% of soil weight (w/w) and the effect on rice growth and grain yield was studied under i) continuous flooding (CF), ii) intermittent irrigation and withdrawal at flowering until soil moisture reached field capacity (IWF-100FC), and iii) intermittent irrigation and withdrawal at flowering until soil moisture reached 80% of the field capacity (IWF-80FC). The application of azolla compost at 2.5, 5.0 or 7.5% of soil weight (w/w) resulted in a higher tiller number by 16.0, 37.8, and 38.9%, respectively, in the first year and by 18.5, 27.8, and 30.2%, respectively, in the second year, compared with the non-amended control. Moreover, the application of azolla compost at 2.5, 5.0 or 7.5% of soil weight (w/w) resulted in higher spike weight by an average (over irrigation regimes) of 8.6, 20.8, and 21.1%, respectively, in the first year and 34.7, 50.4, and 52.5%, respectively, in the second year, compared with the non-amended control. The application of azolla compost at 5.0% of soil weight provided the highest grain yield, which was on average 13.8% higher than that of the non-amended control. The increase of grain yield might be due to efficient absorption of nitrogen and possibly of other nutrients with azolla, which promoted production and translocation of assimilates from source to sink. Overall, azolla compost can be regarded as a desirable managerial practice in rice production, particularly under water deficit conditions. Considering the agronomic benefits and water saving, azolla compost could contribute to the development of low-input cropping systems for rice production.