Green manures are widely used in rice production and may influence methane efflux (CH4). Influence of application of
Azolla (A. caroliniana Wild.), a widely used biofertilizer for rice (Oryza sativa L.), on CH4 efflux from a flooded alluvial
soil planted to rice, and select soil and plant variables were investigated in a field experiment at Cuttack, India. Azolla was
either incorporated as green manure at the beginning of the experiment or grown as dual crop in the standing water along
with the rice crop. Dual cropping of Azolla (equivalent to 30 kg Nha−1) in conjunction with urea (30 kg Nha−1) effected
lowest CH4 flux (89.29 kg CH4 ha−1). Cumulative CH4 flux followed the order of urea > Azolla (incorporated)Curea > Azolla
(incorporatedCdual crop) > no N control > ureaCAzolla (dual crop). Growing Azolla had a moderating effect on CH4 efflux
from flooded soil through an increase in the dissolved oxygen concentration at the soil–floodwater interface. Among the
different soil and plant variables studied, soil redox potential, dissolved oxygen concentration at the soil–floodwater interface
and a-naphthylamine oxidase activity of root base exhibited significant negative relationship with CH4 flux. In addition, Fe2C
and ninhydrin reactive nitrogen (NRN) contents of the flooded soil exhibited significant positive relationship with CH4 flux.
Results indicated that, dual cropping of Azolla in conjunction with urea considerably reduced CH4 efflux without affecting
the rice yields and can be used as a practical mitigation option for minimizing CH4 flux from flooded paddy. ©2000 Elsevier
Science B.V. All rights reserved.
Keywords: Methane efflux; Flooded soil; Azolla application; Rice plants; Grain yield