urea at 60 kg Nitrogen ha−1 (8.15 mg methane m−2 h−1) > Azolla (incorporated) +urea at 30 kg Nitrogen ha−1 (7.80 mg methane m−2 h−1) > no Nitrogen control (5.80 mg methane m−2 h−1) > Azolla (incorporated+ dual crop) (5.40 mg methane m−2 h−1) > Azolla (dual crop) +urea at 30 kg Nitrogen ha−1 (4.61 mg methane m−2 h−1).