In the depth of 0–20 cm in paddy soil (Fig. 5), NO 3 —N levels had a higher average of 2.66 mg kg1 compared to 2.37 mg kg1 for FI. For the FI treatment, nitrification of ammonium was suppressed by lack of oxygen, and denitrification, which could potentially produce in oxygenated depleted conditions, was possibly restricted by the high shortage of nitrate