Relationships between Fungal Biomass and Nitrous Oxide Emission in Upland Rice Soils under No Tillage and Cover Cropping Systems

The relationships between soil microbial properties and nitrous oxide emission were examined in upland Soil under different tillage systems [no tillage (NT), rotary and plow tillage] and cover crop systems (fallow, cereal rye, and hairy vetch) in 2004 and 2005. Microbiological analyses included the determination of soil ergosterol as all indicator of fungal biomass, bacterial plate counting, and MPN estimations of ammonia oxidizers and denitrifiers. The combined practice of NT with rye-cover crop treatment increased fungal biomass but not bacterial populations in 0-10 cm deep soils. Such increase in fungal biomass was not found in 10-20 cm and 20-30 cm deep cover-cropped NT soil. The combined practice of NT with rye-cover cropping resulted in higher in situ N2O emission rates compared with rotary- and plow-till treatments. N2O flux was positively correlated with soil ergosterol content but not with denitrifier MPN and other soil chemical properties. These results suggested a significant contribution of fungi to N2O emission in cover-cropped NT soils.