New incubation device forin situ measurement of acetylene-reducing activity in ricefields

A device forin situ estimation of biological nitrogen fixation in shallow-water ricefields was developed using the acetylene-reducing assay. The device consists of a rigid transparent bottomless plastic bottle provided with an agitation system. Laboratory experiments using flooded pots inoculated withAnabaena UAM 202 indicated that agitation significantly reduced the time needed to detect the production of ethylene by eliminating the slow diffusion of acetylene and ethylene in water. A direct relationship between the abundance of cyanobacteria and the rate of acetylene reduction was observed in laboratory and field experiments. A negative correlation between the amount of combined nitrogen and the abundance of cyanobacteria was observed in the field.