Urease activity and urea hydrolysis in tropical flooded soil unplanted or planted to rice

Hydrolysis of urea associated with different component parts (surface and subsurface soil from unplanted and planted fields and standing water) of tropical flooded rice soil was investigated. Urea hydrolysis followed a first-order kinetics with surface soil having the highest urease activity followed by subsurface soil and flood water. Urea hydrolysis varied with the crop growth stage and was more pronounced at tillering and panicle stages under greenhouse conditions and at maturity stage under field conditions. A certain degree of cultivar variation on urease activity at both surface and subsurface soil was also noticed. Urea hydrolysis was considerably higher in soils from green manure amended field plots than that of control and urea amended plots. Results indicate that addition of green manure to a flooded soil, while increasing microbial activity, could also enhance urea hydrolysis.