Modeling of water and nitrogen balance in the ponded water of rice fields

A water and nitrogen balance model for the surface ponded water compartment of rice fields was developed. The model estimates the daily ponded water depth and the daily losses and the uses of NH4-N and NO3-N in their transformation processes. The model was applied with data obtained from two rice fields during 2005 at Thessaloniki plain in northern Greece. Significant amounts of applied irrigation water were lost with the surface runoff and deep percolation to groundwater. The gaseous losses of nitrogen (volatilization and denitrification) and nitrogen uptake by algae were the main processes of nitrogen reduction in the ponded water of rice fields. The study showed that the system of a rice field is a natural system where an important amount of influent nitrogen applied by irrigation water can be reduced. These processes decrease the possibilities of water resources contamination.