Abstract: To evaluate nitrogen leaching losses from paddy rice culture in Glenn-Colusa irrigation district, a water and nitrogen mass balance model was applied for a seasonal time scale from May through October.Sensitivity analysis evaluated the importance of the denitrification coefficient, harvested crop coefficient, mineralization rate constant for initial organic soil N (km 2) and mineralization rate constant for biological fixed N in soil(km 1)using observed data of residual inorganic soil N after harvest in the 0-1m depth and residual organic soil N after harvest in the 0-1m depth in the field of No.8 and simultaneously calibrated these model parameters. The calibrated model was then used to test fields No.4, No.8 and No.14 using the observed data of average N concentrations in soil solution at 1 m depth and average N concentrations in surface irrigation return flow for further model validation.The calculated results for nitrogen concentrations in soil solution at 1 m depth were 11.1 mg穕iter^-1 for field No.4, 9.99 mg穕iter^-1 for field No.8 and 13.55 mg穕iter^-1 for field No.14 which were in good agreement with measured results (8.7 mg穕iter^-1 for field No.4, 6.3 mg穕iter^-1 for field No.8 and 7 6 mg穕iter^-1 for field No.14). The computed results for nitrogen concentrations in surface irrigation return flow were 1.10 mg穕iter^-1 for field No.4, 1.30 mg穕iter^-1 for field No.8 and 1.11 mg穕iter^-1 for field No.14 which had errors with measured results in the percentage of 15% for field No.4,zero for field No.8 and 14% for field No.14.It was concluded that this water and nitrogen mass balance model for evaluating N leaching losses from croplands could be not only successfully applied on the dry land systems but also on the wetland systems.

Key words: inhalable particulate matter, fine particulate matter, composition, source, forest.