Denitrification as a component of Nitrogen Budget in a Tropical Paddy Field

The direct assessment of denitrification suffers from a number of problems. A mass balance
model is simple and widely accepted to calculate nitrogen (N) loss as a denitrification
component. The objective of study was to estimate the potential N loss a denitrification from a
tropical paddy in the central region of Thailand. N inputs to and outputs from field were
measured by direct method. Inputs of N to the site were commercial fertilizer, precipitation,
irrigation water, seeds and pre-cultivation soils. Outputs of nitrogen from the site were leaching
to groundwater, harvested crops, loads in surface runoff, post harvest soils and loss from the
field as denitrification. Biological N fixation, groundwater contribution, ammonium volatilization
and contribution to weed growth were ignored. Based on the three month observation, the total
amount of N load in irrigation, precipitation, fertilizer, drainage, percolation and plant uptake
were 9.22, 10.85, 100, 4.65, 18.20 and 80.57 kg ha-1 respectively. The difference of total N in
the soil before and after cultivation was not significant and taken as constant value. Sum of N
loss calculated as denitrification component from the nitrogen mass balance model was 16.7 kg
ha-1 and rate of loss was 0.19 kg ha-1 d-1. It means that the contribution of applied N fertilizer to
the atmosphere was 13.6% of total N input; indicating one of the major source pollutants.