Improving the Accuracy of the Nitrogen Removal Equation for Paddy Fields and Wetlands with Special Focus on Temperature Factors

Abstract

The nitrogen (N) removal equation for paddy fields can be used to estimate the N removal rate based on input N concentration and temperature. The objective of the present study was to focus on various temperature factors affecting the accuracy of the equation in estimating the N removal rate. The survey site was a wet paddy field in the Kanto region of Japan. It was always flooded and under non-vegetation, non-penetration conditions. The survey was carried out for about 2 years starting in January 2015. We looked at water temperature, soil temperature (at 10 cm beneath the surface) and the average integrated hourly temperature in terms of how they affect the estimation of N removal rates. The average integrated hourly temperature was determined by AMeDAS. The relationship between the calculated values and measured values were evaluated using the R² value. It was found that the N removal rate correlated more strongly with the soil temperature at 10 cm beneath the surface and the average integrated hourly temperature than with water temperature. We introduced a temperature factor “D” to correct the removal rate. It was found that the most accurate estimation of the N removal rate was obtained when the average integrated hourly temperature was used along with a temperature correction coefficient D = 1.3.