A model for predicting the fate of nitrogen fertilizer in lowland ricefields

Abstract

SUMMARY A sensitivity analysis of the model is given for conditions in which there is no plant uptake of N and over the range of conditions likely in tropical lowland ricefields, and the mechanisms governing inorganic carbon, nitrogen and acidity dynamics in the floodwater and soil are discussed. Changes in the rate of CO2 production in the soil, floodwater algal activity and floodwater carbonic anhydrase activity altered diurnal changes in floodwater pH but little influenced the daily mean pH, and consequently little influenced cumulative N loss by NH, volatilization. Soil pH buffer power and rate of urea application also little influenced cumulative percentage N loss. Increases in soil ammonium buffer power, floodwater depth and downward water flux, and decreases in floodwater‐ and air‐turbulence, moderately decreased N loss. N loss greatly decreased with decrease in urea hydrolysis rate and with urea incorporation in the soil. Incorporation decreased N loss more in the absence of standing floodwater. With low urease activity, deep floodwater gave consistently lower N loss; with high urease activity, shallow floodwater gave lower N loss when urea was incorporated.

Modelling of ammonia volatilisation in fertilised and flooded rice systems

“…Currently, only two models Kirk, 1993a) are available to estimate the floodwater pH in a flooded rice system. The routine developed by was adopted in APSIM-Oryza by .…”

“…The model developed by Singh and Kirk (1993a) can also predict the diurnal fluctuations in floodwater pH. The sub-daily floodwater pH was calculated from the number of protons added or consumed when there was net change of HCO 3 -or NH 4 + , due to processes like urea hydrolysis, NH 3 and CO 2 volatilisation, CO 2 consumption by PAB, soil CO 2 production, and transfer of protons between soil and floodwater.…”

“…The 14 models are NFLOOD v.1 , NFLOOD v.2 , J-M's , S-K's (Singh and Kirk, 1993a), CERES-Rice ), ), Nakasone's (Nakasone et al, 2004), , DNDC-Rice (Li et al, 2004), K-K's (Kirk and Kronzucker, 2005), Liang's , RIWER , RICEWNB , and APSIM-Oryza . With substantial progress in modelling of N dynamics in flooded soil systems since previously published multi-model reviews, this overview provides breadth of knowledge on available models for simulating N dynamics in flooded soil systems, and, therefore, is valuable as a first step in the selection of an appropriate model for a specific application.…”

“…The sub-daily floodwater pH was calculated from the number of protons added or consumed when there was net change of HCO 3 -or NH 4 + , due to processes like urea hydrolysis, NH 3 and CO 2 volatilisation, CO 2 consumption by PAB, soil CO 2 production, and transfer of protons between soil and floodwater. The diurnal uptake or release of CO 2 by the PAB in the floodwater within 24 hours was approximated by a sine curve (Singh and Kirk, 1993a). …”

“…This hypothesis was conceptualised to simulate the hourly floodwater pH in CERES-Rice , and later adopted in APSIM-Oryza . PAB activity as one of the regulators of diurnal floodwater pH was also conceptualised by the Singh and Kirk (1993a) model as one of the regulators of diel fluctuations in floodwater pH.…”