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Impacts of climate change on soil nitrogen kinetics and rice production in Andisol paddy fields

ABSTRACT We constructed a new rice growth model, SIMRIWk, and discuss the impact of climate change on the growth and production of rice plants in relation to soil nitrogen (N) kinetics. We developed a model simulating N availability for rice plants associated with soil N kinetics and rice plant N uptake and combined it with the existing rice growth model SIMRIW to construct SIMRIWk. The model parameters were determined from rice plant growth and soil N experimental data obtained over 25 years under four soil management regimes. SIMRIWk successfully simulated the annual changes and upward trend observed during the 25 years in all treatments. The relationship between measured yields and SIMRIWk calculations in all treatments over the 25 years formed one aggregation defined by the regression equation y = 1.00x and showed a significant correlation (r2 = 0.894). According to SIMRIWk, increasing temperature in the cold season increases the formation of easily decomposable organic N produced under dry conditions and N mineralization during the next warm season, suggesting that rice growth is influenced by both warm-season and cold-season temperatures. We forecast rice yield and soil N kinetics from 2016 to 2100 using SIMRIWk and climate change predictions based on the IPCC’s climate change scenario RCP8.5. Atmospheric warming, a rise in CO2 partial pressure, and increased soil N mineralization caused by soil warming will increase rice plant growth, but the decreased radiation absorbed owing to the shortened growing season and high-temperature sterility will prevent any significant change in yield. Furthermore, the acceleration of soil organic N decomposition will decrease soil organic N concentrations. Understanding the influences of climate change on soil organic matter kinetics is absolutely critical for predicting the future soil production capacity.