Modeling the Effects of Water Temperature on Rice Growth and Yield under a Cool Climate: I. Model Development

Abstract

For paddy rice (Oryza sativa L.), water temperature (Tw) is a major determinant of growth and yield. In rice paddies, Tw is higher than the air temperature (Ta), and this difference significantly affects production, especially in cool climates. However, there is no model to evaluate the effects of Tw on rice yield. To simulate temporal and regional differences in rice productivity under such climates, we developed a simple mechanistic growth model that accounts for the effects of Tw based on the results of previous field trials. The rate of crop ontogenetic change was linearly related with Tw before the heading stage. Leaf area was expressed as a function of leaf emergence and tillering, and leaf senescence was expressed as function of ontogenetic change and spikelet fertility. Radiation use efficiency was less affected by Tw than by leaf area, and its change with respect to ontogenetic changes was expressed using nonlinear functions. Spikelet fertility, which strongly determines grain yield, was expressed as function of cumulative cooling degree‐days (below a threshold temperature), water depth, and the height of developing panicles. This model covered the major processes that are affected by Tw, and can be used for evaluating the role of Tw on rice growth and yield under a cool climate.