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Modeling Flowering Time of Rice Plants under Natural Photoperiod and Constant Air Temperature

Dep. of Farmland Utilization, Natl. Agric. Res. Ctr., Tsukuba Ibaraki 305, Japan
Div. of Agrometeorology, Natl. Inst. of Agro-Environmental Sciences, Tsukuba Ibaraki 305, Japan

^* Corresponding author.

Rice (Oryza sativa L.) plants respond to variations in photoperiod. The prediction of flowering time of photoperiod-sensitive rice plants is important for crop management. The objective of this study was to analyze the photoperiod sensitivity of rice plants under natural photoperiod and constant air temperature, and to derive a simple model to predict flowering time under these conditions. Rice cultivars were sown at 2-wk intervals during I yr in a greenhouse maintained at a constant air temperature. The number of days required from emergence to flowering was constant for rice plants sown between August and February, while those sown between March and July required more time. On the basis of these results, the authors derived an equation describing the cumulative water temperature over the time required for flowering as a function of photoperiod [f(P)] and sowing date. The form of f(P) was calculated using nonparametric methods. The value of f(P) was almost zero when the photoperiod was shorter than the critical photoperiod (Po); when the photoperiod was longer, however, the value of f(P) increased proportionally. The function was simplified to represent the effective photoperiod. The equations of this model were able to analyze quantitatively the photoperiod sensitivity of rice plants, and the observed flowering time was accurately estimated.

Received for publication August 31, 1993.