Prediction of Paddy Rice Development in Northern Japan by Models without Consideration of Water Temperature

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  • 水温を考慮しないモデルによる北日本の水稲発育予測について
  • スイオン オ コウリョ シナイ モデル ニ ヨル キタニホン ノ スイトウ ハツイク ヨソク ニ ツイテ

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Abstract

Water temperature (Tw) is known to have an effect on the developmental rate (DVR) of paddy rice. However, Tw is not employed as input data in most developmental models. Moreover, DVR is often modeled as a function of air temperature (Ta) alone for northern Japan. The purpose of this study is to determine the reason why accurate prediction using models without consideration of Tw is possible and to determine whether the models are valid even for cool years.<br>The results of the first experiment showed that soil temperature (Ts) affects DVR (Ts at a depth of 1 cm was measured instead of Tw in this study). In the second experiment, pot containers with equally raised rice seedlings were buried in nine paddy fields in the three prefectures of Aomori, Iwate and Miyagi. Rice growth, Ta and Ts in all of the fields were monitored. The following results were obtained.<br>(1) A correlation exists between Ta and Ts.<br>(2) Parameters for the five developmental models were determined. Accuracy of the simple EAAT-model, in which only air temperature is employed, is as good as that of other models. This is because the correlation between Ta and Ts is incorporated in the EAAT-model and Ts is implicitly estimated from Ta.<br>(3) The correlations between Ta and Ts in cool years with short periods of sunshine and in other years are not the same. This difference caused larger error in prediction in cool years such as 1993.<br>In conclusion, the EAAT-model can be used for northern Japan for years with normal weather conditions but not cool years with short periods of sunshine. Some method for adjusting the prediction by an existing model should be developed.

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