Accumulated temperature - Accumulated temperature

It is a measure of the amount of heat required for the growth of plants, especially agricultural crops. It is expressed as the cumulative value of the average temperature for each day of growth. The unit is degree (C) days. However, days when the daily average temperature is such that plants cannot grow are not included in the cumulative value. In meteorology, it is called degree-days. The minimum daily average temperature at which plants can grow is called the reference temperature, and anything above that is called the effective temperature. For this reason, the cumulative temperature is also called the effective cumulative temperature. The reference temperature is a uniform 5°C for autumn-sown vegetables and wheat that grow at relatively low temperatures, 10°C for plants that grow in the summer in temperate zones, and 15°C for tropical plants that require high temperatures. The minimum cumulative temperature at which plants can grow normally is called the minimum cumulative temperature. Examples of minimum accumulated temperatures for major crops are 1000 (degree days, same below) for potatoes, 1600 for spring wheat, 2000 for sunflowers, 3000 for corn, 2500 for soybeans, and 2500 for rice.

[Hoshikawa Kiyochika]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

植物とくに農作物の生育に要する熱量を表す目安の一つ。生育日数の各日の平均気温の積算値で表す。単位は度（C）日である。ただし日平均気温が、植物が活動できない日は積算に加えない。なお、気象学上はデグリー・デーという。植物が活動できる日平均温度の最低値を基準温度といい、それ以上を有効温度という。このため積算温度を有効積算温度ともいう。基準温度は、秋播(ま)き野菜やムギ類のように比較的低温で育つものは一律に5℃、一般に温帯で夏季に生育するものは10℃、熱帯植物のように高温を必要とするものは15℃とする。植物が正常な生育ができる積算温度の最小値を最小積算温度という。主要な作物について最小積算温度を例示すると、ジャガイモ1000（度日、以下同）、春播きコムギ1600、ヒマワリ2000、トウモロコシ3000、ダイズ2500、イネ2500などである。

［星川清親］

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