Plants need a certain amount of heat and a low temperature index to start growth and complete a certain stage of growth and development. In Europe and America, temperate deciduous fruit trees generally take 5℃ as the starting temperature of development, that is, biological zero; The biological zero degree of subtropical evergreen fruit trees is 1 10℃, and that of some tropical fruit trees is 15 ~ 20℃. According to years of observation, Zhu Kezhen proposed that the biological zero of flowering of deciduous fruit trees in northern China should be 3℃.
Accumulated temperature is usually divided into two calculation standards: active accumulated temperature and effective accumulated temperature. The calculation formula of active accumulated temperature is:
Where k is the active accumulated temperature, n is the calendar days, 209 173 is the daily average temperature during the development period, and b is the biological zero. The value of 209 173≥B is calculated from the second day of development and accumulated to the end of development. The calculation of active accumulated temperature is convenient, which can not only reflect the relationship between the development process of fruit trees and temperature conditions, but also represent the heat resources in a certain area. However, this calculation method does not deduct the initial temperature value from the daily average, so the results obtained in different years and places are often quite different. For example, the three-day average temperature is 13℃, which is the same as the two-day average accumulated temperature 19.5℃.
Therefore, the effective accumulated temperature (Ae) of fruit trees is often used in agriculture, and its formula is:
N is the development duration (days), which is also calculated from the second day after entering the development period. Because the biological zero degree of development has been excluded from the daily average, it more accurately reflects the requirements for heat. The effective accumulated temperature of fruit trees in a certain development period changes little and stably in different places and years.
The effective accumulated temperature has two purposes. ① As one of the biological characteristics of fruit tree species or varieties, it can be used as a reference for introduction. For example, late-maturing apple varieties need about 2000 ~ 3000℃ from flowering to maturity; Citrus needs 4000 ~ 4500℃; Coconut needs more than 5000℃. ② As a prediction of phenology. For example, the effective accumulated temperature of various main fruit trees from germination to initial flowering period is 90.5℃ for Prunus armeniaca, 65,438+045.5℃ for Prunus armeniaca and 284.3 3.3℃ for Apple, which has certain significance for artificial pollination and frost prevention at flowering period. For another example, the accumulated temperature of Red Star apple from full flowering stage to mature stage is about 17 16.5 17℃, which can predict the relationship between perennial climate and quality and fruit drop in local mature stage. In addition, the daily accumulated temperature (degrees and hours) can be used to study the relationship between fertilization, maturity, nutrient accumulation and consumption of fruit trees and daily temperature changes.
The change of accumulated temperature index is not only due to the difference of tree species, varieties and their development stages in the annual cycle, but also because of the daily difference of a certain accumulated temperature period in different years and regions. Therefore, the cumulative temperature index is neither a constant nor a stable linear relationship with the development speed. In addition, agricultural technical measures, such as pruning and applying growth regulators, also affect the demand for accumulated temperature.
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