The Physiological Basis for Heat Unit Models

J.R. Mauney


 
ABSTRACT

The cotton plant must grow vegetatively to produce the fruiting sites on which the crop is borne. Since vegetative growth is highly dependent on temperature, the development and productive potential of the crop can be effectively monitored by summations of heat units. In general, the rate of development of all plant organs takes about one-third the time at 30 C as it does at 18 C.

There are a few sources of inaccuracies in using heat-unit summations to reflect crop status. They come from effects on growth which are not purely temperature dependent. Some that we recognize are:

1) Effects of physical impedance on emergence. 2) Delays in square initiation due to heat. 3) Growth retardation by water, nutrient or disease stresses.

An additional problem in using heat-unit models is that insect feeding may not be related to the same heat-unit equation as plant growth.

When heat-unit models are used to predict rate of flowering at some future time great care must be used in choosing the baseline upon which the rate of increase is calculated. If the baseline observations are unduly low due to delays caused by stresses such as disease or insect feeding, then the increases in rate of growth or flower production predicted by a heat-unit multiplier will also be unrealistically low.



Reprinted from 1985 Proceedings: Beltwide Cotton Production Research Conferences pg. 366
©National Cotton Council, Memphis TN

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Document last modified Sunday, Dec 6 1998