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Garden with Insight v1.0 Help: Plant next day functions: calculate height and root depth

Both plant height and root depth are simulated simply and driven by the heat unit index.

Plant height follows the same S curve that drives leaf area index (LAI) before it reaches its point of decline from senescence. Height doesn't decline like leaf area index does; the plant attempts to reach its maximum height (a parameter) by the end of the growing season.

We have added a few height parameters to the simulation that are not yet in use. The "supported" and "unsupported" heights are for when we use the stake tool in the future to simulate staking plants up (and for the effect that has on their growth and form). As of this version, however, we are not simulating staking. In fact, plant height in the model has no relation whatever to the size of the drawn plants on the screen. The model uses plant height for a few calculations, mainly wind erosion, but it is not very important.

Root depth is very important to the model because it determines from what soil layers the plants can draw their water and nutrients. Root depth is simulated with a linear function based on the observation that most plants achieve their mature root depth "well before physiological maturity". So the equation for root growth is simply the heat unit index times the maximum root depth times 2.5, meaning that the maximum root depth is achieved at a heat unit index of about 1/2.5 or 0.4. Root depth is not affected by any growth constraints. If root growth is constrained, the roots will be thinner but just as long. Root depth, however, can never exceed the maximum, or the depth of the soil profile. Also, the roots must always be at least as deep as the plant is tall.

Root system diameter is also simulated, but we added that at the last minute and it is not used by any other part of the model. We would like to use it in the future to draw the plant's roots in the browser.

calculation of heat unit index
EPIC Plant Size
Model contents

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Updated: March 10, 1999. Questions/comments on site to
Copyright © 1998, 1999 Paul D. Fernhout & Cynthia F. Kurtz.