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Garden with Insight v1.0 Help: Plant Flowering and Fruiting Submodel

Note: This was originally written as a design document, so there may be some small discrepancies between the processes described here and the actual model in Garden with Insight. The main gist of the submodel is in agreement, though.

This section describes the Garden with Insight flowering and fruiting submodel. The model of plant life-stage development follows these stages:

period              description                         switch to next period                                             
pre-emergence       before germination                  germination                                                       
vegetative period   no sensitivity to inductive forces  HUI = 0.2                                                         
                    (photoperiod and temperature)                                                                            
floral induction    sensitivity to inductive forces     accum. photothermal units = critical value                   
                    (photoperiod and temperature)                                                                            
floral initiation   creation of flower buds             accum. thermal units = critical value                        
                                                        (allocation to reproductive sink starts)
Vegetative Phase

During the vegetative phase, no photoinduction is possible. The duration of the vegetative phase is in terms of the heat unit index (HUI) for the cultivar. This will be a parameter but without any knowledge of this it will be set at 0.2 initially for all plants. For biennial plants, this parameter will be applied only in the second year, after the heat units have been reset to zero in the winter.

Floral Induction

Once the HUI reaches the end of the vegetative phase, photoinduction is calculated as follows. Most of this is from SOYGRO (Jones et al. 1991).

On each day, R(t), the rate of development towards flowering, is calculated thus:

R(t) = F(T) x F(N)

where F(T) is a temperature function and F(N) is a night-length function. The temperature function F(T) is exactly EPIC's temperature stress function with this form:

Relationship between temperature and floral induction

Usually there will be no information on what are the base, optimal and max temperatures for flowering, but we will have these as parameters anyway, for special cases when we do know them. Normally we will just copy the overall temperatures for the plant.

The night length function F(N) can have three forms:

a. For a day-neutral plant, F(N) = 1.0 always.
b. For a short-day plant (which is a long-night plant), the function looks like this:

Relationship between night length and floral induction

This can be done in the same way as other EPIC s curves, with parameters for x and y of two points on the curve (the x's will be the night lengths and the y's will be between 0 and 1).

c. For a long-day plant (which is a short-night plant), the function looks is similar only the slope is reversed. Defaults for these parameters will be: minimum floral induction units per day: 0.1; optimum night length for floral induction: 12.0; critical night length for floral induction: for short-day (long-night plants) 5.0, for long-day (short-night) plants minimum night length. These defaults are all from the SOYGRO model.

You can see that both F(T) and F(N) range between 0 and 1, so multiplying them will also give a number between 0 and 1. Each day R(t) will be summed, and when the sum equals R, the photothermal units required for flowering, floral induction will be complete. The photothermal units required for floral induction parameter will originally be set at 7.0 which is an average of the R values used in SOYGRO (6.85).

This could also be done with the S curve function in EPIC.


For biennial plants that require vernalization (onions, lettuce, cabbage, etc), a thermal time scheme is used to accumulate vernalization units. The same function as for floral induction and temperature stress is used, with minimum, optimum and maximum temperatures for vernalization as parameters. Vernalization units are accumulated over each day the mean temperature falls within the range of correct temperatures. When the plant reaches the end of its vegetative period in the biennial plant's second year, its accumulated vernalization units will affect its flowering.

1. If the cultivar requires vernalization for flowering (is obligate) and the vernalization units accumulated are less than the units required, it will not flower. It will not even attempt to accumulate photothermal units.

2. If the cultivar is quantitative in its response to vernalization, the photothermal units required for flowering will be affected by vernalization units according to this equation:

photothermalUnitsRequiredForFloralInduction *= vernalizationUnitsRequired / vernalizationUnitsAccumulated

So a partial vernalization will make the plant flower later or possibly not at all, but it will not switch off flowering completely if the vernalization was near completion.

Parameters for this will be: vernalizationIsRequired (default: not required); vernalizationObligateOrQuantitative (default: quantitative); min temp for vernalization (default: 0.0); optimal temp for vernalization (default: 2.5); max temp for vernalization (default: 5.0); and vernalization thermal units required (default: 45). Most defaults here are from Manipulation of Flowering (Atherton 1987). Looks like information on this can be found for most crop families.

Floral Initiation

After floral induction is complete, a period of floral initiation will occur when the plant will be creating reproductive buds. The duration of this period will be in terms of thermal days, which are calculated by the same function as is used for the thermal portion of floral induction. This will be a parameter which will be initially set for all plants at 13 thermal days, based on the average value in SOYGRO of 12.86 days. Supposedly some species are also sensitive to photoperiod in this phase, but it's better to ignore that for now. Shorter-lived species will probably want to use a smaller number of days for this parameter. It would also be possible to use HUI for this, in that an increase of 0.1 of HUI would be sufficient, but HUI does not penalize high temperatures, which can ruin floral initiation.

For more information on Garden with Insight extensions to the EPIC model, see the section on the plant biomass partitioning model.

This software product, including its online help system and all printed documentation, is
Copyright (c) 1997 Paul D. Fernhout and Cynthia F. Kurtz All Rights Reserved.
Garden with Insight is a trademark of Paul D. Fernhout and Cynthia F. Kurtz.

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