Garden with Insight v1.0 Help: Differences between EPIC and Garden with Insight

The version of EPIC we translated for use in Garden with Insight was EPIC3090 from March 1993, the version available at the time we started translating it. EPIC has marched on and is no longer identical to the code translated for use in Garden with Insight. Also see our note on the translation of EPIC's FORTRAN code to Pascal.

We have also made substantial changes and additions to adapt the simulation to a home garden. These changes are as follows.

Multiple soil patches and plants

EPIC simulates one field with one crop of plants; Garden with Insight simulates a small garden with multiple soil patches and multiple plants of different species. Since EPIC uses relative measures of quantities, such as tons per hectare, the soil and plant quantities scale down reasonably. Also, some changes have been made in Garden with Insight to accomodate plant competition for nutrients and water within a soil patch. Algorithms from SPUR and ALMANAC were consulted for this work.

Flowering and fruiting

Since EPIC is used mainly for field-scale agricultural crops, crop yield is simulated without considering reproductive growth in detail. For Garden with Insight we needed a much more elaborate reproductive model to be able to draw and harvest flowers and fruits close up in the simulated garden. For the flowering and fruiting submodel of Garden with Insight we consulted several models, including CERES-Maize (Jones & Kiniry 1986) and SOYGRO (Jones et al. 1991), and the plant literature, especially the book Manipulation of Flowering (Atherton 1987). See the section on Garden with Insight's flowering and fruiting submodel for details.

Biomass partitioning

Following the above section on flowering and fruiting, Garden with Insight has a biomass partitioning submodel that is much more elaborate than EPIC's. Some of the thought for this model was derived from SPUR (Wight et al. 1987) and from the literature on plant structure and biomass partitioning (e.g., Sequiera et al. 1991).

Plant drawing algorithm

The plant drawing submodel of Garden with Insight is special to the program and is based on a reading of the literature for plant structure and growth. The plant drawing algorithm is closely linked to the biomass partitioning submodel. Each plant meristem (bud), internode (section of stem), leaf, inflorescence (bunch of flowers), and flower/fruit is simulated as a separate structure. (Flowers and fruits are combined because each flower becomes one fruit.) All of these components have competing growth needs that attempt to simulate the complex relationships between parts of a plant. When a plant is drawn on the screen, each of these plant parts is drawing itself using a 3D turtle graphics engine. More information about how the plant drawing algorithm works will be forthcoming in the next version.

Pests and Pesticides

We did not include the pest damage and pesticide degradation and transport component of EPIC in this version of Garden with Insight, although we have it working. (For a description, see the Pesticide fate section.) While we think the EPIC pesticide degradation model is probably accurate as far as it goes, it does not model the creation of secondary breakdown components or the effect of chemicals on living organisms in the soil. We were concerned that to include the EPIC pesticide model would give home gardeners an unrealistic picture of pesticide safety. We would prefer to put the entire pest/pesticide issue aside in this version rather than deal with it too simply in a teaching simulation such as this.

Other parts not used

The crop yield section of EPIC was not used in Garden with Insight, nor were the sections for animal grazing or economics (these are described in the Auto Operations section).