Garden with Insight v1.0 Help: Tool action functions: apply amendment

The bag holds soil amendments to modify the soil. It is not in the original EPIC model and was added by us. The bag can hold all the quantities that a soil layer can hold, plus all the mulch quantities, plus lime and sulfur.

Addition of soil amendments using the bag goes through these steps:

1. If the bag has any mulch contents (flat residue, fresh organic N and P) in it, these are added to the mulch layer on the soil patch. This is to simulate specifically adding mulch to the soil to insulate its temperature, hold in moisture, and keep down weeds (though we don't simulate weeds here).
2. If the bag has any organic matter in it, the organic matter is added to the top soil layer. The bulk density in the soil layer is adjusted for the addition of organic matter (more organic matter generally reduces bulk density). The settled bulk density is also adjusted because even when the soil is completely settled the bulk density is lower with more organic matter.
3. If the bag has any nutrient substances they are added to the top soil layer. This includes flat residue, nitrate, ammonia, fresh organic N, active and stable organic N in humus (organic matter), labile P, fresh organic P, organic P in humus, and active and stable mineral P.
4. If the bag has any sand, silt, clay and rocks, these are added. These quantities are expressed as percentages in the soil layers (sand + silt + clay = 100, rocks is a separate percent by weight) and in the bag. So both the bag and soil percentages are converted to absolute amounts (by multiplying by soil layer or bag weight), then the absolute amounts are added, then the percentages for the soil layer are recalculated.
5. If there is any water in the bag it is added to the top soil layer. In order to get the bag's water into the right terms for the soil patch (millimeters of water), we need the "thickness" of the bag. This we get by using a constant bulk density for the bag of 1.33.
6. The weight of the bag contents is added to the top soil layer. Since all of the substances in the bag are expressed in relative terms as percentages by weight, the weight is assumed to include all the contents. All the percentages in the bag should add up to one hundred (at this point the program will not check this for you).
7. If the bag has any lime or lime equivalent it is added to the first soil layer only (so that the pH is changed in the first soil layer only). Later if the soil is mixed the pH in the first soil layer will affect the pH in the lower soil layers. "Equivalent" lime means an amount of another form of lime with the same pH-changing action as this amount of pure lime (calcium carbonate). Note that this liming function was derived from the EPIC auto liming function and has not been well tested.
8. If the bag has any sulfur or sulfur equivalent it is added to the first soil layer only as with lime. The function for lowering pH using sulfur was derived from the lime equation and is only a first approximation. It has not been tested.

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