Garden with Insight v1.0 Help: Plant next day functions: calculate general growth constraint
The general growth constraints are: temperature, aeration, water, nitrogen, and phosphorus. The temperature and aeration
growth constraints were calculated earlier in the nextday routine because they were needed by other
functions. The remaining constraints are calculated here.
The water stress growth constraint (or water stress factor) is simply the
ratio of actual plant water use today to the potential plant transpiration, which was the first estimate of plant water uptake. The ratio is limited to the range from zero to one.
The nitrogen and phosphorus growth constraints are derived from a common S curve that describes the effect of N or P deficit on new growth. The X
value for the S curve is the ratio of the amount of N or P in the plant to the amount of N or P that would
be in the plant if it had the optimal concentration of N or P for this
point in the growing season. (Remember that the optimal concentrations of N and P change over the
growing season using a S curve based on heat unit index.)
The combined general growth constraint is the smallest (worst) of the five general growth constraints.
Using the worst of two or more growth factors is called "Leibig's law of the minimum" after
Justus von Leibig who observed in 1862 that the worst factor affecting growth tends to limit growth
regardless of the other factors. This approach is also called the "barrel stave concept" because if
the staves of a barrel (the vertical boards) are all of different heights, only the height of the lowest stave
determines whether water runs out. And for yet another metaphor, "a chain is only as strong as its
weakest link."
calculation of general temperature growth constraint, aeration growth constraint
EPIC Constraints
Model contents
