Garden with Insight v1.0 Help: Plant next day functions: if not dormant or too cold, calculate root growth constraints for layers
The root growth constraints are not calculated if the plant is dormant or
if the general temperature growth constraint is zero.
A root growth constraint is calculated for each soil layer and is used to
reduce root growth in each layer. Remember that all of the growth constraints range from zero (worst) to
one (best). The root growth constraint is the smallest (worst) of three constraints on root growth:
temperature, aluminum toxicity, and soil strength. We will discuss each of these below. But first, if the soil temperature in any soil layer is below freezing, the combined root
growth constraint is set at zero (worst) and the particular constraints are not calculated.
The temperature constraint on root growth is different from the general temperature constraint in that 1)
the temperature of each soil layer is used instead of air temperature, 2) the lower bound on root growth is
at freezing, not at the plant's minimum growth temperature, and 3) only low temperatures, not high
temperatures, reduce root growth. The temperature constraint is calculated from a sine curve with a value
of zero at freezing and a value of one (best) at the plant's optimal
temperature for growth. One could wonder why high temperatures are not considered as hampering root
growth. Probably this is because the soil usually buffers air temperature
well enough that temperatures below the soil surface never get hot enough to limit root growth.
Large numbers of aluminum ions in the soil (Al3+) are toxic to many plants and cause them to have
stunted growth. The aluminum toxicity constraint on root growth is calculated from a simple ratio of the aluminum saturation of the soil layer to the plant's tolerance for
aluminum saturation (a parameter).
The soil strength constraint on root growth reduces root growth based on how hard it is for the roots to
penetrate the soil. Soil strength is the ability of the soil to hold weight without deforming or collapsing.
When engineers build roads and buildings they find areas where the soil strength is greater so that the
roads and buildings will be well supported. However, for plant growth the requirements are reversed, so
soil strength can be used as an indicator of how difficult it is for plant roots to penetrate the soil. The soil
strength constraint depends on bulk density (higher bulk density =
more soil strength), soil texture (coarser texture = more soil strength), and soil water content (wetter =
more soil strength).
calculation of dormancy, the general
temperature growth constraint, soil temperature