Garden with Insight v1.0 Help: Plant params stress tolerance group
Growth optimal temperature: The best temperature for growth
of this plant.
TB  Optimal temperature for plant growth
TB [minimum temperture] and TG [optimal temperature] are very stable for cultivars with in a species.
They should not be changed once they are determined for a species. Varietal or maturity type differences
are accounted for by different sums of thermal units.
Growth minimum temperature: The lowest temperature at which this plant will
grow. This temperature is used as a base to calculate the number of heat
units expected in a typical growing season.
S Curve  effect of air temperature (below freezing) on
frost damage: Proportion of total plant biomass lost in one day (Y) as a result of the temperature
below zero degrees C (X). Note that the sign of the temperature is reversed because it moves down from
freezing as this graph goes up.
FRST1  First point on frost damage curve *
FRST2  Second point on frost damage curve
Two points on the frost damage curve. Numbers before decimal are the minimum temperatures (C) and
numbers after decimal are the fraction of biomass lost each day the sepcified minimum temperature
occurs. NOTE: 10.20 means 20 percent of the biomass is lost when a temperature of 10C is reached. The
negative sign on degrees is added by EPIC since no frost damage is assumed to occur above 0 degrees C.
These two parameters should be based on a combination of research results and observation. Precise data
for field application is subject to microclimate variation across the landscape. Current parameters are
reasonable estimates; However, they are more likely to understate frost damage than to overstate frost
damage.
Hours above minimum day length for year when
winter growth can occur: Number of hours longer than the minimum day length for the year required
for this plant to grow. Cultivarspecific growth reaction to decreased day length. For most plants a value
of 1.0 is reasonable; for wintergrowing plants reduce this value to zero.
Highest aluminum saturation plant can tolerate: The highest aluminum saturation (abundance of
aluminum cations) this plant can tolerate before its growth begins to be stunted.
Critical aeration factor:
The fraction of soil water over porosity (in the top meter of soil) at which poor soil aeration (waterlogging) begins to limit plant growth (by causing aeration stress). Ranges from 0.75 to 1.0, with 0.85 being a reasonable value for
most plants.
CAF  Critical aeration factor
Critical aeration factorfraction of soil porosity where poor aeration starts limiting plant growth. This is
set at 0.855 for most crops, with rice begin the major exception with a value of 1.0.
S Curve  effect of aeration stress on root growth restriction: The affect of the amount of soil
water saturation (X) on the aeration stress (Y) for aboveground plant growth. More precisely, X is the
soil water to pore space fraction in relation to the critical aeration fraction for this plant.
S curve shape: Aeration stress  root growth.
Aeration stress  root growth. The number to the left of the decimal % of storage volume between critical
aeration factor and saturation, and the number to the right of the decimal is % reduction in root growth
caused by aeration stress.
S Curve  effect of rock content on root growth restriction: Reduction
(worsening) in the soil strength constraint on root growth in each soil
layer (Y) based on the percent rocks (by weight) in the soil in that layer (X).
S curve shape: Root growth restriction by rock
Root growth restriction by rock. The number to the left of the
decimal is % rock, and the number to right of the decimal
is fraction reduction in root growth.
1 
 * SCRP1(n)

F 
 *SCRP2(n)
0 __________________________________

X Xu
The equation is: F=X/(X+EXP(SCRP1(n)  SCRP2(n) * X))
The parameter values represent the two points on the "S" curve and are
given in the form (X1 * F1) and (X2 * F2). These values are
identified in EPIC output as SCRP1I and SCRP2I. The model used the two
points to solve the equation simultaneously for the two paramter values
used in simulation they are identifed as SCRP1C and SCRP2C.
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