Garden with Insight v1.0 Help: Plant Growth  Winter Dormancy
The day length growth constraint is used to simulate a winter dormant period for fall planted crops. This
constraint is only imposed for areas that have a growing season of fewer than 12 months. A 12month
growing season is defined in the model as having no month with mean minimum temperature of lower
than 5 degrees C. If there is a dormant winter period, it is defined as the time when day length is within 1
hour of the location's minimum day length.
If a crop becomes dormant in winter, the heat unit summation is set to zero. This provides for rapid new
growth when temperatures increase in the spring. During the dormant period, the plants are not allowed
to grow. The standing live biomass is actually reduced during this period because of frost and short day
length. The day length reduction factor (for biomass) is estimated with the equation [Equation 316] where
FHR is the day length reduction factor, HRLT is the day length on day i in hours, and HRLT(mn) is the
minimum day length for the location.
Equation 316
FHR = 0.35 * (1.0  HRLT / (HRLT(mn) + 1))
Code:
FHR = 0.35 * (1.0  HRLT / (HRLT(mn) + timeOverMinDayLengthForWinterGrowth_hr))
Variables:
FHR = WinterBiomassDayLengthReductionFactor
HRLT = dayLength_hr
HRLT(mn) + timeOverMinDayLengthForWinterGrowth_hr = minDayLengthForWinterGrowth_hr
The frost reduction factor is estimated with the equation [Equation 319] where FRST is the frost damage
factor, T(mn) is the minimum temperature on day i in degrees C, and af(1) and af(2) are parameters
expressing the crop's frost sensitivity.
Equation 319
FRST = T(mn) / (T(mn)  exp(af(1) + af(2) * T(mn)), T(mn) < 1 degrees C
Code:
same except they use abs() instead of ve for the temperature
(works the same because temp is always ve when this is called)
Variables:
FRST = WinterBiomassFrostReductionFactor
T(mn, i) = minTempForDay_degC
T(mn, j) = dailyMeanMinTempForMonth_degC
af(1) = frostReductionFactorParams[0
af(2) = frostReductionFactorParams[1
The reduction in standing live biomass is estimated with the equation [Equation 320] where deltaB(AG) is
the reduction in above ground biomass in t/ha on day i, HUI is the heat unit index, and B(AG) is the
above ground biomass in t/ha on day i. Note that frost damage is greater when plants are small (HUI is
close to zero) and approaches zero as the plants near maturity.
Equation 320
deltaB(AG) = 0.5 * B(AG) * (1.0  HUI) * max(FHR, FRST)
Code:
deltaB = B * (1.0  min(1.0, HUI)) * max(FHR, FRST)
Variables:
deltaB = WinterReductionInBiomass
deltaB(AG) = WinterReductionInStandingLiveBiomass
B = totalBiomassInclRoot_tPha
B(AG) = standingLiveBiomass_tPha
HUI = heatUnitIndex
FHR = winterBiomassDayLengthReductionFactor
FRST = winterBiomassFrostReductionFactor
max(FHR, FRST) = winterBiomassFrostReductionFactor
There is also a provision for frost kill of annual plants. Kill occurs if [Equation 321] is true, where SNOF
is a snow cover factor calculated with the equation [Equation 322] where SNO is the water content of
snow cover in mm.
Equation 321
if (FRST * (1.0  SNOF) >= 0.9) plant dies
SNOF = SNO / (SNO + exp(2.303  0.22 * SNO))
Code:
same
Variables:
FRST = AnnualCropIsKilledByFrost
SNOF = snowCoverFactor
SNO = snowWaterContent_mm
FRST = winterBiomassFrostReductionFactor
