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Garden with Insight v1.0 Help: Plant Growth - Plant Size

Crop height

Crop height is estimated with the relationship [Equation 263] where CHT is the crop height in mm and HMX is the maximum height for crop j.

Equation 263

CHT = HMX * sqrt(HUF)
CHT = PlantHeight_m
HMX = maxHeight_m
HUF = heatUnitFactorForLAIAndHeight

Root biomass and depth

The fraction of total biomass partitioned to the root system normally decreases from 0.3 to 0.5 in the seedling to 0.05 to 0.20 at maturity (Jones, 1985). The model simulates this partitioning by decreasing the fraction linearly from emergence to maturity. Thus, the potential daily change in root weight is computed with the equation [Equation 264] where deltaRWT is the change in root weight in t/ha and ar(1) and ar(2) are crop parameters with typical values of ~0.4 and 0.2.

Equation 264

deltaRWT = deltaB(p) * (ar(1) - ar(2) * HUI)
deltaRWT = B * (ar(1) - ar(2) * HUI) - RWT
if deltaRWT < 0, deltaRWT = -0.01 * RWT
deltaRWT = ChangeInTotalRootWeight_tPha
deltaB(p) = potentialIncreaseInBiomass_tPha
B = newTotalPlantBiomass_tPha
RWT = totalRootWeight_tPha
ar(1) = fractionRootWtAtEmergence_frn
ar(2) = fractionRootWtAtMaturity_frn
HUI = heatUnitIndex

The potential change in root weight through the root zone is simulated as a function of plant water use in each layer of soil with the equation [Equation 265] where RW is the root weight in soil layer l in t/ha, M is the total number of soil layers, and u is the daily water use rate in layer l in mm/day.

Equation 265

deltaRW = deltaRTW * u / (sum with l from 1 to M of) u
if deltaRTW < 0, deltaRW = deltaRTW * RW / RWT
otherwise same
deltaRW = ChangeInRootWeightForLayer_tPha
deltaRWT = changeInTotalRootWeight_tPha
RW = rootWeightForLayer_tPha
RWT = totalRootWeight_tPha
u = plantWaterUseForLayer_mm
U = totalPlantWaterUse_mm
M = numLayers

Rooting depth normally increases rapidly from the seedling depth to a crop-specific maximum. In many crops, the maximum is usually attained well before physiological maturity (Borg and Grimes, 1986). Rooting depth is simulated as a function of heat units and potential root zone depth: [Equation 266] where RD is the root depth in m, RDMX is the maximum root depth in m for crop j in ideal soil, and RZ is the soil profile depth in m.

Equation 266

deltaRD = 2.5 * RDMX * deltaHUF, RD <= RZ
RD = 2.5 * RDMX * HUI
bounded by previous root depth, soil profile depth, max root depth, and crop height
RD = RootDepth_m
RDMX = maxRootDepth_m
HUF = heatUnitFactorForLAIAndHeight
HUF(i-1) = yesterdaysHeatUnitFactorForLAIAndHeight
RZ = soilProfileDepth_m

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Updated: May 4, 1998. Questions/comments on site to
Copyright © 1998 Paul D. Fernhout & Cynthia F. Kurtz.