Garden with Insight v1.0 Help: Plant Growth  Yield
Note: This section on yield is not used in Garden with Insight, since we use a different
biomass allocation system for fruits.
The economic yield of most grain, pulse, and tuber crops is a reproductive organ. Crops have a variety of
mechanisms which ensure that their production is neither too great to be supported by the vegetative
components nor too small to ensure survival of the species. As a result, harvest index (economic yield /
aboveground biomass) is often a relatively stable value across a range of environmental conditions. In
EPIC, crop yield is estimated by using the harvest index concept [Equation 267] where YLD is the amount
of the crop removed from the field in t/ha, HI is the harvest index, and B(AG) is the aboveground
biomass in t/ha for crop j.
very simple, in other code
Water stress constraint on crop yield
Crop yield may be reduced through waterstressinduced reductions in the harvest index. Most grain
crops are particularly sensitive to water stress from shortly before until shortly after anthesis, when major
yield components are determined (Doorenbos and Kassam, 1979). Optimum conditions for growth may
reduce harvest index slightly if dry matter accumulation is large and economic yield is limited by sink
size. The harvest index is affected by water stress according to the equation [Equation 313] where HIA* is
the final estimate of harvest index applied to aboveground biomass to estimate yield, HIA is the simulated
potential harvest index, HIA(o) is the minimum harvest index for the crop, and WUR is the simulated
water use ratio.
Equation 313
HIA* = (HIA  HIA(o)) * WUR / (WUR + exp(6.13  0.0883 * WUR)) + HIA(o)
Code:
same except for bound: if HIA < HIA(o) HIA* = HIA(o)
Variables:
HIA* = HarvestIndex_frn
HIA = unconstrainedHarvestIndex_frn
WUR = waterUseRatio
HIA(o) = minHarvestIndex_frn
The value of HIA is simulated daily using the equation [Equation 314]. The exponential parameters are
set to give HIA = 0.1 when HUI = 0.5 and HIA = 0.95 when HUI = 0.95. Thus, if the growing season is
shortened by frost or for other reasons, the potential harvest index HI is not attained.
Equation 314
HIA = HI * (100 * HUI / (100 * HUI + exp(11.1  0.1 * 100 * HUI))
Code:
same
Variables:
HIA = UnconstrainedHarvestIndex_frn
HI = potentialHarvestIndex_frn
HUI = heatUnitIndex
The water use ratio WUR is estimated at harvest using the equation [Equation 315] where U and E(p) are
the actual and potential plant water use rates in mm for day k and I is the number of days in the growing
season. The exponential parameters in equation 313 are set to give 0.5 * (HIAHIA(o)) when WUR = 0.10
and 0.90 * (HIAHIA(o)) when WUR = 0.50. Thus, if the actual to potential water use ratio is greater than
0.5 there is little reduction to harvest index.
Equation 315
WUR = 100 * (sum of U(i)) / (sum of E(P,i))
Code:
same
(note later changed to remove 100 multiplier)
Variables:
WUR = WaterUseRatioForHarvestIndex
sum of U(i) = cumWaterUse_mm
sum of E(P,i) = cumPotPlantEvap_mm
