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 / above-ground 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 above-ground biomass in t/ha for crop j.
very simple, in other code

Water stress constraint on crop yield

Crop yield may be reduced through water-stress-induced 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 above-ground 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 * (HIA-HIA(o)) when WUR = 0.10 and 0.90 * (HIA-HIA(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