The harvest index (HI) describes the ratio of harvested storage organ to total above ground biomass. For most crops it is <=0.5, but can also be 0.6 for hybrid maize varieties.
The current calibration of agricultural production intensity uses a combined calibration of LAImax (plant performance, density), alphaA (homogeneity of the stand) and harvest index (high-yielding varieties in intensely managed stands only).

HI is a crop-specific parameter and subject to intensity calibration.