Van Genuchten–Gupta model

The Van Genuchten–Gupta model is an inverted S-curve applicable to crop yield and soil salinity relations.

[1] It is named after Martinus Theodore van Genuchten and Satyandra K. Gupta's work from the 1990s.

The mathematical expression is: where: with Y being the yield, Yn the minimum Y, Ym the maximum Y, X the salt concentration of the soil, while A, B and C are constants to be determined by optimization and maximizing the model's goodness of fit to the data.

The equation reads: with Y the yield, X the salt concentration of the soil, while A, B, C and D are constants to be determined by the regression.

These values were calculated with Microsoft Excel The curvature is more pronounced than in the other models.