page_title: Van Genuchten–Gupta model
section_title: Alternative one
hierarchical_section_title: Van Genuchten–Gupta model / Alternative one
caption_attribution_description: English: Logistic S-curve model for the relation between crop yield and soil salinity
context_page_description: The van Genuchten–Gupta model is an inverted S-curve applicable to crop yield and soil salinity relations.
context_section_description: As an alternative, the logistic S-function can be used.
  The mathematical expression is:
  Y^ = 1 / { 1 + e }
  where:
  Y^ = (Y - Yn) / (Ym - Yn)
  with Y =Yield, Yn = minimum Y, Ym = maximum Y, X = 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.
  If the minimum Yn=0 then the expression can be simplified to:
  Y = Ym / { 1 + e }
  In the figure: Ym = 3.43, Yn = 0.47, A = 0.112, B = -3.16, C = 1.42.
caption: Logistic S-curve model for the relation between crop yield and soil salinity
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