| 词条 | Van Genuchten–Gupta model |
| 释义 |
The van Genuchten–Gupta model is an inverted S-curve applicable to crop yield and soil salinity relations.[1] EquationThe mathematical expression is: Y = Ym / [ 1 + {C / C50} P ] where Y = yield, Ym = maximum yield of the model, C = salt concentration of the soil, C50 = C value at 50% yield, P = an exponent to be found by optimization and maximizing the model's goodness of fit to the data. In the figure: Ym = 3.1, C50 = 12.4, P = 3.75 Alternative 1As an alternative, the logistic S-function can be used. The mathematical expression is: Y^ = 1 / { 1 + e (A.XC + B) } 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 (A.XC + B) } In the figure: Ym = 3.43, Yn = 0.47, A = 0.112, B = -3.16, C = 1.42. Alternative 2The third degree or cubic regression also offers a useful alternative. The equation reads: Y = A.X3 + B.X2 + C.X + D with Y =Yield, X = salt concentration of the soil, while A, B, C and D are constants to be determined by the regression. In the figure: A = 0.0017, B = 0.0604, C=0.3874, D = 2.3788. These values were calculated with Microsoft Excel The curvature is more pronounced than in the other models. See also
References1. ^M. Th. van Genuchten and S.K. Gupta, 1993. USDA-ARS, U.S. Salinity Laboratory 4500 Glenwood Drive, Riverside, California, USA, 92501. A reassessment of the Crop Tolerance Response Function. Journal of the Indian Society of Soil Science, Vol. 41, No. 4, pp 730–737. {{DEFAULTSORT:Van Genuchten Gupta model}} 3 : Soil science|Mathematical modeling|Crops |
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