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# EC Fit

EC Fit can fit soil water and electrical conductivity (EC) model to measured data. Copy your data of (Volumetric water content, EC of bulk soil, EC of soil solution) in the textbox below and press "Calculate" button. Before you use your original data you can see how it works by selecting a sample data from the pulldown menu.

## License

This program is a joint research of NARO and Toyo University. The use of this program, i.e., running the calculation, is permitted for non-commercial use such as academic research. The use of this program is permitted only for those who agreed that NARO and Toyo University are not responsible for any damage caused by the use of this program. Please contact Yukiyoshi Iwata at NARO ( iwatayuk@affrc.go.jp ) for the permission of commercial use.

## Method of calculation

Method of estimating the Rhoades parameters in this program is published in the following paper. For least square optimization, Trust Region Reflective algorithm or Levenerg-Marquardt algorithm by scipy.optimize.least_squares of SciPy is used.

Seki, K., Miyamoto, T., and Iwata, Y. (2019). Estimation of electrical conductivity of a soil solution from the monitored TDR data and an extracted soil solution. *International Agrophysics*, 33(1), pp.113-119. https://doi.org/10.31545/intagr/104413 (PDF)

## How to use

Input (θ, EC_{a}, EC_{w}) data in the box, where

- θ is volumetric water content
- EC
_{a} is apparent electrical conductivity - EC
_{w} is soil solution electrical conductivity

(θ, EC_{a}) pair can be measured with TDR or FDR sensors. It will calculate optimized parameter set (a, b, EC_{s}) of Rhoades equation (Rhoades et al., 1976).
EC_{a} = EC_{w}θ(aθ+b)+EC_{s}

Once you get (a, b, EC_{s}) parameter set for a special soil condition, you can estimate EC_{w} from TDR or FDR data of (θ, EC_{a}) by the Rhoades equation.

## Format of input data

- As in the sample data, each line of numeric data represents a set of measured (θ, EC
_{a}, EC_{w}) in this order.
- For each line, parameters are separated with space, tab, or comma (,).
- When there are more than 3 numbers only the first 3 numbers are read.
- Lines not beginning with numbers are not regarded as measured data. Properties of the data can be written as "key = property".
- Some properties have special meaning. With "optimize = ecw", residual of EC
_{w} is minimized. Otherwise residual of EC_{a} minimized. "mineca" sets the minimum EC_{a} other than the input data. When "porosity" key is set, extended Rhoades model is also tried.

EC Fit version 1.0 created by Katsutoshi Seki running with Python 3.11.2 on Linux. See also SWRC Fit.