[(R -- 1) Table of Important Equations, Relationships and Concepts used
in IWM]{.mark}

+-----------------------+---+---------------------+-----------------------+
| **Irrigation          |   | []{.mark}           | **LF = Leaching       |
| planning:**           |   |                     | Fraction. A LF =      |
|                       |   | **TDS (ppm) = ECiw  | 0.1794/Fc^3.0417^ is  |
|                       |   | (dS/m) x 640 (for   | used for High         |
|                       |   | ECiw between 0.1 &  | Frequency             |
|                       |   | 5.0 dS/m;           | Irrigations**         |
|                       |   | calculates Total    |                       |
|                       |   | Dissolved Solids).  | **NIR = Net           |
|                       |   | Used to assess salt | Irrigation            |
|                       |   | load in irrigation  | Requirement**         |
|                       |   | water.**            |                       |
|                       |   |                     | **ETc = Crop          |
|                       |   | # TDS (ppm)         | Evapotranspiration    |
|                       |   | = ECiw (dS/m) x 800 | (crop consumptive     |
|                       |   |                     | use)**                |
|                       |   | **(for ECiw \> 5.0  |                       |
|                       |   | dS/m; i.e.,         | **IWM = Irrigation    |
|                       |   | irrigation waters   | Water Mgmt.**         |
|                       |   | with high salt      |                       |
|                       |   | content).**         | **Ea = Irrigation     |
|                       |   |                     | Application           |
|                       |   |                     | Efficiency**          |
|                       |   |                     |                       |
|                       |   |                     | **Fg = Gross          |
|                       |   |                     | Irrigation            |
|                       |   |                     | Application**         |
|                       |   |                     |                       |
|                       |   |                     | **Q = DA/T: Where Q = |
|                       |   |                     | cubic feet per second |
|                       |   |                     | (cfs); D = inches     |
|                       |   |                     | applied; A = area in  |
|                       |   |                     | acres & T = time in   |
|                       |   |                     | hours**               |
|                       |   |                     |                       |
|                       |   |                     | **SAR = Sodium        |
|                       |   |                     | Absorption Ratio**    |
|                       |   |                     |                       |
|                       |   |                     | **TDS = Total         |
|                       |   |                     | Dissolved Solids (the |
|                       |   |                     | amount of solid       |
|                       |   |                     | minerals dissolved in |
|                       |   |                     | water)**              |
|                       |   |                     |                       |
|                       |   |                     | **ppm = parts per     |
|                       |   |                     | million**             |
|                       |   |                     |                       |
|                       |   |                     | **dS/m =              |
|                       |   |                     | decisiemens/meter     |
|                       |   |                     | (electrical           |
|                       |   |                     | conductivity)**       |
|                       |   |                     |                       |
|                       |   |                     | **D~b~ = Soil bulk    |
|                       |   |                     | density in grams per  |
|                       |   |                     | centimeter cubed      |
|                       |   |                     | (g/cm^3^)**           |
|                       |   |                     |                       |
|                       |   |                     | **CEC = Cation        |
|                       |   |                     | Exchange Capacity in  |
|                       |   |                     | milliequivalents per  |
|                       |   |                     | 100 grams**           |
|                       |   |                     |                       |
|                       |   |                     | **(meq/100 g) of      |
|                       |   |                     | soil, on a dry weight |
|                       |   |                     | basis**               |
|                       |   |                     |                       |
|                       |   |                     | **AWH = Available     |
|                       |   |                     | Water-Holding         |
|                       |   |                     | Capacity in inches of |
|                       |   |                     | available water per   |
|                       |   |                     | acre-foot of soil**   |
+-----------------------+---+---------------------+-----------------------+
| **Fc = ECe~(ct)~/ECiw |   |                     |                       |
| (calculates the ratio |   |                     |                       |
| of the soil salinity  |   |                     |                       |
| to irrigation water   |   |                     |                       |
| salinity). Is needed  |   |                     |                       |
| to calculate the      |   |                     |                       |
| Leaching Fraction     |   |                     |                       |
| (LF)).**              |   |                     |                       |
|                       |   |                     |                       |
| **LF =                |   |                     |                       |
| 0.3086/Fc^1.702^      |   |                     |                       |
| (calculates the LF    |   |                     |                       |
| for conventional      |   |                     |                       |
| irrigation). Accounts |   |                     |                       |
| for extra water       |   |                     |                       |
| needed for salt       |   |                     |                       |
| mgmt.**               |   |                     |                       |
|                       |   |                     |                       |
| **NIR = ETc/(1 -- LF) |   |                     |                       |
| (calculates the Net   |   |                     |                       |
| Irrigation            |   |                     |                       |
| Requirement (NIR)).   |   |                     |                       |
| Used to plan & design |   |                     |                       |
| irrigation systems &  |   |                     |                       |
| IWM Plan.**           |   |                     |                       |
|                       |   |                     |                       |
| **Ea = Irr.           |   |                     |                       |
| needed/Irr. applied   |   |                     |                       |
| (calculates the       |   |                     |                       |
| Irrigation            |   |                     |                       |
| Application           |   |                     |                       |
| Efficiency (Ea)).     |   |                     |                       |
| Used to evaluate      |   |                     |                       |
| irrigation system     |   |                     |                       |
| efficiency & IWM      |   |                     |                       |
| Plan.**               |   |                     |                       |
|                       |   |                     |                       |
| **Fg = NIR/Ea (to     |   |                     |                       |
| calculate Gross       |   |                     |                       |
| Irrigation            |   |                     |                       |
| Application needed    |   |                     |                       |
| (Fg)). Used in the    |   |                     |                       |
| planning & design of  |   |                     |                       |
| irrigation systems    |   |                     |                       |
| and IWM Plans.**      |   |                     |                       |
|                       |   |                     |                       |
| **Q = DA/T (to        |   |                     |                       |
| calculate the amount  |   |                     |                       |
| of flow (cfs) needed  |   |                     |                       |
| per border/field).    |   |                     |                       |
| Used in the planning  |   |                     |                       |
| and design of         |   |                     |                       |
| irrigation systems    |   |                     |                       |
| and evaluation of IWM |   |                     |                       |
| Plans.**              |   |                     |                       |
+-----------------------+---+---------------------+-----------------------+
|                       |   |                     |                       |
+-----------------------+---+---------------------+-----------------------+
|                       |   | **Soils:**          |                       |
+-----------------------+---+---------------------+-----------------------+
|                       |   | []{.mark}           |                       |
|                       |   |                     |                       |
|                       |   | **D~b~ = g/cm^3^    |                       |
|                       |   | (calculates the     |                       |
|                       |   | soil bulk density). |                       |
|                       |   | Used to assess soil |                       |
|                       |   | compaction,         |                       |
|                       |   | available water &   |                       |
|                       |   | soil porosity as    |                       |
|                       |   | they relate to soil |                       |
|                       |   | texture &           |                       |
|                       |   | structure.**        |                       |
|                       |   |                     |                       |
|                       |   | **CEC = meq/100 g   |                       |
|                       |   | (is based on % clay |                       |
|                       |   | & % OM). Is used as |                       |
|                       |   | an indicator of the |                       |
|                       |   | soils capacity to   |                       |
|                       |   | retain nutrients    |                       |
|                       |   | and its buffering   |                       |
|                       |   | capacity).**        |                       |
|                       |   |                     |                       |
|                       |   | **AWH               |                       |
|                       |   | (inches/foot): is   |                       |
|                       |   | based predominantly |                       |
|                       |   | on soil texture.    |                       |
|                       |   | Used in the         |                       |
|                       |   | development,        |                       |
|                       |   | implementation &    |                       |
|                       |   | monitoring of an    |                       |
|                       |   | IWM Plan.**         |                       |
+-----------------------+---+---------------------+-----------------------+
|                       |   | **Definitions:**    |                       |
+-----------------------+---+---------------------+-----------------------+
|                       |   | **Fc = Ratio of     |                       |
|                       |   | soil salinity to    |                       |
|                       |   | irrigation water    |                       |
|                       |   | salinity            |                       |
|                       |   | []{.mark}**         |                       |
|                       |   |                     |                       |
|                       |   | **ECe~(ct)~ =       |                       |
|                       |   | Electrical          |                       |
|                       |   | Conductivity of     |                       |
|                       |   | soil saturation     |                       |
|                       |   | extract (i.e., the  |                       |
|                       |   | Crop Threshold      |                       |
|                       |   | Salinity in dS/m)** |                       |
|                       |   |                     |                       |
|                       |   | **ECiw = Electrical |                       |
|                       |   | Conductivity of the |                       |
|                       |   | Irrigation Water    |                       |
|                       |   | (dS/m)**            |                       |
+-----------------------+---+---------------------+-----------------------+
| # Water Quality:      |   |                     |                       |
+-----------------------+---+---------------------+-----------------------+
| **SAR = Na/√ (Ca +    |   |                     |                       |
| Mg)/2 (calculates the |   |                     |                       |
| Sodium Absorption     |   |                     |                       |
| Ratio). Used to       |   |                     |                       |
| evaluate potential    |   |                     |                       |
| infiltration problems |   |                     |                       |
| (SAR & ECiw are used  |   |                     |                       |
| together in this      |   |                     |                       |
| evaluation).**        |   |                     |                       |
+-----------------------+---+---------------------+-----------------------+