**[(IWM -- 8) Gross Crop Irrigation Water Requirement GUIDE]{.mark}**

+---+-------------------+---+-------+-----------+---+-----------------+
| * |                   | * | **Ex  |           | * | **NM IWM        |
| * |                   | * | ample |           | * | Manual**        |
| S |                   | E | Cal   |           | R |                 |
| t |                   | n | culat |           | e | **References &  |
| e |                   | t | ion** |           | s | Notes:**        |
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+---+-------------------+---+-------+-----------+---+-----------------+
| > | **Fc =            |   | **Fc  |           | * | -   **Crop Salt |
|   | ECe(ct)/ECiw**    |   | =     |           | * |     Tolerance   |
| * |                   |   | 2.    |           | 2 |     Table for   |
| * | **Fc = Ratio of   |   | 0/1.0 |           | . |     NM**        |
| S | the Crop          |   | =**   |           | 0 |                 |
| T | Threshold         |   |       |           | * | -               |
| E | Salinity          |   | ##    |           | * |    **Irrigation |
| P | (ECe~(ct)~ ) to   |   |       |           |   |     Water       |
| > | the Electrical    |   | ## A  |           |   |     Quality     |
|   | Conductivity of   |   | lfalf |           |   |     Sampling**  |
| 1 | irrigation water  |   | a ECe |           |   |                 |
| * | (ECiw). Units:    |   | (ct)  |           |   |                 |
| * | dS/m**            |   | = 2.0 |           |   |                 |
|   |                   |   |  dS/m |           |   |                 |
|   |                   |   |       |           |   |                 |
|   |                   |   | *     |           |   |                 |
|   |                   |   | *ECiw |           |   |                 |
|   |                   |   | = 1.0 |           |   |                 |
|   |                   |   | d     |           |   |                 |
|   |                   |   | S/m** |           |   |                 |
+---+-------------------+---+-------+-----------+---+-----------------+
| > | **LF =            |   | **LF  |           | * | -   **Salinity  |
|   | 0                 |   | =**   |           | * |     Assessment  |
| * | .3086/Fc^1.702^** |   |       |           | 0 |     GUIDE for   |
| * |                   |   | **LF  |           | . |     Selected    |
| S | **LF = Leaching   |   | =     |           | 0 |     Crops**     |
| T | Fraction (for     |   | 0.30  |           | 9 |                 |
| E | conventional      |   | 86/2. |           | 5 |                 |
| P | irrigation; e.g.  |   | 0^1.7 |           | * |                 |
| > | surface           |   | 02^** |           | * |                 |
|   | irrigation).**    |   |       |           |   |                 |
| 2 |                   |   | **LF  |           |   |                 |
| * |                   |   | =     |           |   |                 |
| * |                   |   | 0.30  |           |   |                 |
|   |                   |   | 86/3. |           |   |                 |
|   |                   |   | 254** |           |   |                 |
+---+-------------------+---+-------+-----------+---+-----------------+
| > | **NIR = ETc/(1 -- |   | **NIR |           | * | -   **NM Crop   |
|   | LF)**             |   | =**   |           | * |     Consumptive |
| * |                   |   |       |           | 4 |     Use         |
| * | **NIR = Net       |   | **NIR |           | 4 |                 |
| S | Irrigation        |   | =     |           | . |    Requirements |
| T | Requirement       |   | 40.   |           | 2 |     (NRCS FOTG  |
| E | (in.)**           |   | 01/(1 |           | 1 |     -- Section  |
| P |                   |   | --    |           | " |     1:          |
| > | **ETc = Crop      |   | 0.0   |           | * |     Irrigation  |
|   | E                 |   | 95)** |           | * |     Guide for   |
| 3 | vapotranspiration |   |       |           |   |     NM)**       |
| * | (in.)**           |   | ## NI |           |   |                 |
| * |                   |   | R = 4 |           |   |                 |
|   |                   |   | 0.01/ |           |   |                 |
|   |                   |   | 0.905 |           |   |                 |
|   |                   |   |       |           |   |                 |
|   |                   |   | ## E  |           |   |                 |
|   |                   |   | Tc =  |           |   |                 |
|   |                   |   | 40.01 |           |   |                 |
|   |                   |   |  inch |           |   |                 |
|   |                   |   | es fo |           |   |                 |
|   |                   |   | r Alf |           |   |                 |
|   |                   |   | alfa  |           |   |                 |
+---+-------------------+---+-------+-----------+---+-----------------+
| > | **Ea = Irrigation |   | **Ea  |           | * | -               |
|   | needed (in.) ÷**  |   | =**   |           | * |    **Irrigation |
| * |                   |   |       |           | 0 |     Water Req.  |
| * | **Irrigation      |   | **Ea  |           | . |     Guide (e.g. |
| S | applied (in.)**   |   | =     |           | 8 |     3' root     |
| T |                   |   | 2.06/ |           | 2 |     zone & Silt |
| E | **Ea = Irrigation |   | 2.5** |           | 4 |     Loam soil @ |
| P | Application       |   |       |           | * |     10% LF =    |
| > | Efficiency**      |   | **    |           | * |     2.06"       |
|   |                   |   | 2.06" |           |   |     needed)**   |
| 4 |                   |   | (Irr. |           | * |                 |
| * |                   |   | need  |           | * | -   **QT = DA   |
| * |                   |   | ed)** |           | ( |                 |
|   |                   |   | **÷   |           | 8 |    Calculations |
|   |                   |   | 2.5"  |           | 2 |     for         |
|   |                   |   | (Irr. |           | . |     Assessing   |
|   |                   |   | appli |           | 4 |     IWM         |
|   |                   |   | ed)** |           | % |                 |
|   |                   |   |       |           | ) |  Requirements** |
|   |                   |   | [Irr. |           | * |                 |
|   |                   |   | a     |           | * |                 |
|   |                   |   | pplie |           |   |                 |
|   |                   |   | d:]{. |           |   |                 |
|   |                   |   | under |           |   |                 |
|   |                   |   | line} |           |   |                 |
|   |                   |   | 7.5   |           |   |                 |
|   |                   |   | (cfs) |           |   |                 |
|   |                   |   | x 2.0 |           |   |                 |
|   |                   |   | (     |           |   |                 |
|   |                   |   | hrs.) |           |   |                 |
|   |                   |   | ÷     |           |   |                 |
|   |                   |   |       |           |   |                 |
|   |                   |   | 6.0   |           |   |                 |
|   |                   |   | (a    |           |   |                 |
|   |                   |   | cres) |           |   |                 |
|   |                   |   | =     |           |   |                 |
|   |                   |   | 2.5"  |           |   |                 |
|   |                   |   | app   |           |   |                 |
|   |                   |   | lied. |           |   |                 |
+---+-------------------+---+-------+-----------+---+-----------------+
| > | **Fg = NIR/Ea**   |   | **Fg  |           | * | -   **The       |
|   |                   |   | =**   |           | * |     calculation |
| * | **Fg = Gross      |   |       |           | 5 |     of Fg is    |
| * | Irrigation        |   | **Fg  |           | 3 |     used in the |
| S | Application       |   | =     |           | . |     Planning &  |
| T | needed**          |   | 44.   |           | 7 |     Design of   |
| E |                   |   | 21/0. |           | " |     Irrigation  |
| P |                   |   | 824** |           | * |     Systems and |
| > |                   |   |       |           | * |     the         |
|   |                   |   |       |           |   |     development |
| 5 |                   |   |       |           |   |     of IWM      |
| * |                   |   |       |           |   |     Plans**     |
| * |                   |   |       |           |   |                 |
+---+-------------------+---+-------+-----------+---+-----------------+
| > | **(# Irr. /yr.) x |   | **13  |           | * | -   **Amount of |
|   | (in.              |   | I     |           | * |     Irr. Water  |
| * | applied/Irr.) =** |   | rriga |           | 3 |     applied can |
| * |                   |   | tions |           | 2 |     differ      |
| S | **Total in.       |   | x     |           | . |                 |
| T | applied/ac./yr.** |   | avg.  |           | 5 |   substantially |
| E |                   |   | of    |           | " |     from the    |
| P | **(Note: in.      |   | 2.5"  |           | * |     planned     |
| > | applied/Irr. is   |   | /Irr. |           | * |     Gross       |
|   | based on an       |   | =**   |           |   |     Irrigation  |
| 6 | avg.)**           |   |       |           |   |     application |
| * |                   |   | **(   |           |   |     needed**    |
| * |                   |   | e.g., |           |   |                 |
|   |                   |   | Irri  |           |   |                 |
|   |                   |   | gated |           |   |                 |
|   |                   |   | field |           |   |                 |
|   |                   |   | app   |           |   |                 |
|   |                   |   | roxim |           |   |                 |
|   |                   |   | ately |           |   |                 |
|   |                   |   | ev    |           |   |                 |
|   |                   |   | ery** |           |   |                 |
|   |                   |   |       |           |   |                 |
|   |                   |   | **    |           |   |                 |
|   |                   |   | 2-wks |           |   |                 |
|   |                   |   | on a  |           |   |                 |
|   |                   |   | fixed |           |   |                 |
|   |                   |   | sch   |           |   |                 |
|   |                   |   | edule |           |   |                 |
|   |                   |   | (Apr. |           |   |                 |
|   |                   |   | --    |           |   |                 |
|   |                   |   | Oc    |           |   |                 |
|   |                   |   | t.)** |           |   |                 |
+---+-------------------+---+-------+-----------+---+-----------------+
| > | **Fg -- (Total    |   | **    |           | * | -   **In this   |
|   | in.               |   | 53.7" |           | * |     example, it |
| * | applied/ac./yr.)  |   | (Fg)  |           | 2 |     is clear    |
| * | =**               |   | --    |           | 1 |     that        |
| S |                   |   | 32.5" |           | . |     consumptive |
| T | **(Note: evaluate |   | (     |           | 2 |     use is not  |
| E | reason(s) for the |   | Total |           | " |     being       |
| P | difference        |   | in.   |           | * |     met.**      |
| > | between Fg &      |   | a     |           | * |                 |
|   | Total in.         |   | pplie |           |   |                 |
| 7 | a                 |   | d/ac. |           |   |                 |
| * | pplied/ac./yr.)** |   | /yr.) |           |   |                 |
| * |                   |   | =**   |           |   |                 |
+---+-------------------+---+-------+-----------+---+-----------------+
| * |                   |   |       | **The LF  |   |                 |
| * |                   |   |       | equation  |   |                 |
| E |                   |   |       | used for  |   |                 |
| C |                   |   |       | High      |   |                 |
| e |                   |   |       | Frequency |   |                 |
| ( |                   |   |       | I         |   |                 |
| c |                   |   |       | rrigation |   |                 |
| t |                   |   |       | is:**     |   |                 |
| ) |                   |   |       |           |   |                 |
| i |                   |   |       | **LF =    |   |                 |
| s |                   |   |       | 0.1794/F  |   |                 |
| t |                   |   |       | c^3.0417^ |   |                 |
| a |                   |   |       | (e.g.     |   |                 |
| k |                   |   |       | Drip      |   |                 |
| e |                   |   |       | ir        |   |                 |
| n |                   |   |       | rigation) |   |                 |
| f |                   |   |       | rudy      |   |                 |
| r |                   |   |       | garcia    |   |                 |
| o |                   |   |       | 2008**    |   |                 |
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+---+-------------------+---+-------+-----------+---+-----------------+