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(image from charlessite90.com )
(image from charlessite90.com )
Two weeks ago, pragwater.com started using a free online service called ClusterMaps. We were happy to learn that pragwater.com has received visits from people all over the world, 27 countries in all. Here is the breakdown:
A simple spreadsheet for scheduling irrigation can be downloaded by CLICKING HERE.
(Spreadsheet updated Nov 28, 2018)
The methodology used in the spreadsheet is presented in Crop evapotranspiration – Guidelines for computing crop water requirements – FAO Irrigation and drainage paper 56, Chapter 8
To use the spreadsheet, you need to enter input wherever the cells are yellow. Here are some basic instructions:
Setting up the Spreadsheet
1. In the first Worksheet Tab (Soil Moisture Worksheet), enter the date of the first day of the crop season.
2. Enter soil field capacity and wilting point in percent. If you know the soil texture you can get the field capacity and wilting point online by clicking here.
3. Enter rooting depth for each day of the season. Maximum rooting depths for various crops are given in FAO 56 Table 22.
4. Management Allowed Deficit (MAD) is given in FAO 56 Table 22, however, the FAO refers to it as the Depletion Fraction (P). P and MAD are the same thing.
5. Enter soil volumetric moisture content as a percent on the first day of the season.
6. Enter the evapotranspiration (ETc) each day. Many meteorologic stations will provide estimates of daily reference evapotranspiration (ETo). You will need to multiply the ETo by the appropriate crop coefficient (Kc) for your crop to obtain the actual evapotranspiration (ETc).
7. Enter the rainfall or irrigation each day.
8. In the next Worksheet Tab (Application Rate), enter the date of the first day of the crop season.
9. Enter the area of the field in acres.
10. Enter the percent wetted area. If drip irrigation is used, only a portion of the field may become wet.
11. Enter the percent efficiency of the irrigation system.
12. Enter the pump flow rate in gallons per minute.
Using the Spreadsheet to Schedule Irrigation
The objective of the analysis is to minimize crop stress as indicated by the crop stress factor (Ks). If this parameter is less than 1, then the crop is in a state of water stress. To simplify the analysis the spreadsheet provides the column “Did Stress Occur?” When stress occurs, as indicated by “Yes”, then you should irrigate your crop. To see how much you should irrigate, see the column called “Irrigation Needed”. Enter the amount you want to irrigate in the column called “Applied Irrigation or Rainfall”. Finally, go to the Application Rate Worksheet Tab to see how many hours you should run your irrigation system to put on the desired amount of water.
Soil Moisture Graph Worksheet Tab. Any time that this graph falls below the green line (Threshold Moisture Content) the crop is in stress. Throughout the crop season the graph should never fall below this line if possible. It is also very important that the soil moisture not exceed the field capacity because this water will be wasted, either through deep percolation or surface runoff.
ETcadj Worksheet Tab. The evapotranspiration is shown in this worksheet. ETcadj is the crop ET multiplied by the crop stress factor, and represents the real ET.
Crop Stress Factor Worksheet Tab. This graphs shows the crop stress factor as a function of time throughout the crop season. This line should be as close as possible to 1 throughout the season. Any value lower than 1 indicates that stress occurred. NOTE ALSO!! In this worksheet a value of the relative seasonal crop yield is provided. The yield response factor (Ky) required to calculate the relative yield can be obtained from Table 24 of the FAO 56 document for various crops.
Cumulative ET vs Irrigation Worksheet Tab. The purpose of this graph is to show how close your applied irrigation was to the ET. Throughout the season and at the end of the season, the value of the cumulative irrigation should be as close as possible to the cumulative ET. (Note in this graph that the ET used is the ETc and not the ETcadj).
DISCLAIMER: The information on this website is provided “as is”. The authors and publishers of this information disclaim any loss or liability, either directly or indirectly as a consequence of applying the information provided herein, or in regard to the use and application of said information. No guarantee is given, either expressed or implied, in regard to the accuracy, or acceptability of the information.
Estimate the long-term average weather conditions at any location in Puerto Rico using the PRET computer program. Although the program is intended to estimate the monthly and daily evapotranspiration, you can also obtain monthly values of minimum and maximum air temperature, dew point temperature, wind velocity and solar radiation. Here are the steps:
1. Download PRET from the following link: https://pragwater.com/crop-water-use/ Background documentation is available at this site which describes the methods used to estimate the long-term weather data.
2. Install PRET on your computer.
3. Run PRET. You will see the splash screen below. Click on OK.
4. On the INPUT DATA screen, enter any crop from the drop down screen (e.g., tomato). Do not use “generic”, otherwise you will need to enter some crop coefficient information later. Enter the name of your location (e.g., Juana Diaz), enter your site latitude (e.g., 18.06) and your site elevation (e.g., 55 m). Ignore all other requested input on the page. click Next.
5. Click the icon that says “Have Program Calculate Climate Data (Applicable only for Puerto Rico)”.
6. Click on the appropriate NOAA Climate Division. For example, Juana Diaz, PR, is in Climate Division 2.
7. The next page will give you the results of the long-term monthly weather parameters for your site. If you like you can save the data to a text file.
If you have any questions, contact me at email@example.com
DISCLAIMER: The information is provided “as is”. The authors and publishers of this information disclaim any loss or liability, either directly or indirectly as a consequence of applying the information provided herein, or in regard to the use and application of said information. No guarantee is given, either expressed or implied, in regard to the accuracy, or acceptability of the information.
VLab: An excellent free Online Resource for Hydraulics/Hydrologic Calculations: http://onlinecalc.sdsu.edu/. Thank you to Dr. Victor Miguel Ponce for your contribution to an Open Source web!
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I recommend checking out the above blog. Where do you fall in the transition between the analogue and digital ages?