New Mexico State University
Climate Center's
Potential and Actual Crop Evapotranspiration Wizard
1. Get weather data
Go directly to
http://weather.nmsu.edu/cgi-shl/cns/oldformat.pl
for data from the Climate Center's Campbell network.
If you need assistance using the NMSU Climate Center Data
Retrieval System,
Click
here for a graphical representation of the retrieval process
Click on the number corresponding to your region on the right
which will automatically insert the code into retrieval system.
Either enter the date range you want or click AutoDate to
enter the beginning of the current year to the current date.
Choose desired format, in this case choose ENGLISH (Excel).
Select a crop preset from the pull-down menu.
Click Retrieve Weather Data
The next page will be all of the weather data you requested
Highlight starting from the first date you selected to the
end of the list right above the dotted lines minus the lines
Either go to the menu on your browser and select Edit,
then Copy or press Ctrl+C on your keyboard to copy the table to memory.
2. Now, select the Excel spreadsheet from the table below that is appropriate for your crop. It is recommended that you right click on the file you want and either select Open Link in New Window or Save As. If you choose Save As, you can use the default name and save it to where you want on your computer. Then open the file from where you saved it. If opened in new window, it should automatically open the file.
| New Mexico Climate Center formatted spreadsheets |
| Alfalfa |
| Apples |
| Atriplex-Saltbush |
| Barley |
| Chile |
| Corn |
| Cotton |
| Creosote |
| Eucalyptus |
| Grapes |
| Grasses cool season warm season |
| Lettuce |
| Mesquite |
| Summer Mustard |
| Winter Mustard |
| Onions |
| Pecans |
| Pine |
| Pistachio |
| Potatoes |
| Pumpkins |
| Saltceder Las Cruces, Los Lunas |
| Wheat |
3. In the open spreadsheet, adjust the soil values to
match your soil profile and the default amount of water you irrigate with.
| max root zone depth (inches) | 48 | Enter the maximum root depth that the crop will grow in inches |
| Root growth coefficient inches/degree | 0.01 | This should be adjusted so that the maximum root depth is reached when the the crop coefficient reaches the maximum value of .01 or greater |
| irrigation amount (inches) | 3.6 | Amount of irrigation water that you specify that will be applied at each irrigation automatically by the program . In the spreadsheet under column U this amount will be placed on the day the crop should be irrigated. If the amount or date is different , then enter the correct amount in column AB and the program will not irrigate until a new irrigation is needed. |
| soil water holding capacity inches/ft | 1.5 | This is dependent on the soil type . See the soil table for value for each soil type |
| Management allowed depletion% | 50 | This is the amount of water to be taken out of the soil profile before irrigation. It is crop dependent and should be set at 50% if no information is available. See the table by Sanders for suggested Management Allowed Depletion (MAD) for your crop. MAD=100%-ASM (Available Soil Moisture) |
| Beginning root depth | 6 | This is the soil depth that contains water for evapotranspiration assumed to be at field capacity at planting. The soil profile down to the maximum rooting depth is assumed to be at field capacity. If this value is set to zero then if root grows fast enough then irrigation will not occur because the plants are getting enough water from the soil moisture in the lower depth. However, if the root growth function does not allow the root for shallow rooted plants to grow fast enough then irrigation will have to occur every couple of days. To stop this from occurring will cause some soil moisture stress but save a lot of water. This is accomplished by setting the beginning root depth at some value 6- 12 inches. |
Highlight the first cell that contains the date from the sample data, then press Ctrl+V or do Edit -> Paste to put the desired weather data into the spreadsheet.
Next, Click on Data on the toolbar on top then select Text to Columns. In the following menu, make sure Delimited is selected, click Next. In the next screen click on the checkbox that says Other: and type in a" | " (a bar) into it. You also need the Space box checked and click Next again, and finally click Finish. It will ask if you would like to replace the contents of the destination cells, click Yes. Now, with all of the cells that are highlighted on the left represent the data that you just pasted in. Anything below these highlighted cells is sample data and should be deleted so that it doesn't accidentally interfere with the simulation.
To use the spreadsheet to schedule irrigation , set
the MAD so no stress occurs and then irrigate on of before the date that the
Model irrigates. Put the amount you irrigated into the spreadsheet (Column AB)
and look for the next irrigation date computed by the model (Column U).
The spreadsheet has been broken into three parts due to it's length.
Max temp= maximum temperature in F:
Min temp= minimum temperature in F:
Max Rh= maximum relative humidity:
Min Rh= minimum relative humidity:
Soil Temp= soil temperature at 4 inches
Solar Rad= solar radiation in ly/day
Max Wind and Ave Wind are wind speed in mph
Etr: This is the modified Penman reference evapotranspiration (ET) based on climate data.
Rain inches= rainfall in inches must be changed for current location
Gdd Corn Gdd Cotton Gdd Generic are growing degree days for corn cotton and the generic is the crop selected , in this case chile. The gdd for corn and cotton are to give a range of reasonable Gdd values. If the generic value is 3 times these values, something is wrong with the input data.
Root
depth inches is the depth the roots have reached.
Kc
ET = estimated crop water use for the day under the current soil water
stress conditions.
Water in root zone – note: it is assumed that soil water is at field
capacity at the beginning of season.
Predicted irrigation in inches is the irrigation applied by the model when the selected MAD is reached. If you have irrigated in column AB correctly then the model will not irrigate. If you do not want the model to irrigate set the MAD at 95 and the crop will die before the model irrigates
Drainage = water in
excess of that required to bring root zone moisture to field capacity. Only
calculated for the irrigations applied for the model
Column (W,) is the drainage from applied irrigation by user
Column (y) is the soil moisture stress variable. Et/ Etmax where Etmax is non stressed Et. The variables goes from 1 to 0. At a value of .75 the crop is transpiring only at 75% of potential and crop yields are being lost.
Column Z and AA are the daily non stressed potential Et and Accumulated Stressed Et
Column AC is for notes.
The Graphs at the bottom of the workbook show the water budget and yield calculations.
Figure 1 give a comparison between Samani method of calculating Pet and Penman's method for Las Cruces NM
| If you have any questions please contact webmaster@weather.nmsu.edu Copyright © 1996 New Mexico State University Last Updated: May 29 2003 |
Department of Agronomy and Horticulture Box 30001 / Dept.3Q / Las Cruces, N M 88003-8003 Telephone: (505)646-3405 FAX: (505)646-6041 |