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COOPERATIVE
EXTENSION |
FROM
THE GROUND UP Agronomy News  |
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| Irrigation Management | |||||||||||
| Surge Irrigation | |||||||||||
| Atmometers | |||||||||||
| Cropflex | |||||||||||
| PAM | |||||||||||
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Meet Parviz Soltanpour |
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Irrigation Management |
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| What are Colorado producers doing? | ||||||||||||||||||||||||||||
Irrigation for crop production currently uses about 90% of the 1.8 trillion gallons of water diverted annually Colorado. We have a long history of irrigation innovation in Colorado, but we continually hear discussion of wasted agricultural water and questionable irrigation management, especially from urban water interests. In order to evaluate our irrigation and water management programs at CSU, we mailed a confidential written survey in 1997 to 3,281 known irrigators identified through the Colorado Agricultural Statistics. The survey asked producers about irrigation management and technology used in their operations and included questions about specific fertilizer and pesticide practices. This information should be helpful in documenting progress that Colorado producers are making in protecting water resources and to identify where more effort is needed. Survey results Each respondent was asked to identify a specific field that was representative of their farm to facilitate detailed questioning of how specific irrigation management decision are made. The average “representative field” was 67 acres with nearly one-quarter of the fields identified as rented or leased. Sixty-five percent of respondents described their water supply as highly reliable, providing adequate water ten years out of ten. Regions with higher reliance on ground water sources were found to have higher water reliability, while regions more reliant upon a ditch company, especially in the Arkansas Valley, have lower water reliability. Nearly all center pivot users have upgraded their system in some manner, with low-pressure systems and drop nozzles widely used (Figure 1). Eighty-four percent of survey respondents reported at least one irrigation system upgrade somewhere on their farm. Among gravity systems, flood irrigation components are least frequently improved. Less than 40% of the flood systems in any of the three western regions have received an upgrade. Field leveling and lining ditches occurs frequently among flood systems in the eastern regions and for siphon tube systems across the state. Among gated pipe users, field leveling and surge valves were the most frequent upgrades. Very few producers have adopted flow meters. Irrigation management Half of all producers indicated that “crop appearance” was the primary method used to determine when to irrigate their crops (Table 3 ). Nearly one-third cited a “fixed number of days” between irrigations as their method used. Rule based irrigation scheduling methods such as accumulated ET or available soil moisture were cited by about one-quarter of respondents, but most frequently by those pumping ground water and using center pivots. One in ten producers cited using crop consultants used to determine when to irrigate their crops. Over one-quarter of all producers reported changing some aspect of management in the last five years. Among the irrigation systems, center pivot, side roll, and gated pipe users reported the most changes. Respondents with ground water sources showed the most change. Most changes involved the water application system, with improving water use efficiency the most frequent reason given for the management change. Survey significance Most Colorado irrigators do not keep precise records of crop water use and irrigation water applied. This may be partially explained by the fact that many irrigators feel their water supplies are adequate during most years. The management time and costs required to keep better records or implement higher levels of water management may not be justified or economically feasible for these irrigators. However, the results of this irrigation survey also show that Colorado irrigators will implement technology when it is practical, economical, or when other significant incentives exist. It may be inferred that higher levels of irrigation water management will be adopted as farmers perceive an incentive to do so. The remainder of this newsletter discusses some of the irrigation management tools that Cooperative Extension is working to disseminate. Complete results of this survey may be obtained in the CSU Agricultural Experiment Station technical report entitled “Irrigation Management in Colorado – Survey Data and Findings” (Colo. AES TR-99-5). This report may be accessed at http://www.colostate.edu/Depts/AES/pubs_c.html |
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Table 1. Average irrigation experience of respondents and age of system installed on respondent's "Representative Field.
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Figure 1. Results of the following
question:
Check all irrigation upgrades used on the system identified for this field.
Table 2. Percent of respondents knowing and keeping records on the amount of water applied*.
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Region
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South Platte
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Eastern Plains
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Arkansas Valley
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San Luis Valley
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Mountains
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Western Slope
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Statewide Average
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-----------------------------% respondents per region-----------------------------------
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| Know amount applied | 36 | 38 | 25 | 30 | 17 | 17 | 28 |
| Keep records | 16 | 19 | 15 | 25 | 12 | 12 | 16 |
*Questions read: Do you know how much water was applied
to the representative field in 1996?
Did you keep written or computerized records of water applied throughout the season?
Click here for Word file containing this table.
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Crop appearance
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51 |
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Fixed # days
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29 |
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ET or soil moisture
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27 |
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Other
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20 |
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Consultant
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10 |
Click here for Word file containing figure representing this data.
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Surge Irrigation |
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| A tool for improving irrigation efficiency and uniformity. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Surge irrigation is a surface irrigation method designed to reduce runoff and increase application uniformity. This technology became feasible for producers with the advent of the surge valve, which allows an automated intermittent application of water to furrows in a series of pulses or surges, rather than a continuous furrow stream. The process is simple; irrigation water is alternated between two sets of furrows until the irrigation is completed. Commercial surge valves have an automatic controller that is powered by an internal battery and a solar panel. The surge valve is typically located between two sets of furrows. Through the surge valve controller, the irrigator can time irrigation sets according to the length of the field, slope, and soil texture to determine the number of hours that are needed to complete irrigating each set. This is the time required to wet and reach the end of the field. When the set time is selected, the controller will automatically determine the number of cycles or changes for each set. Typically, it takes 5 or 6 cycles, but this can be altered to reduce runoff. When the number of cycles is completed, then the soak cycles will start at constant time (i.e., 20, 30 minutes) depending on the length of initial time selected to irrigate the field. The soak cycle length also can be changed to reduce any excessive water runoff. The purpose of the soak cycle is to push the water down to the proper depth within the root zone, which depends on the crop's growth stage. Gated pipe is typically used to deliver water to each of the two sets from opposite sides of the surge valve. The main line, which carries water from the well or ditch will be connected directly to the surge valve. Alternating the water between two sets of furrows seals the soil surface, decreasing the water intake rate, and causing the furrow stream to advance farther and at a faster rate to the end of the furrow. This results in a more uniform water distribution. Surge irrigation can be a very effective tool in saving water when water availability is limited. Also, surge can save irrigation time and labor costs by reducing the need to change sets as often. Applications Efficient nitrogen management under surface irrigation is difficult due to the leaching caused by deep percolation. In a 1996-1998 study to demonstrate the use of surge valve for water and N management in the Lower South Platte River Basin, irrigation efficiency was improved to 60-65% under surge irrigation as compared with 40-45% under conventional surface irrigation. The results also show an improvement in N savings under surge irrigation. This saving can be translated into savings of $20.00 per acre on N fertilizer costs. Fertilizing with surge Example: Calculation: |
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Table 4. Nitrogen budget under both surge and conventional irrigation.
Table 5. Suggested nitrogen rates for surge
irrigated row crops.
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Atmometers |
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A flexible tool for irrigation scheduling. |
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Irrigation scheduling based upon crop ET (evapotranspiration) is often perceived as too difficult or too time consuming for many producers and crop advisers. However, there are tools available that reduce the work and the complexity associated with sound ET-based irrigation scheduling. Atmometers are one of these tools. The primary purpose of these instruments is to provide actual crop ET at any field location they are installed. This information is visually displayed on a site tube mounted in front of a ruler on the instrument. Reading the site tube is as easy as reading a rain gauge. Therefore, a grower or consultant can use an atmometer to quantitatively gauge how crop water use varies with changing weather conditions. Essentially, an atmometer acts as mini-weather station that, when properly installed, will provide reference ET (ETr) at a reasonable cost and with little effort. One Colorado supplier sells a modified atmometer (ETgage®) for about $200. They are easy to install and require little maintenance. Studies conducted by CSU and the USDA in Fort Collins show that an atmometer will provide ETr values that closely match ETr calculated from weather station data (Figure 2). This ability to provide reliable ET makes atmometers especially useful for areas that do not have nearby weather stations or for people that do not have ready access to this information. A consultant or grower can install an atmometer to help schedule irrigations for many fields within a several mile radius. Also ET data from an atmometer may be more convenient and site specific than other sources. Atmometers basically consist of a wet, porous ceramic cup mounted on top of a cylindrical water reservoir. The ceramic cup is covered with a green fabric (canvas or Gor-Tex®) that simulates the canopy of a crop. The reservoir is filled with distilled water that evaporates out of the ceramic cup and is pulled through a suction tube that extends to the bottom of the reservoir. Underneath the fabric, the ceramic cup is covered by a special membrane that keeps rain water from seeping into the ceramic cup. A rigid wire extending from the top keeps birds from perching on top of the gauge. Atmometers are typically mounted on a wooden post near irrigated fields. A good location for placement is a border ridge in an alfalfa field. However, you may also locate the instrument alongside a dirt road if surrounded by low-growing irrigated crops. The site should represent average field conditions. Do not install near farm buildings, trees, or tall crops that may block the wind. Additionally, avoid placement near dry, fallow fields. The top of the ceramic cup should be 39 inches above the ground. The manufacturer of a modified atmometer sold in Colorado (ETgage®) provides detailed instructions on how to install and maintain their instrument. The following is a brief description of how to use an atmometer to help schedule irrigations.
Example #1:
Example #2:
As these examples illustrate, once an allowable depletion is determined, using the atmometer to help schedule irrigations is as simple as reading a rain gauge. It is especially useful for center-pivot users or surface irrigators that know their applications amounts. In these cases, you should irrigate when the site gauge drops to the same amount as the typical irrigation application. When using any ET-based irrigation scheduling, field verification of soil moisture status is a good idea. Field probing can confirm needed irrigation and provide confidence in using ET-based scheduling. An atmometer can also be used in conjunction with computer scheduling software such as Cropflex, especially if users do not have internet access. This tool can also help growers deal with salinity problems by providing ET over a period of time to determine leaching rations. A Colorado-based company that manufactures atmometers can be reached at (970) 667-9821. Growers interested in trying an atmometer for a season should contact your regional CSU Cooperative Extension water specialist. |
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Table 6. Examples of allowable depletion for corn for typical Colorado sandy loam soil.
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Cropflex |
| A water and fertilizer management program. |
| Many irrigation scheduling programs that use the water
balance approaches were developed during the last two decades. The
acceptance of these programs by users such as farmers and ranchers was very
slow. Recently a new approach to developing irrigation management
programs, based on expert systems, was developed at Colorado State University.
This approach also calls for integrating water and nitrogen management.
The result is a flexible crop management computer program called “Cropflex,”
developed at the Department of Chemical and Bioresource Engineering and
Cooperative Extension at CSU. This easy to use tool provides irrigation
scheduling and fertility management advice to help producers maintain or
increase yields while minimizing the potential of leaching nitrates into
the ground water. Studies have shown that fertilizer and water applications
can be substantially reduced without reducing yield by proper timing of
irrigation and nitrogen applications. Cropflex is a decision support
system designed to help the producer apply water and fertilizer more accurately.
Cropflex handles a variety of Colorado crops. Basic crop information has been developed for corn, alfalfa, sorghum, onions, potatoes and barley. Entering new or additional crops to the database is simple and straightforward. As a matter of fact, all the databases of the program can be accessed by the user, and crop, soil, and weather station information can be edited or new information can be entered. The program was developed for use by a producer with minimal computer experience and has self-explanatory and easy to understand pull down menus. The new version of Cropflex runs in Windows 95 and is user friendly. Cropflex has some unique features that are not available in other programs such as: Irrigation scheduling based on growing degree days and growth stages, yield prediction capability to refine fertilizer recommendations; full year weather data, which can span years; calculations of water and nitrogen balance will continue after harvest; a daily display of nitrogen balance and nitrogen deep percolation; and a daily soil moisture override is available. The program can be downloaded from our Web site: http://ulysses.atmos.colostate.edu/~crop/. Weather information for different sites in Colorado can be downloaded from our COAGMET site: http://ulysses.atmos.colostate.edu/cgi-bin//coag_raw_form.pl. The weather information should be saved as file with the location name and it then can be imported into CROPFLEX. For help in implementing or running CROPFLEX contact Israel Broner at (970) 491-7872 or email at: israel@engr.colostate.edu. |
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PAM |
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| A cost-effective tool for improving irrigation and protecting soil and water resources. | ||||
The use of PAM in furrow irrigation is probably the fastest growing soil and water conservation technology in irrigated agriculture today. PAM is an acronym for a linear-linked polyacrylamide being used in agriculture to reduce erosion in furrow irrigation. In trials and demonstrations throughout the western U.S., PAM has significantly reduced erosion, up to 99%. The proper use of PAM not only reduces erosion, it also increases infiltration as much as 50% when compared to untreated areas. PAM also helps in high residue furrow irrigation. Because the PAM treated water has a low sediment load and the sediment does not accumulate against the residue, water can flow by the residue. On untreated furrows, sediment stacks up against the residue which can cause the rows to break over. How PAM works Because PAM only treats the wetted perimeter of furrows, and since PAM penetrates the soil only a few millimeters, very small application rates are effective. Several suppliers are marketing PAM in Colorado. Typically, granular PAM costs about $5 per acre for 1 application at a rate of 1 lb/acre or 10 ppm in irrigation water. Liquid PAM runs $8 - 10 per application for the same rate. Usually, the supplier can also provide low cost automated head-ditch applicators and technical assistance to get started. Producers should plan on at least two applications for best results. An application during the initial irrigation and another after the final cultivation pass works well for some farmers. Erosion reduction seems to be more effective on medium textured, silty soils than on sandy soils. The economic benefits of saving topsoil are hard to quantify, but we know that sustaining soil quality is essential for long term profitability. In the initial crop season, many producers are seeing a direct economic benefit from increased yields and labor savings. When applying PAM, it is important that no untreated water wet the furrows ahead of the PAM-treated flow because the untreated water will destroy soil structure before PAM can stabilize it, reducing PAM’s effect. If there is a significant amount of suspended sediment in the ditch water, PAM will cause it to settle out almost immediately. Increasing flow rate with PAM treated furrows is often necessary to offset greater infiltration rates. Research in Idaho showed that you can double inflow rates with PAM and achieve greater overall field uniformity while still reducing sediment loss. Once treated water has reached the end of the furrow, addition of PAM at the head ditch is stopped. Untreated water is used for the remainder of the irrigation and flow rates should be reduced to sustain minimal runoff. Erosion protection declines on the ensuing irrigations, but still is significantly better than non-treated furrows. Furrows disturbed by traffic or cultivation must be retreated. The number of PAM treatments per year will vary with crop and producer objectives but it is common in Colorado to make 2 to 3 applications at 1 lb/acre during a typical growing season. Colorado research with PAM In trials at the Arkansas Valley Research Center conducted by Mike Bartolo, soil loss was reduced 47% when using PAM on 6 of 11 irrigations and still produced similar total market weight on onions of 370 cwt/ac compared to 357 cwt/ac on the untreated check in the 1996 trials. In 1997, soil loss was reduced 22% when PAM was applied on only 3 of 10 irrigations and total yield was significantly increased from 377 cwt/ac on the untreated control as compared to 425 cwt/ac on the PAM treated plots. PAM has also been used to reduce seepage in dirt ditches. Work done by Dan Crabtree of the Bureau of Reclamation on the west slope with models indicated that seepage was reduced as much as 60% by adding PAM and a soil mix to the model troughs. Field work done by Jim Valliant, Colorado State University Cooperative Extension, on a Bureau of Reclamation grant demonstration indicated that adding PAM to water in a dirt lateral ditch carrying 6,000 to 7,000 gallons per minute substantially reduced water levels in two wells located approximately 125 feet from the lateral as compared to the well in the untreated area, also located 125 feet from the lateral. Five (5) pounds of PAM were applied to the flowing ditch water at the rate of one pound per minute. One hour later, another 5 pounds of PAM was applied at the same rate. Since PAM also acts as a flocculent, the sediment load was reduced as much as 67%, from 10,146 to 3,334 pounds per acre-foot. This sediment coated the bottom of the ditch in the 450 foot stretch and reduced seepage to the observation wells below the PAM treated area. So far, no negative impacts have been documented with PAM usage and producers are rapidly adopting this new technology. The environmental benefits of reduced erosion and contamination transport have been phenomenal in test studies. Improved infiltration and lateral wetting rates seen with PAM can also help producers do a better job irrigating and conserve soil and water resources.
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Meet Dr. Parviz Soltanpour Dr. Parviz Soltanpour conducts research in the areas of salinity, soil testing, fertilizer recommendations, and availability of heavy metals to plants. He directs graduate student programs and teaches graduate courses in soil-plant nutrient relationships, tropical soils, and crops and farming systems. At Colorado since 1966, Dr. Soltanpour has served at the CSU research station in Center, Colorado, then at the CSU Soil Testing Lab and presently as a Professor of Soil Science. Parviz has had an extension appointment in the past and can be a resource for information on salinity management, soil testing, and soil fertility. |
| websites |
| World Wide Web Virtual Library for Irrigation http://www.wiz.uni-kassel.de/kww/irrig_i.html#index Multiple links to irrigation topics from around the world WETTING FRONT The Water Management Research Unit Newsletter
Irrigation Engineering Publications
Irrigation Publications
Irrigation and drainage directory
PAM Research homepage
Irrigation & Agronomy Page of Southeast Colorado
USDA Irrigation Information
Irrigation & Agronomy Page of Northeast Colorado
Cropflex download site:
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| Agronomy
News is a monthly publication of Cooperative Extension Department of Soil & Crop Sciences, Colorado State University Fort Collins, Colorado. Web Site: http://www.colostate.edu/Depts/SoilCrop/extension/Newsletters/news.html The information in this newsletter is not copyrighted and may be distributed
freely. Please give the original author the appropriate credit for
their work.
Reagan Waskom
Jerry Johnson
Direct questions and comments to:
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Extension staff members are:
Troy Bauder, Water Quality
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