North Dakota State University
NDSU Extension Service
No. 184, August 2000
http://www.ext.nodak.edu/extnews/snouts
Field Days for August
GPS Receivers are More Accurate
Most Center Pivot Manufacturers have Websites
The Art of Managing Irrigation
The Checkbook Method of Irrigation Scheduling is Computerized
Timing of Last Irrigation
| Staples, Minn. | ||||
| Central Lakes Ag Center Blueberry Field Night (Commercial U-pick Production) |
August 2 | 6 to 9 p.m. | (218) 894-5196 | |
| Dawson | ||||
| 2 miles N of I-94 exit Irrigated Potato Research |
August 8 | 10 am | (701) 231-7076 | |
| Oakes | ||||
| Irrigation Research Site | August 15 | 9 a.m. | (701) 742-2189 | |
| Staples, Minn. | ||||
| Central Lakes Ag Center Disease and Root Rot in Dry Beans, Water Quality and Nitrogen Management |
August 17 | 9 a.m. | (218) 894-5161 | |
If you haven't heard, your global positioning system (GPS) receiver just became a lot more accurate. On May 1, 2000 the US government turned off a feature of the GPS signal called Selective Availability (SA). SA was an error introduced for security reasons into the signal transmitted by the GPS satellites which prevented GPS receivers from being as accurate as possible. With SA turned off, accuracy of a standard GPS receiver increased almost 10 times. So with no additional investment, your GPS receiver became much more accurate. Before May 1 the typical accuracy of a handheld GPS receiver was within plus or minus 300 feet, now it is accurate to plus or minus 30 feet or better. This increased accuracy will improve your ability to mark weed patches, the locations of boulders or any other activity for which GPS is used.
In July of 1952, Frank Zybach of Strasburg, Colorado was granted a patent for a "Self-Propelled Sprinkler Apparatus" which was the birth of the center pivot. Center pivots or "pivots" as they are often called are so common that it surprises people that the industry that makes these machines is only about 45 years old. The real boom for installing pivots really began in the late 1960s. Since 1952 there have been many innovations and improvements to Mr. Zybach's original machine. In addition, they have been used for irrigation projects never dreamed about by their inventor. He would be surprised to see pivots tall enough to irrigate orange trees or go over oil pumps. He would be amazed to see pivots used to clean up groundwater contaminated with volatile chemicals and the new generation of sprinkler packages.
Today you can install a computerized control panel that will perform many functions such as turn on chemigation pumps, slow the pivot at selected locations in the field, reverse the pivot and many more options. You can add a feature that lets you check or control the pivot from a cell phone or regular telephone that uses tones. You can order pivots with aluminum, stainless steel or poly lined pipelines that will handle corrosive, acidic or saline water. Some manufacturers are even looking at using GPS to control corner arms and improve knowledge of the pivot location in the field.
Here are the web addresses for several pivot manufacturers:
http://www.valmont.com/irr/irr.html
http://www.reinke.com/domestic/domestic.htm
http://www.zimmatic.com/
http://www.pierce-irrigation.com/
http://www.tlirr.com/
They all have descriptions of their products along with articles about some of the new features they are working to incorporate into the next generation of pivots.
Tom Scherer, (701) 231-7239
NDSU Extension Agricultural Engineer
tscherer@ndsuext.nodak.edu
Planning an optimum irrigation requires knowledge about the current field conditions and the causes and effects of the Water Atmosphere Soil Plant (WASP) continuum. The interconnectedness of the continuum is a cause for reflection. The notion that all things are connected is given the name "holism." The concept of holism at first strikes most people a bit surreal to have much use. The farmer plants crops and tends to the growth of the crops by providing the best possible environment. He puts the utmost energy in the pursuit of the chosen tasks and yet over time these actions will affect slowly and cumulatively in the quality of his crops. To a grower, a practical holistic approach to management is intrinsic.
The art of managing irrigation is a challenge in growers' list of management tasks. In evolving ways to perfect the art, farmers are not alone. Scientists and engineers have worked on it for years and have devised appropriate solutions. Convergence of both rational and scientific ideas has helped enhance the quality of the solutions.
The Water Air Soil Plant continuum concept is best explained by examining how a plant works. It may seem odd but it is true that a plant is a form of thermal engine. An engine needs energy to do work. The plant derives energy from the sun, which drives:
In the plants work process, the bulk of the water is used as a medium to extract nutrients from the soil. The nutrients dissolved in the water are assimilated into the plant and the excess water released through the leaves. Shortage of water will result in a variety of plant survival mechanisms. One particular mechanism is to cut down transpiration and to put down very deep roots. Because of their depth, these deep roots do not provide for good growth. When soil becomes wet, these roots will become starved of air and stop supplying water and nutrients. The more effective shallow roots will then take over and give much higher growth rates.
Irrigation is the know-how for deciding when to turn on an irrigation application system and how much water to apply. It becomes a challenging subject especially when supplemental irrigation is the rule rather than an exception in most parts of North Dakota. To most growers the moment to turn on a sprinkler is intuitive. The initiation of irrigation could be readily determined from soil moisture probe measurements in the root zone. But to decide how much to water to apply requires a methodical process.
Irrigation is not simply about adding water to the soil. It is about maintaining the "optimum" balance of water, nutrients and air in the root zone. Plants naturally seek water and nutrients from near the surface where nutrients and air are readily available. Roots take in oxygen and expel carbon dioxide, and therefore root access to air is especially important. These nutrient seeking roots are near the surface where water infiltration rates are high. Water and nutrients continuously move through the soil. In the heat of the summer roots may be extracting both moisture and nutrients from within the root zone faster than they can be replaced, setting up moisture gradients (difference in water content) throughout the soil profile. At night, when the plants are not feeding, moisture and nutrients will move from beyond the root zone to restore some of the water and nutrient balance.
To have a high degree of control, growers have the option to look seriously at the hardware aspects (design, construction and operation) of an appropriate irrigation system. There are many irrigation application systems, but sprinkler systems from center pivots are the system of choice in North Dakota. The center pivot system's pumping capacity measured in gallons per minute (gpm) determines the rate soil water can be replenished. To determine the pumping capacity of your system, it is a good idea to regularly have the whole system (well, power source and pump) efficiency checked. The irrigation system capacity is the overall pumping volume minus the losses due to inefficiencies. Currently, well design and development has not been the subject of serious construction objectives. But as energy costs get higher and as relatively `good' aquifer sites are no longer available, the issue of well efficiency will become more relevant.
Efficiencies of the pump and motor are not 100 percent due to mechanical reasons. The well efficiency could also influence the overall irrigation system efficiency to a great degree. Overall the whole irrigation system may be less than what is desired. The chief reason for less efficient wells is excessive drawdown. Excessive drawdown in wells could be grouped under to two classes.
Design factors:
Construction factors:
By holding soil moisture under all conditions at the optimum level growers can expect increased production. Hypothetically, an ideal irrigation would apply water (hence nutrients) directly to the root zone at exactly the rate the plant is using them. This would require a continuously varying flow rate even through a single summer day. In practice, however, irrigation can only apply water at fixed rate, so matching water plants needs is achieved by varying the irrigation timing. Soil moisture measurement is the key to the successful irrigation. There are many ways of doing this, but it is critical to understand what is being actually measured. Instruments such as neutron probe will average soil moisture measurements over relatively wider area than could be measured by tensiometers or gypsum blocks.
A number of irrigation scheduling methods has been developed. The popular method is the `feel' method, a physical examination of the current soil moisture in the root zone and `inspecting' plants for signs of stress or over watering. Newer methods using a combination of soil moisture levels and estimated crop water use are available. The irrigation scheduling outlined in AE-792; Irrigation Scheduling by the Checkbook Method is a practical water use accounting system. This bulletin can be obtained at any county Extension office.
Aung Hla, (701) 652-3194
NDSU Area Irrigation Specialist
aung@daktel.com
In 1977, NDSU Extension circular AE-792, Irrigation Scheduling by the Checkbook Method, was published. Since then it has been revised once and now the charts and methods outlined in the circular have been incorporated into a computer program called Irrigate. The program was a collaborative effort between Jerry Wright of the University of Minnesota Extension service, Dean Steele of NDSU Agricultural and Biosystems Engineering department and I with programming provided by student Nick Pederson.
The program includes the checkbook methods from both NDSU and the University of Minnesota so it can be used in both states. For North Dakota the program can be used to schedule irrigation on corn, wheat, barley, potato, alfalfa, soybean, dry beans, sugarbeets and sunflowers. For Minnesota, the program can be used to schedule irrigation on corn, wheat, soybean, sunflower, potato, sugarbeets and drybean.
The program is based on the familiar spreadsheet format and creates a workbook for each field that is entered. The spreadsheet follows the familiar soil water balance sheet used in the printed versions from both states. For each field the soil type, available water holding capacity of the soil in each 6-inch depth increment, the crop type and emergence date must be entered. In addition, a location of nearest historical weather must be selected. These data "initialize" the program for that field.
After a field has been initialized, the program is ready to help you schedule irrigation events. You have to enter daily maximum temperature as well as the date and measured amounts of irrigation or rainfall. If daily air temperature is not entered, the historical average for the location you selected during field initialization is used.
Using the data you enter for each day, the field's soil water depletion status is estimated for each day. The program contains graphing routines that will visually show the estimated soil moisture deficit (in percent) on a daily basis. Rainfall and irrigation amounts are also shown on the graphs. The program generates a soil water deficit graph for a 30-day period as shown in figure 1 or for the entire growing season as shown in figure 2. The graphs in figures 1 and 2 represent the estimated soil moisture deficit for irrigated potatoes in the Carrington, North Dakota area this growing season. The daily temperature, rainfall and irrigation data were entered up to July 28 and the graphs were printed. The estimated soil moisture deficit on figure 1 shows a steady decline if no irrigation or rainfall amounts are applied to this field. For potatoes, you would try to maintain the soil moisture deficit between 10 and 40 percent during tuber bulking whereas corn and drybean are more moisture tolerant and you would try to maintain soil moisture deficit between 20 and 50 percent.
Figure 1. Soil moisture deficit graph for the 30 day period from July 6 to Aug. 5. July 21 was selected as the center date and the graph was generated on July 28.
Figure 2. Soil moisture deficit graph for irrigated potatoes in the Carrington, N.D., area. This graph was generated on July 28.
The soil moisture deficit should be checked at least every two weeks with an in-field soil
water assessment. This can be done using a soil probe and checking the soil moisture to
the bottom of the effective root zone. If the soil water deficit estimated by the program
is different than the in-field assessment, the program can be corrected using the field
measured value. In addition, if you obtain crop water use values from some other source,
they can be entered directly into the program.
The program will run on any machine using theWindows 3.1, 95 or 98 operating system. The program requires about 5 megabytes of free hard drive space and 5 megabytes of memory. We are selling the program for $30, which includes the disks and a manual. If you would like a copy or have questions, please contact me at the phone number or email address below or in Minnesota, contact Jerry Wright, (320) 589-1711, jwright@tc.umn.edu.
Tom Scherer, (701) 231-7239
NDSU Extension Agricultural Engineer
tscherer@ndsuext.nodak.edu
The last watering of the season can be as important as the first. To ensure optimum yields, adequate soil moisture must be available to crops until they are physiologically mature. Applying excessive irrigation water to the root zone beyond maturity can result in reduced profits. For management decisions on final irrigation, you will need to know the current moisture condition of your soil and the amount available for crop use. Both soil texture and effective root zone will determine the amount of water that can be stored for crop utilization.
Stage of crop maturity and weather conditions will affect the time period when the crop continues to use water prior to maturity. Know the signs and symptoms of physiological maturity in crops you are irrigating. Both the extra savings of eliminating unnecessary irrigation and peace of mind that the crop is safe from frost are worthwhile.
Some crops such as corn can endure an increased soil water deficit as the crop nears maturity, while others such as potato or alfalfa should continue to be irrigated until harvest, maturity or frost.
Corn should be irrigated until sufficient soil moisture is available to ensure that the milk layer of the kernel moves down to the tip of the kernel or black layer formation (physiological maturity). Physiological maturity is reached about 55 days after 75 percent of the plants have visible silks. The grain moisture may range from 32 to 40 percent at the time, depending on the hybrid. Yellow dent corn is usually fairly well dented at physiological maturity. Once corn is physiologically mature, the dry down rate is approximately 0.5 percent moisture loss per day.
Dry edible bean: The last irrigation should be when the first pods are filling, or irrigation stopped when 50 percent of the leaves are yellowing on the plants. When over watered, indeterminate varieties (pinto) may continue to vine and set flower with delayed maturity. For Navy bean, physiological maturity is reached when at least 80 percent of the pods show yellowing and mostly ripe, with 40 percent of the leaves still green in color. Pinto beans are physiologically mature when 80 percent of the pods show yellowing and mostly ripe and only 30 percent of the leaves are still green. Beans within pods should not show evidence of any green. If the beans have begun to dry, irrigation will not be needed because the beans no longer are removing much water from the soil profile.
Soybean should be irrigated until sufficient moisture is available to allow full bean development and pod fill. This stage is when leaves are yellowing (75-80 percent) and all pods filled with lower pods just starting to turn brown. At physiological maturity, pods are all yellow and over 65 percent of the lower pods have turned brown. Beans within pods should have little evidence of green color and should be shrinking. Studies show that yellow pods sprinkled with brown are the best clue of physiological maturity. Usually if one or two pods show this symptom on the upper two or nodes of the plant the plant has reached P.M. The soybeans should be tolerant of a killing frost at this time also.
Sunflower should be irrigated until sufficient moisture is available for the sunflower achenes (seeds) to fill. This is when the backs of the heads turn from a lime green to yellow-green color and ray petals are completely dried.
Potato will utilize soil moisture until harvest. Maturation stage begins with canopy senescence as older leaves gradually turn brown and die. Research has shown final irrigation can be used to reduce bruising during the harvesting process. On sandy soils, a soil moisture content between 60 to 80 percent of field capacity (40 to 20 percent moisture depletion) provides conditions for a desirable soil load into the harvester with optimum separation of potatoes and soil and a minimum of physical tuber damage. If soil is dry before harvest, a final irrigation should be applied at least one week prior to harvest to raise the soil moisture level and also raise the tuber hydration level.
Alfalfa should be irrigated to maintain active growth until growth is stopped by hard frost. Alfalfa going into the winter with adequate soil moisture has a much better chance of little or no winterkill.
Small grains should be irrigated until adequate soil moisture is available to bring the crop to the hard dough stage.
Sugarbeet will utilize moisture until harvest time. Irrigation is usually terminated seven to 14 days before harvest to allow the soil to dry.
Duane R. Berglund(701) 231-8135
NDSU Extension Agronomist
dberglun@ndsuext.nodak.edu
Water Spouts, No. 184, August 2000
NDSU Extension Service, North Dakota State University of Agriculture and Applied
Science, and U.S. Department of Agriculture cooperating. Sharon D. Anderson, Director,
Fargo, North Dakota. Distributed in furtherance of the Acts of Congress of May 8 and June
30, 1914. We offer our programs and facilities to all persons regardless of race, color,
national origin, religion, sex, disability, age, Vietnam era veterans status, or sexual
orientation; and are an equal opportunity employer.
This publication will be made available in alternative formats for people withdisabilities
upon request, 701/231-7881.
