Irrigation for Agriculture in Arkansas

The PHAUCET (Pipe Hole and Universal Crown Evaluation Tool) is a free GNU General Public License (GPL) computer software application.  It was designed by engineers with the National Resources Conservation Service (NRCS) in Missouri to calculate existing irrigation system performance and define alternatives for improving irrigation efficiency. 

PHAUCET assists farmers determine the sizes of the holes in the layflat flexible poly-pipe that best distribute the available water. The program also helps farmers improve timeliness of watering fields having different row lengths.

PHAUCET 2012 version 8.2.20 (self-extracting; 8.7MB)

PHAUCET installation "Read Me" file

 

PHAUCET Training Materials and Design Examples

Delta Plastics' Pipe Planner is a subscription-only Web-based application designed to help create the most efficient irrigation system for row crops.  Pipe Planner features include:

• Store all your information on the Delta Plastics secure server
• Access your data at any time
• Easily maintain and upgrade your plans as needed
• Access real-time support services

To learn more about Pipe Planner offerings and pricing, contact a Delta Plastics representative at 800-277-9172 or at http://www.pipeplanner.com/

Atmometers are simple to setup and require minimal upkeep.  They should be placed adjacent to crop fields, and mounted at least 39 inches high and above the crop canopy, to provide accurate on-site evapotranspiration (ET) information.

At the beginning of the growing season, the atmometer reservoir should be filled with distilled water, and will likely need to be refilled once during the season.  The paper wafer, which prevents rainwater from entering the atmometer, should be replaced annually.

Setting the Atmometer

The following sheets have been developed to help Arkansas producers set their atmometers and may not be appropriate for use outside the region.  Currently, a chart has not been developed for rice.

ET Gauge Sheet - Corn

ET Gauge Sheet - Soybean

The decision process of determining when to irrigate crops is referred to as irrigation scheduling.  There are several different irrigation scheduling methods available to producers who irrigate.  Most of these methods have been evaluated in Research and Extension studies by the University of Arkansas System's Division of Agriculture.  The water balance approach to irrigation scheduling has been determined to be the most practical and suitable method for Arkansas producers.  This approach is also used by producers in Mississippi, Louisiana, Tennessee and Missouri.

The Arkansas Irrigation Scheduling website can be used for corn, cotton, grain sorghum and soybean crops that are irrigated with furrow, center pivot, border or levee irrigation methods.

Arkansas Online Irrigation Scheduler

Center pivots offer the ability to irrigate fields that have surface slopes that make it impossible or impractical to irrigate with surface methods. They also offer more water management options than surface irrigation. The need for good surface drainage still exists with pivot irrigation and should not be overlooked.

Pivots are best suited for large square-, rectangular- or circular-shaped fields free of obstacles such as trees, fences, roads, power poles, etc. Field ditches are also a concern if the pivot towers must be able to cross them. Pivots can cover a range of acreage depending on the allowable length, but the common 1/4-mile system will cover approximately 130 acres of a 160-acre square field. It is also possible to tow a pivot from one field to another. It is usually best for a system not to be towed between more than two points during the season.

The biggest challenge with center pivots is the initial cost. However, it does offer some advantages that can justify the initial cost, especially when surface irrigation is not possible and the cost is spread over an expected service life of at least 15 years.

 

Center Pivot Irrigation Resources

 

The concept of border irrigation is to flush a large volume of water over a relatively flat field surface in a short period of time. Borders are raised beds or levees constructed in the direction of the field's slope. The idea is to release water into the area between the borders at the high end of the field. The borders guide the water down the slope as a shallow sheet that spreads out uniformly between the borders. Most of the border irrigation in Arkansas has been used for soybean irrigation.

Border irrigation is best suited for precision graded fields that have slope in only one direction.

The crop should be flat planted in the direction of the field slope or possibly at a slight angle to the slope. Planting across the slope tends to restrict the water flow, especially on fields with less than 0.1 ft. fall per 100 feet. Fields with slope in two directions are not as well suited to border irrigation, but it may still be possible if the borders spacing is relatively narrow.

Border irrigation will not work on all fields and is not necessarily a better method where the crop is already grown on good beds and furrow irrigated. However, if a grower wants to move toward flat planting and reduced tillage on these fields, then border irrigation may be more appealing than flood.

Border Irrigation Resources

 

Furrow irrigation can be a very effective irrigation method.  One of the biggest requirements for furrow irrigation is that the field must have a positive and continuous row grade.  This usually requires precision land grading, which can be rather expensive.  However, the grading results in positive field drainage that greatly enhances production.  The row grade should be a minimum of 0.1 percent and no more than 0.5 percent; row grades between 0.15 and 0.3 percent are especially desirable.

Furrow irrigation by necessity requires that there be some amount of tail water runoff from the end of the rows.  All the middles will not water out at the same rate, especially those that are wheel middles.  Also, cracking soils can make furrow irrigation management more challenging.  However, irrigating on the appropriate schedule will reduce the problems associated with too much cracking.

Surge Irrigation

Furrow & Surge Irrigation Resources

 

Flood irrigation with levees should really be thought of as flush irrigation. The challenge is to get the water across the field as quickly as possible. It is also important that irrigation is started before the crop experiences drought. If plants are drought stressed and then subjected to an extended wet soil condition, plant development can be delayed and some plants may die.

Levees are often broken in several places or completely knocked down to get the water into the next bay. Rebuilding the levee in time for the next irrigation is often difficult because the levee area tends to stay wet. Some growers install gates or spills in the levees to avoid irrigation delays due to rebuilding the levees between irrigations. When possible, it is recommended that gates or spills are also installed in the outside levee. This provides better drainage of a field in a situation where a rain occurs during or soon after the irrigation.

It is recommended that water not be allowed to stand on any area for longer than two days. This can be difficult on big, flat fields. Some growers are able to divide these type fields into two smaller fields when they start irrigating so they can better manage the water. If this isn't practical, then providing multiple water inlets to the field can be helpful. Multiple inlets help avoid running water too long at the top of the field in order to get water to the bottom of the field. One multiple inlet method is to water the upper half of the field from the pump discharge or riser and then run irrigation pipe or tubing from the discharge down the field to water the lower half. A canal or flume ditch alongside the field can also be used for multiple inlets. The water can be directed from the ditch through cuts or spills into individual bays down the length of the field.

Levee Irrigation Resources

 

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Subsurface Drip Irrigation (SDI) Resources

Irrigators need a mechanism by which to evaluate the state of their pumping systems. With the current high diesel cost, this information is crucial in determining the profitability of switching to an electric motor or rebuilding existing diesel power plants. Additionally, producers need such analyses when applying for federal grant funds from the Resource Conservation & Development Councils (RC&D) or Natural Resources Conservation Service (NRCS) to assist them with electrical infrastructure or well replacements, respectively.

How is pumping efficiency determined?

A pumping system’s efficiency is calculated by comparing the amount of fuel used with the amount of water pumped. This efficiency will change due to the depth of water being pulled from a well, the condition of an engine and the rate at which the motor is turning. The calculated performance is then compared with the performance of the motor under perfect, laboratory standards. Typically, electric pumping systems will have a 75-85% overall efficiency, and diesel-powered pumps will have between 18-35% efficiency, depending on the age and care of the engine.

To calculate a system’s pumping efficiency, several pieces of information are needed. If this information is not able to be collected, assumptions can be made to estimate the efficiency. However, great care needs to be taken to make appropriate assumptions to prevent a gross over- or underestimation of the system’s performance.

Irrigating Smart conserves water, saves money and reduces energy.  The Irrigation Pumping Plant Efficiency Series was developed by the LSU AgCenter, Texas A&M University, University of Arkansas System's Division of Agriculture and New Mexico State University.