SDI and Electrotechnologies
Freddie Lamm Todd Trooien
Gary Clark Dan Rogers
Kansas State University
Subsurface drip irrigation (SDI) and electrotechnologies are excellent partners as each complement the other. This paper will conceptually describe some of the potential interrelationships. The scope, magnitude, and significance of these interrelationships is subject to a host of variables, such as climate, soils, crops, irrigation management, economics of alternative energy sources, and availability of electric power.
REDUCED ENERGY REQUIREMENTS WITH SDI
Large amounts of energy are used for irrigation. Slogett (1985) reported that 50% of the energy used for irrigation in the US in 1983 was used in the Southern and Northern Plains. SDI can reduce energy use through reduced operating pressures, lower water use, and improved fertilizer and herbicide utilization.
SDI systems can be operated at lower pressures than medium to high pressure center pivot sprinkler systems and have comparable pressures to low pressure center pivot sprinkler systems. However, SDI systems will generally have a higher operating pressure than gravity or surface irrigation systems.
Energy requirements can also be reduced through decreased irrigation water use. Various estimates in the literature report that SDI can reduce irrigation water use by 25 to 50% of sprinkler and surface irrigation requirements. Water use reductions can be accomplished with SDI by eliminating or greatly reducing evaporation, runoff and drainage. In addition, SDI can reduce water applications by just meeting and not exceeding plant water needs through more precise and timely small applications of water. The amount of effective precipitation can also be increased with SDI because the soil surface and interrow areas are drier and more receptive to infiltration.
The manufacturing of chemical fertilizers requires large amounts of energy, thus improved fertilizer utilization through spoon feeding the crop with SDI can also save energy. In addition, SDI can potentially result in reduced weed control problems and thus require less herbicides.
SDI AND AUTOMATION FOR MONITORING AND CONTROL
As farming operations increase in size and become more integrated to make use of the economic advantages of such operations (CAST, 1996; NRC, 1996), labor savings through automation become increasingly important. SDI is an irrigation method that is not only well-suited to automation, but is also a method that can utilize automation to achieve high standards of water conservation and water quality protection.
Automation is also required (or desirable) for SDI for the high frequency and precise water and fertilizer capabilities of the system. Automation is also useful for other irrigation and cultural practices, such as chemigation, computer and sensor-aided irrigation scheduling, and pest management.
Automation is more convenient with electrical pumping plants and typically requires electrical monitoring and control systems. Automated systems are also relatively easy to adapt to electrical load management and off-peak power programs. Frequent starting and stopping of the irrigation cycle is more easily accommodated with electric motors and controls as compared to internal combustion engines.
SDI AND LOAD MANAGEMENT
SDI systems can uniformly apply and distribute very small irrigation amounts (< 0.05 inches) for each event as compared to center pivot sprinkler and surface irrigation systems. As a result, SDI systems are well-suited for frequent or intermittent interruption of irrigation service as might be required by electrical load management schemes.
Greater design irrigation capacities are typically associated with SDI systems because higher emitter flow rates are usually required to prevent emitter plugging. Higher irrigation capacities allow for more intermittent irrigation events. Lower irrigation capacities can be designed for SDI systems through dividing the system into more zones, but this increases the investment cost for the system. As a counterpoint to the typical higher irrigation capacities, there is some evidence that a multi-zoned, high frequency SDI system may be utilized in a deficit irrigation mode for field corn to either conserve irrigation water or to increase irrigated acres.
SDI AND SCALE FACTORS
The economics of various size SDI systems are more proportionally adjustable than center pivot sprinklers systems (O'Brien, et al. 1997). As a result, SDI systems can be utilized on smaller irrigated areas and irregularly shaped fields and thus require smaller irrigation pumping plants. On smaller irrigation systems a wider range of continuous duty electric motors are available for pumping than internal combustion engines. In some cases, the smaller SDI systems could use single phase electric motors.
Small SDI irrigation systems that can also tolerate interrupted irrigation cycles could be good candidates for alternative electrical generation schemes such as wind or solar energy.
The use of electrotechnologies with SDI, though not absolutely required, is an excellent combination which can enhance the efficiency and environmental friendliness of irrigation. Similarly, SDI can be a excellent partner to electrotechnologies by reducing and balancing energy loads and also by being a well-managed and predictable load.
The Hugoton natural gas fields in southwest Kansas, formerly one of the world's largest gas reserves, is being rapidly depleted and is nearing the end of its useful commercial life. As this happens along with the further deregulation of natural gas, irrigators in much of the Great Plains region will be scrambling to find alternative energy sources. Electrical power stands to pick up a sizeable share of this market.
CAST (Council for Agricultural Science and Technology). 1996. Future of irrigated agriculture. Task Force Report 127. CAST, Ames IA. 76 pp.
NRC (National Research Council). 1996. A new era for irrigation. National Academy Press, Washington DC. 203 pp.
O'Brien, D., Rogers, D., Lamm, F. and G. Clark. 1997. Irrigation system economics as affected by field size. 1997 Central Plains Irrigation Short Course and Equipment Exposition Proceedings, Colby, Kansas, February 4. pp. 81-93.
Slogett, G. 1985. Energy and US agriculture: Irrigation pumping, 1974-1983. USDA, Agriculture Economic Report No. 545.
This paper was first presented at the EPRI-Agricultural Technology Alliance semi-annual meeting, Boise, Idaho, May 28-30, 1997.
The corresponding author is:
Dr. Freddie Lamm
Research Agricultural Engineer
KSU Northwest Research-Extension Center
105 Experiment Farm Road
Colby, Kansas 67701-1697