Submitted to: Irrigation Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/21/2012
Publication Date: 7/1/2013
Citation: Evans, R.G., Larue, J., Stone, K.C., King, B.A. 2013. Adoption of site-specific variable rate sprinkler irrigation systems. Irrigation Science. 31:871-887.
Interpretive Summary: This paper defines advanced SS-VRI technologies, provides an historical overview of the commercial evolution of self-propelled site-specific variable-rate sprinkler irrigation (SS-VRI) technology (zone control) and some of the barriers to adoption. SS-VRI can be defined as the ability to spatially vary water application depths across a field to address specific soil, crop and/or other conditions. The discussion is mostly directed toward center pivots rather than linear move systems because they comprise about 99% of the self-propelled sprinkler market. Various short-term and some long-term research needs are suggested in order to develop markets for these advanced irrigation technologies for general crop production and to conserve water and other resources. There have been over 20 years of government and private research on SS-VRI and the technology has been generally commercially available since about 2005. Obviously, there are tremendous opportunities for expansion of SS-VRI, but there are some significant barriers to the adoption of these technologies. These barriers can only be overcome by more directed private and public research and education programs to regionally address the specific concerns. Adoption rates of SS-VRI have been quite low for a number of reasons. Almost all of the SS-VRI research done to date has been directed toward development and improvement of hardware and basic control software with little emphasis on sensing and integrated control. The potential economic and water conservation benefits of these advanced systems have not been independently defined and quantified. Little research has been done on the economics, determination of the number and size of zones or sectors, or the management of these systems for greatest agronomic or resource conservation benefits. In addition, there are few economic incentives at this time for optimization of advanced SS-VRI technology for maximum crop water productivity with minimum yield reductions (e.g., managed deficit irrigation), which is where the greatest conservation potentials can be realized and the greatest research challenges lie. Relatively limited work has been done on developing suitable field sensor systems and integrating sensor feedback with the control and evaluation efforts. Furthermore, SS-VRI systems have been generally evaluated and tested under conditions designed to meet full crop ET and maximize yields per unit area with little concern for limited water availability scenarios. Thus, in many ways the current state of the technology is a solution looking for a problem. A major hindrance to research has been the lack of coordination and that there has not been a unified clear definition of the problems to be addressed and the value to be derived from the research. Supporting research on SS-VRI is way behind the industry. Substantial research and extension efforts are definitely needed to develop tools, training and education programs to support current SS-VRI management goals and uses in both the short term and long term. These research activities must be regional because the strategies and procedures for humid and arid climates will be quite different. In the short term, several equipment and research deficiencies need to be addressed to encourage further adoption. Equipment issues include the use of variable frequency pump motor controls for both irrigation and chemigation, and more reliable valves to control individual sprinkler heads. From a research standpoint, the foremost need is the development of guidelines and tools to assist consultants and growers in predefining standards for economically defining sizes and numbers management areas and writing basic prescriptions. Secondly, there is a need to develop tools that determine how to best locate various combinations of sensors for maximum benefit across a field and their use in managemen
Technical Abstract: More than twenty years of private and public research on site-specific variable-rate sprinkler irrigation (SS-VRI) technology has resulted in limited commercial adoption of the technology. Competing patents, liability and proprietary software have affected industry’s willingness to move into a new technology area. Documented and proven water conservation strategies using site-specific irrigation are quite limited. Marginal costs associated with site-specific technologies are high. Although sales of SS-VRI is increasing, they are primarily being used for eliminating irrigation and chemigation on non-cropped areas of a field or for land application of liquid agricultural and municipal wastes. Various aspects of SS-VRI technologies for general crop production are to beginning to slowly gain widespread acceptance; however, their uses are largely focused on addressing symptoms of poor design and sub-optimal water and nutrient management. Although currently underutilized, SS-VRI technology has the potential to positively impact crop water productivity, water and energy conservation, and the environment. There are also few economic incentives to motivate growers to move to higher levels of SS-VRI management. Greater adoption rates will likely require higher costs for water and energy, severely restricted water diversions on a broad scale, and enforcement of compliance with environmental and other regulations. Sustainable use of SS-VRI will require strong research support, which is currently limited. In the short term, adoption of SS-VRI technologies will be enhanced by addressing equipment deficiencies and research developing basic criteria and systems for defining management zones and locations of various sensor systems for both arid and humid regions. Training adequate personnel to help write site-specific variable rate irrigation prescriptions in humid and arid areas to assist growers with the decision making process is also a high priority. There is also a large need to educate government boards and bankers on the potential benefits of these systems. The long term challenges will be to demonstrate that SSVRI will improve water management or increase net returns. There is a critical need to develop fully integrated management systems with supporting elements that accurately and inexpensively define dynamic management zones, sense within-field variability in real time, and then adaptively control site-specific variable rate water applications, which will be challenging as significant knowledge gaps exist.