|King, Bradley - Brad
Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/9/2011
Publication Date: 6/1/2012
Citation: Evans, R.G., King, B.A. 2012. Site-Specific Sprinkler Irrigation in a Water Limited Future. Transactions of the ASABE. 55(2):493-504.
Interpretive Summary: Agriculture will need to increase crop production to meet future societal needs in spite of two major constraints, which are that the productive irrigated land base and the quantity of available water are both declining sharply. Energy availability will also be limited. The development of more efficient water management systems and strategies to improve crop water productivity and support a sustainable agricultural environment will be required. In addition, innovative crop production strategies will have to target inputs to meet yield goals somewhere near the economic optimum (e.g., deficit irrigation management), which will generally be considerably less than conditions of full crop ET for maximum yields. These strongly emergent forces will cause the simultaneous development and integration of: 1) improved irrigation application technologies; 2) broad implementation of managed deficit irrigation of most irrigated crops; and, 3) development of integrated decision support systems to implement these technologies. In addition, wide-scale water shortages will also be the general catalyst to meld all these technologies with several other aspects of existing precision agriculture technologies into comprehensive management systems. There is little doubt that irrigated agriculture can reduce its water use while maintaining reasonable production levels. However, the challenges are substantial. Water shortages will force irrigated agriculture to put these alternative management and cultural practices together into holistic, sustainable systems, but these alternatives have seldom been integrated into complete management systems. Optimal use of available precipitation will obviously be required. It will be mandatory to implement system-wide enhancements of water delivery systems and other supporting monitoring, modeling and control technologies to enable the adoption and use of deficit irrigation and advanced irrigation technologies that include self-propelled sprinklers and microirrigation systems. Irrigation system and management technologies will also benefit from other precision agriculture technologies such as site-specific nutrient and pesticide applications. The implementation of site-specific irrigation technology that can spatially direct the amount and frequency of water (and appropriate agrochemical) applications could potentially be very powerful tools to increase water productivity, reduce inputs and minimize adverse water quality impacts. However, more than twenty years of government and private research has lead to limited adoption of these technologies, mostly because of limited market demand. Thus, it’s time to move from developing hardware to research directed at developing and documenting site-specific water conservation strategies. Integrated, comprehensive decision support tools will be needed to assist growers and managers in optimizing the allocation of limited water among crops. These programs should use holistic approaches that not only include amount of water to apply at specific times in the growing season, but also on yield potential, crop price, cost of operations and other economic factors on a whole farm scale in order to maximize net return to the producer rather than total yield. Site-specific, deficit irrigation strategies with self-propelled sprinkler systems combined with other relevant site-specific precision agriculture technologies are expected to play major parts in this technological evolution.
Technical Abstract: Available water supplies for irrigation are becoming more and more limited in the western USA and other locations around the world, and this trend is accelerating. This will force major changes to physical and managerial aspects as well as design of water delivery and on-farm irrigation systems. Thus, a water and energy limited future will be the likely catalyst that finally brings many of the existing precision agricultural technologies together for irrigated agriculture. Resource conservation as well as achieving environmental benefits under these conditions will probably require the adoption of non-uniform water applications, also known as site-specific irrigation. The goal of site-specific irrigation is to conserve water by directing the amount and frequency of water applications according to established spatial and temporal crop water requirements. However, twenty years of private and public research on site-specific irrigation has resulted in very limited commercial adoption of the technology. The primary reason for the very low rate of commercial adoption appears to be the absence of a market for the technology. Documented and proven water conservation strategies using site-specific irrigation are essentially nonexistent and its cost-effectiveness has not been demonstrated. Simulation studies comparing conventional and site-specific irrigation have reported water savings of 0 to 26%. Ironically for well-watered crop production, water savings from site-specific irrigation maybe greatest in humid climates by spatially maximizing utilization of growing season precipitation. In arid and semi-arid climates, the greatest potential water savings could come from highly managed deficit irrigation where spatial management of soil water deficit timing is used to maximize net return rather than yield. This strategy will require integration of irrigation system hardware, sensor systems, and decision support software, which will be challenging as significant knowledge gaps exist. It will also require a shift in production practices from maximizing yield to maximizing net return. Future research needs to focus on developing and documenting cost-effective site-specific water conservation strategies in order to develop markets for these irrigation technologies. The current status of site-specific sprinkler irrigation and some general barriers to adoption of the technology are reviewed. Keywords. precision irrigation, precision agriculture, spatial variability, water management, irrigation controls, adaptive control systems, decision support, sensor systems.