W2128: Microirrigation for sustainable water use
Statement of Issues and Justification
The water crisis and how microirrigation can address it.The Challenge of the 21st century will be coping with water scarcity according to the Food and Agriculture Organization of the United Nations (FAO) Director-General, Dr Jacques Diouf (FAO,2007). Much effort will be required to meet food and freshwater demands for an anticipated 2030 global population of 8.1 billion. On a worldwide basis there was a five-fold increase in irrigation during the 20th century (ONeill and Dobrowolski, 2005) which probably cannot be repeated in the 21st century. The agricultural industry diverts the largest amount of water on a worldwide basis, so it must take a leading role in achieving sustainable water use that will provide for both the growing need for food and the need for clean and safe water supplies. Within the United States there has also been a realization of our own countrys water crisis and a call for action. According to the U.S. Department of the Interior (USBR, 2005) Water 2025 report, water planning for the year 2025 must be based on the reality that demand for water in many basins of the West exceeds the available supplies even in normal years. Since the West is also home to some of the fastest growing communities in the nation, increasingly frequent water supply crises are anticipated. In the past century water crises were intense but typically occurred in drought years; they only affected resources and economies of local and regional importance. Unless timely action is taken, it is anticipated that water supply-related crises will affect economies and resources of national and international importance. The U.S. Department of Interior has moved forward from its Water 2025 report with what it considers necessary efforts (USBR, 2008a and b) to increase water conservation, improve efficiency, and help secure future water supplies through competitive grants and technical assistance. The U. S. Department of Agriculture Cooperative States Research Education and Extension Service (USDA-CSREES) through its Agricultural Water Security (AWS) Initiative have identified three promising areas for CSREES research, education and extension programs. They are: 1) Exploring new technologies for the use of recycled water and water conservation in agricultural, rural, and urbanizing watersheds; 2) Probing the human, social, and economic dimensions of agricultural water security with a focus on adoption-outreach; and 3) Researching biotechnological improvements in water use efficiency of crop and horticultural plants to yield greater crop per drop. There are many challenges facing irrigated agricultural both domestically and abroad. Howell (2006) points out that until the mid 1990s, irrigated land increased at a faster than did the worldwide population growth rate. After that it appears that overall irrigated area growth has stopped while population continues to grow. He further stated that irrigation would remain vitally important in meeting the growing food and feed demands and that there were still great opportunities through agronomic, engineering, and management technologies to reduce non-productive water use in irrigated agriculture. Most water planners and resource managers recognize that there will be no magic bullet that will remove all of the worlds or nations water problems. Instead there is a growing realization that it will take many tools working together to help avoid the significant disruption in the economies and societies grown accustomed to widespread irrigation use. Microirrigation is just one of the many irrigation and water management technology tools, but it is a tool that has several advantages. Microirrigation can reduce the waste of water to a negligible amount and the transport of contaminants to surface water and groundwater. Irrigation events can be fine-tuned to spoon feed water and nutrients just in time to avoid plant stress. It can optimize crop production (more crop per drop) and in many cases increase the quality of agricultural products.
Issues and Justification for Objective 1 As the pressures on water resources continue to tighten the definition of sustainable water use, even microirrigation which is considered to be the most efficient irrigation method must be closely examined for additional water savings. The simplest and most common definition of irrigation scheduling is simply the determination of when and how much water to apply. Improvements in microirrigation timing and amounts represents an important topic area where additional water savings can be made, but it must be carefully balanced with the primary economic goal of microirrigation which is to improve crop yield and quality. Several microirrigation scheduling approaches could be chosen for a particular crop in a particular environment. There are also many practical factors which must be considered when developing an irrigation schedule (e.g., system type and design), but the most widely accepted framework for understanding overall plant water requirements is a mass balance approach based on the concept of evapotranspiration (e.g., Howell and Meron, 2007.). In this approach, reference ET for a standard canopy is calculated from weather data and then multiplied by one or more crop coefficients (Kc) to estimate the evapotranspiration for the crop in question. This basic approach was already well developed over 40 years ago (Doorenbos and Pruitt, 1977) and has been further refined (Allen et al., 1998), but current research efforts are still underway to reevaluate published crop coefficients, particularly in woody perennials (Snyder, 2008). The methods used for on-farm irrigation scheduling can be roughly classified into three types, depending on the primary basis for the schedule: 1) ET-based, 2) soil-based and 3) plant-based. An ET-based schedule may use current weather data together with a published Kc to primarily determine how much water is used by the crop on a daily basis, and secondarily consider factors such as irrigation system capacity (typically designed to meet maximal crop ET (ETc)), root depth and soil characteristics to determine how often to replace ETc. A soil-based schedule may use a direct or indirect measurement of soil water to primarily determine when water must be added to the soil, and secondarily consider factors such as irrigation system capacity and root and soil factors to determine how much water can be reasonably added during the irrigation event. A plant-based schedule may use a direct or indirect measurement of plant water status to primarily determine when water must be applied, and secondarily consider factors such as irrigation system capacity and soil factors to determine how much can be added during the irrigation event.
While most practical guides to irrigation scheduling (e.g., extension publications such as Ashley, et al., 1998; Ley et al., 1994; Neibling et al., 2004, and Reddy et al., 2007) recommend that all of the above mentioned factors should be considered, it is generally assumed that crop ET needs must be fully met by a combination of precipitation, applied water, and stored soil water, in order to achieve maximum production. However, crops are complex biological systems, and in some crops, economic and/or horticultural benefits of deficit irrigation have been shown (e.g., for "regulated deficit irrigation (RDI)," Boland et al., 1993, Shackel et al., 2000). A key limitation to the use of this approach is that the benefits of RDI have also been shown to be highly site specific, even within a field (Lampinen et al., 1995). Current microirrigation systems are capable of a substantial degree of scheduling flexibility, including the ability to respond to current weather conditions (Shedd et al., 2007), and it is not unreasonable to anticipate that future systems may include the ability to control water application at a very fine spatial scale (e.g., individual trees in an orchard) through wireless networks or by other means. The key issue for each crop and environment however, will be to what extent a deficit and/or spatially variable irrigation strategy will influence ultimate crop productivity (yield, quality). For field corn, Evett et al. (1996) reported that one plant-based approach (based on a threshold canopy temperature) required more irrigation water, but gave significantly higher yields than an approach based on replacing 100% of ETc (based on soil water depletion using neutron scattering) for field corn in Texas. In this study, similar plant-based approaches, but using different temperature thresholds, achieved slightly higher yields (although not statistically significant) compared to the control for about the same amount of irrigation as used in the control. Data are needed from a range of crops and environments to quantify the effects of different irrigation scheduling approaches on the relation of yield or product quality to applied/available water.
Soil-based scheduling methods which use sensors and controls to initiate and terminate irrigation can also be highly appropriate for microirrigation with its high degree of automation and application uniformity. There have been major advances in these sensors, including improved reliability and communication capabilities in the age of the internet. Several participants of the proposed project will be comparing and calibrating different types of sensors and controls for irrigation to more traditional irrigation scheduling techniques.
Issues and Justification for Objective 2
Sustainable water use through microirrigation can be approached through the concept of more crop per drop. Thus in addition to improving sustainable water use through Obj. 1 of the proposed project with water savings obtained with improved microirrigation scheduling, it is also important to improve crop yields through improved microirrigation management and to increase usage and reliability of microirrigation systems through better design and maintenance. Microirrigation is by far not the predominant irrigation method in the United States but interest in the technology is growing. Early and growing adoption of microirrigation usually begins with comparison of microirrigation to more traditional irrigation methods for the region. These system comparisons may be based on pertinent factors such as crop yield and economics, water use and conservation, and environmental issues (chemical leaching and drainage). Although the pertinent factors may differ with region, crop, soil, and climate constraints, the goal is primarily to develop proper management strategies for the various irrigation methods, particularly for those methods such as microirrigation less familiar to producers. In the proposed study, much needed baseline information about alternative irrigation systems for the typical crops in each region will be obtained. The project participants will share results and develop common guidelines for optimizing performance of the various irrigation systems from both an economic and environmental standpoint. Subsurface drip irrigation (SDI) is one of the fastest growing irrigation methods in the non-traditional microirrigation regions of the country because subsurface installation allows for high initial system costs to be amortized over many years. Formal and informal producer surveys conducted under the current USDA-RRF W-1128 project have indicated that SDI is undergoing rapid expansion in some areas of the United States, particularly in TX for cotton production. As SDI continues to penetrate into new areas, there will be greater needs for research and extension efforts to help producers manage for optimal crop production, protect the environment and maximize system life through proper maintenance. Emitter clogging remains the primary cause of microirrigation system failure around the world, so improved emitter maintenance will be a key factor in having sustainable microirrigation systems. There have been few efforts to unify and summarize the emitter clogging results from the diverse regions of the United States primarily because microirrigation is a small evolving technology and because newly emerging regions did not have or could not allocate sufficient expertise to build on earlier research efforts from other regions. Several participants working within Obj. 2 and 4 of the proposed project will be working to create a web-based tool for microirrigation that can extend across the United States.
Issues and Justification for Objective 3
The conjunctive use of agricultural chemicals (agrochemicals) with microirrigation can help achieve sustainable water use in the United States through higher water productivity, through greater crop yields and improved crop quality, and through protection of surface and ground water resources from agrochemical pollution in runoff and leachates.
Agrochemicals, whether applied through the irrigation system or through other means, are used for a wide range of purposes. In maintenance of microirrigation systems, acids, chlorine, herbicides and other products are sometimes used to prevent emitter clogging due to chemical precipitates, biological growths, or root intrusion. Precise application of fertilizers and/or pesticides through the microirrigation system is often cited as an advantage of microirrigation (Ayars et al., 2007). Effective use of fertilizers or other agricultural chemicals applied through other means (ground rig or aerial application, for instance) may require extra considerations in microirrigated conditions. Potential obstacles to agrochemical applications with microirrigation include limitations to applicability of soil injected chemicals and limitations due to limited agricultural chemical labeling for microirrigation application. Microirrigation chemigation is based on the principles of precision farming where system inputs are qualitatively and quantitatively matched to the needs of the crop. Subsurface drip (SDI) and surface drip (DI) systems can be used to for the injection of systemic pesticides and some biocontrol agents while surface microsprinklers may be used to apply biocontrol agents over larger areas and on plant canopies. Use of SDI systems for systemic insecticide or fungicide application has the advantage of compatibility with integrated pest management principles. However, the use of pesticides through microirrigation systems is much less advanced as compared to nutrient fertigation. Current research programs conducted by participants of this proposed project as well as by others across the United States are beginning to address fertigation and chemigation through microirrigation (particularly through subsurface drip irrigation), yet results are generally preliminary or otherwise not sufficiently interpreted for development of best management practices. Research and extension/outreach associated with this project will advance knowledge necessary to develop BMPs and interpret this knowledge into BMP recommendations.
Issues and Justification of Objective 4.
Sustainable water use in the United States can be greatly augmented by microirrigation use of non-potable waters. Extending the concept of sustainability, the sustainable use of microirrigation for use with non-potable waters requires careful selection of system components and appropriate management of the whole microirrigation system. Use of non-potable waters as a microirrigation water sources is becoming more common as limited high quality water sources are first used by municipal and industrial users. Agricultural water needs are then supplied by lower quality water, including saline waters, reclaimed water from treatment plants, and water produced by animal agriculture operations. Use of non-potable water for irrigation has advantages since the water is often rich in nutrients beneficial to crops and use of the non-potable water for irrigation often reduces treatment costs and environmental impacts. Non-potable water use through microirrigation also has disadvantages since some of the water constituents may adversely impact soil quality and plant growth. Operation and maintenance of microirrigation systems may also be a challenge when poor water quality sources are used. Because these non-potable waters can come from processing facilities, homes, municipal treatment plants, rural municipal lagoons, and livestock lagoons, the characteristics of these non-potable water sources can vary widely in terms of chemistry, biological activity, and physical condition. These characteristics will influence filtration requirements, treatment practices, emitter performance, soil quality, and crop and landscape performance. Sometimes the non-potable water is used primarily as a substitute in irrigation, saving fresh water for other uses, while in other cases such as in on-site residential wastewater use this application method is primarily for pathogen reduction and protection of freshwater sources. Additional research is needed to evaluate water treatment practices with non-potable water sources that include assessment of filter systems and the effects of emitter design on long-term performance, as well as other factors. This collaborative research effort being proposed in this project will allow researchers to develop better recommendations for system hardware selection, improved maintenance procedures and guidelines for non-potable water utilization for different geographic locations, environmental conditions, soil characteristics, and water sources.
Why this project and why now?
A cooperative multi-state approach towards technology development can be extremely fruitful as evidenced by the significant body of research and extension efforts developed by W-128 and W1128 participants since 1972. This cooperative approach allows for the evaluation of group hypotheses and for distillation of common results into general guidelines. The multi-state, regional project approach can also be utilized as a peer review process for hypotheses developed by individuals with the hopes of expanding or advancing the overall scientific understanding. Another advantage of the cooperative approach is its utilization as a strong feedback mechanism to point out where there is not enough information or theoretical understanding to develop general guidelines. In the proposed revision, W-2128 members will utilize the distillation process, peer review process and the feedback mechanism to accomplish the project objectives. In many cases, it will be necessary to refine and adapt microirrigation technologies for site specific conditions (crops, soils, water quality and availability, climate and irrigation system characteristics). In other cases, it will be necessary to improve and develop management strategies to take advantage of the inherent capabilities of microirrigation.
Some scientists, water planners, and resource managers have been disappointed with the rate of adoption in microirrigation. The U.S. land area that is microirrigated varies on an annual basis but during the last 10 years has hovered in the range of 3 to 4% of the total irrigated area. It is recognized that some crops and locations are not physically or economically suitable for microirrigation, but this is probably the exception rather than a common situation. Although microirrigation is expensive, there is a growing realization that leaders in the farming community can and will adopt and adapt cutting-edge technologies when given the knowledge and incentives to do so. This is evidenced in the tag line of the recent USDA-NRCS Conservation Security Program (CSP) which is reward the best and motivate the rest.
Success within the proposed project will have a positive impact on addressing the Challenge of the 21st century. The primary consequences of not doing the research are that significant knowledge gaps about the use of microirrigation and its associated technologies will continue to discourage producers from adopting it and through its continued lack of growth, worldwide water problems will continue unabated.
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