The greatest challenges of our time are water security and food security, which are deeply interconnected and require urgent, coordinated action. Weather-associated extremes such as droughts and floods threaten the future of crop production in any part of the world, including the United States. Droughts impact the water supply for many beneficial uses, including irrigation, increasing competition for finite freshwater resources. In addition, the global population is projected to reach 9.5 billion by 2050, requiring more food to be produced using less freshwater resources. Sustainable microirrigation is one of the key solutions with the potential to address these critical challenges by improving water use efficiency and enhancing agricultural resilience. Sustainable irrigated agriculture can protect marginal lands from further development and save water resources. Irrigated agriculture provides about 40% of the world’s food supply utilizing approximately 25% of the land resource. Although irrigated lands were greatly expanded in the 20th century, most experts agree that such additional expansion in the 21^st century will not be possible. The agricultural community must not only increase the food supply, but it must also conserve water and protect water quality. Crop water productivity (CWP, also known as water use efficiency, WUE) is defined as the crop yield divided by the total water used to produce that crop. Thus, it can be easily recognized that the numerator can be increased or the denominator can be decreased to increase CWP. Often, strategies to increase CWP concentrate on the denominator, such as using deficit irrigation to reduce water withdrawals. Implicit with these strategies is the desire to not greatly reduce farm profitability by negatively impacting crop yields to a large extent. There are limitations to using the denominator to increase CWP since the overall reason irrigation is practiced is to increase farm profitability. It can also be shown that appropriate levels of irrigation can increase CWP. In that aspect, sustainable microirrigation has great potential to intensify crop production at a greater level while still efficiently using water and also protecting water quality. We define sustainable microirrigation (SM) as the practice of using efficient, low-volume irrigation techniques, such as drip or micro-sprinkler systems, in a way that conserves water resources, improves agricultural productivity, and reduces environmental impact.

Although SM is widely recognized as the most efficient and environmentally friendly method of irrigation, the US and international land area under SM is still relatively low. Slowly, this is changing as water resources are stretched, more synergistic combinations of crop production technologies are developed, and the sheer need for food production increases. SM will play a large role in these highly productive agricultural systems. Efforts such as those described in Project W5128 add to our ability to intensify crop production with SM, resulting in a secure water and food future for everyone while exacting a less negative impact on the environment.

Unless timely action is taken, it is anticipated that water supply- and water quality-related crises will affect economies and resources of national and global importance (e.g., water supply shortages in Central Valley, Ogallala Aquifer Region, Mississippi Delta, in the US, North China Plain in China, Punjab, and Uttar Pradesh in India, Murray-Darling Basin in Australia, Central Chile, and many parts of Middle East and North Africa). SM can reduce the waste of water to a negligible amount and reduce 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 minimize plant water stress. It can optimize crop production and, in many cases, increase the quality of agricultural products.

Review of Progress in Microirrigation Multistate Project

This multistate project has been working since its initiation in 1972 to address practical issues related to the application of microirrigation technology. Originally formulated as a western U.S. regional project concerning drip and trickle irrigation (W128), over the years, the group has included participants from multiple disciplines, such as agricultural engineers, plant and soil scientists, and agricultural economists from diverse regions (Caribbean to the Pacific U.S. Territories). The project was renumbered W1128 in 2004, W2128 in 2009, W3128 in 2014 and become W4128 in 2019. A major project accomplishment during the early years of the microirrigation project W128 was the publication of the original reference book, “Trickle Irrigation for Crop Production” (Nakayama and Bucks, Eds., 1986). The author group of that book’s successor, “Microirrigation for Crop Production” (Lamm, Ayars, and Nakayama, Eds., 2007) involved many past and present project members. In a plenary paper at the 5th International Microirrigation Congress, Phene (1995) attributed the bulk of coordinated microirrigation research to the regional projects W128 and the now defunct S-247. A significant product of the earlier W2128 was the comprehensive microirrigation maintenance website http://micromaintain.ucanr.edu/ with joint collaboration of CA, TX, and KS. The project has offered project-related technical sessions at the Irrigation Associations (IA) conferences in 2001, 2002, 2004, 2005, 2009, 2012, 2018, 2019 and 2021. Most of these proceedings papers can be accessed at http://www.irrigation.org/technicalpapers. The project has a long history of productivity through publications, with 139 publications occurring under the previous project number, W3128 during the period 2014 through 2018. The project W3128, “Scaling Microirrigation Technologies to Addressed the Global Water Challenge”, had three objectives: 1) Develop robust and appropriately-scaled methods of irrigation scheduling using one or more soil-, plant- or weather-based approaches; 2) Develop microirrigation designs and management practices that can be appropriately scaled to site-specific characteristics and end-user capabilities; and 3) Develop technology transfer products for a diversity of stakeholders to promote adoption of microirrigation. The project W4128  that was accomplished during the period 2020 to 2024 had 4 objectives namely 1) Develop and evaluate irrigation systems, designs, technologies, and management practices that are sustainable and can increase water productivity, 2) Improve methods of irrigation scheduling that are particularly applicable for microirrigation, 3) Develop, evaluate, and adapt models as tools to improve system design, management, and production and 4) Expand technology transfer products for a diversity of stakeholders to promote adoption of water-saving irrigation strategies.

The overall accomplishments of project W4128 were excellent, as evidenced by the publications from 2019 to 2024. The project participants were agricultural engineers, plant scientists, and soil scientists, which has been a healthy, synergistic mix of expertise. The participants remain committed to technology transfer, as evidenced by including it as a distinct objective in both W3128 and W4128. The proposed project (W5128) will be a continuation of project W4128 with a particular emphasis on sustainable microirrigation (SM).

The accomplishments of the recently concluded W4128 project directly feed into further advances in microirrigation technologies that are envisioned in W5128, which can increase sustainability and support water security and food security. In some cases, the proposed W5128 effort will advance the technology (e.g., managing microirrigation to provide multiple benefits, including soil health), while in other cases the effort will concentrate on packaging and promoting the technologies (e.g., smartphone and web applications of decision support tools) that have already been developed in the history of this project since 1972.