8 minute read
Addressing some of the complex irrigation challenges in the United States
Saleh Taghvaeian Associate Professor and Irrigation Engineer
University of Nebraska–Lincoln, USA
I am from Iran and grew up in the capital, Tehran, but my grandparents and two of my aunts were small-scale farmers in the arid northeast region of the country. Every summer after school was over, we would take the nine hour road trip to their village. Getting away from the noise and pollution of a crowded megacity and spending time out in the fields was so refreshing. The sound of cars and buses and construction would be replaced by the sound of water running in meandering farm ditches, and the smell of metal and asphalt and concrete was replaced with the smell of irrigated soil and freshly cut alfalfa. The valley where that village was located had been farmed for thousands of years (some of the hills in the region were excavated for archaeological discoveries). The people and their agricultural practices had changed over the millennia, but one thing that had remained the same, and I did not miss it in my observations as a kid, was the important role of water in bringing people together, feeding them, and allowing them to conserve and expand their community. Water was always a key topic of conversation, whether it was the water rights and possible disputes over allocation, or maintaining and upgrading irrigation ponds and canals, or the effects of deep wells on the sustainability of agriculture in the valley.
Water could not be ignored. My experience as a kid led me to pursue Irrigation and Drainage Engineering as my major in college. I received my Bachelor’s and Master of Science degrees in this field from a university in northeast Iran and then came to the United States to continue my graduate studies. I did my PhD programme at Utah State University, an institution with a long history of regional, national, and international research and training on different aspects of agricultural irrigation and drainage. My PhD research project was about estimating and mapping water use of agricultural crops (mostly alfalfa and cotton) and riparian vegetation (some invasive) along a portion of the southern Colorado River, where water is scarce and in high demand by many competing sectors such as municipalities, agriculture, and environmental uses. We updated and modified several field methods for estimating water use of several agricultural and natural plant species, and investigated irrigation efficiency within and among irrigated fields.
The people and their agricultural practices had changed over the millennia, but one thing that had remained the same, and I did not miss it in my observations as a kid, was the important role of water in bringing people together, feeding them, and allowing them to conserve and expand their community.
After graduation from the PhD program, I was offered an opportunity to work at Colorado State University figuring out a more sustainable solution to a practice that is known as “buy-and-dry.” What was happening at that time at the Colorado Front Range was that cities such as Denver and Boulder were growing rapidly and needed to secure more water resources in a region where available water resources were fully allocated. One approach implemented by the cities was to purchase water rights from senior water rights holders (farmers), transfer the consumptive use portion of the water right to cities, and leave the return flow portion of it in the river. The consequence was that the sellers would stop farming altogether (hence the name buy-and-dry). This had a devastating impact on the economies of rural communities. The solution we were working on was to develop practical methods for on farm management of deficit irrigation, where the farmers would sell a portion of their water right to cities and continue farming with the remaining portion. The goal was to minimise yield reductions by optimising the timing and amount of applying deficit irrigation to ensure the losses from yield reductions were smaller than the revenue from selling a portion of the water right. But accomplishing this was quite challenging in the context of the Colorado water law, since deficit irrigation practices could not have any impact on historical return flows. So the goal was to achieve the reductions by only reducing the consumptive use while ensuring the same amount of return flows took place to satisfy the water rights of downstream users. We worked on and developed sensor-based methods that relied on canopy temperature and soil moisture as input data.
From Colorado, I moved to Oklahoma to serve as the state irrigation engineer and extension specialist. The agricultural water challenges were very different in Oklahoma. In the southwest corner of the state, we had an irrigation district that relied on a surface reservoir as their main water source. However, the flow to that reservoir had been declining dramatically due to a combination of more frequent and severe droughts and more pumping of groundwater right next to the riverbanks upstream of the reservoir. Despite the differences between Oklahoma and Colorado, water laws were once again influencing agricultural water management. While groundwater near local streams is hydrologically connected to water in the stream and thus pumping it could deplete surface flows, the law treated surface and groundwater separately as if there were no interactions between the two. The farmers in the irrigation district were testing different
solutions such as converting from furrow irrigation to subsurface drip (which also helped a lot with labour shortages) and relying more on the lower quality groundwater resources. They were also working with us and state and federal agencies to quantify the magnitude of and address the issue of stream depletion due to pumping close to the river. The story was different in the Panhandle of Oklahoma, where no viable surface water is available. Farmers there relied solely on the Ogallala aquifer, which has been declining rapidly since the expansion of mechanised irrigation in the 1960s and 70s. The recharge rate of that part of the Ogallala aquifer is practically zero (the average depth to water is over 60m). So the water level is always dropping, faster during drought years and slower during wet years, but it never rises. Farmers in the Oklahoma Panhandle were investing in reducing losses from wind drift and direct evaporation of droplets when travelling from sprinklers to crop and soil surfaces, testing drought-tolerant hybrids, and exploring crops with lower water requirements than corn (for example cotton and sorghum). My work in that area focused on improving irrigation scheduling using soil moisture sensors, comparing the water demand of different crops and estimating the reductions in irrigation extractions by large-scale conversion to alternative crops, and conducting pump energy and irrigation uniformity audits.
I have recently moved from Oklahoma to Nebraska, where I have research and teaching responsibilities at the University of Nebraska Lincoln. I am excited about this position and my role in training the next generation of irrigation engineers and managers. With over 8.5 million acres (3.4 million hectares) of irrigated land, Nebraska is the number one state in the US in terms of irrigated area. We are also home to four major manufacturers of centre pivot systems, as well as several other companies in the irrigation industry. Our department (Biological Systems Engineering) has a long history of collaborating with farmers and industry partners in Nebraska to tackle old and emerging issues in agricultural water quantity and quality. One of the issues that has recently received a lot of attention is the high levels of nitrate in groundwater, which could cause a wide range of health problems, especially in children. Several
researchers at University of Nebraska are working on innovative tools and solutions to better manage fertiliser application during the growing season, taking advantage of the two key capabilities of modern centre pivots: fertigation and speed-control variable rate irrigation. We are also working on machine learning and artificial intelligence applications in estimating the current and near-term irrigation requirement of corn and soybean.
In addition, University of Nebraska is home to the Daugherty Water for Food Global Institute, which leads many projects on engineering, environmental, and economic aspects of agricultural water management around the world. The institute has allowed us to exchange knowledge and experience with farmers and decision-makers from other parts of the world. Identifying and implementing sustainable solutions to the challenges that threaten our precious land and water resources and our ability to feed a growing population requires an unprecedented level of collaboration and cooperation among different water users. It requires a commitment to educate the next generation of experts and decision-makers and to equip them with the right skill set to address extremely complicated water issues.
