Scientists have produced a new method that holds the promise of improving groundwater management – critical to agriculture in dry regions. The method sorts out how much underground water loss comes from aquifers confined in clay, which can be drained so dry that they will not recover, and how much comes from soil that’s not confined in an aquifer, which can be replenished by a few years of normal rains.
The research team studied the U.S.’s Tulare Basin in California’s Central Valley and found the key to distinguishing between these underground sources of water relates to patterns of sinking and rising ground levels in this heavily irrigated agricultural region. Although this location makes up only one percent of U.S. farmland, it grows 40 percent of the nation’s table fruits, vegetables and nuts annually. Farmers augment this valley’s 12 to 25 centimetres (five to 10 inches) of annual rainfall with extensive groundwater pumping. In drought years, more than 80 percent of irrigation water comes from underground.
After decades of pumping, underground water resources are dwindling. Wells in the Tulare Basin now must be drilled over 1,000 metres (3,500 feet) deep to find adequate water. There’s no way to measure exactly how much water remains underground, but managers need to make the wisest use of whatever there is. That involves monitoring whether water is being drawn from aquifers or from loose soil, known as the water table. In this large region with tens of thousands of unmetered wells, the only practical way to do that is by using satellite data.
A research team from NASA’s Jet Propulsion Laboratory in Southern California and the U.S. Department of Energy’s Lawrence Berkeley Laboratory in Northern California set out to create a method that would do exactly that. They attacked the problem by combining data on water loss from U.S.-European Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-On satellites with data on ground-level changes from a ESA (European Space Agency) Sentinel-1 satellite. Ground-level changes in this region are often related to water loss because when ground is drained of water, it eventually slumps together and sinks into the spaces where water used to be – a process called subsidence.
The Tulare Basin is subsiding drastically: The current rate is about 0.3 metres (one foot) of sinkage per year. But from one month to the next, the ground may drop, rise or stay the same. What’s more, these changes don’t always line up with expected causes. For example, after a heavy rainfall, the water table rises. It seems obvious that this would cause the ground level to rise, too, but it sometimes sinks instead.
The researchers thought these mysterious short-term variations might hold the key to determining the sources of pumped water. “The main question was, how do we interpret the change that’s happening on these shorter time scales: Is it just a blip, or is it important?” said Kyra Kim, a postdoctoral fellow at JPL and coauthor of the paper, which appeared in Scientific Reports.
Clay vs. sand Kim and her colleagues believed the changes were related to the different kinds of soils in the basin. Aquifers are confined by layers of stiff, impermeable clay, whereas unconfined soil is looser. When water is pumped from an aquifer, the clay takes a while to compress in response to the weight of land mass pressing down from above. Unconfined soil, on the other hand,
rises or falls more quickly in response to rain or pumping.
The researchers created a simple numerical model of these two layers of soils in the Tulare Basin. By removing the long-term subsidence trend from the ground-level-change data, they produced a dataset of only the month-to-month variations. Their model revealed that on this time scale, virtually all of the ground-level change can be explained by changes in aquifers, not in the water table.
For example, in spring, there’s little rainfall in the Central Valley, so the water table is usually sinking. But runoff from snow in the Sierra Nevada is recharging the aquifers, and that causes the ground level to rise. When rainfall is causing the water table to rise, if the aquifers are compressing at the same time from being pumped during the preceding dry season, the ground level will fall. The model correctly reproduced the effects of weather events like heavy rainfalls in the winter of 2016-17. It also matched the small amount of available data from wells and GPS.
Kim pointed out that the new model can be repurposed to represent other agricultural regions where groundwater use needs to be better monitored. With a planned launch in 2023, the NASA-ISRO (Indian Space Research Organisation) Synthetic Aperture Radar (NISAR) mission will measure changes in ground level at even higher resolution than Sentinel-1. Researchers will be able to combine NISAR’s dataset with data from GRACE Follow-On in this model for the benefit of agriculture around the globe. “We’re heading toward a really beautiful marriage between remote sensing and numerical models to bring everything together,” Kim said. ●
Groundwater irrigation enables farmers to grow lush crops in California’s Central Valley, but the underground water resource is dwindling. A NASA study offers a new tool for managing groundwater.
Photo: California Department of Water Resources/Dale Kolke
A growing research partnership in southern Alberta, Canada, between Lethbridge College and Southern Irrigation, will provide valuable insight that could help producers maximize their crop production.
The college and Southern Irrigation are studying the opportunities created by subsurface drip fertigation (SDF), a method that applies water and fertilizer directly to the rootzones of plants through a series of pipes.
The research project is ramping up: last summer, Lethbridge College and Southern Irrigation installed 15 acres of subsurface drip piping on 21 individually controlled zones at the college’s irrigation research farm. The project is significant to this multi-year collaboration as it has graduated to a field-scale study after starting as a small-scale research project in three custom boxes inside the college’s on-campus innovation space.
Lethbridge College’s research is led by Dr. Willemijn Appels, who was recently promoted to senior research chair in irrigation science in the college’s Centre for Applied Research, Innovation and Entrepreneurship (CARIE), and Dr. Rezvan Karimi Dehkordi, research associate on the irrigation science team. This work follows up on an earlier project Dehkordi undertook on a commercial farm in 2019 and 2020. The first phase of the partnership is funded in part by a $105,500 grant and will study SDF on two crops.
“With this study, we’ll get data about water use, fertilizer use and crop yields, as well as information on how the water and nutrients move into the root zone that will allow us to create numerical and empirical models of the field, basically showing us exactly how our field works, which sets the baseline for future experiments,” said Appels.
By partnering with experts from Southern Irrigation, Lethbridge College can access nearly 40 years of technical expertise from a company that is connected to industry and is able to communicate the needs of producers into meaningful applied research opportunities.
The college acquired management of the irrigation research farm from the government of Alberta’s Ministry of Agriculture and Forestry in October 2020. Previously, field-scale research had to be conducted on private farms on plots donated by generous producers. Now, with control over the research plots, Appels has the opportunity to run substantial year-over-year studies.
“We would like to figure out how well we can deliver a substantial amount of fertilizer through SDF under varying weather conditions and what the effects are of varying the timing of fertilizer application with crop growth stage,” says Appels. “This short-term project has helped us do a trial season with the SDI system (in 2021) and will get us started on a longer-term fertigation research project.” ●
Read more about irrigation research by Appels, in the Sept-Oct issue of NAI, here.
Corn grows on a field using subsurface drip irrigation at Lethbridge College’s irrigation research farm. Photo: Lethbridge College
The government of Ghana, the Agence Française de Développement (AFD), and the European Union (EU) have signed a €44.7 million agriculture water management project to build and rehabilitate about 35 irrigation schemes in north-western Ghana.
To be implemented by the Ministry of Food and Agriculture (MoFA) and the Ghana Irrigation Development Authority (GIDA), the project aims at stimulating green and inclusive growth, reducing inequalities and improving Ghana's food security.
The grant would finance the rehabilitation and construction of 15 dams, 11 boreholes and nine pumping stations on the Black Volta River, and 1,300 hectares of irrigated perimeters.
It would enable farmers to move from rain-fed to irrigated agriculture, support the water users associations (WUA) to run the irrigation scheme, and build GIDA's capacity to supervise these schemes. ●
In the Sechura desert, on Peru’s northern coast, drinking water is unavailable and nutritious food is scarce and expensive. Now, thanks to a project backed by the World Food Programme (WFP), drip irrigation systems allow for efficient use of underground waters. The latter can be accessed through communal reservoirs.
Using organic agricultural techniques, local can now grow broccoli, maize, slipper gourd, carrots, beetroots, lemons, alfalfa, tomatoes, lemongrass, coriander, radish, mint, parsley and local pulses such as pigeon peas.
The WFP-backed scheme has so far supported some 250 farms in Sechura. About 40 percent of these are producing surplus which they are able to sell for a profit. ●
Rivulis is expanding its North American footprint with the establishment of a new, state-of-the-art factory in Tijuana, Mexico. The new facility will allow for the needed capacity expansion to better serve the North American agricultural market and also for streamlining its North American manufacturing capacity.
"This multi-million dollar investment highlights our long term commitment to the North American market,” said Fabien Kelbert, president of Rivulis North America. He added the new Rivulis factory is central to the Rivulis business and global footprint strategy and applies the same high quality standards and innovative manufacturing processes.
Rivulis also recently opened a new factory in Manzanares, Spain. Comprising 6,000 square meters on 25,000 square meters of land, the new facility allows for capacity expansion to better serve European and African agricultural markets.
In addition to the new Mexican and Manzanares facilities, Rivulis has manufacturing and distribution facilities in France, Greece, Turkey, Israel, Egypt, Australia, Argentina, Brazil, Chile, India and the U.S. ●
Viridix Ltd. has launched the Gen3 precision irrigation system with AI-based autonomous capabilities – the system connects with remote monitoring and irrigation control solutions.
Viridix's Gen3 Auto-Pilot system is comprised of Viridix's RooTense, a water potential sensor that mimics the plant roots and provides real time data, alongside the company's unique AI-based software that aggregates the RooTense data with external data from other sources, such as water pressure sensors, air humidity and temperature sensors, and remote watering controllers, and analyzes it all to provide operational insights, enabling the system to make and act on autonomous decisions.
Customers can now monitor the root's activity and implement a smart irrigation protocol across their farms in real time, field by field, adjusting irrigation levels according to live conditions. The advanced system uses artificial intelligence to recommend the exact adjustments required to dose the optimum irrigation for individual crops.
"With the introduction of the new Viridix Gen3 Auto-Pilot system, we are unlocking new experiences and setting the standard of performance for precision irrigation," stated Tal Maor, CBO and co-founder of Viridix. "The launch of this new technology is a result of our commitment to invest in the development of innovative and effective solutions that increase crop productivity for improved environmental sustainability.” ●
