Posts Tagged: irrigation
When it comes to watering walnuts, most California growers believe you need to start early to keep trees healthy and productive throughout the long, hot summer. But according to striking results from a long-term experiment in a walnut orchard in Red Bluff, growers can improve crop production if they hold off irrigation until later in the season and directly measure their trees' water needs.
The findings from researchers at the University of California may help farmers optimize water use.
“It's a game-changer,” said walnut grower Hal Crain, who welcomed researchers on to his orchard to test irrigation optimization. “It's clear to me you can improve nut quality and yield by applying water based on what the tree wants and needs, rather than just watering when it's hot outside and the soil is dry. That's a big deal for walnut growers and for the entire agricultural industry.”
Changing the paradigm
Crain is a second-generation farmer whose family has been growing walnuts in Butte and Tehama counties for 55 years. Like most walnut farmers, Crain had always started irrigating in early to mid-May when the days grew warmer and the trees sprouted leaves.
“That's standard practice for probably 90 percent of California's walnut growers,” said Crain, walking amid his trees on a sunny afternoon. “The theory is that when you irrigate early, you preserve the deep moisture in the soil that trees need to survive the heat of summer.”
But that's not how it works, the research shows. Instead, trees that grow in saturated soil early in the season don't develop the deep roots they need to thrive.
“With all the water right there at the surface, the lower roots suffer,” explained Bruce Lampinen, UC Cooperative Extension orchard management specialist with the UC Davis Department of Plant Sciences. “Trees end up with a very shallow root system, which doesn't serve them well as they try to extract moisture from the soil later on.”
Lampinen has long suspected that walnuts were getting too much water in the spring.
“A lot of the symptoms we see like yellowing leaves and various diseases can all be explained by overwatering,” said Lampinen.
So Lampinen did what scientists do: He set up an experiment. Five years ago, with funding from the California Walnut Board and the U.S. Department of Agriculture, he joined forces with Ken Shackel, a plant sciences professor with UC Davis, and Allan Fulton, an irrigation adviser with UC Cooperative Extension. Together, they led a team of scientists testing irrigation on Crain's ranch.
“Hal is an exceptional partner,” Fulton said. “Farmers have a lot to accommodate when they host an experiment like this, with researchers going in and out of the orchard at all hours. He had to work around our people and the timing of our water treatments. He's always eager to experiment with technology and learn new things, and he shares what he learns with other growers. Hal completes the circle.”
Tough nut to crack
When is the best time to irrigate? Researchers say the trees hold the answer. Scientists use pressure chambers, which are air-pressure devices that measure a leaf or small shoot to gauge how hard the plant is working to pull moisture from the soil.
“Just because the soil looks dry doesn't mean the plant is suffering,” said Shackel, who specializes in plant physiology. “Pressure chambers let you ask the tree how it's feeling — sort of like taking a human's blood pressure — which is a much more accurate way to measure a plant's water needs.”
For the last five years, the team has been applying different water treatments to five blocks of trees. One block is getting standard, early irrigation. Crain's orchard managers begin irrigating the other blocks when the trees reach different levels of water stress based on pressure-chamber readings.
The trees that experience moderate stress are doing the best. Their irrigation usually starts in mid-to-late June, several weeks later than when standard watering begins.
“You can tell just by looking at that block that the trees are healthier,” said Crain, standing beneath a canopy of lush, green trees. “And, we're starting to see greater yields and better nut quality.”
Translating the research
The research is helping scientists advise farmers on irrigation.
“My biggest take-away is knowing when to start watering is a really important factor to the health of your trees,” Lampinen says.
Pressure chambers — sometimes called pressure bombs — can cost more than $3,000, and high-tech versions are under development.
“I tell growers a pressure bomb would pay for itself even if you just used it once a year to determine when to start watering,” Lampinen said.
Crain is certainly convinced.
“When you irrigate based on your trees' needs, you optimize water,” Crain says. “I'm not using less water overall, but the water I do use is producing more food. That's good news for everyone.”
This story was originally published in the Fall 2018 issue of Outlook Magazine, the alumni magazine for the UC Davis College of Agricultural and Environmental Sciences.
Connecting 9,000 rural households in Guatemala with improved water management and climate-smart agriculture strategies is the goal of a new project led by a team at UC Davis, to ultimately increase food security and reduce poverty in Guatemala's Western Highlands.
“The opportunity to impact so many farmers' lives on this scale is exciting,” said Beth Mitcham, director of the Horticulture Innovation Lab and a UC Cooperative Extension specialist in the UC Davis Department of Plant Sciences. “We're taking lessons learned from our previous research — in Guatemala, Honduras and Cambodia — and building a team to help more small-scale farmers apply our findings and successfully use these innovative practices.”
The new project is part of the U.S. government's global hunger and food security initiative, Feed the Future. The project represents an additional $3.4 million investment in the UC Davis-led Horticulture Innovation Lab by the U.S. Agency for International Development's mission in Guatemala.
The project's international team also includes representatives from Kansas State University; North Carolina Agricultural and Technical State University; the Centro de Paz Bárbara Ford in Guatemala; Universidad Rafael Landívar in Guatemala; and the Panamerican Agricultural School, Zamorano, in Honduras.
“The learning shared between these three U.S. universities and the universities in Honduras and Guatemala will be enriching for all of the institutions involved,” said Manuel Reyes, research professor at Kansas State University who is part of the team. “I find it satisfying that these academic institutions will be investing intellectually in marginalized groups in Guatemala's Western Highlands — and in turn, learning from them too.”
Helping youth envision a future in agriculture
By partnering with local youth groups and agricultural schools, the team will better prepare students for jobs in commercial agriculture and agricultural extension with knowledge of climate-resilient conservation and water management practices.
“Our local team is training youth as entrepreneurs, to see agriculture as an economic opportunity instead of just back-breaking work,” said Meagan Terry, UC Davis junior specialist who is managing the project in Guatemala for the Horticulture Innovation Lab. “They can envision a future in agriculture, with innovative ways to create value-added products or grow high-value crops for niche markets.”
As rainfall patterns vary with climate change, farmers in this region are expected to face increased competition for water. Practices such as rainwater harvesting, drip irrigation and conservation agriculture will become more necessary for small-scale farmers.
Climate-smart lessons from conservation agriculture, drip irrigation
In previous research, the Horticulture Innovation Lab has found that combining drip irrigation with conservation agriculture practices can successfully grow vegetables on small plots of land, without significant yield reductions. These practices improve soil structure, moisture retention and soil health.
Additionally, women farmers who participated in the Horticulture Innovation Lab studies in Cambodia, Honduras and Guatemala favored using these practices for another important reason: reduced labor in relation to controlling weeds, vegetable bed preparation and manual watering.
“I dream for many women, youth and their families, that their lives will be better off because of 'MasRiego' and the science behind this work,” Reyes said. “As for the research, we are learning how to improve this suite of practices so they can be tailor fitted globally. I am convinced that if this picks up, steep sloping lands can be farmed with the soil quality not being degraded — but even being enriched.”
These lessons, as well as findings from the program's “Advancing Horticulture” report about horticultural sector growth in Central America, lay the foundation for this new project.
Curious about partnering with the Horticulture Innovation Lab? The Horticulture Innovation Lab builds partnerships between agricultural researchers in the United States and researchers in developing countries, to conduct fruit and vegetable research that improves livelihoods in developing countries. The program currently has three research grant opportunities for U.S. researchers: one focused on tomatoes, another on apricots, and a third on integrated crop-livestock systems.
It might be pouring rain today, but soon enough California will be dry again. As demand for water for a growing urban population and for environmental restoration increases, farmers throughout the state are working to grow crops using as little water as possible, and UC is working with them.
"Water supplies are being constrained. Farmers are facing reduced access to water," said Shermain Hardesty, a UC Cooperative Extension specialist in the Department of Agricultural and Resource Economics at UC Davis.
The research involves using some elaborate formulas for determining how much water is needed. UCCE advisor Richard Molinar, working with small farms in Fresno County, is irrigating small plots of strawberries with different amounts of water, some at 125 percent of the normal rate, some at 100 percent, and others at 75 percent and 50 percent of normal. In San Diego County, UCCE advisor Ramiro Lobo is doing similar research on strawberries and blueberries; UCCE advisor Manuel Jimenez is working with blackberries and blueberries in Tulare County; UCCE advisor Aziz Baameur is planting strawberries and blackberries in Santa Clara County, and UCCE advisor Mark Gaskell is studying blackberries in Santa Barbara County.
Once the berries are grown, they need to be tested - and testing means tasting in this project. The research team is holding tasting sessions to let the public judge which berries they prefer. If you've ever tasted a dry-farmed tomato, you might guess the answer. The first tasting session was held at the Davis Farmers' Market in June, with seven more coming soon at farmers' markets and grocery stores around the state.
Taste is a great quality to measure, but only one aspect of the study. Berries are already known for having a high nutrient content, but growing them with less water might give them even higher nutritional value. The team expects to find nutrition density to be highest at the lowest irrigation levels. To test this concept, UCCE specialists Elizabeth Mitcham and Marita Cantwell, experts in postharvest science affiliated with the Department of Plant Sciences at UC Davis, are doing nutritional quality analysis of the berries as they are picked.
Lawrence Schwankl, a UCCE specialist in the Department of Land, Air and Water Resources at UC Davis, says that many farmers are currently over-watering many crops.
"Over-irrigation is cheap insurance, especially for such high value crops," he said.
He explained that more water tends to grow bigger berries. Since the harvest is not mechanized for berry crops, it takes as much effort to pick a small berry as a large berry, making more efficient use of the pickers' time and filling the basket more quickly if the berries are bigger.
Such a trade-off for the farmers! The public may decide that they prefer smaller berries with more taste, and the scientists may decide that smaller berries are more nutritious, but will it be profitable to grow better berries? It may depend on how much smaller, and on how much less water for how much better nutrition and taste. It may depend on the water rates, says Hardesty. She will be taking all of these variables into account to determine the potential impact on profitability of lower irrigation rates on berries.
The team, which also includes UCCE advisors Michael Cahn in Monterey County and David Shaw in San Diego, will report the results of their study to California farmers in the final year of the project. This project is funded by a California Department of Food and Agriculture Specialty Crop Block Grant.