Posts Tagged: crops
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.
Can you help fight the California drought by consuming only foods and beverages that require minimal water to produce?
To begin with, not all water drops are equal because not all water uses impact California's drought, the researchers explain.
So just what water does qualify as California drought-relevant water? You can definitely count surface water and groundwater used for agricultural irrigation as well as water used for urban purposes, including industrial, commercial and household uses.
And here are a few examples of what water is not relevant to California's drought:
-- Water used in another state to produce young livestock that are later shipped to California for food production; and
-- Rain that falls on un-irrigated California pastureland. (Studies show that non-irrigated, grazed pastures actually release more water into streams and rivers than do un-grazed pastures, the researchers say.)
In short, California's drought-relevant water includes all irrigation water, but excludes rainfall on non-irrigated California pastures as well as any water that actually came from out-of-state sources and wound up in livestock feeds or young livestock eventually imported by California farmers and ranchers.
Also, the amount of water that soaks back into the ground following crop irrigation doesn't count – and that amount can be quantified for each crop.
Comparing water use for various foods
I think you're getting the picture; this water-for-food analysis is complicated. For this paper, the researchers examined five plant-based and two animal-based food products: almonds, wine, tomatoes, broccoli, lettuce, milk and beef steak.
In teasing out the accurate amount of water that can be attributed to each food, the researchers first calculated how much water must be applied to grow a serving of each crop or animal product. Then they backed off the amount of water that is not California drought-relevant water, arriving at a second figure for the amount of drought-relevant water used for each food.
They provide a terrific graph (Fig. 3) that makes this all quite clear, comparing total applied water with California drought-relevant water used for the seven food products.
Milk and steak top the chart in total water use, with 1 cup of milk requiring 68 total gallons of water and a 3-ounce steak requiring 883.5 total gallons of water.
But when only California drought-relevant water is considered, one cup of milk is shown to be using 22 gallons of water and that 3-oz steak is using just 10.5 gallons of water. (Remember, to accurately assess California drought-water usage, we had to back off rainwater on non-irrigated pastures and water applied out of state to raise young livestock or feed that eventually would be imported by California producers.)
“Remarkably, a serving of steak uses much less water than a serving of almonds, or a glass of milk or wine, and about the same as a serving of broccoli or stewed tomatoes,” write Sumner and Anderson.
Still skeptical? Check out their paper in the January-February issue of the “Update” newsletter of the Giannini Foundation of Agricultural Economics at http://bit.ly/1XKZxxC.
At 925 million, the number of hungry people in the world is unacceptably high.
To combat world hunger, many scientists are working on developing crops that can resist disease and withstand the elements, from drought to floods. One such scientist is Sean Cutler at UC Riverside, whose breakthrough discovery last year of pyrabactin has brought drought-tolerant crops closer to becoming reality and spawned new research in several labs around the world.
Pyrabactin is a synthetic chemical that mimics abscisic acid (ABA), a naturally produced stress hormone in plants that helps them cope with drought conditions by inhibiting growth. ABA has already been commercialized for agricultural use. But it has at least two disadvantages: it is light-sensitive and it is costly to make.
Enter pyrabactin. This chemical is relatively inexpensive, easy to make, and not sensitive to light. But is it free from drawbacks? Unfortunately, no. Unlike ABA, pyrabactin does not turn on all the “receptors” in the plant that need to be activated for drought-tolerance to fully take hold.
What does that mean? A brief lesson on receptors may be in order.
A receptor is a protein molecule in a cell to which mobile signaling molecules – such as ABA or pyrabactin, each of which turns on stress-signaling pathways in plants – may attach. Usually at the top of a signaling pathway, the receptor functions like a boss relaying orders to the team below that then proceeds to execute particular decisions in the cell.
It turns out that each receptor is equipped with a pocket, akin to a padlock, in which a chemical, like pyrabactin, can dock into, operating like a key. Even though the receptor pockets appear to be fairly similar in structure, subtle differences distinguish a pocket from its peers. The result is that while ABA, a product of evolution, can fit neatly in any of these pockets, pyrabactin is less successful. Still, pyrabactin, by being partially effective (it works better on seeds than on plant parts), serves as a leading molecule for devising new chemicals for controlling stress tolerance in plants.
Each receptor is equipped also with a lid that operates like a gate. For the receptor to be activated, the lid must remain closed. Pyrabactin is effective at closing the gate on some receptors, turning them on, but cannot close the gate on others.
Cutler and colleagues have now cracked the molecular basis of this behavior. In a receptor where the gate closes, they have found that pyrabactin fits in snugly to allow the gate to close. In a receptor not activated by pyrabactin, however, the chemical binds in a way that prevents the gate from closing and activating the receptor.
“These insights suggest new strategies for modifying pyrabactin and related compounds so that they fit properly into the pockets of other receptors,” Cutler says. “If a derivative of pyrabactin could be found that is capable of turning on all the receptors for drought tolerance, the implications for agriculture are enormous.”
So he and his colleagues continue their research on pyrabactin derivatives, having set their eyes on the prize: An ABA-mimicking, inexpensive and light-insensitive chemical that can be sprayed easily on corn, soy bean and other crops to help them survive drought – one effective approach to combating and preventing hunger worldwide. Imagine that!
On a recent trip to the East Coast, our first in almost 13 years, I reflected on our differing coastal experiences with agricultural diversity. Our travels took us through most of the mid-Atlantic farming region – Delaware, District of Columbia, North Carolina, Virginia, West Virginia and Pennsylvania – where we lived for almost 35 years.
We saw the familiar vast fields of corn, soybeans and alfalfa throughout most of the region. There were occasional pockets of other crops: apples, pears and grapes in the more northern parts; sorghum, sweet potatoes, peanuts and tobacco in the more southern states. We also saw occasional plots of sweet corn, green beans, oats and barley. But mostly we saw corn, soybeans and alfalfa.
We stayed at our cousins’ farm in Warriors Mark, Penn. Guess what they were growing – corn, soybeans and alfalfa. However, this year they were also growing Timothy hay for the local “hobby” horse population, as cousin Hank likes to call his high-paying customers. Our cousins have a huge vegetable garden, but do not farm vegetables because, they say: ”We can’t make any money from vegetables, they are not as profitable as the common three field crops." This seems to be the reasoning behind the tri-crop standard.
When we moved from central Pennsylvania to central California 15 years ago, we were intrigued, but mostly mystified, by the crops growing in fields near our home. With the help of new friends and colleagues, we eventually learned to identify fields of sunflowers, tomatoes, walnuts and almonds. We were astonished by the diversity of crops in our new home state, and intrigued by our lack of knowledge about crops we saw by daily. As we traveled throughout the state, our ability to identify roadside field crops grew. We saw acres of artichokes, lettuce, pistachios, figs, olives, kiwi fruit, avocados, all new as field crops to us. Using guides and manuals we found in the ANR Catalog for vegetables, fruit and nut crops, and agricultural production as well as the Fruit & Nut Research and Information Center website photo albums, we were able to identify most of what we saw. We also identified quite a few acres planted in the familiar corn and alfalfa, but hardly any soybeans.
We discovered what was growing in a nearby field when our eyes began to water and our throats close as a field of garlic was harvested. We had the same reaction to rice straw as it burned and canola harvested in a cloud of dust. The first time we saw acres and acres of sunflowers and an almond orchard in full bloom, we couldn’t help but smile. Our sense of smell also assisted in our discovery of newly harvested fields of squash, olives and tomatoes.
You can find more than the acres of corn, soybeans and alfalfa growing along the East Coast, but exceptions are usually planted in a very few acres and in limited locales. However, California’s crop diversity is readily apparent along every highway and byway in every county. Thank goodness!
Equivalent areas covered: mid-Atlantic states = 107,942,470 acres, California = 99,689,515 acres
Alfalfa stretches to the horizon in the Eastern U.S. (USDA photo)