Clear Up Misconceptions About Water Use In Ag

As the drought in the West continued to get worse this year, journalists focused their attention on the largest users of water in Western states: farmers. Reporters wanted to know how much water different commodities require, and which crops use the most and least amount of water.

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They asked what measures growers were taking to conserve water, and which commodities consumers should avoid to help conserve water.

On one hand, it is a welcome change that the public is interested to learn about how their food is produced. On the other hand, it is worrisome to learn about the misunderstandings the public has about water use in agriculture.

Significant errors occur if one makes inappropriate comparisons, as in comparing “apples and oranges.” It will be beneficial for those involved with agriculture to clearly communicate to the public how the industry uses this increasingly scarce resource.

The Complexities Of Water Use
One common “apples and oranges” comparison focuses on the amount of water required to produce different crops. The public has heard about seemingly outrageous amounts of water used to produce some crops (gallons per nut, for example) and has questioned the wisdom of growing such crops. Addressing this concern can be challenging.

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You know the amount of water needed to grow your crops is driven by the weather, or more specifically, by evapotranspiration (ET). Crops grown in regions with high ET conditions will require more water than crops grown in low ET areas.

Grown under comparable climates, most crops will not exceed the water use of a well-watered lawn by more than 10% to 15%. In fact, many crops will use less water than these lawns. This is because most crops have less canopy cover than well-watered grass for a portion of the season. It is also because crops like processing tomatoes and melons can tolerate periods of water stress, so growers can irrigate less than the potential ET demand and still optimize yield.

Since water use of crops is driven by climatic conditions and plant cover, comparing the amount of water to produce a pound of harvested product among different commodities is not appropriate. Almonds may not seem as water efficient as lettuce when one considers that only a portion of the tree, the nuts, are harvested.

In contrast, two-thirds of a lettuce plant is usually harvested. In addition, almonds are a perennial crop that needs water during most of the season, and it needs to be grown in relatively hot regions where ET is higher than where lettuce is produced. However, if both crops were being grown in adjacent fields under the same climatic conditions, lettuce would likely require more water per day than almond trees.

Past Versus Present
It is better to compare past and present amounts of water used to produce a commodity than to compare water use among different commodities. For example, the amount of water used to produce lettuce has decreased per pound of harvested product by 50% during the last 40 years. While improved irrigation methods, such as drip, are part of the reason for the increased water-use efficiency, better cultural practices such as using wide beds to increase plant populations, improved disease and insect control methods, and higher-yielding varieties must also be credited for increases in efficiency.

Similar advances in water-use efficiency have been made for many commodities produced in the West. Varieties, cultural practices, and irrigation technologies have steadily improved. Since evapotranspiration demand of a crop is essentially fixed to the climate and size of canopy, these improvements increase the amount of fruit, nuts, or grain harvested per area of land, thereby increasing water-use efficiency.

Water Supplies Are Not Equal
Another erroneous “apples and oranges” comparison about agricultural water use is the assumption that water supplies are similar among all regions in the West. Journalists who have witnessed thousands of acres fallowed as a result of the drought in the south San Joaquin Valley of California have been surprised by how agriculture seems to be humming along fine in the Salinas Valley, near the coast.

The difference between these production regions is the source of the water. The south San Joaquin Valley has traditionally relied on surface water from rivers and canals to irrigate crops, while the Salinas Valley uses underground aquifers for irrigation. Growers in the Salinas Valley have multiple wells on their farms, while growers in the San Joaquin Valley who did not have wells on their farms had to fallow land when surface water allocations were reduced.

Shift To Other Crops
A final misconception that the public has about agriculture is the assumption that growers can easily shift to crops that require less water during a drought. With a limited water supply, you have to make choices to water crops that result in the greatest returns from your land to stay in business.

Shifting production from a vegetable to a forage crop that can tolerate water stress does not make business sense if your returns are reduced.

Some concerned citizens have asked which foods they should eat to save water, believing that increased demand for low water-using crops might cause growers to produce more of such “water conserving” commodities. However, such small shifts in eating habits are unlikely to affect the supply, demand, and price of a commodity due to the vast size and complexity of these markets.

In the end, if some consumers eat more beans but fewer fruits and nuts, these adjustments to their diets are unlikely to motivate growers to pull out their orchards and plant beans.

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Avatar for Todd Shuman Todd Shuman says:

I am not persuaded. It is totally appropriate to compare the water amounts used to grow different crops. It takes much water to grow livestock feed crops, and then those crops ultimately result in much atmospheric methane produced by livestock that heat up the planet. Compare that with the miniscule amount of water used to grow plant crops that are directly consumed by humans, and which do not generate atmospheric methane emissions. It is necessary to do such comparisons in order for us to make reasonable decisions about how scarce water should be allocated in the future

Avatar for Pierre Pon Pierre Pon says:

Good article that explains a complex, inter-relational problem in simplified terms vs. trying to make it a simple problem with a simple solution.

[…] Clearing up misperceptions about water use in agriculture:  Michael Cahn writes:  “As the drought in the West continued to get worse this year, journalists focused their attention on the largest users of water in Western states: farmers. Reporters wanted to know how much water different commodities require, and which crops use the most and least amount of water.  They asked what measures growers were taking to conserve water, and which commodities consumers should avoid to help conserve water.  On one hand, it is a welcome change that the public is interested to learn about how their food is produced. On the other hand, it is worrisome to learn about the misunderstandings the public has about water use in agriculture. … ”  Read more from Growing Produce here:  Clearing up misperceptions about water use in agriculture […]

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