The USDA Economic Research Service reports a total of “cropland used for crops” as 335 million acres. Cropland used for pasture adds another 36 million acres. Cropland idled is 37 million acres. And grassland pasture and range is 613 million acres. Grand total is 1021 million acres (just over one billion acres). However, cropland used for crops is the major source of food in the U.S.
Based on planted acreage per year and typical crop water needs, the 335 million acres of U.S. cropland uses about 730 billion cubic meters of water per year. The water total includes rainfall during the crop season, irrigation, and moisture in soil. It does not include rainfall outside the crop season. The specific total of 729.3 billion cubic meters is the result of many estimated values, so it is only a gross approximation.
729.3 billion cubic meters is 192.6 trillion gallons, or 591.2 millions of acre-feet. For our population in the U.S. of about 322 million persons, the total water needed for crops is about 600,000 gallons (1.84 acre-feet) per person per year. So that’s about just over acre per person watered to about 540 mm (1.04 acres per person).
At a cost of $2,000.00 US dollars per acre-foot of water, if all the water were hypothetically provided by desalination, the cost would be 1.18 trillion dollars per year ($3680 per person per year). To water 10% of U.S. cropland with desalination would cost $118 billion dollars per year ($368 per person per year).
As an aside, I double-checked the popular claim that each individual almond requires 1.1 gallons of water to produce. The amount of water per almond varies depending on the annual yield per acre. The values I obtained were in a range of about 1.0 to 1.2 gallons per almond. So that popular claim is correct.
Crops water needs vary. Sugarcane needs 2000 mm of water (2 meters), but most annual crops only need 400 to 700 mm of water. The average for all crops, taking into account the greater or lesser area planted, was about 540 mm per crop season.
About 80% of the total cropland land use and about 75% of the total cropland water use is concentrated in the top four crops: Corn, Soy, Wheat, Sugar Beets. A large portion of the corn grown is used for ethanol (40%) and a similar amount is dual use: livestock feed and vegetable oil (40%). Exported corn makes up most of the remainder at 10 to 20% per year. About 43% of the soy crop is exported, and most of the rest is used for livestock feed and vegetable oil. When we add cottonseed, the crop with the fifth largest acreage, to the calculation, the land use for the top five crops is 83%, and the water use is 80.5% — and that is a vast amount of land, fertilizer, and water.
These top 5 crops underutilize the land and water resources. A large percentage of the corn is used for biofuel (ethanol), not food. The use of corn and soy for livestock feed provides less calories and less protein, fat, and carbohydrates in the final animal-source food than is found in the livestock feed itself. Most of those carbs are lost, since animal-source foods do not provide many carbs. And the amount of protein and fat that goes into the feed is always significantly less than is obtained from the animal-source foods.
As for the vegetable oil produced from corn and soy, the land and water needed could produce double that amount of oil if an oilseed crop were grown instead of corn (low oil content) and soybeans (modest oil content). Sugar beets provide only carbohydrates — “empty calories” as they say. And cottonseed provides a small amount of oil per acre, and the oil is of poor nutritional quality. Almost any other vegetable oil would be a better choice. We need cotton lint for some uses; it is a practical textile fiber. But if we reduced our reliance on cotton fibers, we could free up some of that land for food.
The U.S. currently feeds its population of about 322 million persons with 335 million acres of land, which is 1.040 acres per person. However, taking into account the vast amount of underutilized land (ethanol, sugar beet, sugarcane, half of the land for livestock feed, exported corn, exported soy, and half the cottonseed acreage), we are really only using about 192.5 million acres, which is 0.575 acres per person. The underutilized land, if it were used in the same way at the land that is well-used, could feed an additional 248.0 million persons. And since many of the hungry in the world already have some food, that acreage is nearly enough to end world hunger by itself.
What can be done about the excess use of land and water resources for livestock feed? Currently, U.S. produces enough red meat and poultry to provide 167.8 lbs per person per year, which is 7.35 oz. per person per day. Cutting that figure to about half (3.5 ounces per person per day) would free up about 35 million acres for growing a variety of food crops.
Reducing our intake of sugar by at least half would free up about 17 million acres. We should not be growing sugarcane at all. It is an inefficient use of land and water, since the crop takes up the land 12 months of the year and sugarcane uses 2000 mm of water per year. Sugarcane uses just under 1 million acres in the U.S.
We should not be growing corn for ethanol. Growing 5.25 billion bushels (294 billion lbs) of corn to use in our fuel tanks, while hundreds of millions of persons go hungry is reprehensible and indefensible. And as it turns out, it is also not particularly useful for the environment. See this Forbes article.