An acre is defined as a piece of land one chain (66') by one furlong (660' or ten chains) - a total area of 43,560 square feet.

And acre foot is the water required to cover one acre of land to a depth of one foot, or 43,560 cubic feet.

43,560 cubic feet of water is 325,851 gallons.

There are 7.48 gallons of water per cubic foot.

Water weighs 8.33 pounds per gallon or about 62 pounds per cubic foot. This varies a bit based on temperature.

An acre foot of water will weigh about 2,700,00 pounds or 1,350 tons.

Water is one oxygen and two hydrogen atoms. Oxygen has an atomic weight of 16 and hydrogen an atomic weight of 1.

An acre foot of water contains 1,200 tons of oxygen and 150 tons of hydrogen.

Ammonia is one nitrogen and three hydrogen atoms. Nitrogen has an atomic weight of 14 and hydrogen still has an atomic weight of 1.

Using the hydrogen found in an acre foot of water you can produce 850 tons of ammonia.

Typical application rates for corn are 125 pounds per acre. That 850 tons will fertilize 13,600 acres.

13,600 acres is 21.25 sections.

Iowa has about 27,000,000 acres under cultivation and we'd need 1,985 acre feet of water to make ammonia.

Iowa is just over 36,000,000 acres in area and about 34" of rain falls annually.

34" of rain adds up to 102,000,000 acre feet.

1,985/102,000,000 = 0.001946% of our annual rainfall.