If you are collecting metals and you want to have a metal capable of food production you would want the scarcest metal because you would want a manageable amount seeing that these metals are cheap at today's prices. Molybdenum is the scarcest metal/element for food production and it happens to be a transition metal which in today's economy driven by energy and manufacturing makes it attractive and consumed.
To grow edible plants you need specific ratios of elements that are proven to work. I use a reputable product that grows great hydroponic/aeroponic food.
Let's say there is 80 pounds of molybdenum left on Earth. You would add 10,000 pounds of iron, 5000 pounds of manganese, 1500 pounds of zinc, 1000 pounds of copper, 1000 pounds boron(nonmetal) and 50 pounds cobalt to water along with other very abundant elements to grow plants.
In the Earth's crust there is 1 ppm molybdenum, there is 56300 times more iron(56300 ppm) than molybdenum, 950 times more manganese(950 ppm), 70 times more zinc(70 ppm), 60 times more copper(60 ppm), 10 times more boron(nonmetal-10 ppm) and 25 times more cobalt(25 ppm) than molybdenum.
After mixing these micronutrient metals in water you would see that when all the 80 pounds of molybdenum is gone(the actual ratio available on Earth), you would still have all the other elements left over in large amounts because you need a higher ratio of molybdenum to grow plants than the ratio that is available on Earth.
The other abundant elements you would need to grow plants is nitrogen, phosphorus, potassium, calcium, magnesium, sulfur, chlorine and oxygen, hydrogen, carbon(water and air).
Humans need these other elements in our diet, some of these elements are necessary, probable or controversial: nickel, arsenic, chromium, silicon, iodine, fluorine, selenium, vanadium and sodium.
It just so happens that the scarcest element needed in food production i.e. molybdenum, is needed in higher amounts/ratios than is available on Earth, making it even more valuable.
In hydroponic/aerponic growing of plants there are problems associated with minerals entering or being absorbed by the plant, for this reason there are chelating compounds introduced. Also, chelating coats the mineral and makes it an organic compound (every mineral is inorganic on the table of elements), this coating fools the plant and this way the mineral can enter the plant and the mineral can move more freely around the plant. Copper, iron, manganese and zinc are the target minerals for chelating. Chelating naturally with citric acid or chemically with edta, eddha or dtpa would be needed. In soil growing natural microorganisms do the chelating for us e.g. Hydroxamate Siderophores.
Due diligence.
Carlo Biancardi (London, Ontario) Nov. 2011
