Minerals and trace elements in food

Minerals and trace elements play a vital part in human metabolism. They must be ingested via food. Some are reused and accumulated by the human body (e.g. copper), others must be ingested regularly.

Investigations by the probe Phoenix have shown the existence of valuable minerals in the Martian regolith.

Composition of the human body, from Wikipedia (this is very similar for all life forms):

Element	Symbol	% mass in human body	Typical plant (corn silage)	Notes
Oxygen	O	65.0	45	Oxygen is the most common element on Mars. Most of it in the human body is in the form of water (H2O) or in hydrocarbons
Carbon	C	18.5	44	Carbon is a part of CO2 that comprises 95% of the Martian atmosphere.
Hydrogen	H	9.5	6.3	Hydrogen is mostly in water, and in carbohydrates
Nitrogen	N	3.2	1.3	Nitrogen will comes from the Martian atmosphere, but is present in fairly low concentration. It may be one of the limiting factors of settlement growth
Calcium	Ca	1.5	.25	Calcium should be common in the Martian crust.
Phosphorus	P	1.0	.16	Phosphorous salts should be common as well.
Potassium	K	0.4	.9	Potassium is common in the Martian crust
Sulfur	S	0.3	.15	Sulfur is very common on Mars, more than on Earth
Sodium	Na	0.2	.03	Sodium will be found with calcium
Chlorine	Cl	0.2	.15	Chlorine can be found in perchlorates and salts. Perchlorates are so common on Mars they present a health problem
Magnesium	Mg	0.2	.16	Magnesium is a common mineral in the martian crust
Others		< 1.0

All of the above elements can be found in abundance on Mars. Some work will be required to incorporate some of the less common ones into food.

Corn silage is dried, and may not be entirely typical for plants

For example, a future settlement might house 1000 people, massing about 70kg x 1000 = 70 000 kg, or 70 tonnes. So the 'Others' part of the above table, that covers all trace elements required for humans, is about 700 kg for that population of 1000 people. So, until the Mars settlement is entirely independent from Earth, a mass of a few hundred kg per year will be enough to cover the people's needs in trace elements. And a few tonnes might be enough for an entire settlement ecosystem.

The elements N P and K are the most common fertilizers for plant production on Earth. They are usually provided as compounds than can be absorbed by plants, and then by animals and humans. Calcium as a fertilizer is usually delivered on its own.

Note that the "CHNOPS" elements (Carbon, Hydrogen, Nitrogen, Oxygen, Phosphorous, & Sulphur), plus table salt (Sodium Chloride) make up over 99.99% of animal tissue. Of these, the rarest one is phosphorous, so phosphorous deposits would be of great interest to a large and expanding society on Mars. If economic amounts of phosphorous are found on Mars, it might make a valuable export to any colonies in the asteroid belt.