Minerals and trace elements in food
Composition of the human body, from Wikipedia (this is very similar for all life forms):
|Element||Symbol||% mass in
|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)|
|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|
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.