What is the prevalence of nitrogen, phosphorus, and potassium in the asteroid belt and in comets?

Question

As someone with a light background in controlled-environment agriculture, I'm familiar with the importance and use of N/P/K in growing useful plants. This got me thinking about how common these elements are in celestial objects, for potential mining to support spaceship/space station onboard agriculture.

What is the prevalence of nitrogen, phosphorus, and potassium in the asteroid belt and in comets? Is there enough, at least in certain objects, to be mined to support agriculture in space vessels?

Answer 1

https://www.researchgate.net/publication/255828400_The_EUV_Emission_from_Sun-Grazing_Comets/figures?lo=1 lists significant amounts of N in comets (as ammonia and methane) , but P and K don’t make the top 8.

In the universe, N is 300X more common than P and 3000X more common than K https://en.wikipedia.org/wiki/Abundance_of_the_chemical_elements#/media/File:Elements_abundance-bars.svg . The elemental composition of the solar system is about the same as in the universe in general. Unless there is some process which selectively concentrates P and K in comets and asteroids, these elements will be poorly represented.

Rather than 20/20/20 fertilizer, you are looking at 1/0.003/0.0003 fertilizer from ground-up asteroids.

On Earth, P containing deposits are created by biologic processes such as settlement of marine organisms. In space there is a marked shortage of marine life, water and gravity so this mechanism does not apply.

Similarly, K deposits are formed by evaporation of seawater.

On Earth, we use an open-loop system, mining geologic P and K. We use excessive amounts, which is discarded in surface water and ground water.

Any space farming will likely be a closed loop system with P and K recycled as fertilizer.

In space, the P and K would be recycled from sewage and astronaut corpses.

Answer 2

In comets there is a lot of ammonia ice, carbon dioxide adn hydrocarbons. C-Type asteroids have this too. Phosphorus is found in the apatite group minerals, flouroapatite, bromoapatite, chloroapatite, and hydroxylapatite. They can be economically produced with leaching by sulfuric acid, distillation, and precipiatition. Sulfur can be attained in the form of sulfur dioxide. I am not so sure about potassium, but being fairly reactive, I except there to be plenty.