Fertilizer

Fertilizer is used to enrich the growing medium of plants with essential nutrients. It differs from compost in that compost is used as soil or mixed into soil, while fertilizer is added solely as a source of nutrients. Fertilizer can be made with organic waste and enriched with chemicals like Ammonia (for Nitrogen). The purpose of fertilizer is to allow plants to reach essential elements more easily, or to supplement nutrients absent from certain soils.

Plant composition

Element	Corn silage		notes
	ppm, dry wt.	%, dry wt.
oxygen	450,000	45	In water, lignine, cellulose, carbohydrates
carbon	440,000	44	In carbohydrates
hydrogen	63,000	6.3	In water and carbohydrates
nitrogen	13,000	1.3	DNA, ATP
silicon	12,000	1.2
potassium	9,000	0.9	Part of ATP
calcium	2,500	0.25	Element of cell walls and enzymes
phosphorus	1,600	0.16	Part of ATP
magnesium	1,600	0.16
sulfur	1,500	0.15
chlorine	1,500	0.15
aluminum	1,100	0.11
sodium	300	0.03
iron	90	0.009
manganese	60	0.006
zinc	30	0.003
boron	10	0.001
copper	5	0.0005
molybdenum	1	0.0001

Average elemental composition of corn tissue (silage). From Troeh, Frederick and L. M. Thompson. 1993. Soils and soil fertility. Oxford University Press. New York.

This table is for corn silage, so it may be dryer than most plants, and already separated from some biomass. Exact composition for plants will vary, but will generally be in similar proportions.

Requirements

The most important fertilizer is nitrogen(N), followed by potassium (K) and phosphorus(P). Calcium(Ca) and magnesium(Mg) can be supplied by limestone, if it is found on Mars. Silicon is the most abundant element on Mars after oxygen.

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