For more than 20 years NASA scientists have been developing a simple, high performance root medium for plants in space. By "loading" the zeolites with plant nutrients they have advanced the horticultural technology known as zeoponics into the Space Age.
A simple and environmentally friendly way of loading zeolite with nutrients is to mix the zeolite with animal manure. The zeolite adsorbs the harmful ammonia and releases it into the soil as nitrogen.
The following article about NASA's research is very interesting.
"Space Age soil mix uses centuries-old zeolites
NASA's quest for lightweight, nutrient-packed rooting medium produces new amendment for golf course soils. By Earl Allen, Ph.D. and and Richard Andrews.
Scientists at NASA's Johnson Space Center have been working since the mid-1980s to develop a simple yet highperforming root medium for plants in space. Such plants may be crucial to space exploration because they could supply oxygen and food for space crews and recycle wastes as part of a regenerative life-support system. Their root media must not be bulky, however, because spacecraft can carry only small amounts of material. After tests on Earth and in the space shuttle (4, 9, 13, 14, 15), NASA has selected several types of zeolite - mined on earth from ancient volcanic ash deposits - among its primary root media components. The zeolite's high cation-exchange capacity, high porosity, favorable moisture retention and rigid structure suit them well to space."
To read the whole article, which goes on to describe Zeoponics, click here.
Zeolite Gardens in Space
Scientists in Bulgaria have been developing a similar growing medium for their space program, click here to read their report.