Nitrification in a zeoponic substrate.

Clinoptilolite is a zeolite mineral with high cation exchange capacity used in zeoponic substrates that have been proposed as a solid medium for growing plants or as a fertilizer material. The kinetics of nitrification has not been measured for NH4+ saturated zeoponic substrate. Experiments were conducted to evaluate the production of NO2- and NO3-, and nitrifier populations in zeoponic substrates. Small columns were filled with zeoponic substrate inoculated with a commercial inoculum or soil enrichment culture of nitrifying bacteria. In addition to column studies, a growth chamber study was conducted to evaluate the kinetics of nitrification in zeoponic substrates used to grow radishes (Raphanus sativus L.). The zeoponic substrate provided a readily available source of NH4+, and nitrifying bacteria were active in the substrate. Ammonium oxidation rates in column studies ranged from 5 to 10 micrograms N g-1 substrate h-1, and NO2- oxidation rates were 2 to 9.5 micrograms N g-1 substrate h-1. Rates determined from the growth chamber study were approximately 1.2 micrograms N g-1 substrate h-1. Quantities of NH4+ oxidized to NO2- and NO3- in inoculated zeoponic substrate were in excess of plant up-take. Acidification as a result of NH4+ oxidation resulted in a pH decline, and the zeoponic substrate showed limited buffering capacity.

Wheat response to differences in water and nutritional status between zeoponic and hydroponic growth systems.

Hydroponic culture has traditionally been used for controlled environment life support systems (CELSS) because the optimal environment for roots supports high growth rates. Recent developments in zeoponic substrate and microporous tube irrigation (ZPT) also offer high control of the root environment. This study compared the effect of differences in water and nutrient status of ZPT or hydroponic culture on growth and yield of wheat (Triticum aestivum L. cv. USU-Apogee). In a side-by-side test in a controlled environment, wheat was grown in ZPT and recirculating hydroponics to maturity. Water use by plants grown in both culture systems peaked at 15 to 20 L m-2 d-1 up to Day 40, after which it declined more rapidly for plants grown in ZPT culture due to earlier senescence of leaves. No consistent differences in water status were noted between plants grown in the two culture systems. Although yield was similar, harvest index was 28% lower for plants grown in ZPT than in hydroponic culture. Sterile green tillers made up 12 and 0% of the biomass of plants grown in ZPT and hydroponic culture, respectively. Differences in biomass partitioning were attributed primarily to NH4-N nutrition of plants grown in ZPT compared with NO3-N in hydroponic nutrient solution. It is probable that NH4-N-induced Ca deficiency produced excess tillering and lower harvest index for plants grown in ZPT culture. These results suggest that further refinements in zeoponic substrate would make ZPT culture a viable alternative for achieving high productivity in a CELSS.