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

Hydroponic culture has traditionally been used for controlled environment l ife support systems (CELSS) because the optimal environment for roots suppo rts high growth rates. Recent developments in zeoponic substrate and microp orous tube irrigation (ZPT) also offer high control of the root environment . This study compared the effect of differences in water and nutrient statu s of ZPT or :hydroponic culture on growth and yield of wheat (Triticum aest ivum 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 u se 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. Al though 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. Di fferences in biomass partitioning were attributed primarily to NH4-N nutrit ion of plants grown in ZPT compared with NO3-N in hydroponic nutrient solut ion. It is probable that NH4-N-induced Ca deficiency produced excess tiller ing and lower harvest index for plants grown in ZPT culture. These results suggest that further refinements in zeoponic substrate would make ZPT cultu re a viable alternative for achieving high productivity in a CELSS.