Maintaining constant root environments in floating hydroponics to study root-shoot relationships

The design and operation of a floating hydroponic system are described. The nutrient solution temperature and dissolved oxygen concentration in this h ydroponic system were maintained with two simple control mechanisms. During a 24 day growth trial with lettuce (Lactuca sativa L., cv Vivaldi), nutrie nt solution temperature was controlled to 24 +/- 0.3 (sic) C and the dissol ved oxygen concentration to 8.4 +/- 0.2 mg-L-1. Measurements of shoot fresh and dry mass as well as root dry mass of plants aged from 11 to 35 days af ter sowing were taken. Desired nutrition and pH levels in this closed recir culation system were maintained manually. Greenhouse air temperature and da ily integrated light level were precisely maintained at consistent levels t hroughout the experiment. Example data of plant response showed a rapid dec line in root-shoot ratio shortly after transplant, followed by a gradual de cline towards final harvest (35 days after sowing). Root-shoot ratio at fin al harvest was 10%. Percentage of shoot dry matter declined steadily from 8 % at transplant to 4% at final harvest. Results showed an improved environm ent control can result in highly uniform plant production.