CAN LOW NUTRIENT STRATEGIES BE USED FOR POT GERBERA PRODUCTION IN CLOSED-LOOP SUBIRRIGATION?

To determine if pot gerbera (Gerbera jamesonii, Var. Shogun) production could be maintained under a lowered (relative to commercial) nutrient concentration regime, in closed-loop subirrigation systems, plants were grown under one of four nutrient regimes for four weeks. The four treatments comprised of 100%, 50%, 25% and 10% of the nutrient concentrations typically used in commercial pot gerbera production. The average electrical conductivities (EC) of the solutions were 1.7, 1.0, 0.5 and 0.2 dS.m^-1, respectively. There were no differences among the four treatments with respect to leaf net CO₂ assimilation rate, stomatal conductance, photosynthetic capacity (in terms of light- and CO₂-saturated rate of CO₂ assimilation and maximum rate of Rubisco carboxylation), leaf area, flower number and flower appearance. Lower concentration nutrient treatments did not reduce total plant dry weight. There were no significant differences in leaf chlorophyll content between plants receiving the 50% and 100% strength nutrient solutions. During the final week of the experiment, slight interveinal chlorosis, accompanied by reduced leaf chlorophyll content, was observed in some juvenile leaves of plants irrigated with the 25% and 10% strength nutrient solutions. It is suspected that the chlorosis in the 25% and 10% treatments was due to iron and/or manganese deficiency. It is concluded that nutrient solution concentrations typically used in commercial greenhouse operations, can be safely reduced by at least 50% without adversely affecting pot gerbera production. Nutrient salts accumulated in the top section of the growth substrate under all treatments; however, levels were significantly lower in the reduced concentration treatments. No differences in water consumption were observed among treatments. Fertilizer usage was dramatically reduced at lower nutrient feeds. The 50%, 25% and 10% treatments used only 36%, 23.5% and 8.5% as much fertilizer, respectively, as the 100% treatment. The major ionic ratios of all the nutrient solutions in the solution reservoirs were still within an acceptable range after four weeks of recycling.