us to isolate the particular stressor that specifically improves secondary metabolite (WA) production while optimizing other growth conditions. In hydroponics, the roots of the plants are maintained in a static, continuously aerated, or
-end-rot (BER), are not uncommon in hydroponics ( Heuvelink, 2018 ; Nederhoff, 1999 ; Peet, 2009 ). To ensure maximum yields and high-quality fruit, commercial growers typically adjust the nutrient solution depending on environmental conditions and plant
most burdensome tasks with conventional outdoor gardening ( Resh, 2015 ). In addition, water and fertilizer conservation is a feature of most hydroponic systems ( Sharma et al., 2018 ), making them attractive alternatives for gardening. Hydroponics
Mixture experiments were used to study the effect of Rb, K, and Na in combination with a number of bicarbonate concentrations on bean plants grown in hydroponics in a controlled environmental chamber. The objective was to separate the cation effect from the bicarbonate effect. The first experiment was a 3-component mixture-amount experiment using various ratios of Rb, K, and Na at 0 and 7.5 mm of bicarbonate. In the 0 mm bicarbonate control, the pure blends were ranked: Rb > Na > K for their effect on reducing shoot dry mass. The high toxicity to the Rb ion was probably due to direct Rb toxicity in addition to any general salinity effect. At 7.5 mm bicarbonate, shoot dry mass was decreased with all the counter-ions compared to the 0 mm bicarbonate control, and their toxicity was ranked: Rb > Na ≈ K. The next series of experiments were 2-component mixture-amount experiments at various ratios of K and Na at 2.5, 5 and 7.5 mm bicarbonate. In the 0 mm bicarbonate control, shoot dry mass decreased with increasing proportions of Na, indicating a specific Na toxicity. The same trend was observed at 2.5 mm bicarbonate. In the 7.5 mm bicarbonate treatment, both Na and K were equally toxic. At low concentration of bicarbonate, the Na is more toxic than the bicarbonate. At higher concentrations of bicarbonate, both Na and bicarbonate exhibit similar levels of toxicity.
Exudation of organic acids by roots has been implicated in uptake of minerals from soil. Three cultivars within each of two subspecies of summer squash (Cucurbita pepo ssp. ovifera D. S. Decker var. ovifera and C. pepo ssp. pepo var. pepo) were grown in the field. Plants of ssp. pepo had higher concentrations of K, P, and Zn than those of ssp. ovifera. These same cultivars were grown under P sufficient and depleted conditions in hydroponics, to measure exudation of organic acids from roots. When grown in hydroponics, tissues of ssp. ovifera had similar or higher concentrations of nutrients than ssp. pepo. Therefore, differences in tissue composition of field-grown plants are likely due to differences in nutrient uptake ability, not inherent differences in tissue composition between subspecies. Phosphorus nutrition played a significant role in exudation of organic acids into the hydroponics solution. For both subspecies, P depletion resulted in exudation of more citric and succinic acid, and less oxalic and tartaric acid. Under P depletion, ssp. pepo exuded more citric acid than ssp. ovifera. When soil was eluted with solution containing root exudates, the exudates from ssp. pepo eluted more K, Mg, Fe, and Zn than did those from ssp. ovifera. Among subspecies of C. pepo, exudation of organic acids, particularly exudation of citric acid in response to P depletion, is associated with the plant's ability to accumulate more inorganic nutrients when grown in the field.
.05 in all tanks using either phosphoric acid (pH Down; General Hydroponics, Sebastopol, CA) or potassium hydroxide and potassium carbonate (pH Up, General Hydroponics). The average preadjusted pH was 5.86 ± 0.02 for all stock tanks. Expt. 2: Effect of pH
Closed loop hydroponics, where nutrient solution drainage is captured and reapplied to the crop, offers advantages over flow-through or single pass systems by way of water and nutrient resource use efficiency ( Wilfried 2005 ). Increasing
and ecology, it becomes clear that systems of crop production that eliminate soil from the system, such as hydroponics or aeroponics, cannot be considered as examples of acceptable organic farming practices” ( USDA, 2010 ). The implication is that
. 1997 Differential tolerance to copper and zinc of micropropagated birches tested in hydroponics New Phytol. 137 543 549 Zheng, Y. Wang, L. Dixon, M. 2004 Response to copper toxicity for several
-specific nutrient solutions and constant aeration using an air pump (GH2716; General Hydroponics, Santa Rosa, CA) with air stones. Each hydroponic system was able to hold 64 (8 × 8) plants. The deep-flow hydroponic systems were arranged in a double