Crop production under hydroponic environments has many advantages, yet the effects of solution flow rate on plant growth remain unclear. We conducted a hydroponic cultivation study using different flow rates under light-emitting diode lighting to investigate plant growth, nutrient uptake, and root morphology under different flow rates. Swiss chard plants were grown hydroponically under four nutrient solution flow rates (2 L/min, 4 L/min, 6 L/min, and 8 L/min). After 21 days, harvested plants were analyzed for root and shoot fresh weight, root and shoot dry weight, root morphology, and root cellulose and hemicellulose content. We found that suitable flow rates, acting as a eustress, gave the roots appropriate mechanical stimulation to promote root growth, absorb more nutrients, and increase overall plant growth. Conversely, excess flow rates acted as a distress that caused the roots to become compact and inhibited root surface area and root growth. Excess flow rate thereby resulted in a lower root surface area that translated to reduced nutrient ion absorption and poorer plant growth compared with plans cultured under a suitable flow rate. Our results indicate that regulating flow rate can regulate plant thigmomorphogenesis and nutrient uptake, ultimately affecting hydroponic crop quality.

In hydroponics, the flow pattern of nutrient solution in a cultivation container affects the growth of plants. Even if the flow rate of nutrient solution is the same between containers, the flow pattern may differ based on the size and shape of the containers. Therefore, the flow pattern cannot be comprehensively described by flow rate alone. In order to identify the relationship between plant growth, root morphology, nutrient uptake, and flow pattern, a hydroponic cultivation of Swiss chard was carried out. In addition, in order to describe the flow pattern in a specific cultivation container, hydroponic flow patterns were observed via flow field visualization using particle image velocimetry. As a result, with the increase in flow rate, it was found that a specific flow rate can form an ideal flow pattern for plant growth. Under this flow pattern, nutrient absorption is promoted and roots are elongated, thereby absorbing more nutrients and further promoting plant growth. However, when the flow rate exceeds the ideal value, plant growth is hindered. In summary, identifying the ideal nutrient solution flow pattern in hydroponics can facilitate better crop production.

An open-field cultivation combined-type aquaponic system (OCAS) was developed to effectively utilize saline groundwater and prevent soil salinization while ensuring food production in drylands. To achieve the sustainable food production of the OCAS in power-scarce areas, a stand-alone photovoltaic system (PVS) for the OCAS was designed through a feasibility study of utilizing solar energy to meet its power demand. As a case study, the OCAS was established in La Paz, Baja California Sur, Mexico, with power consumption 22.72 kWh/day and annual average daily global horizontal irradiation (GHI) 6.12 kWh/m2/day, considering the 2017 meteorological data. HOMER software was employed for performance analysis and techno-economic evaluation of an appropriate PVS. Thousands PVS configurations were evaluated in terms of total net present cost (NPC) and levelized cost of energy (COE). The PVS that fulfilled the power demand and had the smallest NPC was proposed, for which the NPC and COE were calculated as $46,993 and $0.438/kWh, respectively. The relationship between its annual power supply and power demand of the OCAS was also analyzed in detail. It was found that the operation hours and the amount of power generation by the proposed PVS were 4156 h and 19,106 kWh in one year. Additionally, it was predicted that the excess power would occur almost every afternoon and reach 43% of the generated power. Therefore, the COE can be further reduced by rationally utilizing the excess power during operation.

Aeration is considered beneficial for hydroponics. However, little information is available on the effects of aeration, and even less on solutions that use bubble flow and their agronomic effects. In this study, the effects of aeration intensity on plants were studied through cultivation experiments and flow field visualization. It was found that the growth of plants did not increase linearly with an increase in aeration intensity. From the results of this study, when the aeration intensity was within the low range (0.07–0.15 L·L−1 NS·min−1), increasing the aeration intensity increased the plant growth. However, after the aeration intensity reached a certain extent (0.15–1.18 L·L−1 NS·min−1), some indicators did not change significantly. When the aeration intensity continued to increase (1.18–2.35 L·L−1 NS·min−1), growth began to decrease. These results show that for increasing dissolved oxygen and promoting plant growth, the rule is not “the higher the aeration intensity, the better”. There is a reasonable range of aeration intensity within which crops grow normally and rapidly. In addition, increasing the aeration intensity means increasing energy utilization and operating costs. In actual hydroponics production, it is very important to find a reasonable aeration intensity range.

Unlike in soil culture, a substrate (nutrient solution) in a hydroponics system can flow, and this can affect both nutrient uptake and plant growth. In this study, we hydroponically cultivated Swiss chard (Beta vulgaris L. ssp. cicla) under different flow rates to analyze changes in the growth, nutrient uptake, and nutrient use efficiency. When the flow rate was intensified from 2 to 4 L/min, leaf area, the fresh weight, dry weight, and root length increased. However, when the flow rate was increased from 4 to 8 L/min, values of these growth parameters decreased. The nutrient uptake had a similar trend relative to the growth parameters and nutrient use efficiency of macronutrient elements, increased as the flow rate increased. This indicates that the flow rate affects plant growth by influencing the nutrient uptake, and an increase in the flow rate can aid in improving nutrient use efficiency. In hydroponics, regulating the flow rate at a reasonable volume is recommended to increase yield by enhancing nutrient use efficiency, but too intensive a flow rate may cause excessive physical stimulation to plants and inhibit their growth. Therefore, it is important to choose an appropriate substrate flow rate for optimal hydroponics production.