Tomato plants in greenhouse production are often confronted with light insufficiency in the lower canopy, especially in the winter low irradiation season. In this study, periodic alteration of plant density (PD) was proposed to improve the light environment of plants' lower canopies, leaf photosynthesis, plant growth, and fruit development. These were investigated with winter cultivated tomatoes in a single-truss production system. Seedlings were transplanted to either movable or fixed cultivation benches for treatments with fixed PDs of 14.3 plants•m-2 (F14.3), and 10 plants•m-2 (F10), and unfixed PDs in a movable bench (MB; 25 plants•m-2 after transplanting to anthesis, 16.6 plants•m-2 at anthesis to initial fruit set, 12.5 plants•m-2 at fruit set to mature green, and 11.1 plants•m-2 at mature green to red-ripe). The leaf photosynthesis rates in MB and F10 were generally significantly higher than in F14.3. F14.3 had the tallest stems, but the lowest leaf area and shoot dry weight at end of experiment, while MB and F10 were not significantly different. MB had significantly the highest total yield, while the lowest data were observed in F10. The soluble solids content was increased in MB and F10 compared with F14.3, but no significant differences in ascorbic acid content or fruit hardness were observed among treatments. Therefore, a high PD in the vegetative stage, but a relatively lower PD in the fruit development stage, was highly efficient in intensive tomato cultivation.

Grafted cucumber plants were grown in a new hydroponic system (“Kappa Land”, Mitsubishi Chemical Aqua Solutions, Co., Ltd., Tokyo, Japan). Two different nutrient management methods were applied to the plants as treatments: Electrical Conductivity-based Management (ECM) and Quantitative Nutrient Management (QNM). During the growth period, we examined plant growth characteristics and productivity, fruit growth characteristics and quality, and nutrient use characteristics. The results revealed that the QNM technique significantly reduced the nutrient supply rate per plant for Ca²⁺, SO₄²⁻, and N by 28.5%, 25.5%, and 23.3%, respectively. Similarly, the absorption rates per plant of SO₄²⁻, K⁺, and PO₄³⁻ were reduced by 17.8%, 11.9%, and 10.9%, respectively. However, N, Ca²⁺, and Mg²⁺ absorption rates slightly increased in the QNM treatment. The nutrient wastes generated per kilogram of produced fruits were also reduced by 66.4%, 60.7%, and 30.2% for N, Ca²⁺, and SO₄²⁻, respectively. Although the QNM technique reduced the plant’s leaf area, it significantly increased its total length by 9.4%. The total and marketable yields were not significantly different between the ECM (9.0 and 8.0 kg plant⁻¹) and QNM (9.1 and 8.2 kg plant⁻¹) treatments. However, the QNM treatment produced the highest total dry matter of 617 g plant⁻¹, surpassing the ECM treatment by 6.9%. On the other hand, differences in nutrient management methods did not significantly affect fruit quality, including total soluble solids, water content, skin color, size, and shape. These results suggest that with the QNM method, it is possible to produce quality cucumbers with high nutrient use efficiency while protecting the environment from nutrient wastes.

Plant factories with artificial lighting (PFALs), with well-insulated and airtight structures, enable the production of large quantities of high-quality plants year-round while achieving high resource use efficiency. However, despite the controlled environment in PFALs, variations in plant individuals have been found, which affect productivity in PFAL operations. Plant phenotyping plays a crucial role in understanding how the surrounding microenvironment affects variations in plant phenotypes. In the current study, a modular phenotyping system for seedling production was developed, focusing on practicality and scalability in commercial PFALs. Experiments on seedlings, which strongly affect productivity, were conducted to obtain cotyledon unfolding time and the time series projected area of cotyledons and true leaves of individual seedlings of romaine lettuce (Lactuca sativa L. var. longifolia), using RGB images. This was also undertaken to analyze how the surrounding microenvironment of photosynthetic photon flux densities and nutrients affect growth variations for plant cohort research. In agreement with the actual measurements, variations in seedling growth were identified even under similar microenvironments. Furthermore, the results demonstrated larger variations in seedlings with higher relative growth. Aiming for simplified interactions of phenotypes with the microenvironment, management, and genotype, seedling selection and breeding with plant production in PFALs may enable plant uniformity and higher productivity.

Chronic kidney disease (CKD) has been a global health problem in recent years. CKD patients often restrict their potassium (K) intake to avoid the high risk of hyperkalemia. In this study, quantitative K management in hydroponics was adopted to produce low K cherry-type tomato (Solanum lycopersicom L.) fruit. The total quantity of K supply per plant during the cultivation was 7.2 g (1 K), 3.6 g (1/2 K), 1.8 g (1/4 K), 0.9 g (1/8 K) and 0.6 g (1/12 K), respectively. The total fruit yield decreased to about 75% at 1/2 K and 58% at 1/12 K compared to 1 K. The fruit K content was lower in 1/4 K, 1/8 K and 1/12 K than in 1 K and 1/2 K, and the fruit from 1/8 K and 1/12 K achieved below 100 mg 100 g⁻¹ FW of K. Total soluble solid content (Brix) was 7–8% in 1 K and 1/4 K but was lower in 1/8 K and 1/12 K. Fruit acid content decreased to 87% in 1/2 K to 70% in 1/4 K and 1/8 K, and to 57% in 1/12 K of 1 K. In conclusion, quantitative K management in hydroponics is expected to produce low K tomato fruit. Fruit K content of approximately 100 mg.100 g⁻¹ FW was achieved when the quantity of K supply was 1/4 K and 1/8 K, with a relatively smaller effect on fruit yield, Brix and acid content.

With the increase in dialysis patients worldwide, the demand for low-K vegetables is growing. Thus, a type of lettuce with a low-K content has been marketed in Japan. To learn more about low-K vegetables, information is needed on the physiological differences between these vegetables and those with typical levels of potassium (K). In this study, lettuces ( Lactuca sativa L.) were cultivated using two low-K management methods in an environment-controlled system. One method was based on electrical conductivity (EC) management, and the K was replaced by sodium (Na) at the end of cultivation. The other method was based on quantitative nutrient management, and the nutrients required for low-K lettuce were quantitatively supplied, but no extra Na was added. Meanwhile, lettuce with normal K concentration was cultivated with EC management as the control. Plant growth indices, leaf photosynthesis traits, chlorophyll fluorescence characteristics, concentrations of secondary metabolites (SMs), and antioxidant activity were examined to investigate the physiological effects of low-K and high-Na concentrations during low-K lettuce cultivation. Both low-K treatments significantly restrained the growth of lettuce and increased the concentration of soluble sugar. However, photosynthesis and fluorescence characteristics remained unchanged. This indicates that the biomass reduction of low-K lettuce was due to the wasteful accumulation of carbohydrates rather than the decline in photosynthesis. Concentrations of SMs were increased in the low-K lettuce. In addition, higher concentrations of Na influenced the concentration of SMs, indicating that SMs were more sensitive to environmental stress.

Recently, the number of patients with chronic kidney disease has increased rapidly and kidneys with loss of the K-defecating function have been observed. Thus, providing vegetables with low potassium is an urgent unmet need. In this study, two cultivation methods were used to cultivate lettuce (Lactuca sativa L.) with low K concentrations. One method, dubbed LKEC, was based on electrical conductance management and the K supply was stopped at the end of cultivation. The other method, dubbed LKQM, was based on nutrient quantitative management, and the nutrients required for low-K lettuce were quantitatively supplied. Meanwhile, control lettuce with a normal K concentration, known as CK, were cultivated with electrical conductance management. Compared with CK, both low K treatments reduced the yield by nearly 20% without any visual deficiency symptoms. There was no significant difference between LKEC and LKQM in terms of plant growth. LKQM-treated lettuce contained lower Na and required less fertilizer than LKEC lettuce. Moreover, these plants adapted to K deficiency stress by absorbing more cations to maintain osmotic pressure. N declined with decreasing K. This suggested that the quantitative management method in low-potassium lettuce production reduced the potassium content in the lettuce plants to the same level as the EC management method, and significantly reduced the sodium content compared to EC management.