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Background: A floating system is a suitable low-cost hydroponic method for growing baby leaf vegetables. Among other, an important characteristic of the system is the use of large volume of nutrient solution which is characterized by high heat capacity. The aim of this study was to evaluate the effect of different root-zone temperatures on baby leaves of lettuce and rocket plants grown in a floating system under mild (spring) or extreme environmental conditions (summer and winter)., Results: Root-zone temperature was recorded in two tanks, one powered by a photovoltaic system and one where root-zone temperature was not controlled - this was used as a control tank. Photosynthetic parameters, yield, nutritional quality, and mineral composition were determined. In both baby leaf vegetables, during extreme weather conditions, yield was higher in the tanks with controlled root-zone temperature conditions than the control (+18.9% for rocket, and + 31.4% for baby lettuce), while quality parameters and chemical composition were not significantly affected. Stomatal conductance and net photosynthesis values were positively affected only during summer. On the other hand, control of root-zone temperature under mild weather conditions had no significant effect on baby lettuce and rocket., Conclusion: Control of the root-zone temperature could be a useful tool to improve productivity for baby lettuce and rocket crops cultivated in floating systems under extreme weather conditions. © 2020 Society of Chemical Industry., (© 2020 Society of Chemical Industry.)

This study investigated potential contamination sources in a commercial, closed hydroponic system. Water, substrate and lettuce (Lactuca sativa) samples were evaluated for microbiological indicator populations, including aerobic plate count (APC), coliform bacteria (CB) and yeast and mould (YM). Listeria spp. detection via cultural enrichment and agglutination was negative for all samples. Peat moss substrate (postharvest) had the highest counts for APC (6·8 log CFU per g), CB (4·5 log MPN per g) and YM (5·1 and 4·8 log CFU per g respectively). Roots embedded in plugs demonstrated counts for all populations nearly as high as the substrate. Among water samples, a seedling water reservoir housing germinated plants yielded the highest count for APC (5·1 log CFU per g) and CB (2·4 log MPN per g) likely due to the large numbers of plugs and their close proximity in the reservoir. Harvested lettuce leaves demonstrated higher APC (4·1 log CFU per g) than preharvest leaves (1·7 log CFU per g) due to the transfer of microbes from the root ball. These data suggest that substrates are a significant potential source of contamination in hydroponic systems and likely facilitate microbial transfer to harvested leaves. There is, therefore, the need to further investigate mitigation of potential contamination events. SIGNIFICANCE AND IMPACT OF THE STUDY: Hydroponic production is known to provide safe, clean produce. This study, however, suggests that the hydroponic substrate (peat moss plug) is a possible source of contamination in the hydroponic system. This finding is important as most harvested hydroponic lettuces are packaged and sold with substrate and root ball intact. This implies a high probability of microbial transfer from the root ball to edible harvested lettuce leaves., (© 2019 The Society for Applied Microbiology.)

Silicon can stimulate natural defense mechanisms in plants, reducing foliar diseases like powdery arid downy mildew on several crops, including lettuce. The effect of silicate on Fusarium wilt, caused by Fusarium oxysporum f. sp. lactucae was evaluated under greenhouse conditions on lettuce grown in soilless systems. Silicon, as potassium silicate, was added at 100 mg L(-1) of nutrient solution at three levels of electrical conductivity; 1.5-1.6 mS cm(-1) (E.C.1), 3.0-3.2 mS cm(-1) (E.C.2) and 4-4.2 mS cm(-1) (E.C.3). Pots containing lettuce plants were first inoculated with F. oxysporum f. sp. lactucae (3x10(5) chlamidospores ml(-1)) 15-20 days before transplanting. Disease severity and physiological parameters, including chlorophyll content, were analyzed weekly after transplanting. The addition of potassium silicate slightly reduced Fusarium wilt, at all levels of electrical conductivity under study, compared to the control. On the contrary, the increase of electrical conductivity of the nutrient solution showed no effect on the disease. The use of silicon was previously demonstrated to significantly reduce downy mildew on lettuce in soilless systems, and in this trial it demonstrated to slightly reduce disease severity of an important soil-borne pathogen like F. oxysporum f. sp. lactucae, suggesting the possibility to apply it successfully in soilless crops.

Objective. To develop a nutrient delivery system for space vegetable planting prototype facility to be used in future space station, and to preliminarily testify its feasibility through ground-based demonstration experiments. Method. A nutrient delivery system in a space vegetable planting prototype facility was designed and fabricated, and ground based demonstration experiments of plant cultivation were conducted. Result. Nutrient could be steadily delivered to plant cultivation matrixes through capillary action, water content of planting matrixes could be controlled automatically and maintained constant, and the planted material lettuce showed basically normal morphology and color. Conclusion. The nutrient delivery system in a space vegetable planting prototype facility could basically meet the requirements for plant nutrient delivery under space microgravity environmental condition.

The heat transfer characteristics of a hydroponic system were experimentally verified after theoretical establishment and the effect of nutrient solution cooling on the plant temperature was investigated. About 96 percent of the total heat flow transferred from culture bed to nutrient solution was the conductive heat through planting board and partitioning materials. The average and maximum temperatures of the leaf lettuce decreased 0.6 and 1.5 degrees C., respectively, with cooling of nutrient solution by 6 degrees C. A numerical model for prediction of cooling load of nutrient solution in a hydroponic greenhouse was developed, and the results from the simulation model showed a good agreement with those from experiments. A mechanical cooling system using the counter flow type with double pipes was developed for cooling the nutrient solution. Also the heat transfer characteristics of the system were analyzed experimentally and theoretically, and compared with the other existing cooling systems of nutrient solution. The cooling capacities of three different systems, which used polyethylene tube in solution tank, stainless tube in solution tank, and the counter flow type with double pipes, were comparatively evaluated.

Techniques and algorithms to detect and diagnose disorders in plants grown in a controlled environment have been developed. A video camera senses features of plants which are indicative of disorders. Images are calibrated for size and color variations by using calibration templates. Different image segmentation techniques for separating object from background, have been implemented. Plant size and color properties have been investigated, temporal, spectral and spatial variation of leaves were extracted from the segmented images. Neural network and statistical classifiers were used to determine plant condition.

The results of experiments conducted with higher plants in tightly sealed growth chambers provide definite evidence that the physical closure of a chamber has significant effects on many aspects of a plant's biology. One of these effects is seen in the change in rates of uptake, distribution, and re-release of nutrient elements by the plant (mass balance). Experimental data indicates that these rates are different from those recorded for plants grown in open field agriculture, or in open growth chambers. Since higher plants are a crucial component of a CELSS, it is important that the consequences of these rate differences be understood with regard to the growth and yield of the plants. This paper will focus on the description of a system for elemental analysis which can be used to monitor the mass balance of nutrient elements in CELSS experiments. Additionally, data on the uptake of nutrient elements by higher plants grown in a growth chamber will be presented.

A transparent, cylindrical chamber system was developed to allow measurement of gas-exchange by small crop canopies in the undisturbed plant growth environment. The system is an elaboration of the Minitron system developed previously to compare growth of small plants in different environments within the same general growth area. The Minitron II system described herein accommodates hydroponic culture and separate control of atmospheric composition in individual chambers. Root and shoot environments are compartmented separately to accommodate atmospheres of different flow rate and/or gaseous composition. A series of 0-rings and tension-adjustable springs allow carbon dioxide in the flowing atmosphere to be analyzed without cross-contamination between chamber compartments or from external gas sources. Carbon dioxide has been maintained at set point +/- 9 g m-3 over a range of CO2 concentrations from 382 to 2725 g m-3 and with an atmosphere turnover rate of 136.7 cm3 s-1 by computer-assisted mass flow controllers. Each chamber has dimensions large enough (61 cm internal diameter, 0.151 m3 internal volume) to allow adequate replication of individual plants for statistical purposes (e.g., up to 36 equally-spaced plant holders). No significant variation in growth or photosynthetic rate of leaf lettuce occurred between chambers for a given set of environmental conditions. Gas-exchange rates in different chambers changed to a similar extent as CO2 concentration in the flowing atmosphere or chamber temperature were varied by the same amount. When coupled with appropriate control systems, Minitron II chambers can provide separate controlled environments for multiple small plants with adequate precision and at relatively low cost.