Green roof technology can partially mitigate the adverse effects of urbanization by controlling stormwater runoff, pre-filtering water, minimizing climate change outcomes and reducing heat island effects. However, improvements to current green roof systems and innovative approaches are paramount to advancing environmental benefits and consumer acceptance of this technology. Regular green roofs are hindered by high cost and mass, as well as the incorporation of large amounts of polymers. Hydroponic green roofs (HGRs) require specific setups, maintenance and frequent replacement of plant-growing substrate, with limited energy savings in the heating and cooling load of the building due to the space between the roof surface and the hydroponic setup. In this review, a comparison of regular and HGRs is provided, and research into the environmental benefits of these technologies, including stormwater control, water purification and lifecycle assessment, is summarized. Following this, the prospect of porous concrete (PC), as a combined plant-growth substrate and structural layer in a novel extensive hydroponic green roof (EHGR) design is proposed, through a compilation and analysis of recent studies reporting the feasibility of this construction material for different applications. The mechanical, hydrological and vegetative properties of PC are discussed. Finally, a new green roof system that incorporates both PC and hydroponics, termed the EHGR system, is presented. This new green roof system may help offset the effects of urbanization by providing stormwater and pollution control, runoff delay and physical and thermal benefits, while concurrently producing biomass from a reusable substrate.

This preliminary mixed methods study utilized an online survey and phone interviews to examine the benefits, challenges and user experience of farmers utilizing hydroponic shipping container farms (HSCFs). Due to the novelty of this crop production method, and thus the relatively small number of commercial farmers adopting this technology, 12 commercial HSCF businesses, of 46 identified online and via social media, participated in this study. Because population size was small, and 11 of the 12 farms had been in business a very short amount of time (two years or less), the following results are preliminary. The results showed that HSCFs gave farmers the ability to produce locally, sustainably and in new areas. Seventy-five percent of the farmers (n = 9) strongly agreed or agreed that the HSCF helped their farm become more productive, did everything they expected it to do and was efficient. Most participants were satistifed (n = 8; 66.7%) with their HSCFs; one was very satisfied (8.3%), while others were neutral (n = 1; 8.3%) and dissatisfied (n = 2; 16.7%). Participant expectations were most met regarding incorporation of technology, reduced resource use and efficiency; however, 50.0% of the farmers (n = 6) disagreed or strongly disagreed that the HSCF was profitable. Some farmers reported that HSCFs are efficient in production, although their units were not as productive and profitable, nor as user friendly as they expected. Regarding HSCF challenges, power usage and startup costs were ranked most highly, while finding labor was the least challenging. Following phone interviews with three profitable farmers, it was revealed that their success was due to growing local food that was in demand by their community. While this study identified several challenges of HSCFs, this technology may have benefits, for example in areas with limited arable land and water resources, and may offer some farmers a way to be profitable, especially by tapping the growing consumer demand for local produce.

Water consumption in agriculture is impossible without considering relations between water, soil and plant. In this regard, there are various models and developed software in order to evaluate relation between soil, water and crop growth stages. These models can be used for irrigation planning if properly optimized and applied. AquaCrop is one of the known crop models, which was developed by the Food and Agriculture Organization of the United Nations. In order to optimize this model for crop production and irrigation management, an experiment was developed in a hydroponic cucumber greenhouse. Various parameters including water consumption volume, crop yield and leaf area index were measured during a season. A fuzzy control system was utilized for controlling temperature, relative humidity, planting bed moisture, light intensity and carbon dioxide values. The main purpose of designing a control system in the greenhouse is to achieve the desired values of temperature and relative humidity. In this model, evapotranspiration, irrigation requirements and crop yield were simulated. The results show that the AquaCrop model can estimate evapotranspiration with the least error in the greenhouse environment, which is controlled by a fuzzy controller. Also the system has estimated the crop yield and biomass of the product with a good degree of precision and it may support crop production in a greenhouse, including crop management and environmental control.

Root development and the associated acquisition of water and nutrients are an important part of weed competitiveness. Characterization of root morphological development, however, is inherently problematic because of the complexities of soil–plant interactions. In this study, we used hydroponically grown plants and digital imaging to examine root characteristics of Glycine max and the competing weeds Senna obtusifolia and Amaranthus palmeri. The purpose was to define inherent differences in root length and surface area that would contribute to growth responses during the establishment phase in the field. The methodology involved growing plants for 16 to 22 d, dissecting and staining root segments, mounting subsamples on slides, and imaging using a stereomicroscope and digital camera. Microscopy was required because of the small diameters of a significant proportion of the weed roots. With plants of similar root fresh weights (4.5 to 5.0 g), counting of individual roots revealed that 5. obtusifolia and A. palmeri had 2 and 3.7 times more roots than G. max (4,616 and 7,781 vs. 2,120, respectively). The imaging analyses indicated that roots of S. obtusifolia and A. palmeri had 2.9 and 5 times more length than G. max (10,042 and 17,192 cm vs. 3,418 cm, respectively). Furthermore, the analysis of length in different root diameter classes indicated that weed roots were noticeably finer then those of G. max. Approximately 84% of S. obtusifolia root length was contributed by roots in the 0.1- to 0.25-mm range, whereas 45% of the G. max roots were in the 0.1- to 0.25-mm range and 48% were in the 0.25- to 0.75-mm range. In contrast, 68% of A. palmeri length was contributed by roots smaller than 0.1 mm in diameter with 26% in the 0.1- to 0.25-mm range. Based on the expression of root characteristics observed here, root systems of these weed species would have finer roots with much greater length that would occupy a much larger volume of soil than those of G. max. Presumably, this would result in a competitive advantage in the acquisition of water and nutrients, especially when availability is limited.

Twenty determinate soybean cultivars were grown in hydroponic solutions to determine differential tolerance to chlorimuron and imazaquin at pH 6, 7, or 8. ‘Epps' exhibited tolerance to chlorimuron at each pH, and to imazaquin except at pH 8. ‘9641 Pioneer’ was highly sensitive to both herbicides at each pH, and ‘Asgrow 5979’ was sensitive to chlorimuron, and to imazaquin except at pH 7. ‘Hutcheson’ was sensitive to chlorimuron at each pH, and imazaquin at pH 6. ‘Asgrow 6785’ was sensitive to chlorimuron at pH 6 and 8, with shoot weight reductions of 31 and 28%, respectively, and ‘Coker 686’ was similarly sensitive at pH 6 and 7. ‘Hartz 6200’ was tolerant to imazaquin at pH 6 and 7, ‘Hartz 6686’ was tolerant at pH 6 and 8, and Coker 686 was tolerant at pH 7 and 8. Coker 686 and 'Sharkey’ were tolerant to chlorimuron at some pH levels, though highly sensitive at other pH levels. ‘Asgrow 5403’ and Coker 686 also had varying tolerance and sensitivity to imazaquin across pH levels. Shoot length and shoot weight were the best indicators of differential cultivar sensitivity when compared with previous field studies.

Thirty soybean cultivars were grown in a hydroponic culture to observe differential tolerance to AC 263,222. Root length was reduced with 1.1 mM AC 263,222 in 18 of the 30 cultivars. ‘Bedford’, ‘Asgrow 5403’, and ‘Asgrow 6297’ were cultivars with a root length reduction of 30% or more, whereas roots of ‘DPL 506’, ‘RA 606’, and ‘Coker 6727’ were reduced less than 7%. Root weight was reduced in only 10 of the 30 cultivars. Asgrow 6297, ‘Bragg’, and ‘Narow’ root weights were reduced more than 20%. Shoot weight was reduced in 23 cultivars, and ‘Coker 6955’, ‘Braxton’, ‘Coker 485’, ‘Epps', and Coker 6727 shoots were reduced more than 25%. The most tolerant cultivars were ‘Centennial’, RA 606, ‘Tracy M’, ‘Johnston’, and ‘Hartz 7126’. The most sensitive cultivars to AC 263,222 with all response variables measured were Bedford, Asgrow 6297, Asgrow 5403, Coker 6955, Narow, Bragg, and Braxton. These cultivars all have ‘Jackson’ as a common parent. This suggests a genetic basis for AC 263,222 sensitivity in soybean.