A methodological tool for sustainability and feasibility assessment of indoor vertical farming with artificial lighting in Africa.

African agriculture is bound to face challenges for its future food systems development and economic transformation. Indoor vertical farms with artificial lighting represent an opportunity that has been gaining relevance worldwide, thanks to their potential to enable high productivity rates, food quality and safety, year-round production, and more sustainable use of water and mineral nutrients. The present study assesses the potential for vertical farming technology integration within the African continent, targeting the countries where a more sustainable approach could be achieved. A deep analysis of each territory's major opportunities and challenges was built through an updated database of 147 development indicators from 54 African states. Countries such as South Africa, Seychelles, Egypt, Mauritius, Morocco, Tunisia, Algeria, Cape Verde, and Nigeria showed the best prospective for indoor vertical farming implementation. Moreover, Seychelles, South Africa, and Egypt resulted to be the countries where vertical indoor farming could be more sustainable.

Beyond vegetables: effects of indoor LED light on specialized metabolite biosynthesis in medicinal and aromatic plants, edible flowers, and microgreens.

Specialized metabolites from plants are important for human health due to their antioxidant properties. Light is one of the main factors modulating the biosynthesis of specialized metabolites, determining the cascade response activated by photoreceptors and the consequent modulation of expressed genes and biosynthetic pathways. Recent developments in light emitting diode (LED) technology have enabled improvements in artificial light applications for horticulture. In particular, the possibility to select specific spectral light compositions, intensities and photoperiods has been associated with altered metabolite content in a variety of crops. This review aims to analyze the effects of indoor LED lighting recipes and management on the specialized metabolite content in different groups of crop plants (namely medicinal and aromatic plants, microgreens and edible flowers), focusing on the literature from the last 5 years. The literature collection produced a total of 40 papers, which were analyzed according to the effects of artificial LED lighting on the content of anthocyanins, carotenoids, phenols, tocopherols, glycosides, and terpenes, and ranked on a scale of 1 to 3. Most studies applied a combination of red and blue light (22%) or monochromatic blue (23%), with a 16 h day-1 photoperiod (78%) and an intensity greater than 200 µmol m-2  s-1 (77%). These treatment features were often the most efficient in enhancing specialized metabolite content, although large variations in performance were observed, according to the species considered and the compound analyzed. The review aims to provide valuable indications for the definition of the most promising spectral components toward the achievement of nutrient-rich indoor-grown products. © 2021 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Supplemental LED Lighting Effectively Enhances the Yield and Quality of Greenhouse Truss Tomato Production: Results of a Meta-Analysis.

Intensive growing systems used for greenhouse tomato production, together with light interception by cladding materials or other devices, may induce intracanopy mutual shading and create suboptimal environmental conditions for plant growth. There are a large number of published peer-reviewed studies assessing the effects of supplemental light-emitting diode (LED) lighting on improving light distribution in plant canopies, increasing crop yields and producing qualitative traits. However, the research results are often contradictory, as the lighting parameters (e.g., photoperiod, intensity, and quality) and environmental conditions vary among conducted experiments. This research presents a global overview of supplemental LED lighting applications for greenhouse tomato production deepened by a meta-analysis aimed at answering the following research question: does supplemental LED lighting enhance the yield and qualitative traits of greenhouse truss tomato production? The meta-analysis was based on the differences among independent groups by comparing a control value (featuring either background solar light or solar + HPS light) with a treatment value (solar + supplemental LED light or solar + HPS + supplemental LED light, respectively) and included 31 published papers and 100 total observations. The meta-analysis results revealed the statistically significant positive effects (p-value < 0.001) of supplemental LED lighting on enhancing the yield (+40%), soluble solid (+6%) and ascorbic acid (+11%) contents, leaf chlorophyll content (+31%), photosynthetic capacity (+50%), and leaf area (+9%) compared to the control conditions. In contrast, supplemental LED lighting did not show a statistically significant effect on the leaf stomatal conductance (p-value = 0.171). In conclusion, in addition to some partial inconsistencies among the considered studies, the present research enables us to assert that supplemental LED lighting ameliorates the quantitative and qualitative aspects of greenhouse tomato production.

Sources of Variation in Assessing Canopy Reflectance of Processing Tomato by Means of Multispectral Radiometry.

Canopy reflectance sensors are a viable technology to optimize the fertilization management of crops. In this research, canopy reflectance was measured through a passive sensor to evaluate the effects of either crop features (N fertilization, soil mulching, appearance of red fruits, and cultivars) or sampling methods (sampling size, sensor position, and hour of sampling) on the reliability of vegetation indices (VIs). Sixteen VIs were derived, including seven simple wavelength reflectance ratios (NIR/R460, NIR/R510, NIR/R560, NIR/R610, NIR/R660, NIR/R710, NIR/R760), seven normalized indices (NDVI, G-NDVI, MCARISAVI, OSAVI, TSAVI, TCARI), and two combined indices (TCARI/OSAVI; MCARI/OSAVI). NIR/560 and G-NDVI (Normalized Difference Vegetation Index on Greenness) were the most reliable in discriminating among fertilization rates, with results unaffected by the appearance of maturing fruits, and the most stable in response to different cultivars. Black mulching film did not affect NIR/560 and G-NDVI behavior at the beginning of the growing season, when the crop is more responsive to N management. Due to a moderate variability of NIR/560 and G-NDVI, a small sample size (5-10 observations) is sufficient to obtain reliable measurements. Performing the measurements at 11:00 and 14:00 and maintaining a greater distance (1.8 m) between plants and instrument enhanced measurement consistency. Accordingly, NIR/560 and G-NDVI resulted in the most reliable VIs.

Resource use efficiency of indoor lettuce (Lactuca sativa L.) cultivation as affected by red:blue ratio provided by LED lighting.

LED lighting in indoor farming systems allows to modulate the spectrum to fit plant needs. Red (R) and blue (B) lights are often used, being highly active for photosynthesis. The effect of R and B spectral components on lettuce plant physiology and biochemistry and resource use efficiency were studied. Five red:blue (RB) ratios (0.5-1-2-3-4) supplied by LED and a fluorescent control (RB = 1) were tested in six experiments in controlled conditions (PPFD = 215 µmol m-2 s-1, daylength 16 h). LED lighting increased yield (1.6 folds) and energy use efficiency (2.8 folds) as compared with fluorescent lamps. Adoption of RB = 3 maximised yield (by 2 folds as compared with RB = 0.5), also increasing leaf chlorophyll and flavonoids concentrations and the uptake of nitrogen, phosphorus, potassium and magnesium. As the red portion of the spectrum increased, photosystem II quantum efficiency decreased but transpiration decreased more rapidly, resulting in increased water use efficiency up to RB = 3 (75 g FW L-1 H2O). The transpiration decrease was accompanied by lower stomatal conductance, which was associated to lower stomatal density, despite an increased stomatal size. Both energy and land surface use efficiency were highest at RB ≥ 3. We hereby suggest a RB ratio of 3 for sustainable indoor lettuce cultivation.

Unraveling the Role of Red:Blue LED Lights on Resource Use Efficiency and Nutritional Properties of Indoor Grown Sweet Basil.

Indoor plant cultivation can result in significantly improved resource use efficiency (surface, water, and nutrients) as compared to traditional growing systems, but illumination costs are still high. LEDs (light emitting diodes) are gaining attention for indoor cultivation because of their ability to provide light of different spectra. In the light spectrum, red and blue regions are often considered the major plants' energy sources for photosynthetic CO2 assimilation. This study aims at identifying the role played by red:blue (R:B) ratio on the resource use efficiency of indoor basil cultivation, linking the physiological response to light to changes in yield and nutritional properties. Basil plants were cultivated in growth chambers under five LED light regimens characterized by different R:B ratios ranging from 0.5 to 4 (respectively, RB0.5, RB1, RB2, RB3, and RB4), using fluorescent lamps as control (CK1). A photosynthetic photon flux density of 215 µmol m-2 s-1 was provided for 16 h per day. The greatest biomass production was associated with LED lighting as compared with fluorescent lamp. Despite a reduction in both stomatal conductance and PSII quantum efficiency, adoption of RB3 resulted in higher yield and chlorophyll content, leading to improved use efficiency for water and energy. Antioxidant activity followed a spectral-response function, with optimum associated with RB3. A low RB ratio (0.5) reduced the relative content of several volatiles, as compared to CK1 and RB ≥ 2. Moreover, mineral leaf concentration (g g-1 DW) and total content in plant (g plant-1) were influences by light quality, resulting in greater N, P, K, Ca, Mg, and Fe accumulation in plants cultivated with RB3. Contrarily, nutrient use efficiency was increased in RB ≤ 1. From this study it can be concluded that a RB ratio of 3 provides optimal growing conditions for indoor cultivation of basil, fostering improved performances in terms of growth, physiological and metabolic functions, and resources use efficiency.

Social acceptance and perceived ecosystem services of urban agriculture in Southern Europe: The case of Bologna, Italy.

Urban agriculture has become a common form of urban land use in European cities linked to multiple environmental, social and economic benefits, as well as to diversified forms (from self-production allotments to high-tech companies). Social acceptance will determine the development of urban agriculture and specific knowledge on citizens' perception is required in order to set the basis for policy-making and planning. The ecosystem services provided by urban agriculture can be determinant in this process. The goal of this paper is to evaluate the social acceptance and the perceived ecosystem services of urban agriculture in the city of Bologna (Italy), as an example of a Southern European city. In particular, we evaluated the preferences for urban land uses, for different typologies of urban agriculture and for the resulting products, the perceived provision of ecosystem services and the willingness to engage in new initiatives. A survey that investigated these topics (including open questions, closed questions and Likert-scale evaluation) was performed on the citizens of Bologna (n = 380) between October and November 2016. Results showed that urban agriculture is widely accepted by the inhabitants of Bologna, particularly regarding vegetable production. Although intensive farming systems were the least preferred forms to be implemented in Bologna, citizens highly accepted a large variety of urban agriculture goods, with preference for those obtained from plants as compared to animal products. The willingness-to-pay for urban food products was mostly the same as for conventional ones, although the participants recognised the social values, proximity and quality of the former. Socio-cultural ecosystem services were perceived as more valuable than environmental ones. Policy-making recommendations can be extracted from the results to facilitate the development of urban agriculture plans and policies.

Salinity thresholds and genotypic variability of cabbage (Brassica oleracea L.) grown under saline stress.

BACKGROUND: Two botanical varieties of cabbage, namely Savoy (Brassica oleracea var. Sabauda L.) and White (Brassica oleracea var. Capitata L.) were used in order to understand the morphological, physiological and biochemical elements of functional salt stress response. Thirteen salt concentrations (range, 0 to 300 mmol L(-1) NaCl) were considered in Experiment 1 and, of these 13, three (0, 100 and 200 mmol L(-1) NaCl) were used in Experiment 2. RESULTS: Experiment 1 enabled the definition of two salinity thresholds (100 and 200 mmol L(-1) NaCl), associated with morphological and physiological adaptations. In Experiment 2, moderate salinity (100 mmol L(-1) NaCl) had lower effects on Savoy than in White cabbage yield (respectively, -16% and -62% from control). Concurrently, 100 mmol L(-1) NaCl resulted in a significant increase of antioxidant enzymes from control conditions, that was greater in Savoy (+289, +423 and +88%, respectively) as compared to White (+114, +356 and +28%, respectively) cabbage. Ion accumulation was found to be a key determinant in tissue osmotic adjustment (mainly in Savoy) whereas the contribution of organic osmolites was negligible. CONCLUSIONS: Higher antioxidative enzymatic activities in Savoy versus White cabbage after treatment with 100 mmol L(-1) NaCl were associated with improved water relations, thus suggesting a possible physiological pathway for alleviating perceived salt stress.

Ionic partitioning and stomatal regulation: dissecting functional elements of the genotypic basis of salt stress adaptation in grafted melon.

Vegetable grafting is commonly claimed to improve crop's tolerance to biotic and abiotic stresses, including salinity. Although the use of inter-specific graftings is relatively common, whether the improved salt tolerance should be attributed to the genotypic background rather than the grafting per se is a matter of discussion among scientists. It is clear that most of published research has to date overlooked the issue, with the mutual presence of self-grafted and non-grafted controls resulting to be quite rare within experimental evidences. It was recently demonstrated that the genotype of the rootstock and grafting per se are responsible respectively for the differential ion accumulation and partitioning as well as to the stomatal adaptation to the stress. The present paper contributes to the ongoing discussion with further data on the differences associated to salinity response in a range of grafted melon combinations.

Improved stomatal regulation and ion partitioning boosts salt tolerance in grafted melon.

Grafted plants are often more tolerant to salinity than nongrafted controls. In order to distinguish differential response components in grafted melon (Cucumis melo L.), salt stress was imposed on several rootstock-scion combinations in four experiments. The rootstock used was an interspecific squash (Cucurbita maxima Duch.×Cucurbita moschate Duch.), RS841, combined with two cantaloupe (C. melo var. cantalupensis) cultivars, namely London and Brennus, against both self-grafted and nongrafted controls. Physiological, morphological and biochemical adaptations to 0, 40 and 80mM NaCl were monitored. Upon salinity, plant biomass and leaf area were improved by grafting per se, since self-grafted plants performed similarly to the heterografted ones. However, improvements in the exclusion of Na+ and the uptake of K+ were due only to the rootstock genotype, since ionic composition was similar in self-grafted and nongrafted plants. These results indicate that the favourable effects of grafting on plant growth cannot be ascribed to a more efficient exclusion of Na+ or enhanced nutrient uptake. On the other hand, growth improvements in both self- and heterografted plants were associated with a more efficient control of stomatal functions (changes in stomatal index and water relations), which may indicate that the grafting incision may alter hormonal signalling between roots and shoots.

Beyond the ionic and osmotic response to salinity in Chenopodium quinoa: functional elements of successful halophytism.

Chenopodium quinoa Willd. (quinoa) is a halophyte for which some parameters linked to salt tolerance have been investigated separately in different genotypes and under different growth conditions. In this study, several morphological and metabolic responses were analysed in parallel after exposure to salinity. In vitro seed germination was initially delayed by a 150mM NaCl treatment but eventually reached the same level as the control (0mM NaCl), whereas seedling root growth was enhanced; both parameters were moderately inhibited (~35-50%) by 300mM NaCl. In pot grown plants, plant size was reduced by increasing salinity (0-750mM NaCl). Transpiration and stomatal conductance were decreased at the highest salinity levels tested, consistent with reduced stomatal density and size. The density of epidermal bladder cells (EBCs) on the leaf surface remained unaffected up to 600mM NaCl. Tissue contents of Na+ and Cl- increased dramatically with salt treatment, but resulted in only a 50% increase in Na+ from 150 to 750mM NaCl. Internal K+ was unaffected up to 450mM NaCl but increased at the highest salinity levels tested. Excretion through sequestration into EBCs was limited (generally ≤20%) for all ions. A modest dose-dependent proline accumulation, and concomitant reduction in total polyamines and putrescine efflux occurred in NaCl-treated plants. Results confirm the importance of inorganic ions for osmotic adjustment, the plant's ability to maintain K+ levels and the involvement of putrescine efflux in maintaining ionic balance under high salinity conditions. Conversely, ion excretion and proline appear to play a minor role. Taken together these results indicate which parameters could be used for future comparison among different genotypes.

Steering nitrogen fertilisation by means of portable chlorophyll meter reduces nitrogen input and improves quality of fertigated cantaloupe (Cucumis melo L. var. cantalupensis Naud.).

BACKGROUND: Farming is considered one of the main causes of land degradation and underground water pollution. The increased availability of agricultural inputs has led to a dramatic rise in yields, which has resulted in soil fertility spoilage and overuse of fertilisers. Therefore horticultural practice improvement must consider appropriate nitrogen (N) management. This paper reports results on the application of an optical diagnostic system (N-tester) to guide N fertilisation in muskmelon (Cucumis melo L.) over a 3 year trial. Results on fresh and postharvest quality are also presented. RESULTS: Fertilisation events mirrored increases in N-tester values during the season, and a significant linear relationship (R(2) = 0.628) was observed between N-tester readings and leaf chlorophyll content. The N-tester-guided fertilisation treatments were characterised by yields comparable to the control, but with significantly lower applications of N (down to 17-66% of the N distributed in the control). Moreover, the N-tester treatments yielded fruits with higher sugar content. This was also true after storage, when N-tester fruits also showed reduced weight loss associated with lower transpiration and ethylene emission rates. CONCLUSION: Through the use of 'spy plots' kept at optimal nutritional status and the adoption of a threshold for N application throughout the growing cycle of muskmelon, the N supply was significantly reduced. Therefore a correct application of N-tester allowed the plant N requirement to be reduced and the fruit sugar content and storability to be increased without adversely affecting the yield.

The influence of aluminium availability on phosphate uptake in Phaseolus vulgaris L. and Phaseolus lunatus L.

Aluminium toxicity is one of the major limiting factors of crop productivity on acid soils. High levels of available aluminium in soil may induce phosphorus deficiency in plants. This study investigates the influence of Aluminium (Al) on the phosphate (P(i)) uptake of two Phaseolus species, Phaseolus vulgaris L. var. Red Kidney and Phaseolus lunatus L. The two bean species were treated first with solutions of Al at different concentrations (0, 25, 50 and 100microM, pH 4.50) and second with solutions of P(i) (150microM) at pH 4.50. The higher the Al concentration the higher the Al concentration sorbed but P. vulgaris L var. Red Kidney adsorbed significantly more Al than P. lunatus L. Both species released organic acids: P. vulgaris L var. Red Kidney released fumaric acid and P. lunatus L. fumaric and oxalic acids which could have hindered further Al uptake. The two bean species showed a sigmoid P(i) uptake trend but with two different mechanisms. P. vulgaris L var. Red Kidney showed a starting point of 3h whereas P. lunatus L. adsorbed P(i) immediately within the first minutes. In addition, P. vulgaris L var. Red Kidney presented significantly higher P(i) uptake (higher uptake rate 'k' and higher maximum adsorption 'a' of the kinetic uptake model). The Al treatments did not significantly influence P(i) uptake. Results suggest that P. lunatus L. might adopt an external Al detoxification mechanism by the release of oxalic acid. P. vulgaris L var. Red Kidney on the other hand seemed to adopt an internal detoxification mechanism even if the Al sorbed is poorly translocated into the shoots. More detailed studies will be necessary to better define Al tolerance and/or resistance of Phaseolus spp.