Optimizing irrigation in urban agriculture for tomato crops in rooftop greenhouses.

The rise of population in urban areas makes it ever more important to promote urban agriculture (UA) that is efficient in terms of water and nutrients. How to meet the irrigation demand of UA is of particular concern in urban areas where water sources are often limited. With the aim of determining how to reduce water use for irrigation while maintaining productivity and reducing environmental impacts in UA, this study explores the agronomic performance and environmental life cycle impacts and benefits of three different fertigation management practices used in a rooftop greenhouse for tomato crop in Barcelona: 1) open management (OP); 2) recirculation (RC), in which 30% of the drained, unused water is used to irrigate the crop; and 3) the same recirculated management of RC with a further reduction in fresh water input of 15%(RR). Despite the recirculation and reduction of water and nutrients, all three irrigation management practices resulted in similar yields: 16.2, 17.9, and 16.8·kg·m-2 for OP, RC, and RR, respectively. In terms of water-use efficiency, RR management was the most efficient, requiring 48.7·liters·kg-1 of tomato, followed by RC (52.4·L·kg-1) and OP (75.2·L·kg-1). RR presented an improvement of 7% in water-use efficiency. In terms of environmental performance, RC had the best performance in almost all impact categories during the operational phase, especially in regard to marine and freshwater eutrophication, with 44% and 93% fewer impacts than OP due to the recirculation of nutrients and reduced nutrient loss through leachates. In terms of infrastructure, even though recirculation management requires additional equipment, the materials present better performance in the range from 0.2 to 14% depending on the impact category. This study can support evaluation of agricultural projects in the city, through yields and water consumption presented, incentivizing good practices aligned with the sustainability of UA.

Comparison of organic substrates in urban rooftop agriculture, towards improving crop production resilience to temporary drought in Mediterranean cities.

BACKGROUND: Urban agriculture contributes to meeting the growing food production demand in cities. In the context of low water availability, it is important to consider alternatives that are able to maintain production. Through a circular economy vision, this study aimed to assess the use of substrates made from local materials as an alternative for urban agriculture in periods of low water availability, due to water supply cuts. The substrates used were coir commercial organic substrate, vegetable compost from urban organic waste and perlite commercial standard substrate; a mixture of the urban compost and perlite (1:1) was used for three consecutive crop cycles of lettuce (Lactuca sativa L. var. crispa). The crop cycles were performed in the spring and summer periods of 2018 to observe the performance during warmer periods of the year in an integrated rooftop greenhouse near Barcelona. Each substrate was assessed under conventional irrigation (0-5 kPa) and temporary water restricted conditions (irrigation stopped until the water tension reached -20 kPa perlite). RESULTS: In terms of yield, our results show that the compost and mixture were similar to those obtained from perlite (11.5% and 3.7% more production under restricted water conditions). Organic substrates increased the crop's resilience to water restriction, in contrast to the perlite. In particular, water loss took longer in coir (one- and two-crop cycle); however, when dryness began, it occurred quickly. CONCLUSION: The vegetable compost and the substrate mixture presented tolerance to temporary water restriction when water restriction reached -20 kPa. © 2021 Society of Chemical Industry.

Analysis of urban agriculture solid waste in the frame of circular economy: Case study of tomato crop in integrated rooftop greenhouse.

Within urban agriculture (UA), integrated rooftop greenhouses (i-RTG) have great growth potential as they offer multiple benefits. Currently it is intended to improve environmental benefits by taking advantage of the water, nutrients and gases flows. On the other hand, solid waste (SW) generated by the UA is a new type of waste within cities that has not well been classified or quantified for its use. This could become a new problem for the waste management system within cities in the future, mainly the organic fraction. The objective of this research is to identify what type of i-RTG SW has the potential to be used from a circular economy (CE) perspective and propose a type of management for its material valorization. The results of the case study show that, of the SW generated in i-RTG, the biomass has the greatest potential to be used locally as an eco-material, particularly the tomato stems. Its use is proposed as a substrate for two experimental lettuce crops in i-RTG. The results show that tomato stems have a better yield as a substrate after a prewash treatment, since at first the values of electrical conductivity (EC) are very high with respect to the control substrate, which is expanded perlite. In conclusion, we can say that it is possible to increase the environmental benefits of i-RTG by taking advantage of its biomass locally, helping to foresee a possible future problem regarding the management of the residual biomass of i-RTG within cities. In this way, the paradigm about the perception of the SW of the UA could be changed to give them a by-product treatment from the beginning.

Building-integrated agriculture: A first assessment of aerobiological air quality in rooftop greenhouses (i-RTGs).

Building-integrated rooftop greenhouse (i-RTG) agriculture has intensified in recent years, due to the growing interest in the development of new agricultural spaces and in the promotion of food self-sufficiency in urban areas. This paper provides a first assessment of the indoor dynamics of bioaerosols in an i-RTG, with the aim of evaluating biological air quality in a tomato greenhouse near Barcelona. It evaluates the greenhouse workers' exposure to airborne pollen and fungal spores in order to prevent allergy problems associated with occupational tasks. Moreover, it evaluates whether the quality of the hot air accumulated in the i-RTG is adequate for recirculation to heat the building. Daily airborne pollen and fungal spore concentrations were measured simultaneously in the indoor and outdoor environments during the warm season. A total of 4,924pollengrains/m3 were observed in the i-RTG, with a peak of 334pollengrains/m3day, and a total of 295,038 fungal spores were observed, reaching a maximum concentration of 26,185spores/m3day. In general, the results showed that the most important source of pollen grains and fungal spores observed indoors was the outdoor environment. However, Solanaceae pollen and several fungal spore taxa, such as the allergenic Aspergillus/Penicillium, largely originated inside the greenhouses or were able to colonize the indoor environment under favourable growing conditions. Specific meteorological conditions and agricultural management tasks are related to the highest observed indoor concentrations of pollen grains and fungal spores. Therefore, preventive measures have been suggested in order to reduce or control the levels of bioaerosols indoors (to install a system to interrupt the recirculation of air to the building during critical periods or to implement appropriate air filters in ventilation air ducts). This first evaluation could help in making decisions to prevent the development of fungal diseases, specifically those due to Oidium and Torula.

Improvement of agricultural life cycle assessment studies through spatial differentiation and new impact categories: case study on greenhouse tomato production.

This paper presents the inclusion of new, relevant impact categories for agriculture life cycle assessments. We performed a specific case study with a focus on the applicability of spatially explicit characterization factors. The main goals were to provide a detailed evaluation of these new impact category methods, compare the results with commonly used methods (ReCiPe and USEtox) and demonstrate how these new methods can help improve environmental assessment in agriculture. As an overall conclusion, the newly developed impact categories helped fill the most important gaps related to land use, water consumption, pesticide toxicity, and nontoxic emissions linked to fertilizer use. We also found that including biodiversity damage due to land use and the effect of water consumption on wetlands represented a scientific advance toward more realistic environmental assessment of agricultural practices. Likewise, the dynamic crop model for assessing human toxicity from pesticide residue in food can lead to better practice in pesticide application. In further life cycle assessment (LCA) method developments, common end point units and normalization units should be agreed upon to make it possible to compare different impacts and methods. In addition, the application of site-specific characterization factors allowed us to be more accurate regarding inventory data and to identify precisely where background flows acquire high relevance.

Uptake of microcontaminants by crops irrigated with reclaimed water and groundwater under real field greenhouse conditions.

The use of reclaimed water for agricultural irrigation has emerged as a new strategy for coping with water scarcity in semiarid countries. However, the incorporation of the organic microcontaminants in such water into the diet through crop uptake poses a potential risk to human health. This paper aims to assess the presence of organic microcontaminants in different crops irrigated with groundwater and reclaimed water (secondary or tertiary effluents) in a greenhouse experiment. The determination of microcontaminants in water and vegetation samples was performed by solid-phase extraction and matrix solid-phase dispersion procedure with GC-MS/MS, respectively. The presence of nitrates in the groundwater used for irrigation increased biomass production by a higher proportion than the harvest index. The concentration of microcontaminants in lettuce, carrots, and green beans ranged from less than the limit of quantitation to 571 ng g(-1) (fresh weight). Tributyl phosphate and butylated hydroxyanisole exhibited the highest concentration levels in crops. The concentration and frequency of detection of microcontaminants were lower in green bean pods than in green bean roots and leaves. Although the concentrations were generally low, the simultaneous presence of a variety of microcontaminants should be taken into consideration when assessing the risk to human health.

Uptake and persistence of pesticides in plants: measurements and model estimates for imidacloprid after foliar and soil application.

The uptake and persistence behaviour of the insecticide imidacloprid in tomato plants treated by (i) foliar spray application and (ii) soil irrigation was studied using two plant uptake models. In addition to a pesticide deposition model, a dynamic root uptake and translocation model was developed, and both models predict residual concentrations of pesticides in or on fruits. The model results were experimentally validated. The fraction of imidacloprid ingested by the human population is on average 10(-2) to 10(-6), depending on the time between pesticide application and ingestion, the processing step, and the application method. Model and experimentally derived intake fractions deviated by less than a factor of 2 for both application techniques. Total imidacloprid residues were up to five times higher in plants treated by foliar spray application than by soil irrigation. However, peeling tomatoes treated by spray application reduces the human intake fraction by up to three orders of magnitude. Model calculations suggest that drip-irrigation in a closed hydroponic system minimizes worker and consumer exposure to pesticides and prevents runoff of pesticide by spray drift and leaching into the environment.