Comparing soilless and non-chemical farming food production systems: Nutritional and environmental aspects for food security and sustainability

doi:10.21203/rs.3.rs-4894455/v1

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Comparing soilless and non-chemical farming food production systems: Nutritional and environmental aspects for food security and sustainability

https://doi.org/10.21203/rs.3.rs-4894455/v1

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Plant factory with artificial light (PFAL) technology is a soilless cultivation system that designed to optimize plant growth, productivity, and product quality, as well as ensure efficient use of water and fertilizer. Non-chemical farming (N-CF) systems are a traditional agricultural cultivation method. Both agricultural systems can serve as commodity production methods for ensuring food security. However, concerns about nutritional value and environmental sustainability remain. This study compares the nutritional compositions, antioxidant contents, environmental impacts, and carbon footprint of kale (Brassica oleracea L.) in PFAL and N-CF systems. The proximate values of kale in PFAL and N-CF systems were not significantly different (p < 0.05). However, the results revealed that antioxidant contents, determined by polyphenol, oxygen radical absorbance capacity (ORAC) assay and ferric reducing antioxidant power (FRAP) assay were significantly lower in PFAL-harvested kale than in N-CF-harvested kale after three months. The polyphenol, ORAC and FRAP of PFAL kale were 68.95 mg GAE/100 g, 1,321.25 and 111.95 μmol TE/100 g fresh weight, respectively, while those of N-CF kale were136.06 mg GAE/100 g, 3,519.87 and 220.17 μmol TE/100 g fresh weight, respectively. The carbon dioxide (CO₂) emissions of 3 month-kale from PFAL and N-CF productions were 168.61 and 14.75 Kg CO₂ eq./kg of kale, respectively. Consequently, new policies should be oriented toward reducing environmental pressure by introducing process certification of low environmental impacts. However, not only environmental aspects but also the adequacy of nutritive values of products should be a concern for farming food production systems.

Food security

Environmental impacts

Nutritive values

Carbon footprints

Climate change has become a global concern in recent decades. It causes ozone depletion, impacts agriculture yield, water supply, and transportation, and create several other problems. Climate change may impact food systems in various aspects, increasing crop disease, lowering nutritional quality and reducing crop yield e.g., changes in rainfall patterns can cause drought or flood, or warmer or cooler temperatures can lead to changes in the length of the growing season (Gregory et al., 2005). The world populations are predicted to get larger by over a third or 2.3 billion people in 2050. These trends indicate that food market demand will continue to rise. According to studies, feeding the world's population in 2050 would require a 50 percent increase in overall grain production (Alexandratos & Bruinsma, 2012).

As the world faces the challenge of feeding a growing global population while preserving environmental integrity, two contrasting agricultural systems have gained prominence: Plant Factory with Artificial Lighting (PFAL) and Non-chemical farming (N-CF). PFAL is a soilless close production system characterized by a controlled environment, hydroponics, and artificial lighting, making it a high-tech approach to crop cultivation. Meanwhile, N-CF is a traditional agriculture.

The advancement of PFAL technology could be considered an optional intervention for addressing these concerns. It is claimed that PFAL could lower greenhouse gas emissions by the potential reductions of air pollution, water use, fertilisers, and pesticides. A few reports suggest that PFAL can reduce greenhouse gas emissions (Orsini et al., 2020). There is a report indicating that an improved vertical farm, a type of indoor farm, could emit 0.16 to 0.33 kg of CO₂ equivalents per kg of lettuce (Milestad et al., 2020). Apart from eco-friendly benefits, PFAL could be related to the quality of plants (Butryee, 2020). For example, light is a key factor in phytochemical synthesis, growth, development, and nutritional composition in plants. Myung Jin Lee (2016) found that red, blue, and far-red LEDs at ratios of 0.7 and 1.2 significantly increased total phenolic levels, antioxidant activity, chlorogenic acid contents, and caffeic acid contents in intervention plant groups compared to the control. It was presumed that the appropriate quality and intensity of light can increase the quantity and quality of phytochemicals in plants (Lee et al., 2016). N-CF is an alternative agriculture system that attempts to deliver sustainable and safe foods. It also protects resources and the environment by avoiding synthetic pesticides and using the on-farm resources in the most efficient ways.

Kale (Brassica oleracea L.) is a highly nutritious leafy green vegetable known for its rich content of vitamins, minerals, and antioxidants. It contains high levels of vitamins A, C, and K, as well as calcium, potassium, and fibre. These nutrients promote various health benefits, including improved vision, immune function, bone health, and cardiovascular health (Satheesh & Workneh Fanta, 2020). The consumption of kale has been associated with reduced risks of chronic diseases such as heart disease, diabetes, and cancer due to its high levels of antioxidants and anti-inflammatory compounds (Sikora & Bodziarczyk, 2012). Additionally, kale has gained significant popularity in the health and wellness market, leading to increased demand and market value. It is commonly used in salads, smoothies, and as a cooked vegetable, making it an adjustable ingredient in many diets. The economic value of kale is also crucial, as it has become a profitable crop for farmers, especially those focusing on organic and health food markets (Samec et al., 2018).

Studying the environmental impact and carbon footprint related to the nutritive values of plants should be considered as a benefit for addressing the food shortage problem. Thus, the purpose of this study is to compare the nutritive values in terms of nutritional compositions and antioxidant contents, and carbon footprints of Kale (Brassica oleracea L.) between PFAL and N-CF systems.

Planting materials, sample collection and preparation

PFAL kale trials were conducted at the Agrowlab plant factory in Bangkok, Thailand. The samples were collected 3 months after planting. A total of 32 buckets of kale were separated into 3 parts; 12:8:12, three varieties of PFAL kale were randomly collected from each part.

N-CF kale trials were conducted at a farm in Pathum Thani province, Thailand. There were 180 kale plants in the experimental plot. The N-CF kale samples were collected at 3, 6, and 12 months after planting. The kale plot was divided into three parts; three varieties of N-CF kale were randomly collected from each part of the plot.

An identical quantity of kale seeds was utilised in each agricultural system. In addition, leaf samples for the assessment of nutrition were collected throughout the same growth phases. The sets of kale samples were washed individually with water to remove dirt and contaminants. After washing, the edible part of each set will be cut into small pieces and homogenized. The homogenized samples are going to be divided into two portions for nutritional compositions and antioxidant contents analysis and stored at − 20°C until analysis.

Proximate Analysis

The proximate analysis of kale samples followed standardized methods according to the AOAC (George W. Latimer, 2019). The Kjeldahl method (AOAC 981.10) was used to determine protein content, and fat content following the Soxhlet method (AOAC 922.06). Moisture content was assessed by drying the samples at 100°C in a hot air oven, according to AOAC 925.45 A. Ash content was determined through incineration at 550°C in a muffle furnace (AOAC 920.153). Total dietary fibre analysis was determined by Enzymatic-Gravimetric Method (AOAC 985.29). The total carbohydrate content of the dry mass was calculated using the following formula:

Total carbohydrates (%) = 100 − (protein + total fat + moisture + ash + total dietary fibre)

Total Polyphenol Content

Total phenolic concentration (TPC) was determined according to the method described by Kongkachuichai et al. (2015), with slight modifications based on Brune et al. (1991). Two grams of samples were extracted with 20 ml of 50% dimethylformamide (Sigma–Aldrich, St. Louis, MO, USA) in 0.1 M acetate buffer for 16 h by constant shaking at room temperature. After extraction, samples were centrifuged (20 min, 25°C, 3000 rpm) and then supernatants were collected. The supernatants were diluted to 25 µl with water. Then the samples were added to a 96-well plate, followed by 125 µl of 10% Folin–Ciocalteau reagent (Merck, Darmstadt, Germany) and 100 µl 0.5 M sodium hydroxide to each well and mixed. Absorbance was measured at 750nm using an automated microplate reader (SunriseTM Tecan, Victory, Australia) after standing for 15 min at 25°C. Gallic acid (Sigma–Aldrich, St. Louis, MO, USA) was used as the standard with concentrations ranging from 0.00 to 80.00 ppm. Results were expressed as in milligram gallic acid (GAE) equivalents per 100 g of fresh weight (mg GAE/100 g). (Brune et al., 1991; Kongkachuichai et al., 2015)

Antioxidant activity

Antioxidant activity was analyzed by two methods, oxygen radical absorbance capacity (ORAC) assay and ferric reducing antioxidant power (FRAP) assay.

The FRAP solution was freshly prepared before analzing a sample. The solution consists of 0.3 M sodium acetate buffer solution (pH 3.6), 10 mM 2,4,6-tripyridyl-s-triazine (TPTZ, Sigma–Aldrich, St. Louis, MO, USA) in 40 mM of concentrated HCl and 20 mM FeCl₃ (Sigma–Aldrich, St. Louis, MO, USA) at the ratio 10:1:1 (v/v/v). The sample was added to the FRAP solution and incubated at 37°C for 4 min. The absorbance of each sample was measured at 593 nm using a spectrophotometer (UV-1601 Shimadzu, Kyoto, Japan). The standard curve of Trolox (6-hydroxy-2,5,7,8 tetramethychroman-2-carboxylic acid, Sigma–Aldrich, St. Louis, MO, USA) was used to calculate the FRAP values of the samples. The results were expressed as micromole Trolox equivalents per 100 g of fresh weight (µmol TE/100 g). (Benzie & Strain, 1996; Kongkachuichai et al., 2015).

The ORAC assay was performed using a spectrofluorometer (PerkinElmer LS 55 luminescence spectrofluorometer, Perkin Elmer, Waltham, MA, USA) with excitation and emission wavelengths set to 493 nm and 515 nm, respectively. 6.25 to 100 µM trolox (6-hydroxy-2,5,7,8-tetramethychroman-2-carboxylic acid) was used as the standard. Briefly, a 500 µl sample, a 3.0 ml fluorescein solution (8.16 × 10^− 2 µM), and 500 µl of AAPH (153 mM) were mixed in each tube. All dilutions were prepared using a 75 mM potassium phosphate buffer solution at pH 7.2. The ORAC value was calculated from a linear regression equation of net area under the curve (AUC) of the standard Trolox concentrations. Results were expressed as micromole Trolox (TE) equivalents per 100 g fresh weight (µmol TE/100 g fresh weight) (Huang et al., 2002; Kongkachuichai et al., 2015).

Statistical analysis

Statistical analysis was performed using Statistical Package for the Social Science (SPSS) program 18.0 (IBM Software, Chicago, II, USA). The significant differences are represented by P < 0.05.

An independent t-test was used to compare the results for the quantitative data (nutritional compositions, antioxidant contents, environmental impact, and carbon footprints) between the two groups, kales in PFAL and N-CF systems, to determine whether there is a statistically significant difference.

One-way analysis of variance (ANOVA) was used for the quantitative data (nutritional compositions, antioxidant contents, environmental impact, and carbon footprints) in the 4 sets of kale samples, kale grown in PFAL and three samples from N-CF systems with repeated observations at 3, 6, and 12 months.

Carbon footprint calculation

Goal and scope definition

This study analyzed the carbon footprints of kale production in PFAL and N-CF production systems, whereby the seeding process started in January 2022. PFAL kale production occurred from February 2022 to May 2022 (3 months), and N-CF kale production occurred from February 2022 to January 2023 (12 months). The cultivation practices commonly applied to the kale fields in this study differed slightly between the two systems:

PFAL: Kale was planted for around 3 months and harvesting occurred 45–55 days after planting. Subsequently, kales were collected around 3 times before being removed from the bucket.
N-CF: Kale was typically planted for around 12 months, and harvesting took place 45–55 days after planting. Subsequently, kales were collected weekly until 12 months after planting, after which they were plowed away from the field.

The production systems were analyzed from the gate-to-gate perspective. The functional unit (FU) in this study was a mass-balanced FU defined as 1 kg of edible kale during the planting cycle of PFAL and N-CF. Thus, the life cycle inventory included the material and energy requirements of agricultural activities, as well as the transportation of farm inputs. Figure 1 shows the system boundary as they were underpinned by different farm processes, except for seeding process which was similar in both harvest systems.

(Added Fig. 1)

Life cycle inventory

The inventory analysis quantified the inputs and outputs of the agricultural systems. Inputs and outputs data for both farming systems, including water, fertilisers and manure, pesticides, on-farm electricity use, transportation, and other factors related to kale production, were collected from the experimental farm through questionnaires. All inputs and outputs data were collected through follow-up questionnaires over different periods: 3 months for the PFAL farm and 12 months for the N-CF farm. The agricultural compositions of kale production studied in this work are shown in Table 1.

(Added Table 1)

Description of sites: The study site of PFAL was located at the Agrowlab plant factory in Khlong Kum, Bueng Kum District, Bangkok, Thailand (Fig. 2). The study site of N-CF was located on an experimental non-chemical farm in Khlong Song, Khlong Luang District, Pathum Thani province, Thailand (Fig. 2). Data are collected from a 3 m² kale planting area. Although these two experimental sites were in different provinces, they have similar environmental conditions, including temperature and humidity. In this study, the following assumptions are summarized:

Energy consumption and CO₂ emissions from manual labour are not included in this analysis.
In FPAL, only direct N₂O emission released into the atmosphere was considered, as the mixed-chemical fertiliser was not applied to the soil.

Limitation of this study, N-CF was susceptible to flooding events due to the nature of open-field cultivation, which can damage or destroy the kale crop and impact production yields. Additionally, insect infestations pose a significant challenge in N-CF systems, potentially leading to crop damage and yield losses if not adequately managed, which may impact the overall carbon footprint analysis of the N-CF system.

(Added Fig. 2)

Calculation of Carbon Footprints from PFAL and N-CF

The carbon footprints of kale grown in PFAL and N-CF systems were calculated following the Intergovernmental Panel on Climate Change (IPCC) guidelines (Pörtner et al., 2019). Data pertaining to both systems were collected and validated for accuracy and reliability. Emissions from various sources, including energy consumption, transportation, production processes, and waste management, were calculated in accordance with the IPCC guidelines and the Thai National Life Cycle Inventory (LCI) Database (Thailand Greenhouse Gas Management Organization (Public Organization), 2022).

The Carbon footprint of kale farming systems was calculated using Eq. (1).

Carbon Footprint (kgCO₂e) = EF×Q (1)

where EF is the emission factor for the activity (kgCO₂e per unit) (Table 2) and Q is the quantity of the raw materials, chemicals, and other emissions (in units).

(Added Table 2)

Application of manure and synthetic fertiliser results in direct and indirect emissions of N₂O. N₂O emissions from N-CF came from nitrogen in non-chemical fertilisers applied in the field, including direct N₂O emissions released into the atmosphere, indirect N₂O emissions from atmospheric deposition of volatilized N, and indirect N₂O emissions from nitrogen leaching and runoff. N₂O emissions from the use of nitrogen fertiliser are represented by Eq. (2).

N₂O Emissions (kgN₂O) = N₂O_direct-N_inputs+N₂O_direct-N_os+N₂O_{indirect−volatilize}+N₂O_{indirect−leaching} (2)

where N₂O_direct-N_inputs represent direct N₂O emissions released into the atmosphere from organic N additions to soils, N₂O_direct-N_os represent direct N₂O emissions released from managed areas annually, N₂O_{indirect − volatilize} represent indirect N₂O emissions from atmospheric deposition of volatilized N, and N₂O_{indirect − leaching} represent indirect N₂O emissions form nitrogen leaching and runoff. (Eggleston et al., 2006)

Nutritional values of kale

The outcomes of the proximate analysis and antioxidant content for the kale samples were presented in Table 3 and Table 4. Total fat, protein and carbohydrate contents were similar to previous research conducted by Sikora and Bodziarczyk (Plassmann & Edwards-Jones, 2010). The study suggested that the fat content in kale leaves reported by different authors ranged between 0.26–0.74%, protein content between 3.28–11.67%, carbohydrate content between 2.36%-10.14%, ash content between 1.33–2.11%, and dietary fibre between 1.94–8.39%. However, the moisture content of the kale samples in this study was notably higher compared to the reviewed literature, which was 81.38–82.92%.

(Added Tables 3 and 4)

The influence of different farming systems on the levels of bioactive compounds in kale is shown in Table 3. The results showed that the levels of polyphenol, ORAC and FRAB were statistically lower in the 3 months kale harvested from PFAL compared to 3 months N-CF kale.

Further analysis revealed significant differences in the levels of polyphenols, ORAC, and FRAB among the N-CF kale samples harvested at different periods (Table 4). The reactivity of the antioxidants studied was generally lower in the FRAP assay than in the ORAC assay. Among the N-CF kale samples, those harvested at 6 months showed the highest values of polyphenol, ORAC and FRAB. Conversely, the values were significantly lower in N-CF kale harvested at 3 months and 12 months.

Carbon footprints

The carbon footprints of the two farming systems are presented in Table 5, and divided into 4 phases: seeding, transportation, preparation, and plantation. Carbon footprints in a 3-month PFAL were higher than in a 3-month N-CF. The carbon footprint of PFAL was 168.61 kg CO₂-eq/kg. The carbon footprint values of 3, 6, and 12 months of N-CF kale were 14.75 kg CO₂-eq/kg, 4.51 kg CO₂-eq/kg, and 1.96 kg CO₂-eq/kg, respectively (Table 5). In N-CF, carbon footprints were decreased due to the period of plantation.

(Added Table 5)

Figure 3 shows the contributors in relative percentage from the different farming practices. The electricity part in FPAL including air conditioning, lighting, fan operation, etc. accounts for 99.06% of total emissions. Similarly, other studies have reported that in vertical farming (VF), a type of indoor farming system, electricity contributes over 90% of the total carbon footprint impacts. (Sandison et al., 2023; Sørensen et al., 2021). N-CF systems presented lower carbon footprints as expected since air-conditioning and lighting were not applied. In N-CF systems, electricity along with water usage and waste emissions, including waste management, gasoline combustion and N₂O emissions, were the major contributors to carbon footprints. They contributed 47.87–60.15%, 14.84–25.47% and 12.26–16.32%, respectively, covering 87.25–87.67% of the total carbon footprints of the N-CF system. Other contributors include trays, fertilizer packages, pipes and CO₂, which contribute 6.59–9.10%, fertilisers and pesticides 1.27–4.19%, and transportation 1.96–2.38%.

(Added Fig. 3)

Nutritional aspect

There were two main factors to be considered when studying antioxidant values and other factors. One is biotic factors, such as species, cultivar, and orthogenesis. Another is abiotic factors, such as climate, soil, environmental and agrotechnical conditions. (Biesiada & Tomczak, 2012) The impact of environmental factors such as temperature fluctuations and light intensity have a significant influence on the nutritional composition and antioxidant levels in plants. Recent studies have highlighted how these factors can influence the stress response and subsequent antioxidant production in kale, particularly in different cultivation systems.

Environmental stress, such as temperature fluctuations and varying light intensity were possible reasons that affected the levels of polyphenol, ORAC and FRAB in PFAL and N-CF kale. Temperature fluctuation, the change of temperature during day and night, can lead to irreversible damage in plant cells and this is a stress condition response. On the other hand, light intensity, the key factor in plant photosynthesis and metabolites, significantly impacts plant growth and chemical composition. Previous studies by Islam et al. (2021) and Kacperska (2018) have demonstrated that kale exposed to these environmental stresses exhibits higher levels of antioxidants compared to kale grown under controlled conditions. Specifically, N-CF kale cultivated in an environment exposed to direct sunlight during the day and fluctuating temperatures, experienced more stress than PFAL kale, leading to increased production of bioactive chemicals and antioxidant content (Islam et al., 2021; Kacperska, 2018).

Furthermore, the duration of exposure to environmental stressors influenced the nutritional composition and antioxidant levels of kale over time. These factors caused variations in the nutritional composition and antioxidant levels of N-CF kale across different harvest intervals (3 months, 6 months, and 12 months). These variations were attributed to seasonal changes in temperature and light exposure. For example, days are shorter in winter compared to summer, highlighting the dynamic nature of environmental influences on kale quality (Paolillo et al., 2023).

Additionally, the age of the kale plant plays a crucial role in determining its nutritional composition and antioxidant levels. The nutritional composition and antioxidant properties of fruits and vegetables, including kale, can significantly change as the plant matures, often peaking at specific growth stages before declining (Jaiswal, 2020). This aligns with recent research, which suggested that younger kale plants tend to exhibit higher levels of certain antioxidants and nutrients compared to more mature plants. This is likely due to the plant's response to growth stages and environmental stressors, which vary throughout its life cycle (Islam et al., 2021).

Carbon footprints

The PFAL system relies on artificial lighting, environment control, and other electrical tools, electricity is the most significant source of carbon emissions, accounting for 99.06% of total emissions. Despite the high energy consumption, PFAL systems offer several advantages, including high productivity, consistent production quality, and efficient use of available resources due to its regulated environment, which uses less pesticide and water; up to 90% less than traditional methods (Kozai, 2013). Although PFAL systems are highly efficient in resource use, it has a high carbon footprint that needs to be reduced. Switching to renewable energy sources such as solar or wind power can significantly reduce greenhouse gas emissions associated with electricity consumption (Despommier, 2010). N-CF systems had a more balanced approach, emitting moderate amounts of carbon emissions, primarily from electricity used (47.87–60.15%). However, N-CF production in this study showed more electricity components than usual due to the air-conditioning required during the seeding process. N-CF often utilises less synthetic/chemical inputs compared to conventional farming, lowering emissions related to fertiliser production and use. According to a previous study, in conventional farming, the production and application of fertilisers is the largest contributor, responsible for 51% of total emissions. Transportation contributes 21% of the total emissions, associated with transporting produce to markets. Irrigation accounts for 19% of the emissions due to water pumping and distribution (Yuttitham, 2019).

Food security and sustainability

Sustainable food production should minimise pollution, lessen the loss of natural resources, and maintain the environment. Consequently, preserving the resilience and vitality of the ecosystem promotes long-term food security. (Foley et al., 2011) In our work, kale in the field were grown in the soil, while another was germinated and developed hydroponically in buckets in the growth experiment room. Over the same duration, PFAL kale not only had higher yield and carbon footprints than N-CF kale but also had lower antioxidant values (Table 1,3, 5). Some studies have shown that hydroponically grown lettuce and strawberries contain higher concentrations of bioactive components (ascorbic acid and α-tocopherol) than soil-grown types. The research emphasises the contributions of light and nutrient solutions in enhancing a plant's bioactive compounds. Expanding farm setups and focusing on comparative efficiency should provide greater insight into what to anticipate and emphasise excellent practices from a sustainability perspective. (Ashenafi et al., 2022).

In summary, this PFAL showed potential for sustainable food production with higher yields, although N-CF has higher nutritional value and lower carbon footprints. With continuous experiments in the sector, there is a trade-off between carbon footprint and electricity consumption under the possible future innovation. Furthermore, environmental factors (such as lighting, air temperature, and mineral content) can be greatly optimised for high output and nutritional quality, which is advantageous for agricultural operations as well as customers. Future research ought to examine the potential of certain environmental factors, such as light spectrum or intensity, to improve the quality of nutrition, including food safety of the PFAL system.

Authorship

KS was a principal investigator of the project. KS, WH, US, and KSU conceptualized the research design. WH and KS collected the data. WH, KS and US managed the sample analysis and analysed the data. KS and WH drafted the manuscript. All authors were involved in editing the manuscript.

Acknowledgement

This project is funded by the Office of National Higher Education Science Research and Innovation Policy Council by the “Program Management Unit for National Competitiveness Enhancement (PMU-C)”, Contract number C10F640135.

Conflict of interest

The authors have stated explicitly that there are no conflicts of interest in connection with this article.

Data availability

The data that support the findings of this study are available from the corresponding author upon reasonable request.

ORCID

Kitti Sranacharoenpong. https://orcid.org/0000-0002-1692-9645

Wannaporn Hatongkham. https://orcid.org/0009-0000-2849-2682

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The authors declare no competing interests.

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Comparing soilless and non-chemical farming food production systems: Nutritional and environmental aspects for food security and sustainability

Status:

Version 1

Abstract

Figures

Introduction

Materials and Methods

Planting materials, sample collection and preparation

Proximate Analysis

Total Polyphenol Content

Antioxidant activity

Statistical analysis

Carbon footprint calculation

Goal and scope definition

Life cycle inventory

Calculation of Carbon Footprints from PFAL and N-CF

Results

Nutritional values of kale

Carbon footprints

Discussion

Nutritional aspect

Carbon footprints

Food security and sustainability

Conclusion

Declarations

References

Additional Declarations

Status:

Version 1

Comparing soilless and non-chemical farming food production systems: Nutritional and environmental aspects for food security and sustainability

Status:

Version 1

Abstract

Figures

Introduction

Materials and Methods

Planting materials, sample collection and preparation

Proximate Analysis

Total Polyphenol Content

Antioxidant activity

Statistical analysis

Carbon footprint calculation

Goal and scope definition

Life cycle inventory

Calculation of Carbon Footprints from PFAL and N-CF

​

Results

Nutritional values of kale

Carbon footprints

Discussion

Nutritional aspect

Carbon footprints

Food security and sustainability

Conclusion

Declarations

References

Additional Declarations

Status:

Version 1