Hydroponics

Energy, water and nutrient impacts of California-grown vegetables compared to controlled environmental agriculture systems in Atlanta, GA

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Energy, water and nutrient impacts of California-grown vegetables compared to controlled environmental agriculture systems in Atlanta, GA

Steven W. Van Ginkel, Thomas Igou, Yongsheng Chen*School of Civil and Environmental Engineering, Georgia Institute of Technology, 200 Bobby Dodd Way, Atlanta, GA 30332, United States.

Citation

Van Ginkel, S.W., T. Igou, and Y. Chen. 2017. Energy, water and nutrient impacts of California-grown vegetables compared to controlled environmental agriculture systems in Atlanta, GA. Resources, Conservation and Recycling 122:319-325. Https://doi.org/10.1016/j.resconrec.2017.03.003 (Links to an external site.)

 Background

This paper compares the efficiency of California Based traditional vegetable agriculture to hydroponics and aquaponics systems. Efficiency is defined by water usage, energy and nutrient input as it relates to crop yield. California is the leader in fruit and vegetable agriculture; therefore the rest of the United States is reliant on their system. However, California is also susceptible to severe drought, which can lead to reduce yields. Additionally, California has very large watershed, which can cause runoff of fertilizers in ponds, lakes and other bodies of water. Therefore to mitigate the environmental footprint of agriculture production, the author’s suggests that future generations focus on urban agriculture. Aquaponics is a system that allows the production of vegetables and fish, while reducing the input of fertilizers, and using waste byproducts as the source of nutrients. The authors show that this system reduces the nutrient input, water usage and is more productive that traditional based vegetable production. Therefore the purpose of this paper is to compare and contrast the productivity of each system.

 Experimental Design

California vegetable data was derived from www.casestudies.ucdavis.edu. Data was taken for several crops including tomato, spinach, strawberries, peppers, and broccoli. The data displays yield, nutrient input, energy input for each crop. The data was normalized by dividing each component by yield per acre. For hydroponics, there was one grower who grew lettuce and leafy greens in shipping containers. The data was normalized for energy (lighting and cooling) and water usages over a year divided by yield per container. For aquaponics, there were three growers, one from Hawaii and two from University of Virgin Islands and Atlanta, GA. All growers used deep-water culture and grew leafy greens. The data was normalized for energy and water utilized over a year divided by the yearly productivity. Data from all three systems was then compared using statistical analysis.

 Results

Areal Productivity

When comparing hydroponics and aquaponics there was no significant difference in the areal productivity. However, there was a significant difference between the ponic-systems and the California-based system. Ponic-systems were found to be 10 to 29 times more productive than the California-based system. In addition, areal productivity in hydroponics could be substantially improved increasing vertical production in closed environments.

Energy Usage

Hydroponics uses 30 times more energy (lighting, cooling) than the California-based system. There was no significant difference in energy usage between aquaponics and California-based system. However there were differences in energy usage between aquaponic growers, therefore it is would be wise to compare each aquaponic grower to the California-based system in the future.

 Water Usage

California-system uses 66 and 8 times more water than hydroponics and aquaponics. There were differences in water usage between hydroponics and aquaponics, however the authors suggests that results maybe skewed due to the lack of data points.

Conclusion

Based on the authors study, it seems that ponic-systems are overall more efficient than California-based system. They believe that these systems should be integrated into urban cities. By integrating such systems, cities become less reliant on vegetable and fruit production from California. At the same time it reduces the negative environmental footprint. Nevertheless, the biggest challenge will be to address the socio-economic challenges in integrating the system into urban environments.

Hydroponics vs. Soil Cultivation: Functional and Taste Compound Comparison

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Original Paper
Tamura Y, Mori T, Nakabayashi R, Kobayashi M, Saito K, Okazaki S, Wang N and Kusano M (2018) Metabolomic Evaluation of the Quality of Leaf Lettuce Grown in Practical Plant Factory to Capture Metabolite Signature. Front. Plant Sci.9:665.
doi: 10.3389/fpls.2018.00665

Context

Cultivation of certain crops is moving out of the field. Indoor production has taken the form of greenhouses, tunnels, and plant factories. These growing methods been collectively deemed controlled environment agriculture (CEA). The attraction is in the name – control. Moving crops out of the field helps remove risk of unpredictable weather and can allow for optimized conditions for crop production. It even enables year-round growing that provides a steady source of fresh food to the public and income to the growers instead of the seasonal flux of traditional agriculture.

With food moving indoors under controlled conditions, crops are receiving different types of input in terms of nutrients, lighting, day/night cycling, temperatures, disease and pest stresses, and other variables. Some crops are growing differently and looking different as well. It all depends on the control conditions.

As plant growth and development changes due to these controlled environments, the metabolic processes dictating that growth and development are probably varying as well. As a result, there may be changes in the plant’s profile of chemical compounds, or metabolites, which take part in and are produced by plant metabolism. These compounds are integral to the structure and general function of the plant as well as its defense against pests and disease. Again, with cultivation conditions changing, the metabolite compositions of the plants are likely changing simultaneously.

The Experiment

If we want to know if or how CEA is changing the metabolite profiles of our food compared to field cultivation, we need to isolate each element of the “control” to determine what changes are being caused by which conditions. To this end, a group from RIKEN in Japan that studies metabolite profiles (an analytical chemistry practice called metabolomics) chose to compare compounds of lettuce grown in a hydroponic system (plant roots growing directly into water with an added nutrient solution) within a Keystone Technology Inc. (Japan) plant factory to lettuce grown in a similarly-controlled growth chamber except planted traditionally in soil (Table 1).

Table 1. Plant factory conditions for hydroponic cultivation treatment compared to growth chamber conditions for the soil treatment.

This group chose two lettuce cultivars, ‘Black Rose’ and ‘Red Fire’, with one head of each cultivar grown per treatment – hydroponics and soil – for a total of 4 heads of lettuce in the experiment. Tamura et al. observed smaller and more pigmented leaves from the soil-grown lettuce compared to the hydroponic production. To detect the metabolites present in the lettuce they used precise instruments (gas and liquid chromatography mass spectrometry). They included samples from leaves on the outside of the head and the middle to account for variation in metabolite production in different parts of the plant.

Findings

Analysis resulted in 133 identified compounds and 185 unidentified. Based on the relative abundances of all 318 metabolites, they were able to clearly separate samples of hydroponically grown lettuce from those grown in soil.

Upon further study, they determined that hydroponic lettuce had higher amounts of amino acids (protein building blocks) than the soil-cultivated lettuce. On the other hand, lettuce grown in soil contained more sugars and compounds that contribute to taste and possible health-benefits, such as sesquiterpenes and organic acids. Particularly, glutamate, a metabolite contributing to the umami (or savory) taste profile of a food, was significantly higher in ‘Red Fire’ lettuce grown hydroponically. However, a sugar, sucrose, and a compound associated with bitterness, lactucopicrin-15-oxalate, were both significantly lower in the hydroponic lettuce.

Conclusions and Considerations

This study is valuable due to it being the first of its kind—applying metabolomics to understand how our crops are changing in CEA systems. These results need to be validated by another experiment in which the conditions other than soil/hydroponics are identical. Previous work by Li and Kubota (2009) demonstrated that differences in light intensity and quality can affect metabolite production in a CEA setting.

Additionally, different fertilization regimes largely influence the amount of nitrogen plants can access to produce amino acids. With the hydroponic lettuce receiving almost 3x the fertilizer compared to the lettuce in soil, a higher amino acid content in hydroponic lettuce cannot be completely attributed to hydroponic production itself. Therefore, the differences in control conditions presented in Table 1 above are confounded with the soil/hydroponic treatments, making interpretation of results complicated. This also points to the importance of collaboration across scientific disciplines to ensure the most effective and efficient experiments are conducted.

Citations

Li, Q., and Kubota, C. (2009). Effects of supplemental light quality on growth and phytochemicals of baby leaf lettuce. Environ. Exp. Bot. 67, 59–64. doi: 10.1016/j.envexpbot.2009.06.011