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Global food production systems are under heavy stress of overpopulation, water scarcity, farmland shortage, and climate change. Agriculture is the largest consumer of water globally. While agricultural water demand is still on the rise, the availability of water is shrinking, and its quality is deteriorating. Agriculture is also a major source of nitrogen and phosphorus pollution of natural waterways, which leads to large dead zones where nutrient laden rivers empty into bays and oceans. Global food security is also threatened by the loss of arable land due to development, and decreased fertility due to poor farming practices. Climate change is projected to further exacerbate these problems. Elevated temperatures and increased carbon dioxide levels, combined with changing rainfall patterns, and increased frequency of extreme weather have already been demonstrated to reduce the yield and nutrient profiles of food crops. A response to these challenges may lie in hydroponic food production, as it is more efficient in land and water use relative to conventional farming. Since hydroponic technologies do not rely on soil, they can be utilized in non-arable regions and potentially produce more plant mass per unit horizontal area, due both to increased productivity and to vertical stacking. In addition, hydroponics requires less chemical fertilizer input than soil culture due to the targeted supply of nutrients and recycling of nutrient solutions. Since most hydroponic systems are located in greenhouses, they are less affected by the changing climate and thus are better equipped to sustain year-round food production. The controlled environment also allows optimization of growing conditions for higher plant yield and better product quality. Moreover, hydroponic systems can be operated automatically and easily integrated with technologies such as web-enabled smart devices to achieve precision farming. Our group has been working on the optimization of hydroponic food production.

UV Exposure and Compost Tea Supplementation

Hydroponic food production has its advantages, but its limitations need to be explored and reduced. The soilless nature of hydroponic systems has both positive and negative implications for plant health. Hydroponic crops have reduced risk of developing soil-borne diseases or pest infestations. However, hydroponic systems are not completely pathogen-free. High nutrient concentration of circulating solution can lead to growth of some pathogens and facilitate their spread. Moreover, the lack of soil deprives the plants of beneficial microorganisms that may promote plant growth and/or suppress plant diseases. Intentional supplementation of such microorganisms may improve the productivity and resilience of plants grown in hydroponic systems.  Another challenge for hydroponic food production is that when plants are grown in greenhouses or indoor settings, they are generally not exposed to the natural ultraviolet spectrum, which is critical for plant growth, photosynthetic efficiency, and especially the biosynthesis of health-promoting antioxidant phytochemicals. We studied the effect of variable UV light exposure and compost tea supplementation on growth performance, antioxidant activities, and microbiota composition of hydroponically grown mustard greens. We found that exposure to UV light greatly enhanced the synthesis of anthocyanins and the antioxidant activities of the plants. Compost tea treatment increased beneficial bacteria and decreased fungal pathogens.

The project is published in the ACS Agricultural Science & Technology:

We thank the support from USDA-NIFA-HSI program, Southern California Institute of Food Technologists Section, and SDSU College of Health and Human Services.