Next-generation water-saving strategies for greenhouses using a nexus approach with modern technologies

Abstract

The escalating food and water crisis, propelled by population growth, urbanization, and climate change, demands a reimagining of agricultural practices. Traditional water-saving irrigation methods have reached their limits, necessitating the exploration of innovative approaches. This perspective explores the potential of utilizing excess light and water in greenhouse cultivation through advanced materials and engineering technologies. We investigate the potential of four key technologies-sorption-based atmosphere water harvesting (SAWH), superabsorbent polymer water holding materials (SPWH), radiative cooling (RC), and seawater desalination. The perspective proposes suitable application methods and future development directions for greenhouse water conservation, aiming to introduce novel water-saving strategies and smarter resource management.

Fig. 1. Schematic of water loss in greenhouse.

A considerable amount of irrigation water in agriculture is lost through deep soil seepage and soil evaporation. Water absorbed by plants is also released into the greenhouse environment via plant transpiration.

Fig. 2. The water-saving capacity of SAWH technologies in greenhouses.

a Schematic illustration of various HPPs^–,–. PDA@PP-Cl polydopamin @ PAAS−PNIPAA-HCL, POG hygroscopic photothermal organogel, PGF porous sodium polyacrylate/graphene framework, SMCA solar-driven and moisture-indicating cellulose aerogel, ILCA Loofah grafted calcium alginate sorbent with ink. Reproduced with permission. Copyright 2019, Wiley. Reproduced with permission. Copyright, AAAS. Reproduced with permission. Copyright 2022, Royal Society of Chemistry. Reproduced with permission. Copyright 2022, American Chemical Society. Reproduced with permission. Copyright 2020, Wiley. Reproduced with permission. Copyright 2020, Wiley. Reproduced with permission. Copyright 2021, Royal Society of Chemistry. Reproduced with permission. Copyright 2021, Elsevier. b Schematic representation of a greenhouse with SAWH covers. c Schematic depiction of crops with SAWH hoods. d Temperature and humidity fluctuations in a greenhouse during a typical sunny day in Singapore, where the average RH is ~90%. e Comparison of water production at 90% RH for different types of HPPs^–,–. f Daily harvested water mass for SAWH covers and hoods. Relevant raw data are taken from ref. . Needed water: additional water needed to meet the needs of plant daily growth. Harvested water: water collected from SAWH cover or hood. The dashed lines in the figure represent the needed water amounts at different levels.

Fig. 3. The water-saving capacity of SPWH technologies in greenhouses.

a Water holding capacity of different SPWHs^–,,,. SAH super-absorbent hydrogel, OK-PAA₄ okara-poly (acrylic acid) superabsorbent hydrogels, SH-20RHA superabsorbent hydrogel composite based on the biopolymer starch, and 20 wt% rice husk ash. C-P3-MMT₂ carrageenan/psyllium sodium/montmorillonite clay hydrogels, WS₃-CA_4% wheat straw modified hydrogel crosslinked with 4% citric acid, Gel-1-SN single-network hydrogel. b Soiling water increasing capacity of different SPWHs^–,,,. c SPWHs needed for different crops for their entire growth period without irrigation. Taking SAH as an example of SPWHs. The irrigation needs of corps are taken from refs. ^,. d Schematic illustration of self-watering SPWHs. Passive water irrigation: At night, SPWHs absorb atmospheric moisture and release it as liquid water into the soil, passively irrigating plants. Solar-powered humidification: During the day, sunlight drives water evaporation from SPWHs, increasing humidity and helping retain soil moisture. e Schematic illustration of adding nutrition in SPWHs before bleeding. No more irrigation is needed during the entire crop growth period.

Fig. 4. The water saving capacity of RC films in greenhouses.

a Schematic illustration of the daytime radiative cooling and water saving ability of RC films in greenhouses. b Schematic illustration of the nighttime radiative cooling atmospheric water harvesting ability of RC films in greenhouses. c Water consumption and harvesting for a 500 m² greenhouse covered with RC film during 100 days of planting. Relevant raw data are taken from refs. ^–.

Fig. 5. The water-saving capacity of seawater desalination technologies in greenhouses.

a Schematic illustration of water desalination and energy generation using STIE. Solar-driven evaporation occurs through a selective membrane, which separates clean water from pollutants and salts due to a salinity gradient. b Schematic depiction of the STIE floating farm (STIE-FF). The concentrator acts as a solar thermal collector, enhancing seawater evaporation for desalination. c Schematic depiction of the STMD floating greenhouse (STMD-FG). d Schematic representation of the integration of photovoltaics and multistage membrane distillation using in a greenhouse. e Daily water production rate of STIE-FF and STMD-FG. Relevant raw data are taken from refs. ^,–. Needed water: water needed to meet the needs of plant daily growth.

Fig. 6. Comparisons of features between STIE and STMD.

Cost-effectiveness: evaluates the overall financial viability, considering both initial investment and long-term operational expenses. Technical support: assesses the level of expertise and maintenance required to operate the system efficiently. Efficiency: measures the effectiveness of the system in utilizing resources, particularly in water conversion and utilization. Water quality: refers to the purity and suitability of the produced water for irrigation, taking into account factors such as salinity, contaminants, and overall usability for crops. Environmental impact: considers the ecological footprint of the system, including energy consumption, waste generation, and potential adverse effects on the surrounding environment. Scaling issues: addresses potential challenges related to system scalability, including material degradation, performance limitations, and maintenance frequency when expanding the system for large-scale applications.