Evaluation of Recycled Materials as Hydroponic Growing Media

Abstract

Conventional soilless growing media, such as perlite, are mined from nonrenewable resources and can only be disposed of in landfills after limited use. There is a need to investigate novel, sustainable growing media adapted from waste or engineered to be reused over multiple cycles. This study investigated waste almond shells and a recycled plastic drainage plank as hydroponic growing media alternatives. Physiochemical properties were evaluated, and a germination and greenhouse growth trial was conducted to understand the effect these media have on production and nutritional quality of lettuce (Lactuca sativa L. cv. Catalogna Verde). Drought testing was carried out to understand how the media affected the lettuce’s response to water stress. In comparison to perlite, yields under regular irrigation were reduced by 52% in almond shells and 72% in plastic planks, although lettuce grown in almond shells still obtained commercially relevant yields. Reduced yields in almond shells were likely caused by the shell’s high salinity. Lettuce growth in plastic planks was limited by impeded root growth and low water-holding capacity. In conclusion, with minor alterations, almond shells could be used as a sustainable growing media alternative to perlite in hydroponic lettuce production. More research is needed to manufacture the planks to be conducive to plant growth.

Seasonal Nitrous Oxide Emissions From Hydroponic Tomato and Cucumber Cultivation in a Commercial Greenhouse Company

“…In addition, other reduction possibilities for GHG emissions from greenhouse cultivation should be considered as well. The production of rock wool is associated with high CO 2 emissions, which could be avoided by using alternative (biodegradable) substrates (Dannehl et al, 2015;Kennard et al, 2020). However, there is more research needed on the interaction of different substrates and GHG emissions as well as yield and quality.…”

The Evolution of Soilless Systems towards Ecological Sustainability in the Perspective of a Circular Economy. Is It Really the Opposite of Organic Agriculture?

“…Among the waste materials tested as alternative constituents of growing media in soilless crops, almond shells have been proposed to replace rockwool [27] or perlite [28] with fluctuating results in terms of yield, suggesting that some technical tricks (mainly related to milling or blending of shells, useful to define an ideal balance in particle size) should be developed to improve their performance, given the potential role that these materials could play as substrate in the development of strategies of the circular economy, especially in the regions where they are abundant and immediately available, overriding the transportation costs. Other constituents of substrates with similar potentialities in soilless cultivation could be olive or hazelnut husks, rice or peanut hulls or sheep's wool [28].…”

“…In general, inert substrates are more suitable for reuse, given the higher effectiveness of disinfectant treatments and the absence of absorption or retention processes on their surfaces. Rockwool and perlite are typically inert materials that could be theoretically disinfected and reused numerous times, but are actually reused for up to three growing cycles, bearing in mind that the success of growing with reused substrates also largely depends on the experience of the grower [28]. Organic substrates are subject to biological instability both after reuse in crop cultivation and after applied treatments such as steam disinfection.…”

Lignite Substrate and EC Modulates Positive Eustress in Cucumber at Hydroponic Cultivation

“…Currently, stone wool is used worldwide for hydroponic cultivation of economically important vegetable species such as tomato, bell pepper and cucumber. This is mainly due to the suitable physical properties of stone wool, which allow for increased yields compared to conventional crops [18,19]. However, producing 1 m 3 of this substrate emits 167 kg of CO 2 into the environment and consumes 275 kWh [17], where the CO 2 emitted during transportation of the substrate to the customer and the disposal of stone wool waste after the production process are not taken into account.…”