BY CATH O'DRISCOLL
Recycled glass diverted from landfill could find application as a partial soil substitute – helping plants not only to grow faster, but potentially also with fewer chemicals.
Initial pilot tests found potted coriander, bell pepper and jalapeño plants – the ingredients for Mexican pico de gallo salsa – grew an estimated 20-30% faster when grown in soil with more than 50% recycled glass particles, researchers reported at the ACS meeting in Denver, US, in August. Additionally, plants grown with the recycled glass showed no fungal activity as seen in exclusively soil-potted plants.
If these results are translated at scale in open field conditions, ‘this improvement in growth speed could translate into a proportional increase in agricultural production,’ says research leader Julie Vanegas at the University of Texas Rio Grande Valley, US. ‘This might mean, for example, a reduction in time to harvest, allowing farmers to achieve additional yields within the same growing period or improve the efficiency of resource use, such as water and fertilisers.’ However, she cautions that further large-scale studies would be needed to confirm these results.
‘The crushed glass particles used in the [pilot] study have a larger size range [than sand], between 0.4 and 2mm,’ Vanegas says. The researchers obtained the particles from a company that diverts bottles from landfills, crushes them into particles and tumbles the pieces to round off the edges. The resulting particles are smooth enough for ease of handling and to avoid damage to delicate plant roots.
The researchers say recycled glass is likely to be more effective for certain soil types, eg dense or clay-heavy soils rather than already well-drained nutrient-rich soils. Soil texture and composition and the needs of the specific plant species will also play an important role. As well as improved drainage and aeration, the recycled particles are thought to create a more favourable environment for root development and water retention, potentially reducing the risk of root rot and other issues associated with poor drainage. Additionally, Vanegas says, ‘glass is inert and does not compact over time, maintaining a consistent structure that supports healthy root growth’.
Compared with sand, already used in agriculture, the larger particle size and improved structure of the glass particles allows for better moisture control and air circulation. While glass and sand are composed of more than 80% SiO2, Vanegas points out that elemental analysis shows glass contains trace amounts of sodium, potassium, and other elements that might support overall plant health and indirectly inhibit fungal activity.
‘This is just a pilot study, and the preliminary results need to be verified through further research to determine whether the use of glass could indeed reduce the use of agrochemicals,’ Vanegas cautions. However, the researchers think their recycled glass particles might reduce the need for agrochemicals for several reasons: first, by increasing the amount of sunlight that reaches the plants, potentially inhibiting the growth of fungi and other pests; secondly, by helping to create a more controlled microclimate, reducing the need for chemical treatments; and lastly, by facilitating a more uniform and effective distribution of applied products via the glass surface, decreasing the amount needed to achieve the desired effect.
These initial results are exciting, according to Texas graduate student Andrea Quezada. ‘We’re trying to reduce landfill waste at the same time as growing edible vegetables. If this [technology] is viable, then we might be able to introduce glass-based soils into agricultural practice for people here in the Rio Grande Valley and across the country.’
The team in Texas is now waiting until harvest time to evaluate which soil mixture produces the highest yields and tastiest produce. The plants are being grown in a variety of soil-glass ratios (up to 100% glass) in a greenhouse on campus. Pots with more soil have higher levels of N, P and K, but one promising discovery is there is little variation of pH among pots because plants thrive in a narrow pH range. Soils with more glass also appear better at water retention – a helpful feature in areas prone to drought or water stress.
Other research on the use of crushed glass fragments in agriculture is under way in Grenada, meanwhile, where earlier in 2024 researchers reported testing a soil additive made from recycled glass.
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