Scientists at King Abdullah University of Science and Technology (KAUST) have developed and combined a new nanoplastic and biodegradable mulch to passively cool greenhouses in hot, arid climates like those in the Middle East. Applying their technology, they lowered temperatures of miniature greenhouses by 25 degrees Celsius and increased crop yields of Chinese cabbage by nearly 200%. The study can be read in Nexus .
The nanoplastic consists of polyethylene, the most widely produced plastic in the world, infused with nanoparticles consisting of the molecule cesium tungsten oxide. These nanoparticles absorb infrared light, which greatly contributes to heating the greenhouse, preventing this light from entering with minimal effects on visible light, which is the light that drives photosynthesis and plant growth.
"Most greenhouse covers, whether they are made of glass, polycarbonate or polyethylene, transmit more than 90% of light, including infrared light, which has no benefit to crop yield but generates heat. Our goal was to create a cover that lets good light in and keeps bad light out," said KAUST Professor Qiaoqiang Gan , who developed the nanoplastic and is an expert in passive cooling systems.
Even with the infrared light reduced, solar radiance caused by any light still heats the soil. Mulch is commonly used to reflect sunlight, keeping the soil cooler than otherwise. Cooler soil promotes more photosynthesis and thus more growth and better crop yields. The new mulch designed by Gan's postdoctoral researcher, Yanpei Tian, is made of biodegradable cellulose paper. As the plants grow leaves that offer shade to the soil, this mulch vanishes from the soil, providing a more sustainable solution to greenhouse cooling and better human health.
"Most commercial mulch is plastic and extremely wasteful. It results in about 1.5 million tons of waste, and more than 40% goes unrecycled. Plus, this leaves microplastics in our soil that can enter the food chain," said Tian.
Testing the two technologies in miniature greenhouses in Saudi Arabia to grow Chinese cabbage, the researchers found excellent water retention in the soil and a crop yield that was 200% that of crops grown with commercial covers and mulch. In addition, using public weather data, the KAUST team estimates that adopting their new system could reduce energy consumption in hot cities around the world, like Riyadh and Houston, by more than 40%.
The researchers are now investigating the benefits of their dual technology on larger scale greenhouses and other crops.
"The cooling of greenhouses can be extremely expensive. Our approach can make a number of crops available to arid regions, increasing their food security while at the same time helping meet carbon emission targets," said Gan.
