[Image above] Apples are one of the many fruits that could benefit from kaolin particle films, which offer an environmentally friendly way to reduce pest and sun damage compared to traditional chemical pesticides. Credit: T.W. van Urk, Shutterstock
It’s apple season in North America, and that means I spend way more time and money than necessary at my local orchard, Milburn’s. It is fortunately—or unfortunately, depending on the temporal distance to next payday—physically located just a few miles from my house.
Fruit and vegetable production is a capricious undertaking, subject to the vagaries of the weather and the insatiable appetite of pests. Luckily for growers and their eager consumers, there is a surprising ceramic mineral that can help protect agriculture from nature’s fickleness: kaolin.
The science of kaolin
Kaolin is a soft, white clay traditionally known for its use in fine ceramics and pottery. It was first discovered in Gaoling village in Jiangxi province, China, more than 2,000 years ago. It was used to produce the high-quality porcelain that Jingdezhen, the “Porcelain Capital” of the world, is known for.
The principle mineral in kaolin is kaolinite, a phyllosilicate mineral that develops through chemical weathering of aluminum-rich feldspars contained in igneous rock (granites and pegmatites). Kaolinite consists of hexagonal crystals ranging in size from 0.1 microns to 10 microns, and these crystals form in stacked sheet-like layers. This structure is part of what gives kaolin its desirable properties: nonswelling, adsorbent, and chemically inert.
This combination of properties allows kaolin to be classified as generally recognized as safe (GRAS) by the U.S. Food and Drug Administration. This designation means it can be used in cosmetics to remove excess oils from the skin and as an anticaking agent in powdered foods. Where it really shines, however (pun intended), is as a particle film in agriculture.
The protective power of particle films
Coating agricultural crops with particle films made of nontoxic inorganic substances is an environmentally friendly way to reduce pest and sun damage compared to traditional chemical pesticides. Once the film is sprayed on and dries, it creates a physical barrier that deters insects and reflects excess light.
Kaolin particle films were first developed and field-tested on crops starting in 1994, with research intensifying in the following years. The films successfully repelled and reduced survival of insects and mites on apple and pear trees, and the technology became commercially available to growers in the early 2000s. It has since gained approval by the Organic Materials Review Institute.
(Kaolin can also be used as a carrier for other agricultural chemicals, allowing for reduced quantities of active ingredients.)
There is one big downside to kaolin particle films, however, that has limited its widespread use: poor adherence in rainy conditions. The cost of reapplying the film after each rainfall quickly adds up, and the film can sometimes deter beneficial insects, such as mite predators.
Despite the time- and potentially cost-intensive nature of kaolin particle films, its additional benefit of sun and heat protection makes it an attractive solution for growers in areas with less rainfall.
A plant’s natural reaction to heat stress is to curl its leaves. This behavior reduces the surface area exposed to sunlight and thus helps cool the plant, but it also reduces the area available for photosynthesis.
Kaolin particle films transmit photosynthetically active radiation but partly reflect ultraviolet and infrared radiation. This selective reflection of light helps prevent heat stress and reduce leaf curling, resulting in increased yield of crops treated this way, including mangoes, walnuts, blueberries, and thyme.
With climate change causing increasing periods of extreme temperatures, it provides more impetus to use this technology to gain a competitive edge against drought and heat.
A sustainable solution for a growing industry
There are a couple of complementary forces at work in agriculture that will change how crops are managed in the future. One, as I mentioned, is climate change. The other is a growing awareness of how big agriculture is causing negative health impacts. Both forces are increasing the adoption of organic farming techniques.
Kaolin can play an important role in promoting more sustainable agriculture by reducing reliance on conventional chemical pesticides. So, when you tuck into a meal of fresh vegetables or fruits (preferably local) in the future, it is possible you’ll need to thank a ceramic for its successful arrival to your plate (and as always, take a moment to thank the bees as well!).
