Bentonite is a particular volcanic rock powder of volcanic origin that has been finding useful applications in organic agriculture in recent years. Its classic use is in winemaking, particularly for the crucial wine clarification process. But given its unique physical properties, this mineral powder can also be used directly on crops as an anti-cryptogamic agent, which means it prevents fungal diseases. It’s an element with no contraindications, so much so that it’s available in formulations intended for human use as a dietary supplement. In practice, it’s a natural product with a reasonably low cost, which is worth knowing about.
In this article, we will see how this rock powder can be used in organic farming.
What Is Bentonite
In mineralogy, bentonite is a phyllosilicate, which means it’s a clay-like mineral formed from multiple layers that bond together. Its composition consists of calcium, sodium, and montmorillonite. It’s extracted from volcanic sediments, as it forms through the decomposition process of volcanic ash.
There are numerous bentonite deposits around the world, with the most significant ones located in the United States, particularly in the state of Montana, in the Fort Benton area, from which it derives its common name.
Properties and Classic Uses of Bentonite
The primary physical property for which bentonite is known is its exceptional ability to retain water and moisture. This quality makes it widely used in construction, especially as a waterproofing agent. Another equally common use is in cat litter preparation, as it not only absorbs liquids but also traps odors and tends to form typical clumps that are easy to remove during cleaning. This type of litter can be found in specialized stores. For human use, it is employed in specific purifying and detoxifying formulations, such as for removing residual feces and mucus in the intestine. These products can be readily found in the market.
Bentonite in Organic Winemaking
In the agricultural field, the classic use of bentonite is for wine clarification. It is used in winemaking for its deproteinizing effect. When added to the liquid, the powder swells, takes on a negative charge, and binds to proteins, causing them to precipitate.
In practice, the treatment with bentonite is an enological method for protein stabilization, the only one allowed in organic winemaking. All three types of bentonite available in the market are used in winemaking: sodium, calcium, and activated.
This version is the richest in sodium ions, with the most significant deproteinizing effect. It deposits slowly and in a less compact manner. It is recommended for wines with high protein instability.
It has a lower deproteinizing capacity, with compact deposits and a rapid settling dynamic. It is more suitable for delicate and less unstable wines.
This is the calcium version that has undergone treatment with sodium. It swells less time in contact with the wine and is more effective than the others at the same dosage. It is, therefore, an intermediate type, widely used for most wines. It is also known as gelbentonite.
Bentonite in Viticulture as a Fungicide
Returning to actual field practices, powdered bentonite is gaining popularity as an excellent fungicide in organic viticulture. Of course, it is essential to use the specific product designed for agriculture, which is finely ground calcium bentonite. We know that grapevines are highly susceptible to fungal pathogens, especially during the phenological stages of grape cluster growth and final maturation. It is precisely on the grape cluster that this mineral powder can play a vital protective role. Specifically:
- It heals acinus wounds caused by hail, oidium, and cracking, reducing the risk of parasite proliferation, such as grapevine moths;
- Used in conjunction with sulfur or copper products, it enhances the effectiveness of anti-downy mildew treatments;
- It controls moisture, preventing yeast, bacteria, and fungi proliferation, reducing the risks of botrytis and pre-harvest rot.
Agricultural Uses of Bentonite
In other organic farming practices, bentonite powder proves to be useful. Its use is similar to other rock powders we have previously studied, such as kaolin and zeolite. As a fungicide, this rock is excellent for spraying around the base of vegetable plants to prevent rot. It can be used directly on the soil to improve its drainage capacity. Another interesting application is in the domestic composting process. When added to the compost pile in a 1% ratio, it absorbs moisture and retains nutrients, speeding up the formation of organic matter. It also has another essential function: eliminating the unpleasant odors that compost bins inevitably emit.
On Fruit Trees
In the family orchard, bentonite is used in the preparation of trunk paste, mixed with hydrated lime and copper products. Trunk paste is brushed onto the main stem and protects against wood diseases and pests. Another use is when planting bare-root fruit trees using the heel-in technique. Adding bentonite improves the tree’s root attachment.
Finally, it can be used in pure form or as an adjunct to copper products in preventive treatments against fungal diseases such as downy mildew, peach leaf curl, brown rot, and more.
Agricultural-grade bentonite powder is dissolved in water and sprayed using a shoulder pump (like this one). It is of utmost importance to clean the spray nozzles thoroughly after use to prevent clogging and the need for replacement.