For years there has been plenty of talk on the power of carbon nanotubes to influence manufacturing, electronics, and engineering. Now, adding to this power, is a swathe of new research that is pointing to the benefits of using carbon nanotubes as a fertilizer raw material.
While the use of tiny particles of substances such as silver, silica, copper, iron, and phosphates, has long been known as a nanoscale fertilizer feedstock, to date limited research has been done on the boost plants receive when carbon nanotubes (CNTs) are added to their water supply.
The publication of a review of the research that has been conducted up until is highlighting the potency CNTs hold as a sustainable, safe, and easily administered aid to crop growth. For horticulturalists, farmers, and agrichemical suppliers it is worth taking a look at what we know so far, and the potential carbon nanotubes have as a fertilizer feedstock.
With this in mind, here is what current research on carbon nanotubes as an agricultural raw material can tell us.
What are CNTs?
Nanotubes typically measure between 1 and 100 nanometres wide; where one nm is one billionth of a metre (about 10,000th the width of a human hair). At this scale materials begin to act in a very different way, giving them new and different properties to materials in the macroworld.
By adapting the concentration of nanotubes mixed into other substances, or the way in which they are synthesized, carbon nanotubes can be made; either very flexible or very rigid; electrically conductive or non-conductive; heat resistant or heat absorbent.
For example, the American Chemical Society notes that, “Carbon nanotubes are one hundred times stronger than steel and yet also much lighter.”
How do CNTs help plant growth?
While there is still insufficient research for a full answer, one possibility is that CNTs aid water uptake when they become lodged in both the xylem and inside plant cells.
As a study from the Indian Institute of Technology in Kanpur discovered, “Gram plants treated with water-soluble CNTs showed an increase in the length of roots/shoots and numbers of branches. The noticeable difference observed between the control and the treated plants was the water uptake efﬁciency. The water uptake in the case of treated plants dramatically improved, which indicates a better water retention and absorption capacity of water-soluble CNTs inside the plants.”
How do plants absorb CNTs?
Like other nutrients, CNTs are drawn up into the plants via the root system and transported into the plant via the xylem vessels. In this way, the size of the tubes is important. Research conducted on maize and soybean plants by a team from the University of Iowa found that, “… larger tubes (sized from 50 - 1000 nm) were more frequent in the roots, while shorter tubes (50 – 100 nm) were more evident in the stems and leaves.”
Care must also be taken to maintain the correct concentration of CNTs per litre. It is also necessary to understand that nanotube size, structure, form, water solubility, surface functionalization, the stage of aggregation, and exposure time, all influence the successful use of CNT-fertilizer. Similarly, different plant species will have different responses.
CNT conductivity has also found to be significant, with positively and negatively charged tubes having different absorption rates based on other factors.
Are CNTs toxic to plants?
To avoid toxicity, a high degree of surface functionalization is needed, as under some circumstances carbon nanotubes can pass through the cell walls of a plant, damaging or killing the cell. As a recent review of CNT effectiveness in the scientific journal Academia reports, “Underivatized nanocarbons are sufﬁciently hard and they interact with soft cell membranes to pierce through a cell.”
Adding that, “In contrast, the derivatized nanocarbons are highly dispersed in water and approach almost the solubility limit with enough softness. These may pass using regular channels of the cells and tissues of any living organism without inﬂicting physical damage and finally result in the overall growth of the plants by enhancing water uptake, seed germination, gene regulation, and overall improvements in productivity and soil microenvironments.”
To find out more about carbon nanotubes as a fertilizer feedstock please follow the link to part two of this article to discover what the benefits of this powerful and versatile raw material are.