If you’re a gardener – and definitely if you’re a farmer – you want to spend less on fertilizer but while growing more food. Well, it’s time to send your thank-you basket of fruits and vegetables to researchers at the National University of Singapore, because they’ve created a magic wand for doing just that. Well, actually, a magic needle.

In their Advanced Functional Materials paper “Microneedle-Based Biofertilizer Delivery Improves Plant Growth Through Microbiome Engineering,” Andy Tay and colleagues explore the twin sources for their innovation: microbes in humans, and injections for humans.

“Inspired by how microbes can migrate within the human body,” says Prof. Tay, who led the work as Principal Investigator at NUS’s Institute for Health Innovation & Technology (iHealthtech), “we hypothesized that by delivering beneficial microbes directly into the plant’s tissues, like a leaf or stem, they could travel to the roots and still perform their function, but much more effectively and be less vulnerable to soil conditions.”

To get those beneficial microbes – a living biofertilizer – where the plants needed them, Tay’s team created patches of dissolvable microneedles. Using a plant growth-promoting rhizobacteria (PGPR) cocktail of Streptomyces and Agromyces-Bacillus to improve the metabolizing of nutrients and stimulate plant growth hormones, greenhouse kale and choy sum grew faster in height, leaf surface area, and shoot biomass.

That additional growth came with savings: 15% less biofertilizer than would usually be applied to inoculating soil. Much of the credit for that growth comes from more precise fertilizer delivery and thus less waste, which means reduced damage from fertilizer missing its target and ending up where it shouldn’t go.

So, what is living biofertilizer?

It’s beneficial fungi and bacteria that acts like a “plant nurse” by helping crops tolerate stress and absorb nutrients. Traditionally, farmers have added these living biofertilizers to soil, where acidity – plus the rival microbes who live there – pose a great threat, and thus for every amount of biofertilizers dumped into soil, only a portion gets to the roots. The NUS method, on the other hand, injects the helpful fungi and bacteria right into the stems or leaves, bypassing threats and getting to their targets immediately.

Using polyvinyl alcohol (PVA), an inexpensive, biodegradable, low-cost polymer, the team creates patches (1 cm2, or 0.16 square inches) with a short row of 140-μm microneedles for leaves, or 430-μm microneedles for stems, inside a 40 x 40 array of 140 μm pyramids.

The researchers then blend microbes into the PVA solution which they cast in microscopic molds before locking the microbes into the tips of the needles. Simply by thumb-pressing this “reverse thimble,” or using a manual applicator for even distribution of force, the needles harmlessly remain inside the plants and dissolve after about 60 seconds, leaving their microbes behind.

For easy production and instantaneous delivery, the applicator needle-patches are 3D-printable, and even when used across massive leaves, provide uniform insertion. And because of the patch’s design, its microbes remain viable in storage as long as four weeks, allowing stockpiling. Unlike with soil-delivered biofertilizers, there’s almost no waste or misfiring, meaning that crops – including highly valuable ones – get all their intended medicine.

National University of Singapore

While microneedle technology isn’t new (New Atlas has previously covered microneedle patches that deliver pesticides to plants), “This work is the first to demonstrate that root-associated biofertilizer can be directly delivered into a plant’s leaves or stems to enhance growth,” says Tay. “With this finding, we introduced a new concept of ‘microneedle biofertilizer’ that overcomes significant challenges of soil inoculation.”

Tay and his team express hope that in the near future, the microneedle approach will be a significant component of vertical and urban food and medicinal farms.

“A major focus is scalability,” says Tay. “We plan to explore integrating our microneedle technology with agricultural robotics and automated systems to make it feasible for large-scale farms. We will also test this across a wider variety of crops, such as strawberry, and investigate how these microbes migrate effectively from the leaf to the root.”

Source: National University of Singapore