Nanocoated nitrogen-fixing bacteria help increase rice yields and bring foliar biofertilizers a step closer to practical use

Nitrogen-fixing bacteria naturally convert atmospheric nitrogen — which plants cannot use directly — into ammonia, a form crops can absorb. Most commercial applications involve coating seeds with these bacteria so they colonize plant roots. Applying them to leaves instead is theoretically attractive because it would work for any crop at any growth stage, not just at planting. The problem is that leaves are harsh environments: UV radiation, drought, temperature swings, and the lack of a protective root zone kill most bacteria within hours or days of application.

The researchers wrapped Klebsiella variicola W12 in a two-layer shell. The outer layer uses metal-phenolic networks — a structure formed when tannic acid coordinates with ferric iron ions — which is known for its antioxidant and UV-blocking properties. A second layer of sodium alginate, a natural polymer derived from seaweed, improves moisture retention and biofilm formation. Together, the coating lets the bacteria adhere to leaf surfaces and remain metabolically active long enough to fix nitrogen into the plant, without being killed by environmental stress.

In hydroponic cultivation, nanocoated bacteria colonized rice leaf surfaces 3.3 times more effectively than uncoated bacteria at 14 days post-application. The coated treatment contributed 27.89% of total plant nitrogen — more than twice the contribution of uncoated bacteria — and produced a 1.4-fold increase in fresh plant weight after 54 days. In field trials with Meiliangyou rice, seed dry weight and total biomass both increased in coated versus water-only control plots, though full quantitative data for field conditions were not disclosed in the abstract.

This is laboratory and preliminary field research. Significant work remains before any commercial product could reach farmers. Challenges include optimizing coating formulations for different crops and climates, ensuring the nanocoating materials are safe for soil and human health at agricultural scale, developing cost-effective manufacturing processes, and obtaining regulatory approval in key markets. The research demonstrates proof of concept in rice; application to wheat, corn, and other major cereals will require additional development. Commercial deployment is likely at least a decade away.

The leading commercial biofertilizer for corn is Pivot Bio’s PROVEN product, which engineers soil microbes to fix nitrogen from the atmosphere and deliver it to plant roots. Pivot Bio estimates its products can replace 20–25% of a corn crop’s nitrogen needs. Foliar delivery, if it can be made reliable, would offer a fundamentally different application window — after planting and potentially multiple times during the growing season — and would not depend on root-zone colonization. However, existing root-zone products have the advantage of years of field trials and regulatory approval. The nanocoating approach is complementary rather than competitive at this stage.