Technological breakthroughs

When Traditional Fertilizers Waste More Than They Feed Plants

Most fertilizer applied to soil never actually reaches crops. Depending on fertilizer type and soil conditions, between 40% and 90% of nutrients are lost through leaching into groundwater, volatilization into the atmosphere, or fixation by clay minerals in insoluble forms. Global nutrient-use efficiency currently averages only about 30–35% for nitrogen, 18–20% for phosphorus, and 35–40% for potassium. These losses are both a financial burden for farmers and a major source of nitrate pollution in water and greenhouse gas emissions in the atmosphere.

The core problem lies in how conventional fertilizers work: they dissolve immediately upon contact with water, releasing a large amount of nutrients in a short time, after which the excess disperses into the environment. Plants cannot absorb such a sudden nutrient surge efficiently.

Nanoparticles — Nutrient Reservoirs at the Millionth-of-a-Millimeter Scale

Nano fertilizers approach the problem differently. Instead of allowing nutrients to dissolve freely, this technology incorporates nutrients into particles measuring between 1 and 100 nanometers — roughly 1,000 times smaller than a human hair and smaller than most soil bacteria.

At this scale, materials possess a vastly greater surface area per unit mass compared with conventional granules. One gram of nanomaterial can have a surface area equivalent to several football fields. Greater surface area means higher interaction and reactivity: nanoparticles can interact with root cell membranes, soil enzymes, and plant signaling molecules — interactions that conventional fertilizer particles are too large to achieve.

Four Ways Nutrients Are Retained in Nanoparticles

Depending on their design, nutrients are held within nanoparticles through different mechanisms.

Intercalation Between Material Layers

Some nanomaterials have stacked sheet-like structures, such as layered double hydroxides (LDH). Nutrient ions like phosphate can insert themselves into the spaces between these layers, similar to sheets of paper tucked between book pages. As soil conditions change, the layers expand and gradually release nutrients. Experimental LDH systems containing phosphate extended nutrient release approximately tenfold compared with conventional phosphate fertilizers.

Encapsulation Within Polymer Shells

This mechanism resembles sustained-release pharmaceutical capsules. Nutrients are enclosed within a shell made from biopolymers, commonly chitosan (derived from crustacean shells) or alginate (from seaweed). The coating prevents nutrients from dissolving immediately upon contact with water while protecting them from volatilization and soil fixation. Changes in pH or moisture alter the coating structure and trigger nutrient release. In experiments using chitosan–alginate nanocapsules containing NPK and beneficial bacteria, approximately 33%, 48%, and 68% of nitrogen, phosphorus, and potassium, respectively, were released over 30 days — a release profile much better aligned with plant nutrient uptake than fast-dissolving fertilizers.

Electrostatic Adsorption

Nanoparticle surfaces can be engineered to carry positive charges. Negatively charged nutrient ions such as nitrate (NO₃⁻) and phosphate (PO₄³⁻) are attracted to these surfaces through electrostatic forces. When soil pH changes — for example, in highly active root zones — the attraction weakens and nutrients are released. Surface-modified zeolites treated with cationic surfactants can sustain nutrient release for more than 1,200 continuous hours, compared with only a few dozen hours for conventional fertilizers.

Surface Adsorption

Nutrients can also adhere to nanoparticle surfaces through weak physical interactions such as hydrogen bonding and Van der Waals forces. Loosely attached nutrients are released immediately after application to provide rapid nutrition, while more strongly attached nutrients are released gradually in response to root signals or moisture changes. This dual mechanism enables a single fertilizer to satisfy both immediate and long-term nutrient demands.

Fertilizers That Respond to Signals

An even more advanced direction involves designing nanoparticles that release nutrients only in response to specific signals — not according to a farmer’s fertilization schedule, but according to physiological signals from plants and soil themselves.

pH-Responsive Systems

Root zones actively absorbing nutrients tend to have lower pH than surrounding soil. Nanoparticles containing the polymer PDMAEMA release more nutrients when pH decreases because amine groups on the polymer surface become protonated and more positively charged, pushing nutrients outward. In other words, the more actively the plant absorbs nutrients, the more fertilizer is released.

Temperature-Responsive Systems

The polymer PNIPAm (poly-N-isopropylacrylamide) shrinks when temperatures exceed approximately 32–33°C. As it contracts, it expels nutrients or pesticides from the nanoparticle. During hot seasons, when soil temperatures rise and plants grow more vigorously, the system automatically increases nutrient delivery.

Pest-Enzyme-Responsive Systems

A particularly interesting application in crop protection involves pesticide-loaded nanoparticles coated with alpha-cyclodextrin shells. When diamondback moth larvae (Plutella xylostella) feed on leaves and secrete alpha-amylase enzymes, the enzymes break down the coating and release the pesticide precisely where pests are feeding instead of across the entire field.

Redox-Responsive Systems

Root zones under anaerobic conditions or plant stress exhibit stronger reducing environments. Nanoparticles containing disulfide (-S-S-) bonds are sensitive to glutathione, an antioxidant molecule that increases when plants are under attack. When glutathione breaks the disulfide bonds, the coating opens and releases the active compounds.

How Plants Absorb Nano Fertilizers

Nanoparticles enter plants through two main pathways.

Through Roots

Nanoparticles first interact with the root tip and root hairs, where abundant organic exudates help particles adhere and penetrate. The particles then pass through cell walls — porous structures with openings approximately 5–20 nm wide — into vascular tissues, where they move upward with the water stream to aboveground organs. Nanoparticles smaller than 50 nm and carrying positive charges are generally absorbed more efficiently.

Through Leaves

When sprayed onto leaves, nanoparticles primarily enter through stomata — microscopic pores used for gas exchange — with size limits of roughly 10 nm. Smaller amounts may also penetrate through the waxy cuticle via lipophilic pathways or microscopic water pores. Once inside the leaf, nanoparticles move through the phloem and are distributed to seeds, fruits, and flowers, which do not directly receive sunlight.

Dosage Limits

Nano fertilizers are not harmless at all concentrations. At high doses, many metal-based nanoparticles induce oxidative stress in plant cells. Metal oxide nanoparticles such as ZnO, CuO, and Fe₂O₃ stimulate the formation of reactive oxygen species (ROS) through Fenton-type reactions, damaging membrane lipids and proteins.

CuO nanoparticles at concentrations of 10 mg/L caused root damage in Arabidopsis experiments; at 2,000 mg/L, they inhibited 95–97% of root growth in maize and rice. CeO₂ nanoparticles above 1,000 mg/kg caused DNA strand breaks in soybeans.

Toxicity thresholds vary significantly depending on plant species, growth stage, soil pH, and soil organic matter content. Soils rich in organic matter tend to reduce toxicity because organic compounds coat nanoparticle surfaces and decrease their reactivity. Acidic soils tend to increase toxicity by promoting the dissolution of metal ions from nanoparticles.

Current Status and Remaining Unknowns

Nano fertilizers are currently transitioning from laboratory research to field-scale testing. Most available data come from greenhouse studies or single-season field trials. Long-term effects on soil microbial communities — which play a central role in nutrient cycling — remain poorly understood.

Production costs are currently the greatest barrier for most farmers, especially in developing countries. The lack of standardized large-scale manufacturing processes also leads to major variations in product quality among manufacturers.

In terms of regulation, India introduced the first legal framework specifically for nano fertilizers in 2024. The European Union and the United States regulate them under broader chemical regulations (REACH and TSCA), without agriculture-specific standards. No unified international regulatory framework currently exists.

Source:

Sadiq V. et al., “Re-engineering of nanofertilizers for sustainable agriculture: synthesis, mechanistic insights, toxicity and regulatory frontiers,” Frontiers in Soil Science, Vol. 6, 2026. DOI: 10.3389/fsoil.2026.1677386