Of every kilogram of nitrogen fertiliser applied to agricultural soil worldwide, a substantial fraction never reaches a plant. It leaches through the soil profile into groundwater, volatilises as ammonia or nitrous oxide into the atmosphere, or runs off in irrigation water or rainfall events. The estimates vary by crop, soil, and application method, but losses of 30–50% are typical for conventional urea under typical application conditions.
This is simultaneously an economic problem (fertiliser is expensive, and losing half of it is a direct cost to growers), an environmental problem (nitrate leaching and nitrous oxide emissions are significant contributors to water pollution and greenhouse gas loading), and an agronomic problem (uneven temporal availability of nutrients creates periods of excess and deficit that reduce yield).
Controlled-release fertiliser technology exists precisely to address this — to slow the release of nutrients to better match the rate at which plants can take them up. Polymer-coated fertilisers dominate the commercial market for controlled release, but nanoclay-based approaches offer a complementary mechanism with distinct advantages, particularly around the environmental profile of the carrier itself.
Why conventional fertilisers release too fast
Conventional granular fertilisers — urea, ammonium nitrate, diammonium phosphate — are water-soluble salts. When irrigation or rainfall wets the soil, they dissolve and release their nutrient content into soil solution within hours to days. The immediate concentration spike exceeds what plant roots can absorb, and excess nutrient is lost by the routes described above.
The agronomic ideal is a release profile matched to crop demand: slow initial release during establishment when demand is low, increasing availability through the period of rapid vegetative growth, and declining again as the crop approaches maturity. No single-application conventional fertiliser achieves this.
How polymer-coated fertilisers work — and their limitations
The dominant controlled-release technology uses polymer coatings — typically sulphur, polyolefin, or polyurethane shells — around conventional fertiliser granules. The coating controls water diffusion into the granule and nutrient diffusion out, extending release over weeks to months depending on coating thickness and polymer chemistry.
Polymer-coated fertilisers work well agronomically. The limitation is that the polymer shell does not biodegrade under normal soil conditions. After the nutrient has been released, the spent shells persist in the soil as microplastics — a concern that is generating increasing regulatory and market attention, particularly in the European Union where microplastic restrictions are advancing. Some markets are already moving toward requirements for biodegradable coatings, creating an opening for alternative controlled-release mechanisms.
How nanoclay achieves controlled release
Nanoclay-based fertiliser systems use a fundamentally different mechanism. Rather than encapsulating a soluble fertiliser in a physical barrier, they adsorb nutrients onto the high-surface-area clay matrix and rely on the thermodynamics of adsorption-desorption equilibrium to control release rate.
Montmorillonite, with a theoretical surface area of approximately 700 m²/g (actual measured surface area in well-exfoliated form: 200–400 m²/g), carries abundant exchange sites — both in the interlayer gallery and on external surfaces — that can bind nutrient cations (ammonium, potassium, calcium, micronutrient metals) and, to a lesser degree, nutrient anions (phosphate, through edge-site binding and with appropriate modification).
When nanoclay loaded with adsorbed ammonium is placed in soil, the nutrient is released as soil solution NH₄⁺ concentration drops due to plant uptake and nitrification. The clay acts as a buffer — releasing nutrient when soil concentration is low and holding it when concentration is high. This equilibrium-driven mechanism naturally matches supply to demand more closely than a physical barrier that releases at a fixed rate regardless of plant uptake.
Loading methods
Preparing nanoclay-fertiliser complexes uses several approaches:
Ion exchange loading simply exploits the cation exchange capacity of the clay. Urea (which is not ionic) can be intercalated by exposure to urea solution, where urea molecules enter the interlayer gallery. Ammonium, potassium, and micronutrient cations exchange directly with the sodium or calcium in the clay gallery. The process is straightforward — clay is mixed with concentrated nutrient solution, allowed to equilibrate, and then dried — but loading capacity is limited by the clay’s CEC.
Intercalation of slow-release organic N sources uses the clay gallery to host molecules like glycine (amino acid), creatine, or other slow-mineralising organic nitrogen sources that release N over weeks as soil microorganisms mineralise the organic fraction.
Composite systems combine nanoclay with hydrogels, biochar, or biopolymers (chitosan is frequently studied) to produce materials that simultaneously manage water retention and nutrient release. These systems are more complex to manufacture but offer the closest match to the ideal agronomic release profile.
Performance evidence
Greenhouse and field studies on nanoclay-fertiliser systems have generally shown three consistent findings:
First, release rates are substantially slower than conventional soluble fertilisers. Laboratory leaching studies show nanoclay-NH₄⁺ releasing 50–70% of loaded nutrient over 30–60 days, versus 80–90% release for conventional granular urea within the first 3–7 days.
Second, crop yields on nanoclay-fertilised plots are broadly comparable to conventional fertiliser plots at equivalent nutrient application rates, with some studies showing yield improvements due to reduced peak-concentration stress and better late-season availability.
Third, nutrient leaching losses are consistently lower for nanoclay treatments, with nitrate leaching reductions of 20–50% reported across multiple soil types and crop systems. The environmental performance case is robust across the literature.
What nanoclay does not do well
Phosphorus controlled release is more challenging than nitrogen or potassium. Phosphate is an anion, and montmorillonite surfaces (negatively charged on faces) do not bind anions by the same strong electrostatic mechanism that binds cations. Phosphate binding occurs at positively charged edge sites and requires pH conditions where those sites are protonated — acidic to near-neutral pH. In alkaline soils, phosphate loading efficiency on standard Na-MMT is low.
Modified clays — iron-modified montmorillonite, layered double hydroxides (LDHs, which are positively charged clay analogues) — provide substantially better anion exchange capacity and are better suited to phosphate controlled release. LDHs in particular have been extensively studied for phosphate and nitrate controlled release applications.
Scale economics remain a challenge. The cost of nanoclay-fertiliser preparation at agricultural scale needs to be competitive with polymer-coated fertiliser on a cost-per-unit-nutrient-delivered basis, accounting for the higher fertiliser efficiency of the controlled-release product. This calculation is increasingly favourable as polymer coating restrictions tighten, but it is not yet universally economic across all crop segments.
The regulatory and sustainability case
The European Union’s Fertilising Products Regulation (FPR), which came into force progressively from 2022, has introduced provisions for CE-marked slow-release fertilisers and is developing criteria around microplastic persistence of fertiliser coatings. As those restrictions mature, nanoclay-based systems — which leave only natural mineral components in the soil — have a clear regulatory differentiation from polymer-coated alternatives.
For growers and agricultural input companies tracking where the regulatory environment is heading, nanoclay controlled-release technology is worth monitoring regardless of its current cost position relative to incumbents.
Lawrence Fine is CEO of AGCP Farmacêuticos, a Lisbon-based nanotechnology company with research programs in nanoclay agricultural applications.