Technological breakthroughs

A review study just published in npj Sustainable Agriculture (May 2025) finds that "smart" fertilizers — ranging from nanofertilizers and biofertilizers to controlled-release products — are advancing quickly on the technology side, but most still lack large-scale field trials and standardized evaluation methods needed to confirm their real-world effectiveness.

An Old Problem, New Pressures

Since the mid-20th century, large-scale mineral fertilizer production has helped raise crop yields and fuel economic growth in many countries. But that progress came with an imbalance: in some regions, excess fertilizer use pollutes soil, water and air, while in others, shortages leave land depleted and yields low.

For the past two decades, scientists and agribusinesses have promoted the "4R" framework — applying the right fertilizer source, at the right rate, right time and right place. However, the study's authors — led by Tai McClellan Maaz of the University of Hawaiʻi at Mānoa, together with colleagues from the International Fertilizer Association (IFA) and the Foundation for Food & Agriculture Research (FFAR) — stress that no single formula works everywhere, since soil, climate and crop conditions vary so widely from one region to another. That makes it far more complicated than commonly assumed to judge how effective any particular fertilizer product really is.

Against this backdrop, three emerging categories of fertilizer technology are seen as having potential to help crops absorb nutrients more efficiently while cutting losses to the environment: nanofertilizers, biofertilizers, and next-generation enhanced-efficiency fertilizers (EEFs). The authors reviewed the published scientific literature to weigh the evidence for each category and to chart priorities for future research.

Slow-Release and Stabilized Fertilizers: A Long-Standing Foundation

The idea of slowing down nutrient release dates back to the 1960s, when scientists recognized that crops' nutrient needs shift across different growth stages, while conventional fertilizers are prone to loss through pathways such as volatilization, runoff and leaching into deeper soil layers.

Following IFA's classification, there are three main types:

• Slow-release fertilizers: release nutrients more slowly than conventional products through biological or chemical mechanisms — for example, sulfur-coated urea or neem-coated urea.
• Controlled-release fertilizers (CRF): use physical mechanisms such as polymer coatings to regulate the rate of nutrient release more precisely.
• Stabilized fertilizers: incorporate enzyme inhibitors (urease inhibitors, nitrification inhibitors) that temporarily slow the biochemical transformation of urea or ammonium-based fertilizers in the soil.

Earlier meta-analyses show this category can deliver genuine, if modest, benefits: crop yields rise slightly in many cases, nitrate leaching drops by 17–58%, ammonia volatilization falls by 50–74%, and nitrous oxide (N₂O) emissions — a potent greenhouse gas — decrease by 28–49% compared with conventional fertilizer. One important caveat: nitrification inhibitors can trigger a "pollution swapping" effect — cutting N₂O emissions and nitrate leaching while increasing ammonia volatilization. When urease inhibitors and nitrification inhibitors are combined, this trade-off is largely avoided.

Despite reasonably solid supporting evidence, slow- and controlled-release fertilizers still make up less than 10% of the global fertilizer market, mainly because they cost 30% to ten times more than standard NPK fertilizers. Some products that rely on plastic (polymer) coatings also raise concerns about long-term microplastic pollution in soil. There have even been cases where misuse of inhibitors affected health outcomes in dairy farming in New Zealand. Based on this, the research team proposes six criteria that any new enhanced-efficiency fertilizer should meet to gain wider adoption: it must meet the crop's actual nutritional needs, include a biologically meaningful release mechanism, be safe and easy to transport and apply, pose no environmental harm, carry no risk to human or animal health, and be affordable to manufacture at scale.

Nanofertilizers: Strong Potential, Still Lacking Field Validation

Nanofertilizers use extremely small particles (typically 1 to 100 nanometers) to increase surface area and improve nutrient uptake by plants — particularly useful for elements that are hard for crops to absorb from soil, such as phosphorus, manganese, iron or zinc, when applied as foliar sprays.

The review highlights a notable concern: this field is still largely unregulated, and many commercial products marketed as "nano" actually contain particles well above true nanoscale dimensions.

The synthesis studies cited in the review paint a fairly optimistic picture on paper: most experiments report positive effects on germination, growth or yield. But common weaknesses persist — small sample sizes, scarce data on actual nutrient-use efficiency, almost no studies on cereal crops, and especially very few trials conducted outside controlled settings, with most work confined to laboratories or greenhouses.

One closely examined case involves nano-urea and nano-DAP (nanoscale diammonium phosphate), both already commercialized in India with claims that small foliar applications can match or exceed the yields achieved with much larger amounts of conventional granular fertilizer. However, a rigorously designed field trial — with proper controls, conducted in Punjab, India — found the opposite: rice and wheat yields dropped 13–17% when part of the conventional nitrogen fertilizer was replaced with nano-urea. The study also found no special "biostimulatory effect" from the nanoparticles themselves — yields from foliar-applied dissolved (non-nano) urea were essentially the same as from nano-urea.

Scientists also caution that more needs to be understood about the potential for nanoparticles to accumulate in the food chain and to affect soil microbial communities. They call for stricter peer review at scientific journals, noting that a number of agricultural nanofertilizer studies have been published despite relying on only a superficial understanding of plant physiology and soil science.

Biofertilizers: Effectiveness Highly Dependent on Field Conditions

Biofertilizers contain living strains of microorganisms that colonize the root zone and help plants take up nutrients more effectively — for example, nitrogen-fixing bacteria, phosphorus- or potassium-solubilizing bacteria and fungi, or mycorrhizal fungi. This category has also attracted strong investment from agtech startups in recent years.

The scientific evidence on biofertilizer effectiveness is mixed. One meta-analysis found that inoculating maize with the nitrogen-fixing bacterium Azospirillum brasilense raised yields by about 5%, with the largest gains seen in nutrient-poor soils. Another analysis, however, found no reliable evidence that microbial products can fix agronomically meaningful amounts of nitrogen when used on cereals and other non-legume crops.

A recurring issue noted by many researchers: strains that perform well in the laboratory often underperform once moved to the field, as they must compete with native soil microbial communities or fail to adapt to real-world conditions (soil pH, moisture, nutrient levels, and so on). As a result, research is increasingly shifting from single-strain inoculants toward multi-strain microbial consortia, aiming to improve survival rates and combine complementary effects.

According to the authors, the scientific literature on the environmental impact of biofertilizers remains quite limited. Of 126 field-based studies reviewed in an earlier synthesis, only four concerned biofertilizers, and that review's authors concluded the results were inconclusive — and that biofertilizers are unlikely to fully substitute for chemical fertilizers.

Next-Generation Enhanced-Efficiency Fertilizers: From Physical Mechanisms to "Biosensors"

Beyond traditional physical mechanisms (coatings, super-absorbent hydrogel materials), scientists are developing more sophisticated approaches to time nutrient release more precisely to a plant's actual needs.

One notable direction involves molecules capable of "recognizing" a plant's biological signals — for example, synthetic DNA strands called aptamers, which fold into specific shapes that bind selectively to compounds released by plant roots. In theory, if such molecules were embedded into a fertilizer's coating, the granule could "sense" when a plant needs nutrients and release them at the right moment. This technology, however, is still at a very early stage, remains costly, and faces many technical hurdles before practical application is possible.

Another direction is the development of fully biodegradable coatings (leaving no microplastic residue), potentially even incorporating microorganisms directly into the coating — both to control nutrient release and to support plant growth via microbially produced plant hormones.

Among the field studies reviewed, the majority (66 of 126) focused on polymer-coated urea — indicating that this remains the most thoroughly tested technology in this category, with relatively consistent results in reducing emissions and nutrient losses.

Why a Common Standard Is Needed to Evaluate New Fertilizers

A theme running through the entire review is that, despite their different mechanisms, all three categories of novel fertilizer face the same fundamental obstacle: a lack of large-scale field data, a lack of standardized testing procedures, and a lack of clear criteria for fairly comparing new products against conventional fertilizers.

The research team proposes building a shared evaluation framework spanning the entire pipeline from laboratory to field, built around several principles: establishing minimum standards for comparing fertilizer treatments (with proper controls and accounting for variation across space and time); clearly defining treatments and data requirements so that studies can be meaningfully combined; developing unified sampling and laboratory analysis protocols; and applying modern statistical tools to synthesize data across many locations and time periods.

The authors also point to the lesson of Sri Lanka — a country that suffered a severe food crisis after abruptly cutting off its fertilizer imports — as evidence of how quickly and severely a nation's food security can be affected by fertilizer-related decisions. This, they argue, underscores the importance of investing in rigorous research, fostering public–private collaboration, and promoting more open data-sharing in this field.

Limitations of the Review

The authors also acknowledge limitations in their own analysis: because there is still a shortage of comprehensive, systematic studies directly linking specific fertilizer products to yield or environmental outcomes — compounded by the enormous diversity of farming systems and agronomic conditions worldwide — the conclusions drawn so far remain limited in their generalizability. The authors argue that continued investment in field-based research is needed before the real-world performance of these next-generation fertilizers can be evaluated more fully and reliably.

Source: Maaz, T.M., Dobermann, A., Lyons, S.E. & Thomson, A.M. "Review of research and innovation on novel fertilizers for crop nutrition," npj Sustainable Agriculture 3, 25 (2025). DOI: 10.1038/s44264-025-00066-0. Published Open Access under a Creative Commons Attribution 4.0 license.