Jacqueline S. Rowarth, Adjunct Professor, Lincoln University
- ‘Biologicals’ are being promoted as a way to decrease the use of nitrogen fertiliser without sacrificing yield.
- Interest in their use has escalated, but much of the literature cited is about their potential, rather than being evidenced by data.
- Reviews of field trials suggest low odds on achieving a positive response.
- A recent journal publication allows investigation of factors involved in the marketing claims of those promoting ‘biologicals’.
Background
At the beginning of 2025, the General Manager for Rabobank Australia and New Zealand discussed likely trends for the next five years. The top five included increased use of anti-obesity medicines, increasing alcohol consumption at home (to save costs), increased demand for dairy products targeting ageing, adoption of autonomous vehicles on farm, and:
‘The on-farm usage of ‘biologicals’ is also expected to rise in the five years ahead. These natural products can enhance plant growth and health by improving nutrient uptake, pest resistance and soil health.’
In agriculture, ‘biologicals’ are products derived from natural sources like microorganisms, plants, or beneficial insects to improve crop health, yield, and resilience. The Rabobank GM’s statement matches the increased interest in achieving more production system output (or at least the same) for less, and also reducing potential losses to the environment without compromising yield.
For example, a United Nations report released in 2023 highlights the challenge from the perspective of nitrogen use in production. Specifically, the 2nd European Nitrogen Assessment Special Report on Nitrogen & Food – Appetite for Change: Food system options for nitrogen, environment & health (Leip et al. 2023), had as its first key message:
‘Leakage of reactive nitrogen (Nr) from food systems threatens the environment and human health by causing air, water and soil pollution, while contributing to climate change and biodiversity loss. Nitrogen use efficiency (NUE) of the EU food system was only 18% in 2015. Most of the remaining 82% was wasted by loss to the environment contributing to these environmental and health threats.’
Nitrogen Use Efficiency (NUE) is therefore a hot topic and much has been written about the potential use of ‘biologicals’ to facilitate its improvement (e.g. Mus et al. 2016, Maaz et al. 2025). What-is-more, there appears to be a growing view that ‘natural’ options like biologicals can replace and improve on ‘chemistry’ (e.g. Kumar et al. 2022).
‘Bioactives’ appears to be a popular catch-all term for the biologicals. Among them, ‘biofertilisers’ are claimed to enrich the soil and supply nutrients to the plants through enhanced microbial activity, ‘biostimulants’ enhance plant processes and stress tolerance, without providing nutrients directly, and biopesticides are pest management products derived from natural materials such as animals, plants, microorganisms, and specific minerals. Sometimes the categories overlap – the definitions are not absolute – but in general, the pesticides attack and the others enhance. If pests are supressed, then plant growth will arguably be enhanced in the biopesticide category too.
Most advanced in terms of use and proof within a productive system are the biopesticides. These are described in AgScience Hot Topic #10 (Stewart 2025), while this Hot Topic (#11) will focus on the biofertilisers.
An Expanding Industry
A year ago, headlines proclaimed ‘Agricultural Biologicals Market to Hit US$33.52 Bn by 2030’. The market was growing at an annual compound growth rate of 13.4% https://www.vantagemarketresearch.com/industry-report/agricultural-biologicals-market-1049. A similar report from MarketsandMarkets™ stated that ‘The agricultural biologicals market is estimated to be USD 18.44 billion in 2025 and is projected to reach USD 34.99 billion by 2030, at a CAGR of 13.7% during the forecast period’. In 2022 the global market was estimated at US$12.3 billion. The predicted escalation is ‘fuelled by a drive for sustainability, including cost-savings for the farmer’.
Biopesticides (see Stewart 2025, Hot Topic #10 Biopesticides – NZIAHS) currently constitute over 40% of the products sold, but soil biofertilisers, which contain micro-organisms and are the subject of this Hot Topic, are gaining traction according to market predictions.
The Marketing of Biologicals
There has been enthusiastic marketing of biologicals. Articles such as ‘The Benefits of Biostimulants and the Ag Retailers’ Role in Their Broader Adoption’ (Dan Jacobs, https://www.croplife.com/author/jacobs/) exemplify the approach, noting that it plays on the interest in regenerative agriculture globally (see AgScience 57, https://agscience.org.nz/agscience-magazine/) which promotes, amongst other things, decreased use of synthetic fertiliser, particularly nitrogenous and phosphatic compounds:
“Regenerative agriculture starts from the ground up, and biostimulants play a pivotal role in this transformation,” Acadian’s Maude says. “Acadian’s seaweed technology fosters healthier soils by increasing organic carbon and stimulating beneficial microbial activity. The result? Reduced soil degradation and improved fertility.” Biome Makers’ Jacob Parnell agrees with that sentiment. “Biostimulants are a key resource for regenerative agriculture and are pivotal in sustainable agriculture,” he says. “The proper use of biostimulants can enhance resource efficiency, reduce environmental impact, and support soil and ecosystem health. By promoting nutrient uptake, stimulating beneficial microbial activity, and improving plant resilience to abiotic and biotic stresses, biostimulants complement natural processes,” he continues. “They reduce dependency on synthetic inputs, support biodiversity, and foster long term soil fertility, making them a cornerstone of integrated approaches to sustainable agriculture and climate resilience.”
So what is the likely demand for these biostimulants in New Zealand? The land has a relatively recent genesis as a consequence of the colliding Pacific and Indo-Australian tectonic plates. This results in mountainous or hilly countryside, but also includes expanses of volcanic soils. A reliance on pastoral agriculture and the low human population make it unusual in its requirement for nitrogen, which cannot be supplied in sufficient quantities for optimising plant growth through the recycling of animal bedding or human effluent as is done elsewhere. Its pastoral production systems also typically require additional phosphorus. Chile and Japan have similar parent material deficiencies.
How does nitrogen get to plants beyond the use of nitrogenous fertiliser applications?
Soil contains varying amounts of organic (carbon-containing) matter that provides a nutrient source for soil organisms, including some microorganisms that have the capacity to ‘fix’ nitrogen (i.e. convert atmospheric nitrogen gas (N₂), which most organisms cannot use, into ammonia (NH₃) and other nitrogen-containing compounds that are biologically available). The fixation process is energy-intensive and the contribution of nitrogen to plants from fixation are generally low, perhaps less than 20 kg/ha, restricted not only by energy availability through decomposition of organic matter, but also by metal ion and nutrient availability (reviewed in e.g. Smercina et al. 2019, Khan et al. 2021) unless a symbiotic relationship is involved between plants and specific microorganisms. Temperature and moisture affect nitrogen fixation, and high nitrogen environments (where mineral nitrogen is freely available to the plant) tend to suppress the contribution from biological nitrogen fixation, whether by free-living or symbiotic micro-organisms (e.g. Khan et al. 2021, Ladha et al. 2022).
The symbiotic nitrogen-fixers require a close association with a host plant to carry out the process, and most symbiotic associations are species specific and complex. In this respect, root exudates from leguminous plants (e.g. clover), serve as a signal to certain species of Rhizobium (e.g. Rhizobium leguminosarum biovar trifolii), which are nitrogen-fixing bacteria. The signal attracts the bacteria to the roots, and a complex series of events then occurs to initiate uptake of these bacteria into the root and trigger the process of nitrogen fixation in nodules that form on the roots. The energy cost to the plant varies according to plant host species, bacterial strain and the stage of plant development, but it has been estimated to be 5-8 grams of carbon per gram of nitrogen fixed. This carbon could otherwise be creating growth in the plant. Nitrogen fixation can therefore be considered as an opportunity cost, but the value of the lost yield might be less than the cost of adding nitrogen through, for example, urea.
Biostimulants to improve nitrogen availability
Over the years, attempts have been made to create symbiotic relationships (analogous to the relationship between rhizobia and legumes) with non-legumes and bacteria. There are also other known examples of these symbiotic relationships , such as those that exist between the tree alder (Alnus spp.) and the nitrogen-fixing bacterium Frankia alni (Santi et al. 2013) or the New Zealand native plant Matagouri (Discaria toumatou; https://www.doc.govt.nz/nature/native-plants/matagouri-wild-irishman/#:~:text=Like%20plants%20such%20as%20the,in%20relatively%20nutrient%2Dpoor%20habitats).
Dent and Cocking (2017) reported on the stimulus arising from the discovery of the nitrogen-fixing endophyte bacterium Gluconacetobacter diazotrophicus (Gd) in 1988. Gd is a non-nodulating, non-rhizobial, nitrogen-fixing bacterium that has been isolated from the intercellular juice of sugarcane. Under specific conditions, it can intracellularly colonise the roots and shoots of other species, including wheat, maize (corn) and rice, as well as crops as diverse as potato, tea, oilseed rape, grass and tomato. Field trials using a seed inoculum technology based on Gd (NFix®), improved yields by just under a tonne to approximately 7.5 t/ha, maize grain yield (by approximately 2 t/ha to 11.5 t/ha), and the growth of oilseed rape and grasses in both the presence and absence of synthetic nitrogen fertilisers. (Note: The yield increases were estimated for the purposes of this Hot Topic from graphs presented in the paper – Dent and Cocking simply talked about significant increases in yield indicating potential for the future.)
The authors concluded that the benefit of nitrogen fixation for cereals suggested in the 1980s might now be able to be realised, although not as originally envisaged (i.e. through Rhizobial association with genetically manipulated root nodules on wheat), but instead through the application of Gd to the plant using products such as NFix®.
Additionally, criteria for evaluating the practicality of using any nitrogen-fixing bacterium in agriculture were proposed (Dent and Cocking 2017).
‘They need to at least match those applied for the assessment of the efficacy of rhizobia/legume associations. Leaving aside the need for colonization, intracellularity and the development of symbiosomes (considered above), biological nitrogen fixation (BNF) studies to demonstrate nitrogen fixation should look for increases relative to controls associated with the following criteria (expanded on below):
The measurement of foliage greenness/chlorophyll content
- The measurement of the percentage N in the biomass
- Labelled N studies
- Nif minus mutants
- The measurement of nitrogenase activity by e.g. ARA
- Demonstration of field efficacy and yield benefits in nitrogen poor soils in the absence and/or presence of a nitrogen fertiliser.’
Guidelines for running field trials for evaluating ‘enhanced efficiency fertilisers’ have been published (Lyons et al., 2024) but are not yet in common usage.
In a different approach, researchers from PivotBio, the University of Wisconsin, and Purdue University (Martinez-Feria et al. 2024) were able to switch off the mechanisms that suppress biological nitrogen fixation in high N environments. This allowed the maize they were studying to access ‘a source of N typically not available to maize grown with high levels of synthetic N fertiliser’. Their strategy involved use of the gene-edited bacteria Kosakonia sacchari strain Ks6-5687 and Klebsiella variicola Kv137-2253. These bacteria de-repressed BNF activity in N-rich systems and enhanced ammonium excretion by ‘orders of magnitude’ above the respective wildtype strains. Based on data from small-plot and on-farm trials, Martinez-Feria et al. (2024) concluded that the new technology ‘can improve crop N-status pre-flowering and has potential to mitigate the risk of yield loss associated with a reduction in synthetic N fertiliser inputs’. However, the effect was most apparent at low rates of fertiliser N addition.
Similarly, another investigation (Woodward et al. 2024) with maize (Zea mays L.) and a mixture of gene-edited Klebsiella variicola and Kosakonia sacchari (referred to as NFI and applied in furrow at planting with additional urea-N fertiliser from 0 to 225 kg/ha N), resulted in an average increase in yield of 0.11 t/ha for lower rates of fertiliser addition (45–135 kg nitrogen ha−1). The extra N obtained from the NFI was estimated as 12–38 kg/ha N. At higher rates of fertiliser N, the effect was not apparent, and the authors commented that given the current prices for NFI, fertiliser N, and maize grain; the NFI effects in this study were not large enough to warrant a significant replacement of fertiliser N, but suggested that NFI had potential for future use if fertiliser N was capped.
In a different approach, Tajima et al. (2025) reported that modified DNA from hexaploid wheat plants grown in pots, increased the production of a biofilm-stimulating metabolite, and that this promoted soil bacterial nitrogen fixation and enhanced grain yield under low-nitrogen conditions. Once again, the effect was seen in low-N environments, but it was reasoned that in developing countries, the breakthrough ‘could be a boon for food security’.
In contrast to the above studies, a large set of field trials (Franzen et al. 2023) in 2021 and 2022 did not result in positive results with a range of biological N-fixing products like Envita®, Utrisha, and PROVEN® 40. Sixty-one site years of N-rate trials with and without the use of these products were conducted in corn, spring wheat, sugar beet and canola, and in ten states within the North Central Region of the United States. Of the 61 site-years, 59 site-years had no yield increase with use of the product, compared to just the N rate alone, and only two site-years in corn had yield increases due to product use that were over the N rates alone. The researchers suggested that ‘Given the low rate of positive benefits to the use of these products, growers should be sceptical of products that claim to provide asymbiotic/non symbiotic N-fixation for the purpose of allowing a farmer to decrease fertilizer N rate’.
It should be noted that the quantities of extra N being reported with the biofertiliser treatments, in the absence of application of synthetic nitrogen, are consistent with enhanced degradation of organic matter providing energy for the nitrogen fixation.
Is more research needed?
Many reports on the use of biologicals recommend more research is needed. This recommendation is not uncommon in research in general, because no single study can typically answer all questions and every research finding appears to reveal new complexities and raise further questions. The scientist sets up more research, building on past studies (standing on the shoulders of giants), filling in missing information and validating previous findings. It is a continuous cycle that improves our collective understanding. In new areas of research, such as biofertilisers, the effect of GxGxE (gene by gene by environment) interactions between microbes, plants and the environment should not be underestimated. For example, soil carbon quantities are known to vary substantially, even across a single paddock because the underlying soils can differ, as can slope, aspect, vegetation, grazing intensity and other management practices, all of which can influence soil carbon stocks. To illustrate this variability, a national exercise quantifying soil carbon stocks for New Zealand (Mudge et al. 2025) estimates a standard error of the mean for dairy soils of +/- 6% and for cropping soils of +/- 9%. Additionally, the Olsen measurement for phosphorus (Olsen-P levels) in soil is associated with a variability of 15-20% (Fertiliser Association of New Zealand 2023). The variability in soils means that point 6 of validation (Dent and Cocking 2017) may be difficult to achieve.
Notwithstanding the issues with energy source (the plant or the organic matter in the soil) and the measurement of effect (problematic against a variable background), it is possible that in the future improved understanding, including of the complex GxGxE interactions, will result in improved efficacy (Pankievicz et al. 2019). One of the biggest challenges, however, is actually establishing new micro-organisms (Borkar 2025). Recent research in Kansas (Ginnan et al. 2025) indicates that soil microorganisms adapted to specific environmental conditions such as drought can interact with plants to alter expression of the plant genes that mediate transpiration and intrinsic water-use efficiency. The result mitigated the negative physiological effects of acute drought for a native wild grass species, but not for the domesticated crop species maize. In New Zealand, the establishment of foreign micro-organisms, such as ‘super-rhizobia’ has tended not to meet with success (Ronson and Lowther 1995) and it may be that future research will find that host specificity goes beyond the simple relationship hitherto considered.
Certification
Despite the uncertainties in efficacy of biofertilisers (and biologicals in general) – or maybe because of them – certification schemes have been established ‘to provide a standard for these products and ensure growers and retailers will be able to confidently select the right solutions to fit their programs’ (https://www.croplife.com/crop-inputs/tfi-awards-biostimulant-certification-to-valent biosciences/).
The EU (Regulation – 2019/1009 – EN – EUR-Lex) provides clear instructions about what information must be provided for a product to meet the required standards:
PFC 6: PLANT BIOSTIMULANT
The following information shall be provided:
(a) physical form.
(b) production and expiry date.
(c) application method(s).
(d) effect claimed for each target plant; and
(e) any relevant instructions related to the efficacy of the product, including soil management practices, chemical fertilisation, incompatibility with plant protection products, recommended spraying nozzles size, sprayer pressure and other anti-drift measures.
PFC 6(A): MICROBIAL PLANT BIOSTIMULANT
All intentionally added micro-organisms shall be indicated. Where the micro-organism has several strains, the intentionally added strains shall be indicated. Their concentration shall be expressed as the number of active units per volume or weight, or in any other manner that is relevant to the micro-organism, e.g. colony forming units per gram (cfu/g).
The label shall contain the following phrase: ‘Micro-organisms may have the potential to provoke sensitising reactions’.
Principles to justify biostimulant claims have been established in parallel with the EU regulations (Ricci et al. 2019) and efforts continue to be made overseas in terms of allowing use of new products (e.g. New legislation would help keep the U.S. a global leader in crop innovation – Brownfield Ag News). The situation for New Zealand has been outlined in Hot Topic #10 (Stewart 2025).
Despite the above challenges and scientific complexity, the marketing of biostimulants products continues. Further, the statements in some of the marketing blurbs (e.g. … delivering steady nutrition throughout the most critical growth stages, regardless of weather and soil type…) fail to explain the mechanism of efficacy and might therefore fail credibility tests in New Zealand whilst potentially misleading customers and consumers.
The Sceptic’s Questions
An industry programme investigating biopesticides (A Lighter Touch – Changing the way we protect our crops, for the better) has developed questions for farmers and growers to consider before deciding to adopt their use. These questions are equally applicable to biofertilisers and were indicated in the EU regulations presented earlier.
What is the active ingredient? If the biofertiliser is described simply as a crude preparation or mix of micro-organisms, ask for more details about the active ingredient. If the biofertiliser is based on a single micro-organism, ask for specific identification. If the answers are vague – beware.
Ask how the product works. This is the key to understanding how to use it properly and to achieve a good response. Cross reference what the company representative tells you with label claims.
What trial data exist to back up the claims and did the protocol follow guidelines (Lyons et al. 2024)? Do not accept pot trial data (it doesn’t translate well to field efficacy) and be cautious with field data that aren’t applicable to your situation. Unlike overseas soils, New Zealand soils tend not to be nitrogen deficient.
In addition, check what the base yield is with no fertiliser in the research, and the yield potential with conventional fertiliser. Are any yield increases
– consistent?
– statistically significant?
– biologically meaningful?
– economically compelling?
Conclusions
The importance of nitrogen, and the benefits of fixation are indisputable. What is considerably in dispute is whether free-living associations or microbial additives can supply sufficient nitrogen to provide crop needs. Reports of positive benefits tend to be based on relatively low yields of crops. If fertiliser nitrogen is added to enable the potential yield of the crop to be achieved, the effect of the biostimulant disappears.
Franzen et al. (2023) concluded from the low rate of positive benefits to the use of these products, that growers should be sceptical. ‘It is good for farmers to be curious; however, the wise grower needs to test products of interest on their own farm in a replicated manner and search for unbiased data on product performance before using them on whole fields.’
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