A solid or a liquid formulation – that is the question inoculant distributors are facing with every new product cycle. This decision has key strategic implications due to technical and practical differences between the two formulations. The ease of chemical manipulation common for most agricultural chemicals doesn’t apply to microbial inoculants, and choosing the right formulation can make or break product performance, and consequently, market success. Answering the question and making a wise choice is a bit more challenging than it appears initially. To paint a picture of this challenge, let’s take a Rhizobia inoculant as an example.
Rhizobia inoculants are already well-established high-performers in the seed inoculant market, with experimentally and practically proven benefits. However, it is not a rare occurrence that a product meets its specification at the time of production, yet it doesn’t deliver on its promises in the field. The fact that microbial inoculants contain living organisms that must remain viable during storage, transport and application, implicates that the relevant performance window extends beyond production.
This creates a formulation challenge with very practical consequences.
Solid and liquid Rhizobia formulations differ in their handling characteristics, storage requirements and ability to maintain viable cells under different environmental conditions. For seed inoculant distributors, this often means that choosing between the two is both a technical and a strategic decision. It directly affects how the product will be distributed and used, and for most, it is always an OR decision – either solid or liquid.
To go beyond this challenge and unlock new market opportunities, Evologic ventured out to develop both formulations and prove that differences in performance are a matter of manufacturing, not inherent biology. Using the well-established Bradyrhizobium japonicum as the subject organism, Evologic approached this critical challenge with the idea to explore the technical advantages and readiness of solid and liquid formulations to meet different market requirements.
The Formulation Question Starts With the Distribution Model
The reality of production timelines, sowing times, geography and supply chain characteristics create a situation in the market where much depends on timing. These factors can get increasingly complicated to manage with international clients. As a result, a microbial seed inoculant may follow very different routes depending on the season, crop plant, technical capabilities, logistics, and regional infrastructure. A successful formulation must enable the product to withstand unfavorable conditions and deliver effects in the field.
In some markets, the inoculant is applied to seed shortly before planting. The time between treatment and sowing may be only a few days. In others, seeds are treated centrally and distributed through commercial seed programs. Treated seeds may then be stored and transported before they reach the grower. Consequently, the period between inoculation and planting can be considerably longer.
These systems impose different requirements and constraints on the product. Inoculants intended for short treatment-to-planting intervals do not face the same requirements as a product intended for extended storage on seed. Similarly, a distribution network with reliable, refrigerated storage imposes different constraints from one operating across warm climates with limited cold-chain infrastructure.
These differences were the starting point for developing two formulations.
One was designed around high on-seed survival. The other was developed as a high-concentration liquid formulation with defined cold-storage stability and straightforward application characteristics. The two products contain the same bacterium, but they address different constraints.
What the Two Formulations Showed
The most significant difference between the two formulations emerged after seed application. Both products were developed to deliver high concentrations of viable Rhizobia cells, but their survival profiles were designed to address different use conditions.
The solid formulation contains more than 5 × 10¹⁰ CFU/g. In a 120-day on-seed survival study, soybean seed treated with the formulation and a compatible sticker system was stored at 28°C and monitored over a course of 120 days. A benchmark of 10⁵ CFU per seed was used as a practical threshold for maintaining biologically relevant inoculum levels during storage and distribution.
The result – average viable populations remained above the threshold throughout the entire 120-day study. Even after four months of storage at ambient temperature, viable populations remained more than twice the target level.
This matters because Rhizobia cells on treated seed are exposed to prolonged desiccation and environmental stress, and substantial losses in viability are frequently reported within days or weeks of inoculation. The formulation was developed to address precisely this problem: maintaining viable populations during the period between seed treatment and planting.
The full comparative dataset, including the commercial reference product, is discussed in Conrad Reichelt’s article in the AgroPages 2026 Seed Treatment Special.
The liquid formulation was developed around a different set of requirements. Providing concentrations of more than 5 × 10⁹ CFU/mL, it demonstrated nine months of stability under cold-storage conditions. In field testing, the formulation achieved a 131% yield relative to the untreated control. With an eight-week production-to-delivery lead time, this format also addresses the timing pressure that seasonal demand creates.
The specs of this formulation are most suited for supply chains where refrigerated storage is available and where the operational advantages of a liquid product are relevant. Liquid inoculants are easily incorporated into the existing seed-treatment infrastructure and are suitable when the interval between treatment and planting is relatively short.
These results clearly indicate that the same organism can provide two different performance profiles, and address different market needs.
Three Questions Before Choosing a Formulation
So, the answer to the question presented in the very first sentence of this article is – asking more questions. It is necessary to get an overview of the conditions product will be exposed on its way to the field. Three questions can help determine which format is the better pick in the particular context.
1. How long is the interval between seed treatment and planting?
If inoculated seed is planted within a short period after treatment, the decline in viable cell numbers on the seed has less time to affect the final population at planting. In this case, the number of CFU at production can serve as a good indication of performance.
However, the situation changes for centrally treated seed that may be stored and distributed for weeks or longer. In this case, choosing the formulation that provides the best on-seed survival profile becomes crucial. Instead of looking strictly at the CFU count at the point of manufacturing, distributors should also know how many viable cells are expected to remain when the seed enters the soil.
2. What conditions does the product encounter in the distribution chain?
Storage and logistics determine the environmental conditions experienced by the product before use.
Refrigerated storage offers very different technical capabilities compared to storage at ambient or more variable temperatures. Long transport distances, multiple storage points or limited temperature control. These conditions should be considered before selecting a formulation.
3. Does the market require one product format or several?
Distributors operating in one region may have a relatively consistent set of requirements, but distributors supplying international clients may not. In these cases, a portfolio containing both solid and liquid products may be more appropriate than pushing a single format into the market.
Developing both formulations at the same facility ensures that the same quality standards are met, and eliminates the need for separate manufacturing relationships for each product format.
Choosing the Right Partner
A reliable product depends on the ability to manufacture it consistently, maintain high product quality over the entire production process, and respond to the timing constraints of an agricultural season. After choosing the most suitable formulation format, the next step is to find a reliable supply partner. Working with a partner that understands both microbial production and formulation provides more flexibility than sourcing a predefined product and adapting the market around it.
Evologic offers manufacturing and formulation expertise fit to solve challenges across a wide array of market demands and specific customer needs. Both Rhizobia formulations we talked about in this article are manufactured in-house, and free samples are available upon request and ready to ship
For more information about the supply challenges associated with seasonal inoculant markets, read Missed Season, Missed Opportunity? How Agile Manufacturing Solves the Rhizobia Supply Bottleneck.
For a detailed analysis of formulation-dependent Rhizobia survival on treated seed, including the results of our 120-day comparative study, read Conrad Reichelt’s article in the AgroPages 2026 Seed Treatment Special.
Customer use case: Turning tight timelines into success – large scale fermentation of Bradyrhizobium japonicum.
