Appropriate formulation is required for a high-quality product. Microorganisms need to
be well protected to survive in high numbers in the formulation under variable and
potentially harsh conditions during storage. During storage, high temperature is
typically the most detrimental condition for the microorganisms.
Formulations are broadly divided into those using solid carriers or liquid
formulations. Choice of formulation depends on the microorganism, cost, shelf-life and
application requirements among other factors. But it is important to remember that no
formulation is perfect, and each has its advantages and disadvantages.
Historically, peat, known as carrier-based, is the most commonly used carrier for
microbial inoculants; given its low cost and the ability to provide a protective and
nutritive environment for the microorganisms. The major drawback of it is the variability
in its quality and composition, leading to differences in its capacity to support cell
survival.
Dry formulations have longer shelf-life as the microbes are forced into a dormant state
during drying; however, desiccation of microbial cells during drying can cause high
levels of cell death, particularly for non-spore forming microbes. Advancements in
drying technologies and formulation are leading to more dry microbial inoculants being
developed, with high concentration and longer shelf-life of 1 year and greater. Keeping
in mind that desiccation loss during application can be avoided if the dry carrier can
provide a protective environment.
On the other hand, liquid formulations tend to have a shorter shelf-life, given that
metabolic activity of microbes continues during storage; but can be produced in high
concentrations and are easy to handle and apply. However, liquid formulations make up
over 80% of the market in, especially in South America because liquids are easier to
produce by industry and easier to use by farmers. Their application to seed involves
drying of the microbe solution in an uncontrolled environment, causing subsequent
desiccation loss of cells which could impact performance.