From micronutrient adhesion to nutrient delivery platforms

Granular fertiliser coatings are often described as a way to add micronutrients to the granule. In practice, the engineering challenge is more demanding: delivering a high-loading, stable micronutrient system onto a friable granular substrate, while preserving storage stability, granule integrity and flowability across extreme ambient conditions.

Background and the core engineering problem

At Crommelin AgriCoatings, the platform began in 2012 and 2013 with a single objective: develop a zinc and copper coating system capable of dispersing micronised Zn and Cu oxide particles in a liquid phase, then applying that slurry to granular fertiliser with uniform coverage and durable adhesion. The first commercial deployment followed in 2014, with full production scaling in 2015.

The original challenge: high-solids stability meets real-world logistics

The early coating problem was never simply getting zinc and copper onto fertiliser. It required achieving several constraints simultaneously:

• High-solids dispersion (circa 60% solids) with rheology suitable for pumping, metering and application.
• Suspension stability so micronised particles do not settle, segregate or hard-pack during storage. Early targets were two to four months, later extended toward roughly 12 months as a practical commercial standard.
• Adhesion to friable granule surfaces without excessive dusting, flaking or coating loss through conveying and augering.
• Granule compatibility that preserves free flow and reduces bridging and caking risk in bunkers and silos.
• Thermal and humidity resilience, avoiding brittleness and cracking in hot, dry conditions, including storage environments reaching 40 to 50°C, while avoiding tacky or greasy behaviour in cold, wet, high-humidity winter conditions.

These constraints matter because the supply chain is unforgiving. Imported product is stored, trucked inland, held on farm and repeatedly handled before it reaches the soil. A coating that cannot tolerate those realities fails commercially, regardless of nutrient analysis.

The platform shift: coatings are no longer just attachment

As the zinc and copper coating systems matured, the carrier and binder phase evolved from a means of adhesion into a functional contributor. Across the industry, expectations have shifted from nutrient attachment to nutrient delivery and compatibility at the granule to soil interface, including multi-input coatings that add value without changing handling or application systems.

How it works: speciality lignins and biostimulants in a micronutrient coating system

A key step in moving from attachment to a delivery platform is designing the coating to include ingredients with complementary roles, physical, chemical and biology-adjacent, while still meeting the non-negotiables of stability, handling and flowability. Two useful classes of ingredients are speciality lignins, including lignin and lignosulfonate-type materials, and biostimulants.

1. Speciality lignins: binder and dispersant performance with mild complexation

Speciality lignins can be formulated to provide multiple functions in a granular coating system:

• Binder and adhesion: improved film formation and particle anchoring on the granule surface, reducing dusting and shedding during handling.
• Dispersion support: improved wetting and steric or electrostatic stabilisation that reduces rapid settling and hard-pack tendencies in high-solids slurries.
• Mild complexation: weak complexation of cations such as Zn, Cu, Mn and Fe, which can moderate rapid fixation reactions at the interface without behaving like a strong synthetic chelator.
• Compatibility leverage: better tolerance when coating common phosphate-based granules such as MAP, DAP and NPK blends, where antagonistic reactions can limit micronutrient effectiveness.

2. Biostimulants: rhizosphere support and early-season interception

A biostimulant component plays a different role. Rather than acting primarily through chemistry, it can support early uptake by influencing root and rhizosphere dynamics. One example class is seaweed-derived biostimulants, including calcified seaweed sources, that can contribute calcium, magnesium and biologically active organics such as polysaccharides and amino acid fractions.

• Root growth and early vigour: increasing the plant’s capacity to intercept nutrients placed with or near seed.
• Rhizosphere biology: supporting microbial activity and root exudation patterns that can indirectly improve access to micronutrients.
• Soil physical micro-environment: supporting moisture dynamics and aggregation at the microscale around the granule and root zone, relevant under variable moisture conditions.

3. Integration and compatibility

In an integrated system, speciality lignins can stabilise and retain micronised Zn and Cu on the granule and moderate rapid fixation at the interface, while biostimulants support the biological conditions that increase the probability of uptake. This chemical to biological bridge is particularly relevant in sandy, low-organic soils where micronutrient dynamics can be unforgiving.

Formulation discipline remains critical. Water-based biostimulants can interfere with curing or adhesion in fast-setting granular coating systems if not engineered appropriately. Where inclusion in the coating is not practical, biostimulant use may be better positioned as in-furrow, fertigation or foliar application, while the coating platform remains focused on durable micronutrient delivery.

Failure modes we design against, and why they matter

A robust coating system has to be engineered around predictable failure modes that occur in both the liquid dispersion and the coated granule state. In the tank, micronised Zn and Cu dispersions can fail through particle settling (gravitational separation), flocculation (agglomeration driven by surface interactions or ionic strength) and subsequent hard-pack formation, where settled solids compact into a dense layer that is difficult to re-disperse, creating batch-to-batch variability in nutrient loading and application rate.

On the granule, the dominant risks shift to dusting (poor adhesion or brittle film fracture leading to fines), caking and bridging (granules sticking under pressure and humidity in bunkers and silos), and cold, high-humidity plasticisation, where the binder phase absorbs moisture and softens, increasing tackiness and flow resistance. At the opposite extreme, hot, low-humidity storage can drive thermal embrittlement, where film shrinkage and loss of flexibility promotes cracking and coating loss during handling.

The practical impact of these failure modes is not academic. They determine whether micronutrients remain uniformly present on the granule at seeding, whether product maintains free-flowing behaviour through augers and metering systems, and whether the coating adds value without introducing operational risk.

Why coatings matter in WA: flexibility without system disruption

Granular fertiliser manufacturing and distribution is relatively static, particularly where significant volumes are imported and moved through established port to farm logistics. Growers, meanwhile, face increasing variability and an increased need for nutritional flexibility, without added complexity in handling systems. Coatings can add formulation flexibility and functional performance to the granule while keeping the grower’s workflow essentially unchanged.

Where the platform is heading

The next stage of development extends beyond micronutrient attachment into mechanisms that influence nutrient dynamics after application, particularly phosphate availability and biology-adjacent effects in the rhizosphere, while still preserving the fundamentals: suspension stability in the tank, durability on the granule and free-flowing behaviour through distribution and seeding systems.

Takeaway

The original Crommelin AgriCoatings technology solved a non-trivial engineering problem: a stable, high-solids micronised Zn and Cu dispersion system that can be applied to granular fertiliser and remain durable through extreme storage and handling conditions. The next evolution is larger. Coatings are becoming delivery platforms, designed not only to attach nutrients, but to influence availability, compatibility and early uptake at the granule to soil interface. The integration of speciality lignins and biostimulants is part of that trajectory: physically robust, chemically intelligent and biologically supportive systems that add value without disrupting established grower logistics.