Biological Inputs: Are we asking the right questions?

Dr Aurelie Quade & Dr John Rochecouste

Global trade disruptions have driven price spikes in fuel and fertiliser, accelerating interest in agricultural biological inputs. Although the broader trend is relatively recent roughly two decades old some products, such as microbial inoculants, have been in use for over a century. As our understanding of soil systems has grown, so too has an entirely new segment of the agricultural market: biological inputs and their many derivatives. 

The range of products on offer, their modes of action, and their formulations has expanded rapidly. Even major companies traditionally focused on agrochemicals and synthetic fertilisers now offer biological alternatives. Meanwhile, farmers and advisors are facing growing information fatigue as new products continue to enter the market.

This interest in biological inputs is not simply environmental marketing. Farmers are running businesses, and many are recognising that continued reliance on synthetic fertiliser alone is not always translating into yield gains particularly where soil function has become the limiting factor. Productivity is no longer determined solely by what comes out of a bag, but increasingly by what the soil system itself can support.

The principle seems simple: look after the soil and it will look after you. Yet biological inputs have so far struggled to meet the productivity expectations of the Australian agricultural industry, particularly in grains.
The issue may not be the products themselves.

Biological products are complex tools

Biological inputs belong to a relatively young commercial industry, and like most emerging markets, the sector has seen periods where claims have moved ahead of the evidence. This is not entirely surprising. Synthetic fertilisers have benefited from more than 150 years of research across countless soil types, climates and cropping systems. Their behaviour is well understood, and their effects are typically visible within weeks.

Biological products are still building that evidence base, and they operate differently. Many influence soil processes microbial activity, nutrient cycling, root interactions rather than delivering nutrients directly to the plant. These processes are inherently more complex and often slower to affect crop performance

Some biological products also require more careful handling than conventional fertiliser inputs. Microbial inoculants may need refrigeration, have a limited shelf life, and must be applied under specific environmental conditions. Others depend on soil moisture or rainfall to activate. In research trials these

conditions are carefully controlled; in the field, storage, transport and application can vary considerably. Small deviations can reduce performance and when that happens, the product is often blamed rather than the conditions. Biological inputs behave less like universal inputs and more like specialised tools that interact with living soil systems.

The wrong benchmark

Another challenge lies in how biological inputs are evaluated. Agriculture has traditionally measured success through plant response: yield, growth and fertiliser response. New technologies are therefore expected to outperform existing inputs on the same criteria. Under that framework, biological products often appear disappointing. But the benchmark itself deserves scrutiny.

Modern crop varieties are developed through breeding programs where fertiliser is applied generously to ensure nutrients are not limiting. This creates uniform trial conditions and allows meaningful comparisons between varieties. Those performing best in fertilised systems are selected and released.

Over time, this process has unintentionally produced crops that perform particularly well with generous fertiliser supply. When biological inputs replace synthetic fertiliser, we are effectively changing the environment these varieties were bred for. A yield drop under those circumstances should not be surprising.

This does not mean biological products lack value. It means they operate in a different part of the production system. Synthetic fertiliser acts as fuel delivering nutrients directly. Biological inputs tend to influence the soil processes that support growth. Servicing an engine does not immediately make a car faster, but it allows the vehicle to run more efficiently and travel further. Improving soil function may not produce an immediate yield jump, but it can build the productivity and resilience that matter over longer time horizons. Judging biological inputs solely on immediate yield response risks measuring the wrong outcome entirely.

Diagnosis first, products second

A further reason biological inputs produce inconsistent results is that they are frequently applied without first identifying the soil constraint they are meant to address, and without a clear plan for how the farming system is meant to evolve over time

Soil performance is shaped by several interacting factors: biological activity, soil structure, chemical fertility and management practices. When one becomes limiting, productivity can decline even when others appear adequate.

For example, if poor soil structure is restricting water infiltration and root development, stimulating microbial activity alone will not resolve it. Structural constraints must be addressed first. If nutrient availability is the primary limitation, products that improve nutrient cycling may be more relevant. Without identifying the dominant constraint, applying biological products becomes trial and error.

This is where many biological programs fall short. Products are added to a system without a clear starting assessment, without defining what they are meant to address, and without enough time to determine whether they are working. Some paddocks respond; others do not and the product is then written off as unreliable.

The bigger issue is that transitioning from a synthetic-only system to one that relies increasingly on biological function is not a one-season decision. It is a systems transition. It requires a plan.

A farming system needs to know where it is starting from: what constraints are limiting soil performance now, what can realistically improve in the short term, and what may take several seasons to shift. In the early years, the goal may not be higher yield, but better infiltration, more stable nutrient cycling, improved input efficiency, or reduced exposure to nutrient loss. Over time, those gains support more resilient and productive systems.

Without a strategy, biological inputs are often expected to do too much, too quickly, in soils that are not yet ready to respond. With a plan, they can be introduced in a way that matches where the soil is, what the farm business can support, and what the grower is actually trying to achieve.

Farmers who achieve the most consistent results with biological inputs are often not the ones chasing the newest product, but the ones working from a clear roadmap, reviewing progress regularly, and giving the system the time it needs.

Take-home message
1. Biological inputs are not a fertiliser replacement they operate in a different part of the system.
2. Evaluate them on the right criteria: soil function and long-term resilience, not just immediate yield.
3. Diagnose the dominant soil constraint before selecting a product. 4. Build a transition plan biological programs need time and a clear starting point to be assessed fairly.

Dr Aurelie Quade is the founder of Soil Resilience and supports farmers, agribusinesses, and food supply chains to turn soil health into practical, measurable action. Her work focuses on soil function, data interpretation, and strategies that improve productivity, resilience, and environmental outcomes. She brings a science-based approach to soil health, with a strong focus on making complex information useful for real-world decision-making. contact@soilresilience.com.au Dr John Rochecouste has extensive experience in research and extension across both private and public sectors and is currently an independent consultant in rural sustainability.