Tailor biological inputs to your context

It is important to understand your soil and crop needs. What are your major limiting factors? Plant and soil testing will help identify nutrient deficiencies, pH imbalances and other factors that may influence your decision making. Consider the current condition and management history of your paddocks and which input might help you address specific crop growth constraints or soil health issues that you have.

Do a trial

As with all new practices and products, consider running a small trial of the product before applying the input across the whole farm or paddock. You could trial a full length of the paddock or a block trial across different zones. You could also get out with a small spray bottle and spray a 1 m2 section to see how the crop responds.

Check for product quality

Quality checks are important for both store-bought products and those you make on your farm. Assessing quality not only boosts confidence in using biological inputs, but also helps reduce the risk of contaminants being introduced to your paddocks and crops. 

If buying a product, consider asking for an ingredient list and details about how it was made, handled, stored and what analyses have been done. Keeping a record of these details can allow you to track fertiliser applications and quality over time.¹¹D Chrohne, ‘Assessing Compost Quality for Agriculture’, University of California Agriculture and Natural Resources, 2016, accessed 1 November 2024. If the supplier cannot provide sufficient information, you can consider arranging your own lab analysis of a sample before committing to a large purchase.

• Physical assessment: Does the product look, smell and feel like it should? For example, composts should be moist, dark in colour, fine crumbly texture with uniform particles and smell somewhat pleasant. 
• Lab analysis is one of the main ways of getting quality assurance on a biological input. Many of the same laboratories that offer soil sample analysis also offer soil amendment/compost analysis. Get in touch with a lab to find out what they can test or and how to take a sample and post it to them. 
  • Micro and macronutrients: Sampling micro and macronutrient concentrations can help you decide what rate (kg/ha) to apply a product. 
  • Microbial species: For microbial inoculants, you can check whether the target microbial species are in abundance and whether any potentially pathogenic microbes (e.g. E. coli or Salmonella spp.) are present. Some farmers look for a higher fungi to bacteria ratio with certain products and use a microbiometer as a handy (but less accurate) at-home check. 
  • Salt/sodium levels: Monitor some bulk products, like compost, manures and biosolids, to ensure that plant growth-limiting salt concentrations don’t build up in the soil. These are commonly monitored via the electrical conductivity (EC) results on a soil sample or product analysis.
  • Carbon:nitrogen (C:N) ratio: Understanding the C:N ratio is especially important for bulk amendments like composts because the amount of carbon and nitrogen present in applications may have a strong impact on how the soil and the fertiliser will interact. The ideal C:N ratio is generally considered to be around 25–30:1 by weight.¹²Agriculture Victoria, Compost and farm biosecurity [website], 2024, accessed 29 November 2024.  

Contaminants

Checking for contaminants is especially important if using recycled organic materials from waste streams as feedstock for composts or other products. Many of the laboratories that test soil samples also test compost quality. Give labs a call to discuss what services they offer and how to sample. 

Possible contaminants to look out for: 

• Plastic, glass and metal: There shouldn’t be any visible plastics, glass or metal in the product. Microplastic contamination is also a consideration. If you’re concerned about microplastics, many labs offer microplastic testing.
• Weed seeds: Organic materials like compost need to reach 55°C degrees for a number of days to destroy weed seeds.¹³AC Grundy, JM Green and M Lennartsson, ‘The effect of temperature on the viability of weed seeds in compost’, Compost Science & Utilization, 1998, 6(3):26–33, doi:10.1080/1065657X.1998.10701928. One quick-test is spreading a small amount of compost out (away from your paddocks) and watering it over a few weeks to see if anything germinates.
• PFAS and other chemical contaminants: PFAS is a group of synthetic ‘forever’ chemicals that don’t break down and are ecologically damaging. Talk to your compost/recycled organics provider about how they monitor for PFAS and other chemical contaminants.
• Heavy metals: Heavy metals (e.g. lead, cadmium and arsenic) are important to keep out of your paddocks. Biosolids/sewage is known to be a potential source of heavy metal contaminants. Lab tests are the main way to assess if the product is over the maximum acceptable levels of heavy metal contaminants.
• Biosecurity risks of pests and diseases: Consider consulting your farm’s biosecurity plan when making decisions about bringing in materials and products. Because biological inputs are often microbially active, there is a risk of microbial pathogens and diseases, especially if animal wastes are used as feedstock for compost. Ask about the origin of feedstock ingredients and how pest and disease risks are being managed.¹⁴Agriculture Victoria, Compost and farm biosecurity [website], 2024, accessed 29 November 2024.

Composting is the process of using microbes to break down organic materials like food wastes, straw, manures and wood chips to form a nutrient and microbially-rich biological fertiliser and soil conditioner. Bulk compost is a loose product that can be purchased or produced on a farm. Granulated compost is a pelletised version and is usually purchased from a supplier. 

There are many different ways to compost and this guide doesn’t attempt to provide a comprehensive summary of all of them. Instead, it provides a few general principles for common ‘hot’ composting methods and then focuses on how the case study farmers have approached sourcing and using compost in their unique context. 

Equipment: Making compost at scale often requires loaders capable of moving and mixing bulk products. Compost turners/aerators are specialised tractor attachments that can make turning windrows of compost easier.

Image 6. A compost aerator which is usually pulled by a tractor working a windrow of compost. This aerator is the one used by Rhonda and Bill Daly on their farm near Young NSW. Source: Soils for Life.

Ingredients: When making compost, you’re generally aiming for a mix of carbon-rich (e.g. straw or woody materials) and nitrogen-rich (e.g. manures and food waste) materials. A rule of thumb is to have a C:N ratio of 30:1 to start the composting process, which should end up at around 20–15:1 when the compost is mature.²⁰New South Wales Department of Primary Industries, How to Compost on Farm [website], 2021, accessed 2 March 2025. The nutrient content of composts depends on what feedstock materials were used and how it was made. The quality of compost is closely linked to how stable and mature (well-composted) it is.²¹K Azim et al., Composting parameters and compost quality: a literature review’, Organic Agriculture, 2017, 8:141-158. doi:10.1007/s13165-017-0180-z. Immature composts may actually contain compounds that prevent plant growth, so it’s important to know that you’re using mature compost. A mature compost should have an earthy smell and have a moisture content of around 50%, at which point it will feel spongy but no moisture is released when a handful is squeezed between your fingers.

Application: One of the major challenges with compost use in cropping is the application, which often requires specific machinery able to handle a loose product, like spreaders or trucks with belt conveyors. If you’re buying bulk compost you can purchase it in pelletised or granulated form to make it easier to get onto paddocks with existing farm equipment on a broadacre scale. 

Subsoil applications of compost have also been investigated in Australia, with some great results for soil health and yield, especially deeper and stronger crop root growth.²²B Grant, ‘Sub-soil amelioration using composts in cropping and grazing systems in Victoria’, Federation University Future Regions Research Center, accessed 1 March 2025. Subsoil application requires modified deep ripping equipment, noting that the benefits of this type of application need to be balanced against the negative impacts on soil structure caused by this type of disturbance.

Compost extracts are often used in systems or equipment suited to liquid rather than bulk applications. Compost extracts are usually classified as a biostimulant because they are applied at relatively diluted rates with the goal of stimulating plant growth rather than delivering a bulk increase in nutrients. Compost extracts are made by thoroughly mixing compost with water. Microbes and soluble nutrients are extracted from the bulk product into the water and then can be applied in a liquid form. Compost teas are a different type of product made by ‘brewing’ compost for a longer period in continually aerated water.

Equipment: Making compost extracts require: (1) tanks and equipment capable of agitating the water; (2) mixing the compost and water together or suspending the compost in the water; and (3) filtering the final product to ensure that the liquid doesn’t block up application equipment.

Ingredients: Compost extract is generally made with loose, mature compost and clean water. The better the quality of compost, the better the extract will be. Compost can be bought or made (see the Bulk and granulated compost section of this guide for details).

Application: Compost extracts are often applied as liquid ground drenches or through a liquid inject system at planting. Extracts can also be applied as a foliar application to the crop foliage to support in-season plant and grain growth. Compost extracts are variable depending on how they are mixed and the feedstock product that is used, so it’s challenging to recommend any specific rates. Keep an eye out for blockages of any unfiltered coarse material during application.

Biofertilisers are fermented liquid products containing micro and macronutrients and beneficial microbes dissolved in water. They can be purchased, but are generally much more cost-effective if made on farm. Ideally, biofertilisers are tailored to the crop’s specific needs at the time of application, which can be easier when they are produced on farm.

Equipment: The equipment used to brew biofertilisers will depend on the process or recipe, quantity and ingredients. Many farmers start small with a 200-litre barrel or 1,000-litre shuttle and invest in large tanks as they refine their processes. 

Key considerations for equipment:

• Cleanliness: Make sure you’re able to clean and sanitise equipment before and after use. Some farmers use hydrogen peroxide to sanitise their tanks. 
• Logistics: Consider the practicalities of adding and mixing ingredients and transporting your ferment to be used in the sprayer or liquid inject. 
• Non-corrosive equipment: Use plastic or stainless steel as fermentation creates an acidic product.
• Temperature control: Ensure your ingredients and ferment are brewed and stored at the right temperature (under shelter and not exposed to sunlight in most cases).
• Sieves: Consider sourcing a sieve to filter the final product before application to minimise blockages in your equipment.

Ingredients: According to agroecologist David Hardwick from Soil Land Food, there are several key ingredients required for a biofertiliser. 

• Microbes/starter or base culture: Microbes can be cultured on farm or purchased (e.g. kefir from the supermarket).
• Energy: Microbes need to be fed simple carbohydrates. Most farmers will look for low-cost sources of carbohydrate like molasses and sugar.
• Nutrients: Micro and macronutrients can be sourced from traditional fertiliser and mineral products, plant or animal biomass, seaweed and nutritional yeast. Nutrients should be selected based on deficiencies or limitations indicated by soil and plant test results or observations.
• Water: Clean rainwater is preferable.

Fermentation process: There are many different biofertiliser recipes and methods to be found online. This is an example of a general process for fermenting biofertilisers. See below for an example of how the Fitzpatricks apply this process.

1. Brew a starter
2. Mix the starter with the other ingredients
3. Ferment
4. Monitor until mature
5. Apply.

Application: Biofertilisers are often applied during the growing season as a foliar application or at sowing in a liquid inject system. Rates and timing of application can vary widely, and many farmers are still experimenting with what works best in different situations. Deciding when to apply biofertilisers and at what rates should be informed by any deficiencies or limitations you’ve identified through observation and soil and plant tests. For example, a biofertiliser product might be applied at the first sign of a pest or pathogen.

Below is a list of some of other common biological inputs and fertilisers, including descriptions of each and how they might work in a cropping system.

Biochar is created in a process where organic materials like wood, manures, straw, biosolids and other feedstock are burnt at high temperatures in a low-oxygen environment (called pyrolysis).²⁶S Joseph et al., ‘How biochar works, and when it doesn’t: A review of mechanisms controlling soil and plant responses to biochar’, Gcb Bioenergy, 2021, 13(11):1731–1764, doi:10.1111/gcbb.12885. This process produces a charcoal-like material full of pores, stabilising the carbon in the feedstock. Especially when matured through composting, biochar can help increase soil microbial activity, pH, water and nutrient retention and soil carbon storage.²⁷ S Joseph et al., ‘Microstructural and associated chemical changes during the composting of a high temperature biochar: Mechanisms for nitrate, phosphate and other nutrient retention and release’, Science of the Total Environment, 2018, 618:1210–1223, doi:10.1016/j.scitotenv.2017.09.200; S Joseph et al., ‘How biochar works, and when it doesn’t: A review of mechanisms controlling soil and plant responses to biochar’, Gcb Bioenergy, 2021, 13(11):1731–1764, doi:10.1111/gcbb.12885. It’s important to take care with application rates, as very high rates can have negative effects on plant growth and soil function.

Biochar is often applied in a broadacre setting in a mix with other inputs, for example, as a coating on mineral fertilisers or as an ingredient in compost. In its powdered form, it can be applied as a loose product if you have the right equipment. Consider using biochar for its ability to improve soil health, particularly structure and water retention over time, and its contribution to long-term productivity and sustainability on your farm.

Humic and fulvic acids are formed when plant and animal materials break down.²⁸G Lyons and Y Genc, ‘Commercial humates in agriculture: real substance or smoke and mirrors?’, Agronomy, 2016, 6(4):50, doi:10.3390/agronomy6040050. Most commercial humic and fulvic acid products are made from brown coal.²⁹LP Canellas et al., ‘Humic and fulvic acids as biostimulants in horticulture’, Scientia Horticulturae, 2015, 196:15–27, doi:10.1016/j.scienta.2015.09.013. Note that this reference is from a horticulture research. These organic acids can have a biostimulant effect and can promote plant growth. They can be applied directly on the soil or as a foliar spray; generally, humic acids are used for soil applications and fulvic acid products for foliar applications. Humic and fulvic acids are believed to increase nutrient-use efficiency when applied alongside other fertilisers,³⁰MT Rose et al., ‘A meta-analysis and review of plant-growth response to humic substances: practical implications for agriculture’, Advances in Agronomy, 2014, 124:37–89, doi:10.1016/b978-0-12-800138-7.00002-4. and are also being used to buffer chemicals, improving their efficiency and reducing their negative impacts on soil biology. Some farmers are seeing good results from using 5% humic granules with their urea, MAP (monoammonium phosphate) and DAP (diammonium phosphate) applications.

Seaweed extracts also have a biostimulant effect on plant growth and are known to be especially helpful for improving crop resilience to drought and other stressful conditions.³¹MT Rose et al., ‘A meta-analysis and review of plant-growth response to humic substances: practical implications for agriculture’, Advances in Agronomy, 2014, 124:37–89, doi:10.1016/b978-0-12-800138-7.00002-4; MTI Mattner et al., ‘Applications of seaweed extracts in agriculture: An Australian perspective’, Journal of Applied Phycology, 2024, 36(2):713-726. doi:10.1007/s10811-023-03120-x. Seaweed extracts are thought to prime plant growth and defense mechanisms. Because seaweed extracts are usually liquid products, many of the farmers that use them find them to be a practical way to enhance plant health and stress tolerance while applying other liquid soil or foliar nutrients.

Manures (granulated and bulk) can provide a steady, long-term release of nutrients and improve soil organic matter, making them a useful choice for building soil health while also helping to reduce the need for other nutrient applications.³²Grains Research and Development Corporation, ‘Chicken Litter as Fertiliser for Broadacre Grain Crops’, 2015, accessed 21 October 2024. Nutrient levels vary depending on the animal, so consider getting the manure product analysed to get a clear idea of what nutrients are being applied.³³B Hughes, ‘Alternative Fertilisers and Soil Amendments’, Government of South Australia, Natural Resources South East, 2012, accessed 21 October 2024. Transporting and applying bulk manures, especially in no-till systems, can be challenging. Granular or pelletised manure products that can be applied in the similar way to granular fertilisers can help overcome this.

Vermiproducts are sourced from earthworm composting. Vermiproducts contain nutrients, microbes and plant growth-promoting substances, such as plant hormones and humic acids, and tend to be used on farms as a way to stimulate and boost soil and plant microbes.³⁴M Blouin et al., ‘Vermicompost significantly affects plant growth. A meta-analysis’, Agronomy for Sustainable Development, 2019, 39:1–15, doi:10.1007/s13593-019-0579-x; AM Yatoo et al., ‘Sustainable management of diseases and pests in crops by vermicompost and vermicompost tea. A review’, Agronomy for Sustainable Development, 2021, 41(1):7, doi:10.1007/s13593-020-00657-w. They are also thought to be especially useful in the suppression of some plant and soil pathogens.³⁵ AM Yatoo et al., ‘Sustainable management of diseases and pests in crops by vermicompost and vermicompost tea. A review’, Agronomy for Sustainable Development, 2021, 41(1):7, doi:10.1007/s13593-020-00657-w. At scale, it is more common to use liquids made from washing water through a worm composting system or an extract made from worm castings once they’ve been removed from the worm composting system. Vermiliquids tend to be applied as a ground drench, in a liquid inject system, or as a foliar application. 

Microbial inoculants containing specific bacteria or fungi are sometimes applied as biocontrol for pests and diseases or to support soil and plant functions like nutrient uptake. Microbial inoculants tend to be applied as foliar applications onto plant leaves. Be aware of pressure in hoses and nozzles when applying microbial inoculants, as too much pressure can impact the microbes. The Haggertys try to keep hose pressure lower than 2 bar and use large nozzles to avoid damage to any living microbes during the application process.

Protein hydrolysates are derived from the proteins in animal and plant materials (e.g. soy, corn, fish, bone or feather meal). The proteins are are mixed with water and broken down by enzymes, resulting in a liquid product that contains amino acids and other compounds. These tend to be emerging products on the market, some with specific amino acids blends. Some farmers are starting to experiment with using these as plant biostimulants and non-synthetic nitrogen sources. As liquid products, protein hydrolysates tend to be applied as a ground drench, in a liquid inject system, or as a foliar application.