In an era of climate change, where the likelihood and risk of wildfire is heightened, and as the human health and safety impacts of particulates and smoke are increasingly understood, it’s no wonder that many jurisdictions around the world have moved to ban crop stubble burnoff. Add to this the impact of smoke taint on other agricultural commodities such as grapes or citrus, and the lost opportunity for recovering energy from this material also, not to mention the cost to obtain permits and manage the burnoff activity itself, and the question must be asked – is it time to ban the burn? 

The harvest season is over and the fields are covered with crop stubble – what to do with it? The options for treatment or usage are varied and likewise, the associated consequences and potential trade-offs are equally varied. The options right now broadly shake out to the following:

  • Combust it in the paddock and the entire community, including farmers, have to deal with the health and environmental consequences, with limited benefit in pest, disease and weed control. Notably, research seems to indicate that soil organic carbon (SOC) declines the most during burnoff of all handling methods, with Chan et al. (2011) reporting that SOC was lost at 98 kg/ha/year using this method at a trial in Wagga Wagga.
  • Leave it all in the field and sow the next crop through it, with the benefits of ‘no till’ being good for soil structure and moisture retention, as well as reduced wind and water erosion. Stubble retention can also support an increase in the population of beneficial predator species who can mitigate the effects of unwanted insects and pests.

Nevertheless, this method has several drawbacks in that beyond a certain point, excess stubble over and above the requirements of soil microbes simply breaks down and ends up as CO2 in the atmosphere in a matter of weeks or months anyway – from a carbon perspective, it may as well have been burnt – and it can also encourage slugs and other pests, including mice, weeds etc. Benefits for nutrient retention and carbon management are somewhat ambiguous also, with the GRDC observing that “stating the nutrient content of stubble as equivalent to fertiliser inputs (Early et al. 1997) implies a complete loss of nutrient with burning of stubble, and that the nutrient retained with stubble is highly plant available, which is not the case. Nitrogen (N) and phosphorus (P) contained in stubble are slow to recycle into a plant-available form.”

  • Plough it back into the soil and the pros/cons are similar in many ways to the above, albeit this requires more mechanical processing, cost and time, noting that it does make getting the next crop out there a bit easier. Overall, the GRDC observes that “no-till and stubble retention, compared with cultivation and stubble burning has little effect on soil organic carbon in Australian temperate cropping areas, at least when average annual rainfall was about 500 mm or less”. 
  • Use it as livestock feed, which will reduce the high stubble load prior to seeding, consume residual grain from the harvest as well as allow for summer growth, including weeds. On the downside, grazing can lead to some damage to soil structure and reduced water egress into the soil due to compaction by the animals’ hooves. 
  • Harvest, bale and sell the stubble to existing markets such as animal bedding, mushroom farming etc noting this demand can be somewhat seasonal and variable, while it could lead to a nutrient, mineral or carbon deficiency on farm, with a significant residual stubble load to deal with.
  • Harvest, bale and sell the excess stubble to a biogas plant and receive beneficiated digestate as biofertilizer back on farm, with the benefits including additional, stable farm income and diversification, improved health and environmental outcomes, improved bioavailability of nutrients, increases in soil carbon and moisture management, potential for net reductions in GHG balance through displacement of natural gas usage and regional economic development (jobs, investment attraction, GDP impact etc).

Management of stubble on farms is a delicate matter and there are certainly many aspects to be considered. Retention of root stock and a small amount of ground stubble is important for soil carbon and moisture retention, and something we vigorously support, but the opportunity to better manage the vast bulk of above ground stubble for energy recovery is currently a missed opportunity at a continental scale. Clearly, it is our thesis that the final option makes sense for a whole host of reasons and for many farmers faced with a seasonal residue management headache, this offers a ‘value-adding’ pathway that is hard to ignore.

Environmental Impacts

As the world slowly but surely moves towards a net zero emissions environment by 2050 the obvious farming solution must and should include the elimination of crop stubble burning.

Each tonne of stubble burnt releases approximately 1.65 tonnes of CO2 emissions, plus other harmful gases such as carbon monoxide, methane, sulphur dioxide and nitrogen dioxide, not to mention particulates that we cannot see but nevertheless enter our lungs with every breath, potentially causing long term, irreparable harm. Likewise, smoke taint can directly impact other agricultural commodities e.g. grapes or citrus, food processing, and smoke from burnoff can create localised safety hazards by obstructing roads.  Unexpected wind direction and speed changes can make management of a burn challenging, leading to a potential threat of fire to neighbouring properties and infrastructure.

2016-17 data from the Australian Bureau of Statistics states that in excess of 1.4 million hectares of land under farming management was subjected to ‘hot burning’ of crop residues. Assuming a conservative crop residue yield of 2 tonnes per hectare, this statistic alone indicates that burning of crop residues is releasing at least 4.62 million tonnes of CO2 into our atmosphere. This is equivalent to 1% of Australia’s estimated CO2 emissions of 464 million tonnes for the 12 months ending March 2023, albeit 7.6% of that produced by the agricultural sector overall.

In reality, our own work appears to indicate that the total volume of available stubble and likely burnoff (or disposal) could actually be far higher, especially in bumper years such as those experienced in the southern grain belt over the last three years. Noting this fuel load can vary enormously with production cycles in different seasons, and from cycle to cycle, other data from ABARES indicates that between 26-61% of stubble is burnt off, depending on location, and with our own satellite-driven AI analysis predicting a volume of perhaps 7-8MT of crop stubble and waste generated across wheat, barley, oats and canola cropping within a 150 km radius of Ararat alone in Victoria during  the summer of 2023, this  potentially leaves a vast quantity of stubble available for energy recovery purposes that is otherwise literally, going up in smoke.

Health Impacts

As previously mentioned, burning crop stubble releases a multitude of harmful gases and particulates into the atmosphere. These emissions can have detrimental effects on the health and well-being of members of the surrounding community, particularly those who have respiratory problems, are elderly, young or pregnant.

While on one level, we object to the presence of a coal-fired power station in our backyard because of the harmful gas and particulate emissions that are released into the air that we breathe, why should we accept similar harmful (uncontrolled) emissions from the burning of crop stubble?

The simple answer is there are other options.

Soil Impact

What does burning off mean to the farmer? While potentially assisting with pest and disease control, burning stubble can have a detrimental impact in terms of:

  • Soil carbon loss,
  • A loss of nutrients, nitrogen, sulphur and phosphorus to the atmosphere,
  • Increased soil erosion,
  • Increased soil moisture loss, and;
  • Contribution towards acid rain formed from sulphur dioxide emissions.

Burning can therefore reduce both soil fertility and crop productivity and consequently can  impact a farmer’s income, livelihood and prosperity over the long term.

The Opportunity

Every year Australia torches a vast quantity of dry, high energy dense and valuable crop residue that could ultimately be displacing fossil fuel in the energy system. Instead, it is adding to our environmental burdens and creates an annual management headache for many farmers that represents a net cost to their operation, when it could be delivering a positive dividend to their farm, the environment and their community.

Biomethane represents a genuine opportunity for the agricultural sector to make a significant and meaningful contribution towards achieving net zero targets by 2050, which is greatly enhanced through  the elimination of crop residue burning. Furthermore, the use of what is otherwise combusted can take place without impacting on the existing uses and markets for straw.  Stubble burnoff has already been banned in many parts of the European Union, for instance, and they are arguably the leaders in straw-to-energy systems, and with good reason. 

Arguably, the EU situation is not ‘black and white’ but under Article 94 of Regulation (EU) 1306/2013 on the financing, management and monitoring of the Common Agricultural Policy, `Member States shall ensure that all agricultural area (..) is maintained in good agricultural and environmental condition´(referred to in the second extract below as GAEC), taking into account `the specific characteristics of the areas concerned, including soil and climatic condition, existing farming systems, land use, crop rotation, farming practices, and farm structures´. Annex II accordingly provides for a ban on arable stubble burning ‘to preserve soil quality’. 

 By decree of 6 January 2020, the French Government ended these exemptions. In the EU he “Common Agricultural Policy” (referred to as the CAP) requires compliance with a set of rules made up of ‘Statutory Management Requirements’ (SMRs) and ‘Good Agricultural and Environmental Conditions’ (GAECs) that must be adhered to in order to receive Common Agricultural Policy (CAP) support payments.

Like all policies it evolves and changes over time. The most recent changes covering the period 2023-2027 have the CAP seeking to align with the European Green Deal (EGD), a set of policy initiatives underpinning sustainable development and climate neutrality in the European Union. However there are challenges and misalignments between the CAP and the EGD and one such challenge relates to burn off, in that there is a “ban on burning arable stubble, except for plant health reasons” (GAEC 3). However, GAECs are not mandatory for all farmlands and for plant health reasons, exceptions are spelt out such that, “arable stubbles must not be burnt except for disease control or to eliminate plant pests”.

Overall, the point to be made is that, on balance, there is evidence to suggest that crop stubble burnoff is a practice whose time has come. More importantly, it is what such a ban would enable that excites bioenergy advocates, since it opens up a whole new feedstock resource for the sector. It allows farmers to take a leading role in climate change and Circular Economy solutions, at a meaningful scale, while delivering a whole host of regional economic, social and environmental benefits, including the delivery of low carbon gas, liquid and even solid fuel products that are important to accelerating our moves to net zero. Making this move at a regulatory level must be done with a view to assessing alternative, benign and affordable methods for weed and pest control, as well as soil moisture retention in particular, while ensuring that the overall agronomic impact of a ban is demonstrably net positive.