Agriculture’s problem child: rethinking the management and application of fertiliser

Interventions like applying fertiliser at different times can create win-win situations for both farmers and the environment.

Fertiliser is agriculture's problem child.

On the one hand, synthetic, nitrogen-based fertilisers are hugely important to increasing crop yields and securing the global food supply. It would be no exaggeration to say they revolutionised food production in the 20th century. On the other hand, the same nitrogen-based fertilisers represent an enormous threat to the integrity of our ecosystems. They not only emit nitrous oxide – a gas 300 times more powerful than carbon dioxide in terms of global warming potential – but also seriously damage soil health, pollute water systems, and put biodiversity at risk in their current quantities. According to the IPCC, the usage of synthetic fertilisers has gone up by an enormous 800% since 1960. That increase has left a huge footprint: the synthetic fertiliser supply chain was responsible for around 2.1% of emissions globally in 2018.

If you're a company in the forest, land use and agriculture (FLAG) sector, your decarbonisation journey must encompass accounting for your land management emissions, and fertiliser usage will play a critical part in this. The release of the Science Based Targets initiative's (SBTi) FLAG guidance earlier this year provided all companies with direct or indirect links to land-intensive activities with clear recommendations on the FLAG targets they need to set to achieve emission reductions in line with the goals of the 2015 Paris Agreement. You can't manage what you can't measure, so to reduce FLAG emissions, the first steps are to proactively:

• Understand fertiliser use in the supply chain: Identify your key supplier locations (smallholders or plantations) and work with farmers to obtain primary farm-level data, and understand current farm practices and any other biological factors that affect the emissions for specific commodities and regions.

• Estimate emission reduction potential: Once you have a picture of current practices, you can start identifying commodity- and location-specific interventions related to fertiliser which can reduce emissions and create climate-resilient farms. This might involve a new fertiliser regime that improves the efficiency of nitrogen-based fertiliser applications.

• Engage farmers: Working with farmers to obtain farm-level data goes hand in hand with providing advice to them on sustainable fertiliser usage practices. Stakeholder engagement and training exercises are an effective way to share knowledge, understand on-the-ground challenges, and collaborate on identifying location-specific farm-level interventions. You might also help farmers gain access to the financial tools needed for the implementation of interventions.

• Provide implementation support: Developing partnerships with farmers, government bodies, and other supply chain actors increases everyone's chances of success in delivering farm-level interventions. The benefits will create shared value for a variety of players in the value chain by lowering emissions, ensuring financial stability, contributing to climate targets, and creating a resilient ecosystem which is protected against climate risks.

But what do better fertiliser management and production practices actually look like? Interventions that satisfy crop productivity goals while also making meaningful cuts to greenhouse gas emissions all focus on being more precise about fertiliser application. It's a question of making sure fertiliser is applied in the right quantity, at the right time, and at the right rate. Supporting agricultural producers with developing a balanced and custom fertiliser regime for different crops and regions is also crucial, as is pursuing conservation practices to improve soil health.

• Efficiency is the name of the game: Excessive and inefficient fertiliser application not only leads to increased emissions, it can also cause pollution, leading to toxicity in organisms, oxygen depletion in aquatic ecosystems, and soil and water acidification, all of which can impact biodiversity. A high-impact intervention is therefore to improve nitrogen use efficiency, applying the fertiliser so that a higher proportion of it is taken up by the crops and less escapes as nitrous oxide via direct and indirect biological processes. Applying the majority of fertiliser a few weeks after, instead of at the point of, or before, planting can reduce the amount of fertiliser lost to leakage. This creates a win-win situation for both the farmer and the environment, increasing yield and profitability while decreasing the nitrogen surplus in the soil that may be lost as emissions and leaching. The Nutrient Stewardship provides a 4R framework to support these efforts, defining the best management practices to match nutrient supply with crop requirements.

• Driving innovation in nitrogen products: Improvements in nitrogen efficiency can also take place at the level of the nitrogen-based fertiliser itself. Products such as urease and nitrification inhibitors are compounds that increase the time that the active nitrogen component remains in the soil, meaning that less fertiliser needs to be applied overall. Initial research and pilot projects suggest that these interventions can reduce nitrous oxide emissions by up to 40%-60%, although their efficacy is dependent on factors such as soil type, temperature, soil water content, and the amount of inhibitor applied. Slow-release or controlled-release fertilisers represent another opportunity for emission reduction potential as they release a gradual and steady stream of nutrients over time instead of releasing them too quickly for crops to absorb all of it.

• Practising no-till agriculture: This is a sure-fire way to improve soil health by diminishing soil erosion, increasing soil organic matter, and recycling crop residues, thus reducing the fertiliser needed to meet the crops' nutrient requirements. One study shows this intervention has the potential to reduce nitrous oxide emissions by up to 50%-60% (although more data is needed to understand the optimum conditions for creating emission reductions). Planting cover crops, similarly, can have multiple co-benefits. In addition to protecting soil from wind and water erosion, these crops serve as sink for plant nutrients that could otherwise be lost to volatilisation. They can also act as a source of supplementary nitrogen (e.g. legumes) and slow-release nutrients, again reducing the amount of fertiliser required.

• Go organic? In organic fertilisers, the nitrogen is released much more slowly into the soil, again leading to efficiency gains. This fertiliser also has a much lower production-related carbon footprint compared to its synthetic counterpart, although it is not yet clear whether the emissions profile of each fertiliser is significantly different (it may be dependent on local factors such as crop, soil type, and agronomical conditions). A 2020 review which attempted to quantify the emissions from both organic and inorganic fertiliser use found a very high variability in emissions intensities and cautioned that emissions should be calculated on a case-by-case basis where possible. Elsewhere, research comparing urea and organic fertiliser shows that the use of organic fertiliser will produce higher indirect nitrous oxide emissions, but overall lower greenhouse gases. Instead of a simple switch, farmers should therefore develop a balanced fertiliser regime that uses a combination of organic and synthetic fertiliser to improve soil quality, increase crop yield, and reduce greenhouse gas emissions.

Agriculture is one of the most difficult sectors to decarbonise and the key to reducing its footprint undoubtedly lies in the more efficient, sustainable application of fertiliser, especially given the estimated increase in global usage by over 50% by 2050. There is no silver bullet that will solve the challenge of producing more food for a larger global population at a lower environmental impact… yet collaboration between farmers and FLAG-sector companies can drive meaningful reductions today and speed progress towards a net zero future.