Fertilizer use and emissions in agriculture
Agriculture is a significant emitter of greenhouse gases, but agricultural soils are also an important carbon sink. Emissions of greenhouse gases are mostly related to the following activities:
CO2 emissions: CO2 from the applied urea and ABC, land conversion to cropping, use of agricultural machinery, livestock production;
N2O emissions: Use of nitrogen fertilizers, manures and nitrogen-fixing legumes, as well as microbial conversion of other nitrogen sources in agricultural soils;
Methane (CH4) emissions: Livestock and irrigated rice production.
With regard to climate change, inappropriate nitrogen management may increase the atmospheric concentration of N2O, a greenhouse gas considered 296 times more potent than CO2. The Intergovernmental Panel on Climate Change (IPCC) estimates all N2O emissions from soils at some 2.1 Pg CO2-eq per year (of which about 605 Tg CO2-eq per year related to mineral fertilizer use). (Smith et al. 2007).
It is important to manage all sources of agricultural nitrogen in an integrated manner because the nitrogen from manure and nitrogen-fixing legumes also contributes to N2O emissions. Reduction of N2O losses should not result in increased losses of other N compounds (e.g. NH3 , NO3-) to the environment.
The conversion of forest or natural land to cropping results in an estimated 5.9 Pg CO2-eq emissions annually. This is nearly three times the annual N2O emissions from soil, underscoring the importance of preventing land conversion from forests to crops.
When managed properly, fertilizer use fosters carbon capture
To obtain a more complete idea of the greenhouse gas emissions performance of the fertilizer industry throughout its products’ life cycles, it is important to weigh emissions against the energy and carbon capture that fertilizer use promotes. When fertilizers are used properly, they help plants to produce more energy than is consumed during the production, transport and application of fertilizers. They also encourage the conversion of carbon dioxide to biomass through photosynthesis, although the length of time during which the carbon is bound will depend on whether the biomass is used immediately, ploughed into the soil, part of a perennial plant or used for bioenergy/biomaterials.
Using Fertilizer Best Management Practices (FBMPs) to improve agricultural GHG balances
The IPCC has identified three ways to make agriculture’s overall carbon balance more positive. Appropriate fertilizer use can contribute to all three.
- Reducing emissions of greenhouse gases
Agricultural releases of CO2 , N2O and methane (CH4) can be reduced through better management of carbon and nitrogen flows in agricultural ecosystems. Improving nutrient use efficiency is key to achieve these reductions. The fertilizer industry promotes Fertilizer Best Management Practices (FBMPs) in many countries to help farmers reduce emissions from fertilizer use. In Canada, the industry is working with government officials to develop a protocol through which improved fertilizer management can be translated into carbon credits for farmers.
- Enhancing CO2 removals from the atmosphere
The net flux of CO2 between agricultural land and the atmosphere is currently estimated to be more or less in balance, with net CO2 emissions at around 40 Tg CO2 per year (IPCC 2007). Concerning future mitigation, the IPCC estimates that some 89% of agriculture’s future mitigation potential is based on soil carbon sequestration, 9% on reducing CH4 emissions, and only 2% on reducing N2O emissions from soils (UNFCCC 2008). Judicious fertilizer use helps increase cultivated soil carbon reserves by increasing the photosynthetic conversion of CO2 to biomass that is subsequently converted, in part, to soil organic carbon. The potential gain could be very large in the case of degraded soils, as in much of Sub-Saharan Africa, with positive knock-on effects for other sustainable development priorities, including land rehabilitation, food security and, ultimately, poverty alleviation.
- Avoiding (or displacing) emissions
There are two techniques for avoiding emissions. The first is to increase productivity and thus prevent conversion of additional land to cropping and the significant emissions that result. The second consists of using agricultural products as bioenergy sources or as raw materials for industrial processes that would otherwise use fossil fuels as feedstock.
“An effective way to reduce emissions associated with the conversion of land to agriculture is by intensifying agriculture, that is, producing more crops on land already in production” (UNFCCC 2008). In this scenario, the overall use of agricultural inputs such as fertilizers would increase, but improved management practices would make it possible for overall GHG emissions per unit of agricultural output to be lower than if the additional crops were produced on land newly brought under cultivation.
A corollary of increasing food production per area of land is the use of agricultural crops as feedstock for bioplastics, pharmaceuticals and other industrial processes. Biofuels are one of the best-known examples. The overall implications for greenhouse gas emissions will depend on knock-on effects for food production and land-use change, whether transport distances increase and several other factors.
Fertilizer Best Management Practices (FBMPs) are essential in order to minimize unwanted impacts of intensified agriculture. They also increase the resilience of agricultural systems to the expected impacts of climate change. For example, higher levels of soil organic matter (carbon) enhance the ability of soils to retain moisture.
IFA has developed a global framework for the elaboration and adoption of site- and crop-specific FBMPs that can result in lower N2O emissions during crop production, and in greater carbon sequestration in agricultural soils, among other positive outcomes.
Key resources on fertilizers and climate change
- FAO/IFA (2001) Global estimates of gaseous emissions of NH3, NO and N2O from agricultural land . Food and Agriculture Organization (FAO) of the United Nations. Rome, Italy. / International Fertilizer Industry Association. Paris, France.
- IFA (2007) Fertilizer Best Management Practices: General Principles, Strategy for their adoption and voluntary initiatives versus regulation . Paris, France.
- IFA (2007) Sustainable Management of the Nitrogen Cycle in Agriculture and Mitigation of Reactive Nitrogen Side Effects . First edition. Paris, France.
- Kongshaug, G. (1998) “ Energy Consumption and Greenhouse Gas Emissions in Fertilizer Production ”. IFA Techical Conference Marrakech, Morocco. September/October 1998.
Mosier, A.R. et al. (ed.) (2004)
Agriculture and the Nitrogen Cycle: Assessing the impacts of fertilizer use on food production and the environment
. Island Press: Washington, DC, USA.