Overuse of nitrogen fertilizers—a frequent phenomenon in agriculture—results in the production of nitrous oxide, a potent greenhouse gas. More judicious use of fertilizers can curb these emissions and reduce energy-intensive fertilizer production.
Reducing fertilizer overuse on 373.98–750.52 million hectares of farmland by 2050—up from an estimated 139 million hectares currently—could avoid nitrous oxide emissions equal to 2.77–11.48 gigatons of carbon dioxide. No investment is required, and farmers could save $22.82–63.84 billion from reduced fertilizer costs. Our analysis assumes adoption that roughly parallels conservation agriculture, as farmers are likely to be amenable to both practices.
Nitrogen fertilizers have vastly improved the productivity of agriculture in the past century. Some is taken up by crops, increasing growth and yield. The nitrogen that plants don’t use, however, destroys organic matter in the soil, pollutes waterways, and contributes to climate change as bacteria convert it into nitrous oxide, a potent greenhouse gas.
Farmers can reduce the risk of these harms by matching fertilizer choices with plant needs, applying when and where needed, and not applying in excess. And, because fertilizer production takes a lot of energy and produces a lot of carbon dioxide, reducing fertilizer application will also abate emissions associated with its production.
Project Drawdown defines the Nutrient Management solution as fertilizer application practices that use right source, right rate, right time and right placement principles. These principles are important for both countries where fertilizer consumption is high and nitrogen use efficiency low (e.g., US, China) and those where crops need increases in nutrient inputs (e.g., sub-Saharan Africa).
Education, assistance, incentives, and regulation can accelerate adoption. The true solution to nutrient management, however, is the use of land management practices that eliminate most, if not all, need for synthetic nitrogen.
Total Land Area
To evaluate the extent to which a Food, Agriculture, and Land Use sector solution can reduce greenhouse gas emissions and sequester carbon, we need to identify the total land area available for that solution in millions of hectares. To avoid double counting, we use an integration model that allocates land area among all Food, Agriculture, and Land Use sector solutions. This involves two steps. First, we classify the global land area into agro-ecological zones (AEZs) based on the land cover, soil quality and slope and assign AEZs to different thermal moisture regimes. We then classify the AEZs into “degraded” and “nondegraded.” Finally, we allocate the solutions to AEZs, with the solution most suited to a given AEZ or sets of AEZs assigned first, followed by the second-most-suited solution, and so on. Because it’s hard to predict future changes, we assume the total land area remains constant.
Total available land for nutrient management is 1,411 million hectares (essentially all annual and perennial cropland). We estimated current adoption (defined as the amount of functional demand supplied in 2018) at 139.1 million hectares. In the absence of data on current adoption of nutrient management, this figure is based on current adoption for conservation agriculture and areas that achieved 70 percent of nutrient efficiency.
Future adoption projections for nutrient management used the same scenarios as those for Conservation Agriculture, along with regional and country-level nitrogen-use efficiency estimates. We calculated impacts of increased adoption of nutrient management from 2020 to 2050 by comparing two growth scenarios with a reference scenario in which the market share was fixed at current levels.
- Scenario 1: Adoption reaches 373.98 million hectares (27 percent of the total available land area).
- Scenario 2: Adoption reaches 750.52 million hectares (53 percent of the total available land area).
Emissions reduction was 0.49 metric tons of carbon dioxide per hectare per year (based on 20 data points from 14 sources) and 0.44 metric tons of nitrous oxide carbon dioxide equivalent per hectare per year (based on 65 data points from 17 sources).
All monetary values are presented in 2014 US$.
The net first cost of nutrient management was $0 per hectare because reducing the over-application of fertilizer costs farmers nothing. Operational cost was US$19.86 per hectare per year (savings in fertilizer cost), compare with the operational cost of US$23.06 per hectare per year for the conventional practice, based on five regional data points from the Food and Agriculture Organization (FAO)’s Statistical Service (2017).
Drawdown’s Agro-Ecological Zone model allocates current and projected adoption of solutions to the planet’s forest, grassland, rain-fed cropland, and irrigated cropland. All cropland is suitable for nutrient management, and nutrient management can occur on land with other solutions (e.g., Conservation Agriculture) implemented because the reduced emissions operate independently from biosequestration and other Food, Agriculture, and Land Use sector solutions.
Scenario 1 saves 2.77 gigatons of carbon dioxide equivalent emissions by 2050. The net first cost is US$0, and the lifetime net operational savings are US$22.82 billion.
Scenario 2 saves 11.48 gigatons of carbon dioxide equivalent emissions by 2050. The net cost is US$0, and the lifetime net operational savings are US$63.84 billion.
The Intergovernmental Panel on Climate Change (IPCC) reports that the emissions reduction from all agricultural nitrous oxide (including fertilizers, manure, and other sources) is projected to be 0.9 to 1.84 million metric tons of carbon dioxide equivalent per year by 2030 (Smith, 2007). Griscom et al. (2017) show 0.63–0.71 gigatons of carbon dioxide equivalent saved per year in 2030, based on a higher percentage reduction of fertilizer use than we used. Though this is not a precise benchmark, our model calculates 0.01–0.33 gigatons of carbon dioxide equivalent per year in 2030 from nitrogen fertilizer alone, not including manure and other nitrous oxide sources.
This study could be improved should better data on current adoption of nutrient management become available.
This solution should be adopted regardless of its mitigation impact because it saves farmers money and reduces water pollution. That it reduces emissions of a powerful greenhouse gas, and emissions associated with producing that gas, makes it a clear win-win.
FAOSTAT (2017). Fertilizers By Nutrient [Data set]. Food and Agriculture Organization.
Griscolm, B. W., Adams, J., Ellis, P. W., Lomax, G., Miteva, D. A., Schlesinger, W. H., Shock, D., Siikamäki, J. V., Smith, P., Woodbury, P., Zganjar, C., Blackman, A., Campari, J., Conant, R. T., Delgado, C., Elias, P., Gopalakrishna, T., Hamsik, M. R., Herrero, M., Kiesecker, J., Landis, E., Laestadius, L., Leavitt, S. M., Minnemeyer, S., Polasky, S., Potapov, P., Putz, F. E., Sanderman, G., Silvius, M., Wollenberg, E., Fargione, J. (2017). Natural Cliamte Solutions. Proceedings of the National Academy of Sciences, 114(44) 11645-11650. DOI: 10.1073/pnas.1710465114
Smith, P., Martino, D., Cai, Z., Gwary, D., Janzen, H., Kumar, P., McCarl, B., Ogle, S., O’Mara, F., Rice, C., Scholes, B., Sirotenko, O, Howden, M., McAllister, T., Pan, G., Romanenkov, V., Schneider, U., Towprayoon, S., Wattenbach, M., Smith, J. (2008). Greenhouse gas mitigation in agriculture. Philosophical Transactions of the Royal Society B: Biological Sciences, 363 (1492) pp 789-813. DOI: 10.1098/rstb.2007.2184