About This Project

The environmental costs of fertilizer use in the tropics are understudied. Mato Grosso, Brazil, once an Amazon deforestation hot spot, is expanding Nitrogen fertilizer use for maize production. Fertilizer use can cause NO gas loss (which drives smog and ozone production), and release N2O (a potent greenhouse gas). We will measure these gases at a large commercial farm in Mato Grosso to inform policy in the Amazon region and tropical agriculture.

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What is the context of this research?

Meeting the growing demand for food and livestock feed will require tropical regions to intensify agricultural production. However, the environmental costs of agricultural intensification in the tropics are understudied. Within the tropics, one of the most crucial agricultural regions is Mato Grosso, Brazil. Once an Amazon deforestation hotspot, Mato Grosso now contains a rapidly intensifying agricultural landscape covering ~100,000 km² (about the size of Kentucky) and is now the world’s second-largest soy producer. Mato Grosso is shifting from single-cropping of soy, a nitrogen (N)-fixing legume, to double-cropping of soy and maize, which requires N fertilizer inputs to highly-weathered tropical soil.

What is the significance of this project?

Nitrogen fertilizer is often necessary to maintain yields, but it can cause significant environmental problems. For example, nitric oxide (NO) gas loss has significant negative consequences for human health and plant productivity (it drives smog and ozone production), and nitrous oxide (N2O) is a potent greenhouse gas (GHG). To date, researchers have measured N2O but not NO emissions from this agricultural region. Measured N2O emissions are much lower than what we would expect given the fertilization inputs. A study from a different tropical, fertilized agriculture site with a similar soil (but in Kenya) found higher NO than N2O emissions, suggesting that measurements of this smog- and ozone-producing gas at Mato Grosso would be highly informative.

What are the goals of the project?

I aim to answer the following questions: How do N2O and NO emissions vary between three land uses (soy, maize, and intact tropical forest)? What impact does irrigation have on N2O and NO emissions in maize fields?

Hypotheses: (H1) N2O and NO emissions will be higher in fertilized maize than in tropical forest and unfertilized soy because of a higher N cycling rate from fertilizer inputs. (H2) Irrigation of fertilized maize will shift N emissions from primarily NO to primarily N2O, lowering oxygen level in soil pores compared to non-irrigated, fertilized maize.