As land resources come under more and more pressure — to grow food, support cities and house valuable ecosystems — scientists, activists and others are on the hunt for better ways to manage the terrestrial biosphere. One strategy is to increase the efficiency of croplands and pasture lands, particularly in ecosystems such as the Amazon forest where converting more land to agricultural use is environmentally costly.
As the world’s largest contiguous tropical forest, Amazonia is an important store of carbon, provides habitat for biodiverse communities and plays a part in regulating the global water cycle.
Moreover, the Amazon is a prime candidate for exploring whether increasing efficiency can help make agricultural land use more sustainable. Recently, David Lapola of Universidade Estadual Paulista and colleagues pointed out in the journal Nature Climate Change that agriculture in Brazil, including Amazonia, is intensifying and becoming more dominated by commodity production, leading to systematic changes in land use. This intensification has been accompanied by lower rates of deforestation.
There are open questions, however, about how these intense cropping systems will affect the environment. Here in the U.S. and in Minnesota, we associate high-yield farms with water pollution, runoff and declining soil fertility. Will the same environmental impacts manifest when we put an intensified cropland farm into the Amazon?
In my position with the Institute on the Environment’s Global Landscapes Initiative, I’m working with colleagues around the world to try and answer this and other questions via a field study in Mato Grosso, Brazil. Since 2012, we have been measuring how the nitrogen cycle has been altered as a result of cropland intensification; whether emissions of nitrous oxide, a powerful greenhouse gas emitted from soils, have gone up or down as nitrogen fertilizer use becomes common; how soil nitrogen availability has changed; and if more nitrogen is running off into streams or moving through the soil column into groundwater. These effects — nitrous oxide emissions and nitrogen runoff into the freshwater system — may accompany improved cropland efficiency in the region. If it does, it could change how we assess sustainability on tropical croplands.
Our pursuit of data that can help us investigate sustainability on Amazonian cropland has brought us to a large industrialized farm in Mato Grosso. Working with local research partner Instituto de Pesquisa Ambiental da Amazonia and colleagues at Centro de Energia Nuclear na Agricultura – Universidade de São Paulo, Woods Hole Research Center, the Marine Biological Laboratory and the University of Vermont, we have taken greenhouse gas, soil and water measurements for the last year in primary Amazon forest on the farm’s property and on intensified croplands that are planted twice a year — once with soybeans, a nitrogen-fixing crop, and once with corn, which receives nitrogen fertilizer. As on many large, intensified farms, both crops are also treated with pesticides, herbicides, phosphorus, potassium, micronutrients and lime to manage the acidic soils common in tropical forests.
Field research is my favorite way to engage with science. Having boots on the ground gets me thinking more creatively and puts small but potentially crucial details into my line of sight. Rainstorms can be so patchy that they affect one field but not another one directly next to it. How much light is available in these forests, and what might that mean for how plants below the canopy use nutrients? Does it matter to the nitrogen cycle that wild tapirs might leave the forest to forage in these soybean fields? These are observations or questions that wouldn’t have occurred to me had I not been tromping around this landscape collecting data in croplands and their adjacent primary forests.
When it comes to the environmental impacts of intensified — and efficient — Amazonian croplands, the verdict is still out. But exploring those impacts is exciting because it allows us to learn more about the nitrogen cycle in the context of an actively changing socio-environmental context. The agricultural frontier of the eastern Amazon is a dynamic system that on first glance is following the trajectory of the intensification of American farms — but in fact is forging its own path to land use efficiency. The ecological and farming conditions are different and we hypothesize that the environmental impacts will also be different. Just how different remains to be seen.
Banner photo: Christine S. O’Connell. Intensified croplands that grow commodities such as soybeans and maize are becoming more common in the eastern Amazon; here, primary Amazon forest exists meters away from high-productivity agricultural fields.
Christine O’Connell is a doctoral student in the Department of Ecology, Evolution and Behavior and a research fellow with the Global Landscapes Initiative. She uses ecosystem ecology to ask questions about tropical ecosystems on a changing planet when not riding her bike or scrambling around outside.