Report prepared by:

Monica Daane, Department of Plant Pathology and Agroecology Program, UW-Madison, mdaane@wisc.edu
Jordan DeLong, Department of Agronomy, UW-Madison, jgdelong@wisc.edu

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Scenario

A grain exporting business in the U.S. is interested in determining if soybeans grown in the U.S. are more or less sustainable compared to soybeans grown in Brazil. To analyze each system, they have hired our private sustainability consulting firm to determine which system is more sustainable. The grain company is interested in finding the most sustainable option because they can receive more money per bushel from more sustainable beans. Much of the world including the Pacific Rim countries and European countries want to eat food with a lower emission footprint. The company will incentivize growers in the country where the beans create fewer emissions. Sustainability should be focused on the agricultural production portion of the system. In essence: how does changing land use and different farming practices between the two systems affect overall sustainability and greenhouse gas emissions?

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Abstract

Soybeans are a major agricultural crop globally, used  the production of human food, livestock feed, oils, and biofuels. Increasing demand for this commodity is driving farmers to increase production, both by increasing yields and total acreage grown. The environmental impacts of rising production can be multi-fold, including increased land conversion, tillage, and synthetic fertilizer use. The environmental consequences of these production increases can be particularly significant with respect to climate change through loss of soil carbon, emission of carbon dioxide (CO₂₎ and nitrous oxide (N₂O), and embedded emissions associated with field activities and agricultural inputs. As producers of a major agricultural commodity, soybean farmers could substantially reduce the overall footprint of agriculture on climate change by optimizing practices to reduce emissions. In this report we compare soybean production practices in the top two soybean-producing nations (the U.S. and Brazil), examining the differences in greenhouse gas emissions related to production practices. We have determined that the Brazilian soybean production system is more sustainable than that of the U.S., with Brazil producing fewer emissions from cropland conversion and agricultural practices on-farm, including less carbon loss from soil, increased adoption of no-till practices, and reduced fertilizer use.

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Methods

We will be investigating the sustainability of soybean production in terms of greenhouse gas (GHG) emissions between Brazil and the United States. We will base our conclusions on differences in the production systems, focusing on emissions produced through land conversion and agricultural management practices, including tillage and fertilizer usage. We are using data from on-farm production practices only as other data useful in GHG calculations, such as transportation, are sparse and inconsistent, especially for Brazil. Data will be drawn from scholarly articles and state/federal reports, including the USDA and US EPA. The country indicating the lowest amount of GHG emissions based on predicted land use change and agricultural management practices will be deemed the most environmentally sustainable in the face of climate change.

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Background

Soybean production by country or continent. Over time, the U.S.'s share of global soybean  production has decreased, while Brazil's has increased. Between 2005 and 2007, the U.S.  produced 37% of the world's soybeans, while Brazil produced 25%. (Masuda and  Goldsmith, 2009)

For much of the 20th Century, the United States was the dominant player in the soybean production and export process. However countries in South America, particularly Brazil and Argentina, have made strong strides within the past 30 years. Since the year 2000, the United States has been challenged by Brazil and Argentina in terms of soybean production. Many researchers believe that the United States needs to focus more on soybean production in order to stay competitive with Brazil. In particular they believe that more research needs to be done to develop better hybrids to withstand our climate (Sutton et. al., 2005).

Soybean production in Brazil first began in the early 1900’s, however its first commercial origins date back to the 1940’s in the Brazilian state of Rio Grande do Sul. Moto Grosso is currently Brazil’s largest state for soybean production. Brazilian soybeans are primarily exported, usually to China where demand has skyrocketed throughout the past two decades. In 2012 32.5 million tons of soybeans were exported from Brazil (Cerdeira et. al., 2011). Unlike most of the Midwest, Brazil has two growing seasons per year. This is referred to as “safrinha.” The first growing season stretches from late September to early January and the second growing season goes from January to June. The two most common crops in this rotation are soybeans and corn. Three factors have made Brazilian soybean production more environmentally friendly throughout the past few decades (Cerdeira et. al., 2011). Reduction of deforestation, widespread use of no-till production, and the creation of the Soy Moratorium have all helped the system (Raucci et. al., 2014). However the high usage of inputs on the farm including fertilizers, fuel, machinery, and pesticides still allow for improvement (Cerdeira et. al., 2011).

Soybeans are a major agricultural commodity crop, and are used by a large variety of industries worldwide. 92% of soybean production occurs in just 5 countries, and the vast majority of these beans are used for livestock feed, vegetable oil manufacturing, or biofuel feedstocks (Masuda and Goldsmith, 2009). Of the top-producing countries, the United States and Brazil ranked first and second for total soybeans grown between 2005-2007, representing 37% and 25% of global soy production respectively (Masuda and Goldsmith, 2009).

Growing demand for crops such as soybeans does not come without environmental consequences. Agriculture serves as a driving force for production of greenhouse gases (GHGs). Land conversion to agriculture by clearing areas of their native vegetation leads to the release of CO₂ from carbon stocks stored in natural soils (Lal, 2004). Agricultural practices during the production process can contribute to GHG emissions as well, particularly through tillage and fertilizer applications.

Soybeans, as a major commodity crop, provide an opportunity for improving sustainability in agricultural systems. As the top soybean growing countries are not likely to change in the near future, it will be their task to ensure that systems remain productive through more sustainable and lower GHG-emitting practices. The objective of this study is to compare production differences and their related emissions between the two top global producers of soybeans, the United States and Brazil. Comparing these two nations could provide insight into production locations and management practices that will lessen the impact of soy production on climate change.

As previously mentioned, Brazil has a high rate of no-till adoption in its soybean production systems. This coupled with a lower rate of fertilizer usage gives Brazil an advantage in sustainability that the United States currently does not have due to higher rates of tillage and fertilizer additives. Based on agricultural management practices alone, we predict that Brazil will be more sustainable than the United States for future soybean production. However, this sustainable advantage may be called into question based on the effects of land use change. Though it occurs in both countries, we will see that Brazil has a much larger potential to continue soybean expansion than the U.S. Future behaviors of farmers and land use trends are difficult to determine, thus we cannot make a prediction of which country will be more sustainable based on land conversion practices.

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Land Use Change

GHGs released through land use change, or the expansion of agricultural cropland onto land not previously used for this purpose, is a driver for climate change. The major concern with cropland expansion, in the United States or Brazil, is the release of CO₂ to the atmosphere from the natural carbon stocks in native vegetation and soils (Lark et. al., 2015; Persson et. al., 2014). As land is converted from its natural vegetation to agricultural production, soils are exposed that may not have been open to the atmosphere for many thousands of years. This provides a route for carbon stocks found in soil to escape. Soils rich in carbon stocks, like those found in the Midwestern prairie regions of the United States, generally have higher potentials to release more CO₂ than those low in carbon, such as rainforest soils of Brazil (Lark et. al., 2015; Lal, 2004). As soils lose this stored carbon, a reduction in soil productivity is seen over time (Lark et. al., 2015).

As demand for soybeans increases, it is likely that we will see continued land conversion to agriculture in order to accommodate increased production capacity of this commodity. The amount of land available for conversion in Brazil and the United States differs greatly, however. It is estimated that cropland in the United States totals 430 million acres, whereas cropland in Brazil totals 103 million acres (Flaskerud, 2003). While the majority of land best-suited for agriculture has already been converted, Brazilian acreage could be expanded by 500% for a total of 519 million acres (Flaskerud, 2003).

There are also great differences between the two countries in the type of land being converted. In the U.S., the majority of land being used for new soybean production was previously grassland in the Midwestern United States (Lark et. al., 2015). These soils were naturally very high in carbon content, increasing their potential to release CO₂ if converted to agricultural use. Some of the land expansion for soybean cultivation includes pre-existing agricultural land taken out of production as part of the Conservation Reserve Program (CRP) . This program encouraged farmers to remove land from production that was deemed highly erodable through government payments (USDA, 2013). The majority of agricultural land put into CRP was originally carbon-rich grassland as well, and CRP allowed this land to return to a more natural state. As soybean prices increase, however, farmers are removing their land from CRP in favor of planting soy.

Agricultural expansion by most commonly planted crop in the United States.  Green on this map indicates areas where soybean was the major crop related to expansion. (Lark et. al., 2015)

Soybean expansion in Brazil. Blue and purple areas indicate regions soy has expanded  since 2002, with the purple being after the Soy Moratorium was implemented. (Gibbs et.  al., 2015)

Brazil has a very different look in terms of which land is being converted for soybean production. Two biomes make up the majority of land being cultivated for soybeans: the Amazon and the Cerrado. The Amazon represents a tropical rainforest ecosystem, areas which are hotspots of biodiversity and very sensitive to disturbance. The Cerrado is a savannah ecosystem, interspersed with small forests. In 2006, a voluntary agreement among soybean traders called the Soy Moratorium was begun (Gibbs et. al., 2015). This agreement was implemented as a means to protect the sensitive Amazon biome from soybean expansion. Soybean traders will no longer purchase beans from growers expanding into the Amazon post-July 2006 (Gibbs et. al., 2015). Unfortunately, this has simply driven the expansion elsewhere. The Cerrado is now the main area in which soybean expansion is occurring, and with few regulations limiting this expansion, this area of Brazil remains vulnerable.

Recent Soybean Expansion in Brazil and the U.S.

Country	Primary Biome	Land  Area Converted to Soy From 2008-2012 (ha)*
U.S.1	Grassland	600,000
Brazil2	Rainforest/Savannah	3.4 million

*Numbers are rounded estimates
¹U.S. Data: (Lark et. al., 2015)
²Brazil Data: (Gibbs et. al., 2015)

It is difficult to determine exactly how much land has the potential to be newly converted or returned to agricultural production in either country. Incentive programs in the U.S., such as CRP, make farmer behavior difficult to predict. What we do know is that much of the land being converted is not ideal for agricultural use, and is highly susceptible to increased erosion and losses of carbon to the atmosphere in the form of CO₂ (Lark et. al, 2015). Brazil has a much larger pool of land available for new cultivation than the U.S. does. Land areas on the order of 2 Mha in the Amazon and 11 Mha in the Cerrado could still legally be cleared of their native vegetation for soybean production (Gibbs et. al, 2015).  Lack of government regulation could mean that even more land could eventually be cleared legally, or illegally without many repercussions. Expansion onto already cleared lands, such as pasture, further complicates the problem. As pasture is converted to soy, beef producers seek new areas on which to raise their cattle. In this manner, soybean expansion indirectly contributes to additional deforestation.

Carbon Dioxide Emissions from Soybean Expansion per Year 2008-2012 (Tg)

United States1	Brazil2
3.4	1.5

Upon investigating the literature, CO₂ emissions due to soybean expansion in the U.S. and Brazil were determined. According to Lark et. al., 1.48 million acres of unused land were converted to soybean production between 2008 and 2012. This land accounted for a release of approximately 3.4 Tg of CO₂ equivalents per year between 2008-2012 to the atmosphere (US EPA, 2014). In contrast, Brazil showed a much greater increase in land converted for soybean production. In total,  about 8.4 million acres were used for soybean expansion from 2008-12 (Gibbs et. al., 2015). However, this greater land area was associated with fewer emissions in total. Land conversion for Brazilian soy only contributed about 1.5 Tg of CO₂ per year between 2008-2012 (Castanheira and Freire, 2013; Persson et. al., 2014). It is clear that despite higher land conversion rates, Brazilian soils release less CO₂ emissions than United States soils. This may be due to the lower starting carbon content of soils in the Brazilian region compared to the carbon-rich prairie soils of the U.S. (Lal, 2004). The figure below shows some of the data that was used to calculate the Brazilian CO₂ emissions associated with soybean expansion.

Carbon and Land Use Change Footprints of Soybean Production in Brazil

Carbon and land use change footprints of soybean expansion in  Brazil in 2010. Approximately 0.9 tons of CO2 are released per ton  of soy produced, and over 3 hectares of land are converted per  1000 tons. (Persson et. al., 2014)

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Agricultural Management Practices

Tillage Operations

Although tillage may have benefits in preparing the soil for the seed, tillage increases the amount of carbon dioxide emitted to the atmosphere (Kristof et. al., 2014). The loss of soil carbon in the form of carbon dioxide is due to the process of diffusion. The rate of organic matter decomposition, organisms within the soil, and roots of the plants all affect the rate of diffusion (Kristof et. al., 2014). Other environmental factors such as soil type, temperature, and soil moisture also affect the rate of decomposition and gas flux (Kristof et. al., 2014).

​Soil tillage operations such as moldboard plowing and chisel plowing are responsible for CO₂ fluxes in the field because they expose microbes to new substrates that are easily oxidized (Kristof et.al., 2014). These intensive tillage operations disturb the soil a great deal. When microbes are exposed to these conducive conditions, they begin to break down the organic matter, emitting carbon dioxide (Johnson et. al., 2010). Long-term studies have demonstrated a large decline in U.S. soil organic carbon levels is due to the heavy reliance on tillage for most of the 20th century (Johnson et. al., 2010). Technologies like no-till are reducing the CO₂ fluxes in the U.S (Johnson et. al., 2010).

No-till Adoption

The first commercial farmers in Brazil realized the importance of residue management. They noticed that the warm, moist climate increased decomposition and that soil carbon levels became minimal without proper residue management. This residue issue plagued farmers until a new tillage technique entered the market.

No-till tillage, planting soybeans directly into the previous crops residue, is one way to combat the low-residue issue. Unlike tillage, no-till allows the residue to accumulate on the surface, decreasing erosion and adding to the soil carbon pool. Its adoption was slow from the 1970’s through the 1990’s because of weed control. There wasn’t an effective herbicide to kill the weeds. On most farms tillage was used to control weeds before one herbicide became mainstream and changed the soybean production system (Cerdeira et. al., 2011).

No-till really became mainstream in Brazil when glyphosate-resistant soybean varieties were legalized in 2003/2004 (Cerdeira et. al., 2011). Before their legalization, some glyphosate-resistant varieties were planted illegally, starting in 1998 (Cerdeira et. al., 2011). Glyphosate-resistant varieties have expanded tremendously since they became legal. In 2011/2012 it was estimated that 80% of the total soybean acreage in Brazil was planted with glyphosate tolerant varieties (Cerdeira et. al., 2011). For comparison the United States in 2009 planted 95% of their beans with glyphosate-resistant varieties (Cerdeira et. al., 2011).

No-till adoption in the United States has been slower and remains less than in Brazil. Our production system is based more off corn production. Many farmers use conventional or reduced tillage equipment for their corn production and won’t make an investment in a no-till planter because of the high cost. A recent study found that farmers in Iowa paid almost 39% more for equipment such as no-till planters compared to their Brazilian counterparts (Horowitz et. al., 2010). These higher equipment costs may be a reason that no-till adoption has been slower in the U.S.

Tillage Practice Usage in Brazil and the U.S.

¹U.S. Data: Horowitz et. al., 2010
²Brazil Data: Wingeyer et. al., 2015

Fertilizer Usage

Dry fertilizer stockpiles in a warehouse. Photo credit: DeLong Company

Unlike corn, soybeans' nitrogen requirements are very low due to their ability to fix nitrogen through specialized bacteria that reside on roots. It is estimated that soybeans produce enough nitrogen via fixation to satisfy 70-85% of their nitrogen requirement (Raucci et. al., 2014). In corn systems, nitrogen fertilizers are a great source of N₂O emissions because corn doesn’t have the ability to fix nitrogen. However, in soybean systems other fertilizers such as lime are a greater indication of greenhouse gas emissions (Raucci et. al., 2014).

Lime is commonly applied to agricultural soils in the U.S. to increase soil pH and raise the fertility of the soil. The use of lime correlates strongly with the use of nitrogen fertilizer on farmland. Nitrogen fertilizers cause acidification of the soil throughout nitrification. On acres with a corn and soybean rotation, high rates of nitrogen fertilizer and lime are expected. Lime is commonly referred to aglime in the agricultural sector. Crushed limestone (CaCO₃) and crushed dolomite (MgCa(CO₃)₂), are the two products that can be used. The IPPC (Intergovernmental Panel on Climate Change) has found that all carbon in aglime is eventually released to the atmosphere as CO₂. In 2011, 20 Tg of lime was applied to farmland in the United States. An estimated 9 Tg of of CO₂ was released from this application (West and McBride, 2005). Several studies indicate that the United States has much higher lime application rates compared to Brazil, nearly 10 times as much (Laboski et. al., 2006; Raucci et. al., 2014). This lime is emitting a great amount of CO₂ into the atmosphere and contributing to climate change.

Nutrients Used for Soybean Production in Brazil and the U.S.

¹U.S. Data: Johnson et. al.,2010; Laboski et. al., 2006
²Brazil Data: Raucci et. al., 2014