Latin America’s Nitrogen Challenge and Pongamia as One Solution

Rise of soybean cultivation in Latin America

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Figure 1: Relative production of soybeans by country, 2012

Latin America (Brazil, Argentina, Paraguay, and Bolivia in particular) account for 40% of global soybean production, and this region has experienced major growth in large-scale agriculture operations that take advantage of modern management methods (ftp://ftp.fao.org/docrep/fao/008/af135e/af135e00.pdf)

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Figure 2: Soybean exports by country, 2010

While driving economic growth, the gain from this rise in production and export of soybeans has come at both environmental costs that include a significant impact on the Nitrogen Cycle and the social costs of further exasperating Latin America’s legacy of inequitable distribution of wealth & power inherited from its colonial history.

In a recent opinion piece in the Journal Science, a group of scientists from Argentina, Brazil, Venezuela, Bolivia, and Mexico assert that ecosystem and human health in Latin America depends on managing the human impact on the N cycle (Austin, A. T., et al. “Latin America’s Nitrogen Challenge.” Science 340.6129 (2013): 149-149) and that new practices are needed to solve the problem.  In addition to calling for financial support from developed nations, the authors recommend the following agriculture practices and policies to promote sustainable economic growth for Latin America:

  • Enhanced nitrogen fixation
  • Agricultural techniques including no-till agriculture, cover crops, and crop rotation
  • Agricultural practices to increase functional diversity, mimicking natural ecosystems
  • Policies that include small farmers as well as large landowners

Focused on sustainable agriculture solutions including the cultivation of environmentally and economically sustainable crops, TerViva is partnering with Investancia to introduce pongamia to Paraguay’s Gran Chaco.

 The Nitrogen Cycle

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Figure 3: The Nitrogen Cycle

First a description of the Nitrogen Cycle.  All living cells need nitrogen (N) to grow.  Nitrogen is one of five key nutrient for all living cells as it is a component of both amino acids that are incorporated into proteins and of nucleic acids that are incorporated into RNA and DNA.  In plants, N is further needed to synthesize chlorophyll molecules that are key to photosynthesis and growth.  Thus the abundance or scarcity of N in the soil directly determines the quantity of food a given parcel of land can grow.

Although atmospheric N is the earth’s largest source of this element, 78% of the atmosphere is molecular (N2); most organisms cannot use the gaseous form of N.  Most living organisms depend on “reactive” nitrogen (Nr) that is “fixed” by biological or physical processes into inorganic forms of nitrogen like ammonia, ammonium, nitrogen oxide, nitric acid, nitrous oxide, and nitrate, and organic compounds like urea, amines, proteins, and nucleic acids (http://initrogen.org/index.php/about/).

The nitrogen cycle is the set of processes by which nitrogen is converted from gaseous nitrogen to fixed nitrogen in the soil and water bodies and back to gaseous molecular nitrogen in the atmosphere. (http://en.wikipedia.org/wiki/Nitrogen_cycle)

Human activities including fossil fuel combustion, use of artificial nitrogen fertilizers, and release of nitrogen in wastewater have negatively altered the global nitrogen cycle.  Latin America is suffering from similar forces found globally that are creating a nitrogen challenge.  Total global fixation of Nr in soil has doubled in recent history and excess fixed Nr has leaked into the environment impacting soils, waterways, and the atmosphere.  In addition to Nr excess from human activity, mining of natural soil Nr and over cultivation of crops creates Nr deficits in some areas.

In Latin America, high concentrations of untreated sewage in poor urban areas experiencing uncontrolled growth is causing rises in nitrogen in addition to phosphate in these areas.    Even though soybeans are a legume and could fix nitrogen in symbiosis with soil bacteria, this crop is being cultivated in Latin America under high yield management practices that are depleting natural levels of fixed nitrogen. In the Argentina Pampa region where soil is naturally fertile, nitrogen fixation has not been stimulated, and N has been exported in soybeans grown in this region.  In Brazil, converting pristine ecosystems high in natural N fixation rates to cultivated fields where fixation is not high is also causing reduction in N in soils.  Biomass burning to clear land for agriculture, including soybean production transfers a large amount of Nr from land to gaseous forms of N in the atmosphere (nitrogen and nitrogen/oxides), redistributing N from one area to another and from fixed to atmospheric.  Once removed from the soil and moved via the nitrogen cycle, this N is unavailable to plants in the region that was burned.  The scale of biomass burning in Latin America is still estimated at 150,000 km2/year.

Among biological processes that fix Nr, a key beneficial process occurs as the result of a symbiotic relationship between a group of soil bacteria and a group of plants, the legumes.  Legumes create root nodules in which these nitrogen-fixing bacteria live and convert gaseous nitrogen to Nr that other living organisms can utilize.  Increased efficiency of land already under cultivation without N fertilization would help Latin America, in particular, a great deal.  (Austin et al, 2013)

Sustainable Agriculture to Solve Nitrogen Challenge

TerViva is partnering with Investancia to bring cultivation of its new crop, pongamia, to the Gran Chaco, a vast un-developed area of northern and western Paraguay.  This area is currently home to fewer than 100,000 people who manage 25 million cattle in an area about the size of the state of Pennsylvania in the US.  As luck would have it, the Chaco also has a tropical climate with monsoonal rains where pongamia, is expected to thrive.

Figure 4:  Root nodules on  pongamia plants grown in nursery ready for field planting

Figure 4: Root nodules on pongamia grown in nursery ready for field planting

As a legume, pongamia will be planted in areas previously cleared for cattle and cultivated as a perennial crop with annual seed harvests.  Thus pongamia plantations will provide carbon sequestration in addition to nitrogen fixation.  Trees will be planted in strip-tilled rows, leaving ground cover intact between rows.  Once processing resources are in place, Investancia will develop programs that support farmers of small land holdings to cultivate pongamia.

Pongamia’s raw oil product will be similar to soybean, high in oleic acid (eighteen carbon chain with 1 double bond) that is amendable to production of renewable transportation fuel or chemicals.  However, pongamia harvests will be more economically beneficial at 400 gallons/acre compared to 60 gallons/acre for soybeans.

With high financial returns per acre, environmental benefits, particularly nitrogen fixation, pongamia can help Latin America solve its nitrogen challenge while providing for further economic development

Note:  For further information regarding the global nitrogen challenge and initiatives including those in Latin America to optimize nitrogen’s beneficial role in sustainable food production and minimize nitrogen’s negative effects on human health and the environment resulting from food and energy production, see the International Nitrogen Initiative web page  (http://initrogen.org/)

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