**2. Nitrogen fertilizer: An unsustainable reliance in modern agriculture**

Current agriculture practices are heavily reliant on nitrogen-based fertilizers to achieve high yields (Peoples *et al.,* 2009; Jensen et al., 2012). Indeed, it is estimated that half of the world's population is fed as a direct result of nitrogen fertilizer use (Erisman et al., 2008). Although this approach works well to maximize crop production, it is a very risky dependence that is not sustainable, and is inefficient, expensive, and often pollutes. Hence, there are a number of very sound reasons to lessen these nitrogen inputs and alleviate the current reliance.

The production of industrial nitrogen fertilizers requires a great deal of fossil fuel, involving what is known as the Haber-Bosch process. Once manufactured, additional fossil fuel is needed to transport the fertilizer to its place of sale, and then even more fossil fuel is needed to apply it in the field. Collectively, this accounts for a staggering 50% of fossil fuel use in modern agriculture and 5% of the world's annual consumption of natural gas (Crutzen et al., 2007; Canfield et al., 2010). As a direct result, the purchase and application of nitrogen fertilizer can be quite expensive, preventing many farmers in developing regions of the world from being able to use it. Moreover, as the cost of fossil fuel continues to rise, so too does the cost of nitrogen fertilizer. This can considerably cut into farmer profits and often leads to costs being passed on to the consumer.

In addition to the monetary costs associated with nitrogen fertilizer use, there are often con‐ siderable environmental costs. It is reported that industrial manipulation of the nitrogen cy‐ cle has already exceeded safe boundaries for global environmental change (Rockstrøm et al., 2009; Canfield et al., 2010; Charpentier and Oldroyd 2010; Beatty and Good 2011). Due to the combustion of fossil fuel, the production and application of nitrogen fertilizer results in large quantities of carbon dioxide (CO2) being released into the atmosphere. This contributes to the greenhouse effect, as does the release of nitrous oxide (N2O), which is produced dur‐ ing the decomposition of nitrogen fertilizer in the soil and is estimated to be 292 times more active as a greenhouse gas than CO2 (Crutzen et al., 2007).

Each year >100 million tonnes of nitrogen are applied to crops worldwide (Glass 2003). This excessive use of nitrogen reduces the levels of trace nutrients in the soil and increases soil acidity. Moreover, the application of nitrogen-based fertilizers is a largely inefficient proc‐ ess, with as much as 30 - 50% lost to leaching. This nitrogen run-off can cause significant environmental damage, including the eutrophication of waterways resulting from associat‐ ed algal blooms, *etc*. (Vance 2001). Recent reports indicate that the cost to fix this environ‐ mental damage will significantly outweigh the economic benefit gained from nitrogen fertilizer use (Sutton et al., 2011).

The excess runoff from nitrogen fertilizer can also contaminate drinking water. High levels of nitrogen in drinking water can lead to methemoglobinaemia, commonly referred to as Blue-baby syndrome because of the blue-grey skin colour displayed by affected infants (Murphy 1991; Knobeloch et al., 2000). Blue-baby syndrome is potentially fatal and occurs when the hemoglobin of an infant's red blood cells is oxidized to methemoglobin, which is unable to properly transport oxygen.

tion, some legumes are being exploited as a source of sustainable biofuel. Species such as soybean, and the tree legume *Pongamia pinnata*, offer the most promise due to their high

A Comprehensive Survey of International Soybean Research - Genetics, Physiology, Agronomy and Nitrogen

**2. Nitrogen fertilizer: An unsustainable reliance in modern agriculture**

Current agriculture practices are heavily reliant on nitrogen-based fertilizers to achieve high yields (Peoples *et al.,* 2009; Jensen et al., 2012). Indeed, it is estimated that half of the world's population is fed as a direct result of nitrogen fertilizer use (Erisman et al., 2008). Although this approach works well to maximize crop production, it is a very risky dependence that is not sustainable, and is inefficient, expensive, and often pollutes. Hence, there are a number of very sound reasons to lessen these nitrogen inputs and alleviate the current reliance.

The production of industrial nitrogen fertilizers requires a great deal of fossil fuel, involving what is known as the Haber-Bosch process. Once manufactured, additional fossil fuel is needed to transport the fertilizer to its place of sale, and then even more fossil fuel is needed to apply it in the field. Collectively, this accounts for a staggering 50% of fossil fuel use in modern agriculture and 5% of the world's annual consumption of natural gas (Crutzen et al., 2007; Canfield et al., 2010). As a direct result, the purchase and application of nitrogen fertilizer can be quite expensive, preventing many farmers in developing regions of the world from being able to use it. Moreover, as the cost of fossil fuel continues to rise, so too does the cost of nitrogen fertilizer. This can considerably cut into farmer profits and often

In addition to the monetary costs associated with nitrogen fertilizer use, there are often con‐ siderable environmental costs. It is reported that industrial manipulation of the nitrogen cy‐ cle has already exceeded safe boundaries for global environmental change (Rockstrøm et al., 2009; Canfield et al., 2010; Charpentier and Oldroyd 2010; Beatty and Good 2011). Due to the combustion of fossil fuel, the production and application of nitrogen fertilizer results in large quantities of carbon dioxide (CO2) being released into the atmosphere. This contributes to the greenhouse effect, as does the release of nitrous oxide (N2O), which is produced dur‐ ing the decomposition of nitrogen fertilizer in the soil and is estimated to be 292 times more

Each year >100 million tonnes of nitrogen are applied to crops worldwide (Glass 2003). This excessive use of nitrogen reduces the levels of trace nutrients in the soil and increases soil acidity. Moreover, the application of nitrogen-based fertilizers is a largely inefficient proc‐ ess, with as much as 30 - 50% lost to leaching. This nitrogen run-off can cause significant environmental damage, including the eutrophication of waterways resulting from associat‐ ed algal blooms, *etc*. (Vance 2001). Recent reports indicate that the cost to fix this environ‐ mental damage will significantly outweigh the economic benefit gained from nitrogen

The excess runoff from nitrogen fertilizer can also contaminate drinking water. High levels of nitrogen in drinking water can lead to methemoglobinaemia, commonly referred to as

seed oil content (Scott et al., 2008).

Relationships

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leads to costs being passed on to the consumer.

active as a greenhouse gas than CO2 (Crutzen et al., 2007).

fertilizer use (Sutton et al., 2011).
