USC Dana and David Dornsife College of Letters, Arts & Sciences > Blog

April 22, 2012

California Agriculture and the Nitrogen Cycle

Filed under: California Agriculture,Nitrogen Cycle — dginsbur @ 9:23 pm

Agriculture is one of the largest and most important industries in California, supplying half of all the produce for the nation. According to the California Department of Food and Agriculture, agriculture generates almost $100 billion for the state’s economy. The strength of the agricultural industry was built on the diversity of crops from almonds and broccoli to grapes and squash that can be grown in the mild climate and fertile soil available in California.

The nitrogen cycle is key to making sure that crops continue to grow so that the agricultural industry can maintain the same level of crop yields and keep on feeding the country. Nitrogen is used by plants not only in nucleic acids and proteins, but also specifically with chlorophyll, which is key to photosynthesis, the process that provides plants with food to continue growing. However, plants cannot access atmospheric nitrogen in the form of N2—the nitrogen gas needs to be converted or fixed into a different form that is accessible to plants.

Therefore, the current problem that farms are facing is that not enough nitrogen is being naturally fixed to promote plant growth and fulfill the demand for produce. Farms in California are beginning to rely more and more heavily on nitrogen fertilizers to boost plant productivity. However, this input of manufactured nitrogen has many effects on the nitrogen cycle. Many plants do not absorb all of the nitrogen from the fertilizer, leaving excess nitrogen in the soil, which causes an imbalance to the ecosystem. This nitrogen can also be deposited in bodies of water through runoff, causing eutrophication due to its role as a limiting nutrient. As agriculture in California has risen to be major industry, more synthetic fertilizers are being used to grow crops, and the excess nitrogen is becoming an important problem.

Fortunately, this issue has been recognized by organizations like the Environmental Protection Agency and the California Department of Food and Agriculture. In 2010, the Agricultural Sustainability Institute at UC Davis sponsored the California Nitrogen Assessment, an attempt to assess California’s current agricultural needs in regards to nitrogen and to discuss possible solutions. In the information and progress report, they stated, “Our researchers are working to establish a baseline of credible knowledge about nitrogen, which includes comprehensive accounting of nitrogen flows, agricultural practices, and the policies that shape these practices. They will also assess the quality of information and knowledge about these issues.”

Some solutions to be considered are utilizing a crop-rotation system with nitrogen-fixing crops, or developing crops that use endosymbiotic nitrogen-fixing bacteria to reduce the amount of synthetic, nitrogen-rich fertilizers used. Another option would be genetically modifying crops to be more nitrogen efficient, but there are many controversies surrounding such practices.

In terms of recent developments, the CDFA posted a press release stating “The California State Board of Food and Agriculture will discuss a variety of topics related to the nitrogen cycle and the proactive work by California farmers and ranchers on the issue at its upcoming meeting on March 6th [2012] in Sacramento.” While they have yet to release a summary of the meeting, the conference shows that there is still state interest in regulating the nitrogen cycle in regards to agriculture. As the agriculture industry continues to grow, it is important to be aware of the nitrogen cycle and the impact humans have on it.


Harriet Arnold and Divya Rao are undergraduates in the USC Dornsife College of Letters, Arts and Sciences.

February 27, 2012

Soil Restoration via Increases in Biodiversity: Do Greater Amounts of Fungi Lead to Healthier Soil?

Filed under: Nitrogen Cycle,Soil Sustainability — dginsbur @ 10:36 am

In the dark world below the top soil, there are millions of livings that play crucial roles in the ecosystem, which human beings know little about. The soil microbe communities include fungi, bacteria, protozoa, nematodes and arthropods. Although tiny individually, their existence sustain the health of the soil and sometimes even the air above.

Many studies have shown that microbes are the key to the decomposition process, and such the nutrient cycling and nitrogen fixation of the soil. Protozoa, for example, is a single-celled animal that mainly feed on bacteria and release nitrogen and nutrient that benefit plants, whose roots protozoa normally concentrate around. Protozoa would be consumed by nematodes which can decay organic matters. This food web in the soil cannot even be detected by naked eyes but the lack of it could result in the degraded soil.

With increasing population, the loss of agriculture land due to the soil degradation would be a disaster to human beings. Some soil bacteria have surprising significance in the overall ecosystem. Evidence shows that some “rain making” bacteria would be brought to the atmosphere by wind and function as ice former in the air, which would result in cloud and precipitation under proper conditions.

Many studies have attempted to restore soil biodiversity in order to soil quality and ecosystem functioning. For example, a study administered in Colorado linked soil degradation, which leads to biodiversity loss, to an increase in the presence of pathogens and pests that are detrimental to the health of humans, plants, and animals. This can lead to a decrease in soil and plant productivity. Therefore, it is essential to maintain soil biotic communities in order to “assure long-term soil sustainability”. Another experiment conducted in New Mexico in 2005 was extremely successful in restoring 1.8 million acres of degraded landscape. This was due to an increase in vegetation variety and the healthy functioning of watersheds.

However, soil degradation is not only a problem in the United States but in many other parts of the world as well. For example, due to the fact that “physical disturbance is one of the principal causes of biodiversity loss in all world ecosystems”, farmers in Southern Brazil stressed minimum disturbance and thereby produced better environments for soil macrofauna, thus becoming more sustainable. The outcome of this study proved that the diversity of soil macrofauna such as termites, ants, snails, millipedes, and centipedes among many others, play a crucial role in the successful functioning of no-tillage systems

As evident, the maintenance of soil biodiveristy is an integral part of restoration ecology and the improvement of soil quality because due to its significant role in soil function and the potential risk of losing creatures that have stunning values unknown to mankind. The need for healthy soil will only become more significant in the near future as food production will have to increase to meet the demands of a growing population.


Jay Bhayani and Hongxi Zhao are undergraduates in the USC Dornsife College of Letters, Arts, and Sciences.

October 30, 2011

Overuse and Abuse of Nitrogen Fertilizers in California Agricultural Lands

Without the use of nitrogen fertilizer, California agricultural lands could risk not reaching its optimum yield. As a consequence, food production companies would lose a certain amount of profit and consumer demands could possibly not be reached. Often times as nitrogen passes through plants and soil in a repetitive cycle the loss of nitrogen is greater than the benefit and as a result, the plant growth is no longer as significant. This ultimately puts a limit on crop production rate. However, scientists have come up with farming techniques that have revolutionized agriculture. Nitrogen fertilizer is one of those inventions and is a product of the Haber-Bosch process. This fertilizer has ‘allowed agricultural production to keep pace with world population growth,’ according to the International Fertilizer Industry Association.

Nitrogen fertilizers have many effects on the Nitrogen cycle that can lead to negative anthropogenic effects as well as environmental. There are several disruptions in the natural cycle of Nitrogen that can occur.

First of all, artificial nutrients dumped into soil can result in a loss of its capacity to hold nutrients (Lowe, pg.10). It is estimated that plants have no use for up to 50% of the chemical fertilizers placed on them.

Agricultural regions of the Southwest are composed of mainly shallow, coarse-textured and therefore highly permeable soils and aquifers. It is common for these areas to be vulnerable to nitrate contamination (Harter pg.3).

Nitrates are the most readily formed and available use of Nitrogen, and they are extremely soluble. It is easily carried through the soil with water to be taken up by plants. If the land is irrigated, there is a chance nitrate can move past the plant roots and into the groundwater or other agricultural tile drainage or surface waters (Mosier, pg.13). In major agricultural areas such as the Imperial, Central, Salinas, and other coastal valleys in California, there is groundwater nitrate contamination (Harter pg.3). When nitrate levels exceed those of the EPA’s Maximum Containment level set at 10mg/l, certain health risks occur. One of these being methemoglobinemia (infants especially are vulnerable).

In addition, when converting ammonium into nitrate, nitrite will naturally occur. Nitrite is similar to nitrate in its movement through the soil and possibility of contaminating groundwater (Reid para.7).

Ammonia volatilization also contributes to nitrogen losses.  Ammonia volatilization occurs in areas where the soil is warm, dry, and too much of a nitrogen fertilizer is applied (Buchholz). There is a concern with concentrations becoming toxic. This can happen when too many of these tiny particulates enter a confined area. Ultimately, one of the biggest concerns is reducing air quality (Reid, pg. 11).

Moreover, the effects that Ammonia and nitrate can have on biodiversity can be disastrous. Eutrophication that can lead to algal blooms and a die-off of fish species are a concern from Nitrogen fertilizer use such as ammonia emissions that can deposit on bodies of water and nitrate leached from the soil (Mosier pg.17). Ultimately, the impacts this is having can decrease fish populations resulting in less available resources for people to consume.

Lastly, the process of denitrification can transform the nitrogen fertilizer into nitrous oxide. This is a greenhouse gas, which has approximately three hundred times more impact than carbon dioxide on climate change (Lowe, pg.10). The effects of using these nitrogen fertilizers may not be shown right away as can be seen from eutrophication, but the long-term impacts may be detrimental.

If California continues with overusing and abusing its Nitrogen fertilizer use, it makes itself susceptible to the outcomes seen in China’s croplands. The soil became more acidic so that it was unproductive, and in addition to water contamination, China experienced increases in greenhouse gas emissions. All of these disastrous consequences were negligent monitoring of nitrogen fertilizers.

China’s overuse of nitrogen fertilizers has forced the government to take action against the pollution. One of their solutions is a five-year plan, which calls for a reduction in carbon intensity by implementing new domestic laws that legally require companies to meet emission reduction targets.

Although California may not have a government plan to target the nitrogen pollution, there are other ways in which farmers, themselves can become proactive in reducing the pollution. Some example solutions include securing stored manure in order to prevent runoff or enforcing livestock feed rations that are not above the necessary.

Another solution is to completely phase out chemical fertilizers and instead use organic fertilizers. According to the Third World Network’s report, “Avoiding Nitrogen fertilizer over-use is a “multiple win”: farmers save money, there is less water pollution, smaller greenhouse gas emissions, and a smaller acidification burden on soil and water.”

Image Source:

Harter, Thomas. “Agricultural Impacts on Groundwater Nitrate.” Nitrates in Groundwater. University of California, Davis, July-Aug. 2009. Web. 10 Oct. 2011. <>.


Mosier, Arvin, John K. Syers, and J. R. Freney. Agriculture and the Nitrogen Cycle: Assessing the Impacts of Fertilizer Use on Food Production and the Environment. Washington, D.C.: Island, 2004. Print.

Lowe, Marcy, and Gary Gereffi. “A Value Chain Analysis of Selected California Crops.” Center on Globalization. Duke University, 04 July 2008. Web. 10 Oct. 2011. <>.

Reid, Keith, Kevin McMcKague, and Hugh Simpson. “Environmental Impacts of Nitrogen Use in Agriculture.” Ontario Ministry of Agriculture, Food and Rural Affairs / Ministère De L’Agriculture, De L’Alimentation Et Des Affaires Rurales. Web. 10 Oct. 2011. <>.

Harter, Thomas. “Agricultural Impacts on Groundwater Nitrate.” Nitrates in Groundwater. University of California, Davis, July-Aug. 2009. Web. 10 Oct. 2011. <>.

Buchholz, Killpack. “WQ257 Nitrogen in the Environment: Ammonia Volatilization | University of Missouri Extension.” University of Missouri Extension Home. Department of Agronomy. Web. 10 Oct. 2011. <>.

About the authors: Ticia Lee and Wendy Whitcombe are working towards their bachelor degrees in the USC Environmental Studies Program.