Soil Nitrogen Uses and Environmental Impacts

Rattan Lal, B.A. Stewart, Rattan Lal, B.A. Stewart

• Editore: CRC Press
• Anno: 2018
• ISBN:
  9781351857406
• Edizione: 1
• Argomento: Biological Sciences
• Categoria: Environmental Conservation & Protection

Nitrogen (N) is potentially one of the most complex elements on the Earth. It is necessary for all biological activity, but creates negative impacts on water and air quality. There is a balancing act between deficiency and surplus and the forms of N available further complicate our understanding of the dynamics. Biological fixation provides some plants with N supply while others are totally dependent upon N being available in the soil profile for the roots to extract. Nevertheless, the demand for N will increase because the human population with its increasing growth requires more protein and thus more N. Understanding the global N cycle is imperative to meeting current and future nitrogen demands while decreasing environmental impacts.

This book discusses availability, production, and recycling of N in air, water, plants, and soils. It features information on N impacts to soil and water quality, management of N in agroecosystems, and techniques to maximize the use efficiency while minimizing the risks of leakage of reactive N into the environment.

This volume in the Advances in Soil Science series is specifically devoted to availability, production, and recycling of N with impact on climate change and water quality, and management of N in agroecosystems in the context of maximizing the use efficiency and minimizing the risks of leakage of reactive N (NO-3, N¬2O) into the environment.

1Benefits and Unintended Consequences of Synthetic Nitrogen Fertilizers

B.A. Stewart

1.1Introduction

1.2Brief History of Development of Synthetic N

1.3Dependency of Worldwide Food Security on Synthetic Nitrogen

1.4Unintended Consequences of N Fertilizer Usage

1.4.1Earliest Concerns

1.4.2Phosphorus Effect

1.4.3Translocation of Nutrients

1.4.4Water Quality Consequences

1.4.4.1Toledo, Ohio

1.4.4.2Des Moines, Iowa

1.4.4.3Phosphorus Fertilizer Bans

1.5Why Does the Nitrogen Problem Defy a Solution?

1.6Conclusions

References

1.1Introduction

Nitrogen (N) is the most important essential element for crop production because it is required in large amounts and is nearly always the first nutrient that becomes limiting after an ecosystem is converted to cropland. However, since the development of synthetic N that requires only energy to combine hydrogen from the energy with nitrogen gas (N2) from the air to produce ammonia (NH3), N fertilizers have become readily available. Economics have constrained the use of N fertilizers in some cases, particularly in developing countries, but they have greatly increased crop yields and especially so in favorable rainfall areas and on irrigated lands. As will be discussed in more detail later, it has been estimated that synthetic N is responsible for feeding more than 50% of the world’s population of 7.4 billion level of today. Without the use of synthetic N, the world population could not have increased to more than about one-half of the 7.4 billion level of today (Erisman et al. 2008; Smil 1999, 2001).

This chapter will look at some of the history of N fertilizer and its importance. Although it is a partial review, the author will also inject some personal viewpoints. I started my career after receiving a B.S. degree as a soil scientist jointly employed by USDA and Oklahoma Experiment Station. The project was to conduct wheat fertilization studies in western Oklahoma and the first publication summarized the first synthetic N studies conducted on farmer fields (Eck and Stewart 1954). We also conducted the first study in Oklahoma that directly applied anhydrous ammonia into the soil (Eck et al. 1957). After completing an M.S. degree while working at Stillwater, I transferred to the newly established USDA Agricultural Research Service Nitrogen Laboratory in Ft. Collins, CO where I also pursued a Ph.D. in soil science. It was during that period that I first became acquainted with possible unintended consequences of using synthetic N. Barry Commoner (1971) raised concerns that fertilizer N applied to soil in the U.S. Corn Belt was causing high levels of nitrate in river waters that subsequently led to methoglobinemia (blue-baby syndrome) in infants. Commoner concluded that the country’s N cycle was seriously out of balance, and this led to controversy between agriculturalists and environmentalists. About the same time, large concentrated animal feeding operations were becoming common raising more questions about N, particularly nitrates, polluting surface and groundwater. The USDA Agricultural Research Service Nitrogen Laboratory was one of the early investigators to address this issue (Stewart et al. 1967). The U.S. Environmental Protection Agency (EPA) was established in 1970 and this increased the attention of the effect of N fertilizers and other chemicals on the environment. I chaired a five-scientist committee to author a two-volume manual Control of Water Pollution from Cropland jointly published by the USDA Agricultural Research Service and the Office of Research and Development of the Environmental Protection Agency (Stewart et al. 1975). Later, as a member of the Committee on Long-Range Soil and Water Conservation organized by the National Research Council, I was one of the authors of the book Soil and Water Quality: An Agenda for Agriculture (National Research Council 1993). From 1997 to 2003, I was a member of the Farmlands Work Group of The John Heinz III Center for Science, Economics and the Environment that had the goal of developing indicators to measure the state of the nation’s ecosystems. In addition to the farmlands group, they had working groups for coasts and oceans, forests, fresh water, grasslands and shrublands, and urban and suburban areas. A comprehensive (Heinz Center 2002) report was published listing indicators that could be measured over time to monitor changes in the state of various ecosystems.

The activities above were listed to show that while I am an agriculturalist that believes strongly the world’s food and fiber needs cannot be met without the use of synthetic N, I am also passionate about protecting the environment. As a young scientist in the 1950s studying the benefits of N fertilizer on wheat (Triticum aestivum) production, there was no thought given to what happened to the N that was not used by the plant. The recommended rate of N fertilizer was mostly determined by economics and adding more than an adequate amount was often considered good insurance in case favorable weather conditions resulted in a bumper crop. As environmental issues began to surface, there developed serious conflicts between agriculturalists and environmentalists. Today, while almost everyone recognizes that the use of synthetic N has resulted in serious unintended consequences, there is little agreement on developing meaningful policies. Developing policies is particularly difficult because it is an international problem because use of synthetic N increases greenhouse gases (GHGs) as well as affects water quality. Furthermore, phosphorus (P) is in many cases causing more environmental problems than N and the two are closely linked. For approximately every 5 units of N removed from cropland with cereal grains and many other crops, there is about 1 unit of P removed. While N is nearly always the first limiting essential nutrient for crop production, P is nearly always the second limiting nutrient. Thus, the use of N fertilizer is closely followed simultaneously by the use of P. As N use increases, P use also increases. Stewart et al. (2016) estimated that 1 Mg P was added for every 5.8 Mg N worldwide in 2010. Phosphorus is readily adsorbed by soil particles and causes serious eutrophication problems in surface waters. Also, unlike N2 that occupies 78% of the atmosphere that is an endless supply for producing synthetic N, P fertilizer is derived from phosphate rock located in mines that is a finite resource. About 90% of the world’s known reserves are controlled by five countries: Morocco, Jordan, South Africa, the United States, and China (Amundson et al. 2015).

The objective of this chapter is (1) to take a brief look at the history of the development of synthetic N; (2) evaluate the impact its use has had on food production and how dependent worldwide food security is on its use; (3) assess the seriousness of the environmental p...