Nutrient pollution can have a negative impact on the aquatic environment, with loss of biodiversity, toxic algal blooms, and a deficiency in dissolved oxygen in surface waters. Agricultural production is one of the main contributors to these problems; this article provides an overview of and background for the main biogeochemical processes causing agricultural nutrient pollution of surface waters. It discusses the main features of the agricultural impact on nutrient loads to surface waters, focusing on nitrogen and phosphorus, and describes some of the main characteristics of agricultural management, including processes and pathways from soil to surface waters. An overview of mitigation measures to reduce pollution, retention in the landscape, and challenges regarding quantification of nutrient losses are also dealt with. Examples are presented from different spatial scales, from field and catchment to river basin scale.
Agricultural Nitrogen and Phosphorus Pollution in Surface Waters
Marianne Bechmann and Per Stålnacke
Industrial Fertilizers in Agriculture
Gregory L. Willoughby
Agriculture has been said to be the key to civilization development. The longevity of the production of the soils which sustained the population development influenced, in fact caused, the rise and often the collapse of those ancient cultures. Furthermore, the fertilization of those soils, if by new sediment or by other means, enabled some civilizations to survive longer than others. It was only with the development of more consistent fertilization and newer, higher-analysis materials that crop production entered an era where it could reliably feed beyond the family unit but feed the city, and then the whole country. This modern industrial fertilization required fewer people to be devoted to food production so that their efforts could be directed to more secondary and tertiary careers. The growth of the use of fertilizer by over 200% in 40 years has led to an increased scrutiny of its environmental aspect in the early 21st century, and this has led to a revaluation of application procedures and to an increase in research and development of new forms of fertilizer and into ways to change modern fertilizers’ environmental footprints to better steward food production and remedy systems that are off target environmentally. These technologies are sometimes very basic, such as including combinations of elements which help stabilize each other (e.g. sulfur and nitrogen or phosphorus and sulfur). Other technologies include polymer-coating (e.g. slow-release coatings) and impregnatable coatings (e.g. nitrapyrin, NBPT). In other cases, new materials have been developed (e.g. methylated urea) and in yet others progress has come from a mixing of other compounds with the fertilizer (e.g. gypsum to phosphorus fertilizer, or humic acids to nitrogen formulations). Lastly, there has been a rise in the importance of micronutrients as production has increased (e.g. zinc, manganese, and boron) especially as yield levels have increased.