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Methods of determining exchangeable ammonium, nitrate, and nitrite in soils are described. They involve extraction of the soil sample with 2M KCl (10 ml/g of soil) and analysis of the extract by steam‐distillation methods in which magnesium oxide is used for distillation of ammonium, ball‐milled Devarda alloy for reduction of nitrate and nitrite to ammonium, and sulfamic acid for destruction of nitrite. The distillation methods are rapid, accurate, and precise, have high specificity, and are applicable to turbid, colored, and unfiltered soil extracts. They give quantitative recovery of ammonium, nitrate, and nitrite added to soil extracts and permit nitrogen isotope‐ratio analysis of these forms of nitrogen in N15‐tracer studies of nitrogen transformations in soils.

Changes to the global nitrogen cycle affect human health well beyond the associated benefits of increased food production. Many intensively fertilized crops become animal feed, helping to create disparities in world food distribution and leading to unbalanced diets, even in wealthy nations. Excessive air‐ and water‐borne nitrogen are linked to respiratory ailments, cardiac disease, and several cancers. Ecological feedbacks to excess nitrogen can inhibit crop growth, increase allergenic pollen production, and potentially affect the dynamics of several vector‐borne diseases, including West Nile virus, malaria, and cholera. These and other examples suggest that our increasing production and use of fixed nitrogen poses a growing public health risk.

A U.S. farm policy shift to joint production of commodities and ecological services will advance sustainable agriculture.