No abstract

No abstract

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.

No abstract

The available literature on the fate of nitrogen in waters and sediments is reviewed. Emphasis is placed on the importance of N to aquatic productivity, the pathways leading to N gains or losses in aquatic ecosystems, and the availability of N in sediments to the overlying waters. Important biological reactions include N mineralization and immobilization, nitrification and denitrification, and N fixation. The effect of sediment properties, lake morphology and environmental factors (pH, temperature, dissolved oxygen, oxidation‐reduction potential) on the pathways and rates of turnover are considered. The mixing process in sediments appear to be the most important in releasing sediment‐N to waters. Several facets of the N cycle in waters and sediments require further elucidation. Research needs are outlined.

It is generally assumed that infiltration of sprinkler irrigation and rainfall under potato is uniform. However we observed non‐uniform infiltration beneath the hills of sprinkler‐irrigated potatoes (Solanum tuberosum L, var. Russet Burbank) grown on Plainfield loamy sand (Typic Udipsamment; sandy, mixed, mesic). The objective of this field study was to determine the effects of foliage interception and hilling on non‐uniform infiltration, since concentrating water in local zones would increase deep drainage and nitrogen leaching. To do this we traced the rainfall and irrigation infiltration pattern with Rhodamine WT dye and collected the stemflow in stem collars. Throughfall of rainfall, the soil water content, and soil water tension also were measured. From 20 to 46% of the irrigation and from 4 to 23% of the rainfall on the canopy flowed down the stems. Stemflow increased the soil water content around the stems and moved Rhodamine dye deep beneath the soil surface. Deep movement of dye beneath the furrows was caused by runoff from the hills and by leaf drip from the outer foliage. The results obtained suggest that irrigation and fertilizer management could be improved by taking this non‐uniform infiltration pattern into account. Smaller irrigations should improve water use efficiency and minimize nitrate leaching. Further, evaluation of solute movement by soil sampling should consider the spatial variation introduced by the non‐uniform infiltration. Finally, predictive leaching models should account for non‐uniform infiltration.