Nonexchangeable ammonium in soils following applications of nitrogen-15-labeled fertilizers
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The Department of Agronomy seeks to teach the study of the farm-field, its crops, and its science and management. It originally consisted of three sub-departments to do this: Soils, Farm-Crops, and Agricultural Engineering (which became its own department in 1907). Today, the department teaches crop sciences and breeding, soil sciences, meteorology, agroecology, and biotechnology.
History
The Department of Agronomy was formed in 1902. From 1917 to 1935 it was known as the Department of Farm Crops and Soils.
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1902–present
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- Department of Farm Crops and Soils (1917–1935)
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- College of Agriculture and Life Sciences (parent college)
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Abstract
Ammonium (NH[subscript]4[superscript]+) fixation is the trapping of NH[subscript]4[superscript]+ ions within clay lattices. This reaction may temporarily render fertilizer N unavailable to plants and nitrifiers. Although NH[subscript]4[superscript]+ fixation has been studied under laboratory conditions, there is a lack of information on NH[subscript]4[superscript]+ fixation and its importance under field conditions on timescales of interest for crop production. This dissertation describes results from several studies using nitrogen-15-labeled urea and anhydrous ammonia (NH[subscript]3) fertilizers applied to field soils. The objectives were to determine amounts of fertilizer N found as nonexchangeable (fixed) NH[subscript]4[superscript]+ throughout the growing season and to acquire a better understanding of NH[subscript]4[superscript]+ fixation and release under field conditions. Associated studies report the effects of long-term soil management practices on NH[subscript]4[superscript]+ quantity/intensity (Q/I) relationships in Iowa soils;The amounts of fertilizer N found as nonexchangeable NH[subscript]4[superscript]+ were highly variable, even without adjacent soils in a toposequence. Environmental factors such as soil moisture content and rainfall amounts greatly affected amounts of fixation. Concentrations of fertilizer-derived exchangeable and nonexchangeable NH[subscript]4[superscript]+ were highly correlated in NH[subscript]3-fertilized soils at 10 days after application of NH[subscript]3. Concentrations of fertilizer-derived exchangeable and nonexchangeable NH[subscript]4[superscript]+ in urea-fertilized soils were also highly correlated within and across soils. These results suggested a period of net fixation when exchangeable NH[subscript]4[superscript]+ concentrations were high, followed by a period of net release after depletion of exchangeable NH[subscript]4[superscript]+ by nitrification or other processes;Studies of NH[subscript]4[superscript]+ Q/I relationships in long-term rotation plots showed that indexes of NH[subscript]4[superscript]+ availability based on Q/I relationships were similar to those based on measurements of exchangeable NH[subscript]4[superscript]+. Furthermore, long-term soil management practices did not significantly affect the affinity of the soil exchange complex for NH[subscript]4[superscript]+;Overall, the results indicated that NH[subscript]4[superscript]+ fixation is an important transformation of N fertilizers in some Iowa soils. The nonexchangeable NH[subscript]4[superscript]+ is transitory and concentrations decrease throughout the growing season. Amounts of fixation are highly variable and depend upon environmental conditions following fertilizer application. Ammonium fixation is a reaction that deserves more attention in studies of fates and transformations of N fertilizers.