McSwiney, C.P. and G.P. Robertson
Presented at the All Scientist Meeting (2002-10-04 )
The most important proximal controls on N2O production in soils are N availability (as NO3- and NH4), organic carbon, and oxygen levels. In the current IPCC assessment, agriculture’s contribution to the global N2O load is calculated as a set percentage of N fertilizer used in all cropping systems, which may not be an accurate representation of the way that ecosystems respond to N. In order to better understand the role of N availability in N2O production we conducted an N rate study at the Kellogg Biological Station in southwestern Michigan. Nitrogen, as NH4NO3, was added to 4 replicate fields in continuous corn at 9 levels, ranging from 0-291 kg N ha-1 yr-1. We measured surface N2O fluxes before and after fertilizer was added to the soils to determine the threshold where N2O fluxes began to increase. Corn yields were determined at harvest and soil mineral N was determined after each flux measurement.. The threshold for N2O flux occurred at 134 kg N ha-1 yr-1, which is just above the rate at which corn is fertilized in the LTER experimental site at KBS. Gains in grain yields decreased at N addition rates above 101 kg N ha-1 yr-1. N availability, measured as 1 N KCl-extractable NO3- and NH4, increased at the point along the N-availability gradient where increases in yield drop off and N2Ofluxes increase. If these patterns are representative of other crops and growing seasons, fertilization rate may be adjusted to maximize yield and minimize unwanted losses of N from the managed system as N2O and NO3-. The most important proximal controls onN2O production in soils are N availability (as NO3- and NH4), organic carbon, and oxygen levels. In the current IPCC assessment, agriculture’s contribution to the global N2O load is calculated as a set percentage of N fertilizer used in all cropping systems, which may not be an accurate representation of the way that ecosystems respond to N. In order to better understand the role of N availability in N2O production we conducted an N rate study at the Kellogg Biological Station in southwestern Michigan. Nitrogen, as NH4NO3, was added to 4 replicate fields in continuous corn at 9 levels, ranging from 0-291 kg N ha-1 yr-1. We measured surface N2O fluxes before and after fertilizer was added to the soils to determine the threshold where N2O fluxes began to increase. Corn yields were determined at harvest and soil mineral N was determined after each flux measurement.. The threshold for N2O flux occurred at 134 kg N ha-1 yr-1, which is just above the rate at which corn is fertilized in the LTER experimental site at KBS. Gains in grain yields decreased at N addition rates above 101 kg N ha-1 yr-1. N availability, measured as 1 N KCl-extractable NO3- and NH4, increased at the point along the N-availability gradient where increases in yield drop off andN2Ofluxes increase. If these patterns are representative of other crops and growing seasons, fertilization rate may be adjusted to maximize yield and minimize unwanted losses of N from the managed system as N2O and NO3-.
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