Characterization of Denitrification and Leaching Losses of Fertilizer Nitrogen From Soil (Evolution, Isotope, Nitrous Oxide, Dinitrogen)

99 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1986.Quantification of leaching and denitrification losses of fertilizer N from soil requires that appropriate methods be developed for their measurement. The objectives of this work were to: (1) evaluate potential errors in measuring denitrification by use of ('15)N-tracer techniques recently developed for determination of N(,2) and N(,2)O evolved from soil; (2) evaluate three methods of estimating fertilizer N loss under field conditions (grain yield reductions, an ('15)N difference method, and a direct measurement of denitrification using the procedures in 1); and (3) evaluate the extent of N loss through leaching and denitrification in a laboratory study using semi-disturbed soil columns.Computer simulation studies showed that when nitrate undergoing denitrification is not isotopically uniform, N evolution rates will be underestimated. The degree of error increases with an increase in the number of NO(,3)('-) pools present where their isotopic diversity increases (range or standard deviation of the ('15)N enrichments). The error will generally not exceed 25% where the ('15)N enrichments are low (40 atom %), the error generally will not exceed 10%.The ('15)N difference study was conducted to determine the amount of fertilizer N loss that would occur from ambient rainfall (0-cm addition) and ambient rainfall plus 7.6 cm of additional water (7.6-cm addition). Of the 168 kg N/ha applied, 141 and 104 kg N/ha were accounted for at harvest for the 0 and 7.6-cm water additions, respectively. Gas analyses accounted for losses of 24 and 44 kg N/ha, respectively, with very little leaching occurring for either treatment. Essentially all of the N loss occurred by the time of the 11-leaf growth stage. The yield study indicated that average corn (Zea mays L.) yield reductions across N rates of 0-224 kg N/ha were great enough to justify application of supplemental N. Using yield as a measure of N loss provided larger estimates than either the ('15)N difference method or gas analyses.The soil column study included water and fertilizer treatments similar to those used in the field study. Nitrogen evolution amounted to only 1 kg N/ha for the highest water treatment. A separate investigation indicated C availability was apparently limiting denitrification despite the addition of plant residue. The reason for the discrepancy between large N evolution rates under field conditions and small losses under laboratory conditions was not evident.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD