Denitrification and the Dinitrogen/Nitrous Oxide Ratio as Affected by Soil Water, Available Carbon, and Nitrate

Abstract

Biological denitrification is affected by many environmental factors that control the amount of N 2 and N 2 O entering the atmosphere. This study was conducted to measure the effect of water-filled pore space (WFPS), available C, and soil NO, concentration on total denitrification (N, + N 2 O), using acetylene (C 2 H 2) inhibition, and to ascertain if denitrification could be estimated from N 2 O measurements in the field using an average N,/N 2 O ratio. Repacked cores of four benchmark soils were brought to 60, 75, and 90% WFPS by applying treatments of glucose-C (O, 180, and 360 kg ha-1) and NO,-N (O, 50, and 100 kg ha~'). The cores were incubated at 25 °C, with and without 100 niL C 2 H 2 L-1 , for 5 d during which daily gas samples of the headspace were analyzed for N 2 O and CO 2. Total N loss due to denitrification generally increased as soil texture became finer and WFPS increased. The only exception to this was the C-amended sand, where N losses up to 26 and 66% were recorded at 60 and 75% WFPS, respectively. Denitrification rates at high N concentrations were quite small in the absence of an available C source but increased with increasing available C (glucose). The Nj/N 2 O ratio generally increased with time of incubation after the initial treatment application. The largest ratios (up to 549) were found at the highest available C rate and generally at the highest soil water content. The presence of high NO, concentrations apparently inhibited the conversion of N 2 O to N 2 , resulting in lower N 2 /N 2 O ratios. Using an average Nj/N 2 O ratio for estimation of denitrification from N 2 O field measurements cannot be recommended because of the variation in this ratio due to the many environmental factors altered by field management that influence denitrification and the relative production of N 2 and N 2 O.

Evidence for sensitivity of dune wetlands to groundwater nutrients

“…It is also likely that in areas of contamination a shift in the microbial community 355 composition has occurred, which supports higher levels of microbial activity (Peacock et al, 2001) and 356 therefore maintaining low organic matter build up. Although denitrification rates can also be limited by 357 other nutrients such as available carbon (Weier et al, 1993). 358…”

Nitrogen enrichment and the emission of nitrous oxide from streams

“…No effect Increased dissolved organic carbon Denitrification Increase Decrease [Weier et al, 1993] c Unknown Nitrification Decrease [Bernhardt and Likens, 2002;Strauss and Lamberti, 2000;Strauss et al, 2002] Unknown/ no effect d…”

“…No effect [Strauss et al, 2002;Strauss et al, 2004] Increased temperature Denitrification Increase to maximum [Silvennoinen et al, 2008a] Decrease [Silvennoinen et al, 2008a] Unknown Increase [Garcia-Ruiz et al, 1998b;Martin et al, 2001] No effect [Martin et al, 2001] Nitrification Increase [Starry et al, 2005] Decrease [Maag and Vinther, 1996] c Unknown No effect [Kemp and Dodds, 2002] Increased oxygen Denitrification Decrease [Kemp and Dodds, 2002;Silvennoinen et al, 2008a] Depends on temperature, range of O 2 [Silvennoinen et al, 2008a] Unknown Increase [Cavigelli and Robertson, 2000] c , [Betlach and Tiedje, 1981] c , [Weier et al, 1993] c Nitrification Increase [Kemp and Dodds, 2002] Decrease [Goreau et al, 1980] c ; [Khalil et al, 2004] c Unknown Increased pH Denitrification Increase [Müller et al, 1980] c Decrease [Cavigelli and Robertson, 2000]…”

General model for N2O and N2 gas emissions from soils due to dentrification

“…To derive appropriate equations to represent how denitrification responds to changes in one of the major input variables (soil NO 3 concentration, respiration, or WFPS), data points that were subjected to strong limitation due to levels of the other inputs were eliminated. The soils used to develop the original denitrification model [Weier et al, 1993] were sieved and repacked to specific bulk densities and treated with various levels of NO3, glucose, and water. Gas flux measurements showed peak N gas emission rates from denitrification occurring at lower WFPS in the sandy soil than in the clay soil [Weier et al, 1993].…”

“…The soils used to develop the original denitrification model [Weier et al, 1993] were sieved and repacked to specific bulk densities and treated with various levels of NO3, glucose, and water. Gas flux measurements showed peak N gas emission rates from denitrification occurring at lower WFPS in the sandy soil than in the clay soil [Weier et al, 1993]. However, as an anaerobic process, denitrification is thought to occur at higher rates in poorly aerated fine-textured soils than in coarse-textured soils at an equivalent WFPS.…”