Stable Isotopes Reveal Rapid Cycling of Soil Nitrogen after Manure Application. Issue 2 (1st March 2017)

• Record Type: Journal Article
• Authors: Snider, David M.; Wagner‐Riddle, Claudia; Spoelstra, John
• Is Part Of: Journal of Environmental Quality. Volume 46:Issue 2(2017)
• Page Start: 261
• Page End: 271
• Publication Date: 2017-03-01
• Subjects: Agricultural ecology -- Periodicals; Environmental engineering -- Periodicals; Pollution -- Periodicals; 630
• DOI: 10.2134/jeq2016.07.0253
• Languages: English
• ISSNs: 0047-2425

Abstract

Abstract : Understanding the fate of applied nitrogen (N) in agricultural soils is important for agronomic, environmental, and human health reasons, but it is methodologically difficult to study at the field scale. Natural abundance stable isotope measurements (δ 15 N) were used in this field study with micrometeorological measurements of nitrous oxide (N2 O) emissions to identify the biogeochemical processes responsible for rapid N transformations immediately after application of liquid dairy manure. Fifteen samplings occurred between 16 Mar. 2012 and 5 Apr. 2013, with a focus on spring manure application (before and after) and a winter snowmelt period. Concentrations and δ 15 N values of ammonium (NH4 + ), nitrate (NO3 − ), N2 O, and total N were measured throughout the year. Approximately 56 (±7)% of the NH4 + –N applied in the spring could not be accounted for 3 d after manure application and was presumably lost by ammonia volatilization before it was tilled into the soil and/or removed from the inorganic N pool by microbial assimilation. Almost all of the remaining manure‐NH4 + (95 ± 1.1%) was converted within 3 wk to NO3 − and N2 O by nitrification and nitrifier‐denitrification, respectively. The in situ 15 N isotope effect for nitrification (εNitrate–Ammonium ) was calculated to be −32.0 (±5.3)‰. Overall, field‐scale measurements of δ 15 N at natural abundance provided valuable information that was used to distinguish sources of NH4 + (manure vs. soil organic N) and to follow the production and consumption of NO3 − and the pathways of N2 O production in soil. Core Ideas: 49 to 63% of the manure‐NH4 + was volatilized, assimilated, or fixed 3 d after application. Only 4 to 6% of the manure‐NH4 + remained in the soil 3 wk after application. In situ 15 N isotope effect for nitrification (ammonium–nitrate) was −32.0 (±5.3)‰. N2 O emissions after manure application were produced by nitrifier‐denitrification. The δ 15 N values showed active production and consumption of NO3 − during winter thaw.