Stable Isotopes Reveal Rapid Cycling of Soil Nitrogen after Manure Application

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 (δN) were used in this field study with micrometeorological measurements of nitrous oxide (NO) 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 δN values of ammonium (NH), nitrate (NO), NO, and total N were measured throughout the year. Approximately 56 (±7)% of the NH-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-NH (95 ± 1.1%) was converted within 3 wk to NO and NO by nitrification and nitrifier-denitrification, respectively. The in situ N isotope effect for nitrification (ε) was calculated to be -32.0 (±5.3)‰. Overall, field-scale measurements of δN at natural abundance provided valuable information that was used to distinguish sources of NH (manure vs. soil organic N) and to follow the production and consumption of NO and the pathways of NO production in soil.

Isotopic Composition of In Situ Soil NOx Emissions in Manure‐Fertilized Cropland

“…Therefore, the 8–20‰ differences in δ 15 N‐NO x between injected no‐till and broadcast without tillage are likely associated with different rates of NO production via nitrification and NO consumption. This association with nitrification is generally consistent with Snider et al (), who reported 56% of NH 4 + applied via liquid dairy manure application (broadcast with incorporation) in silt loam soil was lost after 3 days via NH 3 volatilization and 95% of the remaining NH 4 + was nitrified within 3 weeks.…”

A modelling framework to simulate field‐scale nitrate response and transport during snowmelt: The WINTRA model

“…NO 3 is negatively charged, so it is not retained by the soil particles (Martius, Rudenko, Lamers, & Vlek, ) like other nutrients, such as ammonium (NH 4 ). Heterotrophic microbiological activity occurs during snowmelt (Brooks, Williams, & Schmidt, ; Clark, Chantigny, Angers, Rochette, & Parent, ), but has also been observed in snow‐covered soils during winter (Brooks et al, ; Clark et al, ; Pellerin et al, ; Sebestyen et al, ; Snider, Wagner‐Riddle, & Spoelstra, ). Net mineralization and nitrification may occur in frozen soils before snowmelt (Brooks et al, ; Clark et al, ), therefore presenting a risk of NO 3 net gains between fall and spring, particularly in the presence of organic amendments and in fine‐textured soils (Clark et al, ).…”

“…This has implications for runoff‐soil interactions with possible anticipation of the timing of the first and major surficial soil NO 3 flush. As the water moves downstream, runoff NO 3 concentrations tend to decrease due to biological assimilation and denitrification, even in agricultural areas (Snider et al, ). However, at the spatial scales of nutrient release and mobilization (i.e., field‐scales), the spatial distribution of snow mass and melt rate are critical determinants of the spatial and temporal dynamics of NO 3 export.…”

A 300-year record of sedimentation in a small tilled catena in Hungary based on δ13C, δ15N, and C/N distribution

“…Thus, most studies on δ N focused on processes within the uppermost 10 cm of soil (Wang et al 2014;Snider et al 2017). Depth-related distributions were studied only in the upper 30 cm by Kerley and Jarvis (1997).…”