TY - JOUR

T1 - Nitrogen fertilization-induced acidity and suitability of δ13C to study the dynamics of soil inorganic carbon in agroecosystems

AU - Abdollahpour, Mostafa

AU - Hollemann, Dennis

AU - Sauheitl, Leopold

AU - Guggenberger, Georg

AU - Zamanian, Kazem

N1 - Publisher Copyright: © 2025 The Author(s)

PY - 2025/5

Y1 - 2025/5

N2 - Neutralization of soil inorganic carbon (SIC), i.e., dissolution of carbonate minerals caused by N fertilization-induced acidity, is an ongoing reaction in agroecosystems that leads to significant contribution of SIC to soil CO 2 emission. Analyzing δ 13C natural abundance of the emitted CO 2 is commonly used to quantify the contribution of SIC in total CO 2 emission. However, carbonates recrystallization in isotopic equilibrium with soil respiration can lead to miscalculation, where despite detecting δ 13C signal from carbonates in the emitted CO 2, the SIC stock may not necessarily change. We tested the effects of ammonium sulfate, urea, chicken manure, liquid pig manure and no fertilization (i.e. control) on soil carbonates neutralization and the contribution of SIC in total CO 2 emission over a 21 day incubation experiment. The alkali trap method was used to measure the total CO 2 emission and the isotopic composition of carbon (C) in the emitted CO 2 from the soil. Liquid pig manure followed by ammonium sulfate apparently led to the highest cumulative SIC-originated CO 2 emissions, while chicken manure and urea showed equally the smallest amount. Nitrate can support the estimation of SIC-originated CO 2 emission when nitrification is the only source of soil acidification. Dissolved Ca 2+ concentration was a more robust proxy than NO 3 - for quantification of SIC-originated CO 2 emission in our batch experiment, however, more evidences have to be collected before using Ca 2+ as a proxy in open soil systems. Verification of the δ 13C values by dissolved Ca 2+ showed that the contribution of SIC to the total CO 2 emission is overestimated after organic N fertilization, whereas an underestimation in the contribution of SIC to the soil CO 2 emission was observed after inorganic N fertilization. In summary, the δ 13C analysis could yield inaccurate results regarding the effects of N fertilization on the contribution of SIC in soil CO 2 emission which should be considered in the future studies. From an environmental point of view, it can be concluded that when the amounts of N, especially in ammonium form e.g. amino groups are relatively high in organic fertilizers as it was the case in liquid pig manure compared to inorganic fertilizers, organic and inorganic N fertilizers lead to comparable amounts of SIC loss. This should be considered in applying organic fertilizers as a sustainable strategy to slow down the rate of soil acidification.

AB - Neutralization of soil inorganic carbon (SIC), i.e., dissolution of carbonate minerals caused by N fertilization-induced acidity, is an ongoing reaction in agroecosystems that leads to significant contribution of SIC to soil CO 2 emission. Analyzing δ 13C natural abundance of the emitted CO 2 is commonly used to quantify the contribution of SIC in total CO 2 emission. However, carbonates recrystallization in isotopic equilibrium with soil respiration can lead to miscalculation, where despite detecting δ 13C signal from carbonates in the emitted CO 2, the SIC stock may not necessarily change. We tested the effects of ammonium sulfate, urea, chicken manure, liquid pig manure and no fertilization (i.e. control) on soil carbonates neutralization and the contribution of SIC in total CO 2 emission over a 21 day incubation experiment. The alkali trap method was used to measure the total CO 2 emission and the isotopic composition of carbon (C) in the emitted CO 2 from the soil. Liquid pig manure followed by ammonium sulfate apparently led to the highest cumulative SIC-originated CO 2 emissions, while chicken manure and urea showed equally the smallest amount. Nitrate can support the estimation of SIC-originated CO 2 emission when nitrification is the only source of soil acidification. Dissolved Ca 2+ concentration was a more robust proxy than NO 3 - for quantification of SIC-originated CO 2 emission in our batch experiment, however, more evidences have to be collected before using Ca 2+ as a proxy in open soil systems. Verification of the δ 13C values by dissolved Ca 2+ showed that the contribution of SIC to the total CO 2 emission is overestimated after organic N fertilization, whereas an underestimation in the contribution of SIC to the soil CO 2 emission was observed after inorganic N fertilization. In summary, the δ 13C analysis could yield inaccurate results regarding the effects of N fertilization on the contribution of SIC in soil CO 2 emission which should be considered in the future studies. From an environmental point of view, it can be concluded that when the amounts of N, especially in ammonium form e.g. amino groups are relatively high in organic fertilizers as it was the case in liquid pig manure compared to inorganic fertilizers, organic and inorganic N fertilizers lead to comparable amounts of SIC loss. This should be considered in applying organic fertilizers as a sustainable strategy to slow down the rate of soil acidification.

KW - Carbon cycle

KW - Carbon sequestration

KW - Global warming

KW - Manure

KW - N fertilizer

KW - Nitrification

KW - Soil acidification

UR - http://www.scopus.com/inward/record.url?scp=105003254490&partnerID=8YFLogxK

U2 - 10.1016/j.geoderma.2025.117309

DO - 10.1016/j.geoderma.2025.117309

M3 - Article

VL - 457

JO - GEODERMA

JF - GEODERMA

SN - 0016-7061

M1 - 117309

ER -