Denitrification Rate and Its Potential to Predict Biogenic N2O Field Emissions in a Mediterranean Maize-Cropped Soil in Southern Italy

Abstract

The denitrification rate in C2H2-amended intact soil cores and soil N2O fluxes in closed static chambers were monitored in a Mediterranean irrigated maize-cropped field. The measurements were carried out during: (i) a standard fertilization management (SFM) activity and (ii) a manipulation experimental (ME) test on the effects of increased and reduced application rates of urea at the late fertilization. In the course of the SFM, the irrigations following early and late nitrogen fertilization led to pulses of denitrification rates (up to 1300 μg N2O-N m−2 h−1) and N2O fluxes (up to 320 μg N2O-N m−2 h−1), thanks to the combined action of high soil temperatures and not limiting nitrates and water filled pore space (WFPS). During the ME, high soil nitrates were noted in all the treatments in the first one month after the late fertilization, which promoted marked N-losses by microbial denitrification (from 500 to 1800 μg N2O-N m−2 h−1) every time the soil WFPS was not limiting. At similar maize yield responses to fertilizer treatments, this result suggested no competition for N between plant roots and soil microbial community and indicated a probable surplus of nitrogen fertilizer input at the investigated farm. Correlation and regression analyses (CRA) on the whole set of data showed significant relations between both the denitrification rates and the N2O fluxes with three soil physical-chemical parameters: nitrate concentration, WFPS and temperature. Specifically, the response functions of denitrification rate to soil nitrates, WFPS and temperature could be satisfactorily modelled according to simple Michaelis-Menten kinetic, exponential and linear functions, respectively. Furthermore, the CRA demonstrated a significant exponential relationship between N2O fluxes and denitrification and simple empirical functions to predict N2O emissions from the denitrification rate appeared more fitting (higher concordance correlation coefficient) than the predictive empirical algorithm based on soil nitrates, WFPS and temperature. In this regard, the empirically established relationships between the denitrification rate on intact soil cores under field conditions and the soil variables provided local-specific threshold values and coefficients which may effectively work to calibrate and adapt existing N2O process-based simulation models to the local pedo-climatic conditions.

Effects of the Fertilizer Added with DMPP on Soil Nitrous Oxide Emissions and Microbial Functional Diversity

“…Among these, enhanced fertilizer use efficiency by crop is a promising tool for mitigating climate-altering gas emissions [24]. Better fertilizer use efficiency may be achieved through the development of fertilizers added with specific inhibitors of biological transformations occurring in the soil, particularly nitrification [5].…”

“…The contribution of denitrification to total N 2 O fluxes was evaluated by the acetylene inhibition technique (AIT). Soil samples were collected near autochambers at 0.0-0.10 m depth by a PVC cylinder and put into a homemade PVC incubator [5]. The head-space of the incubator was filled with C 2 H 2 to inhibit the nitrification and samples incubated for 6 h at ambient temperature [5].…”

“…Soil samples were collected near autochambers at 0.0-0.10 m depth by a PVC cylinder and put into a homemade PVC incubator [5]. The head-space of the incubator was filled with C 2 H 2 to inhibit the nitrification and samples incubated for 6 h at ambient temperature [5]. Untreated samples were also prepared.…”

“…Some of N applied to the soil is lost as nitrate (NO 3 − ) by leaching or gas emission, mainly nitrous oxide (N 2 O), making agriculture a sector with a great impact on climate Agriculture 2021, 11, 12 2 of 11 and global environment [1]. The N loss as N 2 O is due to nitrification and denitrification processes, which are controlled by soil physical-chemical conditions such as humidity, temperature, nitrogen and oxygen availability, and pH [2][3][4][5][6]. During nitrification occurring under aerobic conditions, ammonium nitrogen is oxidized to nitrite and nitrate, then reduced in the denitrification process under anaerobic conditions.…”

“…During nitrification occurring under aerobic conditions, ammonium nitrogen is oxidized to nitrite and nitrate, then reduced in the denitrification process under anaerobic conditions. The supply of ammonium-based fertilizers or organic fertilizers to soil determines an enrichment of ammonium in the soil, leading to the production of NO 3 − and N 2 O [4,5]. Different strategies have been utilized in order to mitigate the emissions of climatealtering greenhouse gases (GHGs) from agricultural sites [7].…”