Forschungsdaten – Titel und Zusammenfassungen von Publikationen, extrahierte Daten und Katalogeinträge – erscheinen in ihrer Originalsprache Englisch.
Process of denitrification in flooded rice soils
Tharangika Ranatunga, Ken Hiramatsu, Takeo Onishi, Yasushi Ishiguro
KI-Zusammenfassung
72 % KonfidenzThis review examines denitrification in flooded rice soils, a major pathway of nitrogen loss from fertilizer. The authors synthesize mechanisms of N transformation (nitrification, denitrification, DNRA, anammox, coupled processes) and their environmental drivers—redox potential (Eh), oxygen, organic carbon, nitrate availability, and water regime. They propose that microbial fuel cell technology based on soil redox chemistry could control denitrification rates. The paper emphasizes that complete denitrification to N₂ dominates in flooded rice (not N₂O), and identifies water-filled pore space thresholds and seasonal N₂O emission patterns as critical control points.
Zentrale Erkenntnisse
Schwellenwert Denitrification initiates at water-filled pore space ≥60%, and N₂O is a minor product in flooded rice because prolonged submergence drives complete reduction of N₂O to N₂ via nos genes.
Was heißt das. Maintain flooded conditions to suppress N₂O emissions; intermittent drying or natural drying cycles increase N₂O flux, so avoid alternating wet–dry regimes if N₂O mitigation is the goal.
Mechanismus Soil redox potential (Eh) ranges from −1 to +3 pE in flooded rice, and negative Eh values are attained within 2 weeks after submergence in high-carbon soils but take longer in low-carbon soils.
Was heißt das. Carbon availability controls the rate of Eh decline; pre-flood carbon amendment accelerates transition to anaerobic denitrifying conditions, enabling faster N₂O reduction.
Zielkonflikt N₂O emission response to N fertilizer input is exponential, not linear; emission grows significantly faster than linear for synthetic fertilizers across most crop types.
Was heißt das. Avoid over-application of synthetic N fertilizer; small reductions in excess N input yield disproportionately large reductions in N₂O emissions.
Mechanismus Coupled nitrification–denitrification in the root rhizosphere causes 29% loss of applied NH₄⁺–N in 18 days, driven by O₂ entry through rice aerenchyma creating aerobic–anaerobic microhabitats.
Was heißt das. Deep placement of N fertilizer below the root zone and timing application after root establishment can reduce nitrification–denitrification losses.
Mechanismus narG-containing denitrifiers (nitrate reductase) correlate more strongly with N₂O flux than nosZ-containing denitrifiers (N₂O reductase) during flooding–drying cycles, and narG copy number increases with flooding and decreases with drying.
Was heißt das. Monitor narG abundance as a biomarker for N₂O production risk; drying cycles suppress nos gene expression, blocking the final reduction step and causing N₂O accumulation.
Widersprüche1
Nur Konflikte, die die Publikation selbst zeigt, jeweils am Text geprüft.
Innerhalb der Publikation N₂O is described as both negligible and significant in flooded rice systems
Eine SeiteN₂O emissions are not considered significant compared to CH₄ in flooded rice (abstract and Section 3)
“Nitrous oxide (N2O) emissions are not considered as significant, compared to that of methane (CH4) emissions from flooded rice soils”
Andere SeiteRice paddies are recognized as one of the main agricultural sources of N₂O and a potent greenhouse gas (Section 3)
“Rice paddies are regarded as one of the main agricultural sources of N2O and the available data was summarized by Akiyama et al. (2005)”
Einordnung der Autoren. The authors reconcile this by clarifying that N₂O is minor relative to CH₄ in flooded rice specifically (due to complete denitrification to N₂), but rice paddies remain significant global sources of N₂O compared to other agricultural systems. The distinction is relative (flooded rice vs. CH₄) versus absolute (rice vs. other crops).
Ansatzpunkte6
Konkrete Lücken in dieser Publikation, jeweils mit einem Experiment, das sie schließen würde.
Hoch No experimental data on cathode or anode potential windows for controlling denitrification rate in bioelectrochemical systems applied to flooded rice soils
The abstract and conclusion propose MFC/MES for redox control but provide no electrochemical operating parameters (cathode Eh, anode potential, current density, HRT) tested in this system
Versuch. Vary cathode potential (−0.4 to +0.2 V vs. Ag/AgCl) and measure denitrification rate, N₂O vs. N₂ ratio, and soil Eh response in a bioelectrochemical cell with flooded rice soil
Hoch No quantification of the relationship between soil Eh and the ratio of nos gene expression (N₂O reductase) to nir gene expression (nitrite reductase)
Section 3 shows narG and nosZ copy numbers respond to flooding–drying cycles, but the paper does not measure how Eh directly controls the expression ratio that determines N₂O vs. N₂ product distribution
Versuch. Maintain flooded rice soil at controlled Eh values (−200 to +100 mV) and measure nosZ/nir gene expression ratio and N₂O:N₂ product ratio over 4 weeks
Mittel No data on C/N ratio optimization for minimizing N₂O while maintaining denitrification in flooded rice
Section 2.6 mentions C/N ratio controls mineralization vs. immobilization, and Section 3 shows N fertilizer rate drives N₂O exponentially, but no study varies C/N ratio to find the window that maximizes N₂ production and minimizes N₂O
Versuch. Test C/N ratios from 5:1 to 20:1 in flooded rice microcosms and measure denitrification rate, N₂O flux, and narG/nosZ expression
Mittel No measurement of nitrite (NO₂⁻) accumulation under different Eh or oxygen regimes in flooded rice bioelectrochemical systems
The paper describes NO₂⁻ as an intermediate in denitrification (Section 1.2) and notes that nir genes catalyze its reduction, but does not report whether NO₂⁻ accumulates under any condition tested, which would indicate incomplete denitrification
Versuch. Monitor NO₂⁻ concentration in pore water during controlled Eh transitions (flooding to drying) and correlate with nir gene expression and N₂O flux
Mittel No data on the effect of catholyte pH on denitrification rate or N₂O production in an MES applied to flooded rice
Section 2.5 shows pH controls ammonia volatilization via the HCO₃⁻/CO₂ equilibrium, and nitrifier-denitrification is favored at low pH (Section 2.3), but no study tests how pH in a bioelectrochemical cathode chamber affects denitrification pathway selection
Versuch. Vary catholyte pH from 6.5 to 8.5 in an MES with flooded rice soil and measure denitrification rate, N₂O:N₂ ratio, and nitrifier-denitrification vs. heterotrophic denitrification markers
Mittel No comparison of ammonia recovery efficiency vs. denitrification loss under different redox potentials in flooded rice bioelectrochemical systems
The paper proposes MFC for redox control but does not quantify the trade-off between recovering NH₄⁺ (via DNRA or dissimilatory reduction) and minimizing N loss via denitrification at different Eh values
Versuch. Operate an MES at cathode potentials from −0.6 to 0 V and measure NH₄⁺ recovery, N₂O flux, and N₂ production to identify the potential window that maximizes recovery while minimizing N₂O
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- MFC
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Zusammenfassung
Denitrification, which converts soil nitrogen to nitrogen gas, involves a great loss of nitrogen fertilizer. Controlling the process of denitrification rate could help reducing the losses of applied nitrogen fertilizer in crop fields. Fertilizer nitrogen is one of the major concerns due to the high energy demand for its production. Since flooded rice soils are known to have strong denitrifying activity, innovative techniques are emerging as needs to improve nitrogen fertilizer retention efficiency in flooded rice soils. Nitrous oxide (N2O) emissions are not considered as significant, compared to that of methane (CH4) emissions from flooded rice soils, most probably due to its complete denitrification process with prolonged submergence that favors the production of nitrogen (N2) gas. This is due to a further reduction of N2O to N2. However, efficient use of nitrogen in the rice soils could have the benefits of saving energy costs that are being spent on nitrogen fertilizers in many developing countries. While conventional approaches are less efficient in controlling denitrification, technical solutions are emerging to solve this need. Technical solutions based on soil redox potential (Eh) for the control of denitrification have not been adequately covered. We propose that applicability of microbial fuel cell based on soil redox chemistry would be more promising for the control of denitrification in flooded rice soils.
Schlagwörter
Kennungen
- Zeitschrift
- Reviews in Agricultural Science
- Jahr
- 2018
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