Abstract
Among strategies suggested to decrease agricultural soil N2O losses, the use of nitrification inhibitors such as DMPP (3,4-dimethylpyrazole phosphate) has been proposed. However, the efficiency of DMPP might be affected by soil amendments, such as biochar, which has been shown to reduce N2O emissions. This study evaluated the synergic effect of a woody biochar applied with DMPP on soil N2O emissions. A incubation study was conducted with a silt loam soil and a biochar obtained from Pinus taeda at 500 °C. Two biochar rates (0 and 2% (w/w)) and three different nitrogen treatments (unfertilized, fertilized and fertilized + DMPP) were assayed under two contrasting soil water content levels (40% and 80% of water filled pore space (WFPS)) over a 163 day incubation period. Results showed that DMPP reduced N2O emissions by reducing ammonia-oxidizing bacteria (AOB) populations and promoting the last step of denitrification (measured by the ratio nosZI + nosZII/nirS + nirK genes). Biochar mitigated N2O emissions only at 40% WFPS due to a reduction in AOB population. However, when DMPP was applied to the biochar amended soil, a counteracting effect was observed, since the N2O mitigation induced by DMPP was lower than in control soil, demonstrating that this biochar diminishes the efficiency of the DMPP both at low and high soil water contents.
Highlights
N2O emissions by reducing ammonia-oxidizing bacteria (AOB) populations and promoting the last step of denitrification
Partial ƞ2 values indicate that most of the effect on N2O emissions was due to water filled pore space (WFPS), followed by fertilizer treatment and into a lesser extent by to biochar addition
To other studies where the AOB population was unaffected at high soil water content[11], dimethylpyrazole phosphate (DMPP) showed a high efficiency mitigating N2O emissions at both soil water contents via a direct effect on nitrification, since AOB abundance was significantly reduced at both conditions
Summary
N2O emissions by reducing ammonia-oxidizing bacteria (AOB) populations and promoting the last step of denitrification (measured by the ratio nosZI + nosZII/nirS + nirK genes). The main microbial N-transforming processes contributing to N2O formation are nitrification and denitrification[3]. The end product of nitrification, nitrate, can be reduced to nitrogen gas (N2) via the formation of NO2−, nitric oxide (NO) and N2O. Such sequential denitrification processes are carried out by nitrate reductase (encoded by the narG gene), nitrite reductases (encoded by the nirS/nirK genes), and nitrous oxide reductase (encoded by the nosZ genes) under anaerobic soil conditions[4]. Nitrification is the preferential source of N2O fluxes from well-aerated soils, with WFPS 70% denitrification dominates N-transformation in soils causing emission of N2O7
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