Publications
2017 |
Friedl, J; Scheer, C; Rowlings, D W; Mumford, M; Grace, P R Soil Biology & Biochemistry, 2017. Abstract | Links | BibTeX | Tags: Soil Biology and Biochemistry @article{Friedl2017, title = {The nitrification inhibitor DMPP (3,4-dimethylpyrazole phosphate) reduces N_{2} emissions from intensively managed pastures in subtropical Australia, Soil Biology & Biochemistry}, author = {J. Friedl and C. Scheer and D.W. Rowlings and M. Mumford and P.R. Grace}, doi = {10.1016/j.soilbio.2017.01.016}, year = {2017}, date = {2017-01-22}, journal = {Soil Biology & Biochemistry}, abstract = {Intensively managed pastures receive high inputs ofnitrogen (N) fertilizer, rendering them prone to high N losses via denitrification following intensive rainfall events. Intense rainfall events, which are predicted to increase in frequency with changes in global climate, increase the risk of denitrification losses from agro-ecosystems. Nitrification inhibitors (NI) have been promoted to mitigate N losses, however their effect on total denitrification (N_{2} and N_{2}O) and therefore their agronomic viability remains largely unknown. This study investigated the efficacy of the NI 3,4-dimethylpyrazole phosphate (DMPP) to reduce N_{2} and N_{2}O emissions after heavy rainfall from three pastures with different soil textures in subtropical Australia. Emissions of N_{2} and N_{2}O were measured over three weeks following the application of ^{15}N urea (36.8 kg N ha^{−1}) with and without DMPP. An intense rainfall event was simulated 10 days after fertilization to create saturated conditions in the topsoil. Emissions of N_{2}O decreased after day 1, reflecting a rapid shift towards complete denitrification. Unlike N_{2}O, N_{2} fluxes responded to the rainfall event with peak fluxes up to 3.8 kg N_{2}-N ha^{−1} day^{−1}. The main product of denitrification was N_{2}, which accounted for more than 95% of cumulative denitrification losses across sites. Cumulative N_{2} losses over 21 days remained below 4 kg N ha^{−1} for the well-drained sandy loam, while up to 28 kg N_{2}-N ha^{−1} were emitted from the clay and loam soils, demonstrating N_{2} emissions as a major pathway of N loss from intensively managed pastures. The magnitude of N_{2} losses across pasture sites reflects the combined effect of reduced soil gas diffusivity and microbial oxygen consumption on denitrification. DMPP reduced these N_{2} losses by more than 70%, but had no effect on N_{2}O emissions, providing the first field based evidence that DMPP can substantially reduce N_{2} emissions. The reduction of agronomically significant N_{2} losses highlights the potential of DMPP to mitigate the impact of increased rainfall intensity on denitrification losses thereby improving N use efficiency for intensively managed pastures.}, keywords = {Soil Biology and Biochemistry}, pubstate = {published}, tppubtype = {article} } Intensively managed pastures receive high inputs ofnitrogen (N) fertilizer, rendering them prone to high N losses via denitrification following intensive rainfall events. Intense rainfall events, which are predicted to increase in frequency with changes in global climate, increase the risk of denitrification losses from agro-ecosystems. Nitrification inhibitors (NI) have been promoted to mitigate N losses, however their effect on total denitrification (N2 and N2O) and therefore their agronomic viability remains largely unknown. This study investigated the efficacy of the NI 3,4-dimethylpyrazole phosphate (DMPP) to reduce N2 and N2O emissions after heavy rainfall from three pastures with different soil textures in subtropical Australia. Emissions of N2 and N2O were measured over three weeks following the application of 15N urea (36.8 kg N ha−1) with and without DMPP. An intense rainfall event was simulated 10 days after fertilization to create saturated conditions in the topsoil. Emissions of N2O decreased after day 1, reflecting a rapid shift towards complete denitrification. Unlike N2O, N2 fluxes responded to the rainfall event with peak fluxes up to 3.8 kg N2-N ha−1 day−1. The main product of denitrification was N2, which accounted for more than 95% of cumulative denitrification losses across sites. Cumulative N2 losses over 21 days remained below 4 kg N ha−1 for the well-drained sandy loam, while up to 28 kg N2-N ha−1 were emitted from the clay and loam soils, demonstrating N2 emissions as a major pathway of N loss from intensively managed pastures. The magnitude of N2 losses across pasture sites reflects the combined effect of reduced soil gas diffusivity and microbial oxygen consumption on denitrification. DMPP reduced these N2 losses by more than 70%, but had no effect on N2O emissions, providing the first field based evidence that DMPP can substantially reduce N2 emissions. The reduction of agronomically significant N2 losses highlights the potential of DMPP to mitigate the impact of increased rainfall intensity on denitrification losses thereby improving N use efficiency for intensively managed pastures. |
2016 |
Mitchell, E; Scheer, C; Rowlings, D W; Conant, R T; Grace, P R; Cotrufo, M F; van Delden, L The influence of above-ground residue input and incorporation on GHG fluxes and stable SOM formation in a sandy soil. Journal Article Soil Biology Biochemistry, 101 , pp. 104-113, 2016. Abstract | Links | BibTeX | Tags: Soil Biology and Biochemistry @article{Mitchell2016, title = {The influence of above-ground residue input and incorporation on GHG fluxes and stable SOM formation in a sandy soil.}, author = {E. Mitchell and C. Scheer and D. W. Rowlings and R.T. Conant and P.R. Grace and M.F. Cotrufo and L. van Delden}, doi = {10.1016/j.soilbio.2016.07.008}, year = {2016}, date = {2016-07-20}, journal = {Soil Biology Biochemistry}, volume = {101}, pages = {104-113}, abstract = {Carbon sequestration in agricultural soils has been promoted as a means to reduce atmospheric concentrations of greenhouse gases (GHG) whilst improving soil productivity. Although there is broad agreement on practices that increase carbon (C) stocks, there is a lack of understanding on the stability of these gains and how changes in soil organic carbon (SOC) pools can influence GHG fluxes. We tracked the fate of above-ground residues into functionally different SOC pools and GHG fluxes using isotopically labelled residues (^{13}C and ^{15}N) over 12 months in a pasture soil in sub-tropical Australia. Agricultural residue management was simulated by: (1) altering the rate of residue input and, (2) mixing residue with topsoil. GHG fluxes were significantly greater at high residue input levels due to the priming of existing SOC and elevated N_{2}O losses, fuelled by a greater availability of labile substrate. There was evidence of an asymptotic relationship between C input and residue-derived C accumulation in stable soil C pools at higher input levels, indicating that the soil was reaching its protective capacity. Mixing of residues contributed to a 40% increase in GHG fluxes in comparison to surface applied treatment, most notably from residue-derived C and N. This can be attributed to (i) the physical disruption of soil, particularly that of aggregates, which changed the microenvironment stimulating microbial activity, and (ii) greater residue-soil contact. Greater residue-soil contact through mixing also contributed to a 2 fold increase in the residue-derived C recovered in the mineral soil with the majority (56%) in the active C pool. Over a 12 month period, C sequestration was outweighed by GHG fluxes at high rates of input and when residues were mixed with the topsoil. C sequestration policies and associated management approaches must be assessed holistically under a range of conditions and in the long-term to ensure that detrimental practices are not promoted.}, keywords = {Soil Biology and Biochemistry}, pubstate = {published}, tppubtype = {article} } Carbon sequestration in agricultural soils has been promoted as a means to reduce atmospheric concentrations of greenhouse gases (GHG) whilst improving soil productivity. Although there is broad agreement on practices that increase carbon (C) stocks, there is a lack of understanding on the stability of these gains and how changes in soil organic carbon (SOC) pools can influence GHG fluxes. We tracked the fate of above-ground residues into functionally different SOC pools and GHG fluxes using isotopically labelled residues (13C and 15N) over 12 months in a pasture soil in sub-tropical Australia. Agricultural residue management was simulated by: (1) altering the rate of residue input and, (2) mixing residue with topsoil. GHG fluxes were significantly greater at high residue input levels due to the priming of existing SOC and elevated N2O losses, fuelled by a greater availability of labile substrate. There was evidence of an asymptotic relationship between C input and residue-derived C accumulation in stable soil C pools at higher input levels, indicating that the soil was reaching its protective capacity. Mixing of residues contributed to a 40% increase in GHG fluxes in comparison to surface applied treatment, most notably from residue-derived C and N. This can be attributed to (i) the physical disruption of soil, particularly that of aggregates, which changed the microenvironment stimulating microbial activity, and (ii) greater residue-soil contact. Greater residue-soil contact through mixing also contributed to a 2 fold increase in the residue-derived C recovered in the mineral soil with the majority (56%) in the active C pool. Over a 12 month period, C sequestration was outweighed by GHG fluxes at high rates of input and when residues were mixed with the topsoil. C sequestration policies and associated management approaches must be assessed holistically under a range of conditions and in the long-term to ensure that detrimental practices are not promoted. |
2015 |
Friedl, J; Scheer, C; Rowlings, D; McIntosh, H; Strazzabosco, A; Warner, D; Grace, P Denitrification losses from an intensively managed sub-tropical pasture – Impact of soil moisture on the partitioning of N2 and N2O emissions Journal Article Soil Biology and Biochemistry, 92 , pp. 58-66, 2015. Abstract | Links | BibTeX | Tags: Soil Biology and Biochemistry @article{Friedl2015, title = {Denitrification losses from an intensively managed sub-tropical pasture – Impact of soil moisture on the partitioning of N_{2} and N_{2}O emissions}, author = { J Friedl and C Scheer and D Rowlings and H McIntosh and A Strazzabosco and D Warner and P. Grace}, doi = {10.1016/j.soilbio.2015.09.016}, year = {2015}, date = {2015-09-25}, journal = {Soil Biology and Biochemistry}, volume = {92}, pages = {58-66}, abstract = {Intensively managed pastures in subtropical Australia under dairy production are nitrogen (N) loaded agro-ecosystems, with an increased pool of N available for denitrification. The magnitude of denitrification losses and N_{2}:N_{2}O partitioning in these agro-ecosystems is largely unknown, representing a major uncertainty when estimating total N loss and replacement. This study investigated the influence of different soil moisture contents on N_{2} and N_{2}O emissions from a subtropical dairy pasture in Queensland, Australia. Intact soil cores were incubated over 15 days at 80% and 100% water-filled pore space (WFPS), after the application of ^{15}N labelled nitrate, equivalent to 50 kg N ha^{−1}. This setup enabled the direct quantification of N_{2} and N_{2}O emissions following fertilisation using the ^{15}N gas flux method. The main product of denitrification in both treatments was N_{2}. N_{2} emissions exceeded N_{2}O emissions by a factor of 8 ± 1 at 80% WFPS and a factor of 17 ± 2 at 100% WFPS. The total amount of N-N_{2} lost over the incubation period was 21.27 kg ± 2.10 N_{2}-N ha^{−1} at 80% WFPS and 25.26 kg ± 2.79 kg ha^{−1} at 100% WFPS respectively. N_{2} emissions remained high at 100% WFPS, while related N_{2}O emissions decreased. At 80% WFPS, N_{2} emissions increased constantly over time while N_{2}O fluxes declined. Consequently, N_{2}/(N_{2} + N_{2}O) product ratios increased over the incubation period in both treatments. N_{2}/(N_{2} + N_{2}O) product ratios responded significantly to soil moisture, confirming WFPS as a key driver of denitrification. The substantial amount of fertiliser lost as N_{2} reveals the agronomic significance of denitrification as a major pathway of N loss for sub-tropical pastures at high WFPS and may explain the low fertiliser N use efficiency observed for these agro-ecosystems.}, keywords = {Soil Biology and Biochemistry}, pubstate = {published}, tppubtype = {article} } Intensively managed pastures in subtropical Australia under dairy production are nitrogen (N) loaded agro-ecosystems, with an increased pool of N available for denitrification. The magnitude of denitrification losses and N2:N2O partitioning in these agro-ecosystems is largely unknown, representing a major uncertainty when estimating total N loss and replacement. This study investigated the influence of different soil moisture contents on N2 and N2O emissions from a subtropical dairy pasture in Queensland, Australia. Intact soil cores were incubated over 15 days at 80% and 100% water-filled pore space (WFPS), after the application of 15N labelled nitrate, equivalent to 50 kg N ha−1. This setup enabled the direct quantification of N2 and N2O emissions following fertilisation using the 15N gas flux method. The main product of denitrification in both treatments was N2. N2 emissions exceeded N2O emissions by a factor of 8 ± 1 at 80% WFPS and a factor of 17 ± 2 at 100% WFPS. The total amount of N-N2 lost over the incubation period was 21.27 kg ± 2.10 N2-N ha−1 at 80% WFPS and 25.26 kg ± 2.79 kg ha−1 at 100% WFPS respectively. N2 emissions remained high at 100% WFPS, while related N2O emissions decreased. At 80% WFPS, N2 emissions increased constantly over time while N2O fluxes declined. Consequently, N2/(N2 + N2O) product ratios increased over the incubation period in both treatments. N2/(N2 + N2O) product ratios responded significantly to soil moisture, confirming WFPS as a key driver of denitrification. The substantial amount of fertiliser lost as N2 reveals the agronomic significance of denitrification as a major pathway of N loss for sub-tropical pastures at high WFPS and may explain the low fertiliser N use efficiency observed for these agro-ecosystems. |
2014 |
Scheer, C; Rowlings, D W; Firrel, M; Deuter, P; Morris, S; Grace, P R Impact of nitrification inhibitor (DMPP) on soil nitrous oxide emissions from an intensive broccoli production system in sub-tropical Australia Journal Article Soil Biology and Biochemistry, 77 , pp. 243-251, 2014. Abstract | Links | BibTeX | Tags: Soil Biology and Biochemistry @article{Scheer2014, title = {Impact of nitrification inhibitor (DMPP) on soil nitrous oxide emissions from an intensive broccoli production system in sub-tropical Australia}, author = { C Scheer and D. W. Rowlings and M Firrel and P Deuter and S Morris and P. R. Grace }, doi = {10.1016/j.soilbio.2014.07.006}, year = {2014}, date = {2014-07-06}, journal = {Soil Biology and Biochemistry}, volume = {77}, pages = {243-251}, abstract = {Vegetable cropping systems are often characterised by high inputs of nitrogen fertiliser. Elevated emissions of nitrous oxide (N_{2}O) can be expected as a consequence. In order to mitigate N_{2}O emissions from fertilised agricultural fields, the use of nitrification inhibitors, in combination with ammonium based fertilisers, has been promoted. However, no data is currently available on the use of nitrification inhibitors in sub-tropical vegetable systems. A field experiment was conducted to investigate the effect of the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) on N_{2}O emissions and yield from broccoli production in sub-tropical Australia. Soil N_{2}O fluxes were monitored continuously (3 h sampling frequency) with fully automated, pneumatically operated measuring chambers linked to a sampling control system and a gas chromatograph. Cumulative N_{2}O emissions over the 5 month observation period amounted to 298 g-N/ha, 324 g-N/ha, 411 g-N/ha and 463 g-N/ha in the conventional fertiliser (CONV), the DMPP treatment (DMPP), the DMMP treatment with a 10% reduced fertiliser rate (DMPP-red) and the zero fertiliser (0N), respectively. The temporal variation of N_{2}O fluxes showed only low emissions over the broccoli cropping phase, but significantly elevated emissions were observed in all treatments following broccoli residues being incorporated into the soil. Overall 70–90% of the total emissions occurred in this 5 weeks fallow phase. There was a significant inhibition effect of DMPP on N_{2}O emissions and soil mineral N content over the broccoli cropping phase where the application of DMPP reduced N_{2}O emissions by 75% compared to the standard practice. However, there was no statistical difference between the treatments during the fallow phase or when the whole season was considered. This study shows that DMPP has the potential to reduce N_{2}O emissions from intensive vegetable systems, but also highlights the importance of post-harvest emissions from incorporated vegetable residues. N_{2}O mitigation strategies in vegetable systems need to target these post-harvest emissions and a better evaluation of the effect of nitrification inhibitors over the fallow phase is needed.}, keywords = {Soil Biology and Biochemistry}, pubstate = {published}, tppubtype = {article} } Vegetable cropping systems are often characterised by high inputs of nitrogen fertiliser. Elevated emissions of nitrous oxide (N2O) can be expected as a consequence. In order to mitigate N2O emissions from fertilised agricultural fields, the use of nitrification inhibitors, in combination with ammonium based fertilisers, has been promoted. However, no data is currently available on the use of nitrification inhibitors in sub-tropical vegetable systems. A field experiment was conducted to investigate the effect of the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) on N2O emissions and yield from broccoli production in sub-tropical Australia. Soil N2O fluxes were monitored continuously (3 h sampling frequency) with fully automated, pneumatically operated measuring chambers linked to a sampling control system and a gas chromatograph. Cumulative N2O emissions over the 5 month observation period amounted to 298 g-N/ha, 324 g-N/ha, 411 g-N/ha and 463 g-N/ha in the conventional fertiliser (CONV), the DMPP treatment (DMPP), the DMMP treatment with a 10% reduced fertiliser rate (DMPP-red) and the zero fertiliser (0N), respectively. The temporal variation of N2O fluxes showed only low emissions over the broccoli cropping phase, but significantly elevated emissions were observed in all treatments following broccoli residues being incorporated into the soil. Overall 70–90% of the total emissions occurred in this 5 weeks fallow phase. There was a significant inhibition effect of DMPP on N2O emissions and soil mineral N content over the broccoli cropping phase where the application of DMPP reduced N2O emissions by 75% compared to the standard practice. However, there was no statistical difference between the treatments during the fallow phase or when the whole season was considered. This study shows that DMPP has the potential to reduce N2O emissions from intensive vegetable systems, but also highlights the importance of post-harvest emissions from incorporated vegetable residues. N2O mitigation strategies in vegetable systems need to target these post-harvest emissions and a better evaluation of the effect of nitrification inhibitors over the fallow phase is needed. |