Amplitude and frequency of wetting and drying cycles drive N2_{2} and N2_{2}O emissions from a subtropical pasture

This study investigated the effects of irrigation frequency on N$_{2}$ and N$_{2}$O emissions from an intensively managed pasture in the subtropics. Irrigation volumes were estimated to replace evapotranspiration and were applied either once (low frequency) or split into four applications (high frequency). To test for legacy effects, a large rainfall event was simulated at the end of the experiment. Over 15 days, 7.9 ± 2.7 kg N$_{2}$ + N$_{2}$O-N ha$^{-1}$ was emitted on average regardless of irrigation frequency, with N$_{2}$O accounting for 25% of overall N$_{2}$ + N$_{2}$O. Repeated, small amounts of irrigation produced an equal amount of N$_{2}$ + N$_{2}$O losses as a single, large irrigation event. The increase in N$_{2}$O emissions after the large rainfall event was smaller in the high-frequency treatment, shifting the N$_{2}$O/(N$_{2}$O + N$_{2}$) ratio towards N$_{2}$, indicating a treatment legacy effect. Cumulative losses of N$_{2}$O and N$_{2}$ did not differ between treatments, but higher CO$_{2}$ emissions were observed in the high-frequency treatment. Our results suggest that the increase in microbial activity and related O$_{2}$ consumption in response to small and repeated wetting events can offset the effects of increased soil gas diffusivity on denitrification, explaining the lack of treatment effect on cumulative N$_{2}$O and N$_{2}$ emissions and the abundance of N cycling marker genes. The observed legacy effect may be linked to increased mineralisation and subsequent increased dissolved organic carbon availability, suggesting that increased irrigation frequency can reduce the environmental impact (N$_{2}$O), but not overall magnitude of N$_{2}$O and N$_{2}$ emissions from intensively managed pastures

Gross Ammonification and Nitrification Rates in Soil Amended with Natural and NH4-Enriched Chabazite Zeolite and Nitrification Inhibitor DMPP

Using zeolite-rich tuffs for improving soil properties and crop N-use efficiency is becoming popular. However, the mechanistic understanding of their influence on soil N-processes is still poor. This paper aims to shed new light on how natural and NH4+-enriched chabazite zeolites alter short-term N-ammonification and nitrification rates with and without the use of nitrification inhibitor (DMPP). We employed the 15N pool dilution technique to determine short-term gross rates of ammonification and nitrification in a silty-clay soil amended with two typologies of chabazite-rich tuff: (1) at natural state and (2) enriched with NH4+-N from an animal slurry. Archaeal and bacterial amoA, nirS and nosZ genes, N2O-N and CO2-C emissions were also evaluated. The results showed modest short-term effects of chabazite at natural state only on nitrate production rates, which was slightly delayed compared to the unamended soil. On the other hand, the addition of NH4+-enriched chabazite stimulated NH4+-N production, N2O-N emissions, but reduced NO3-N production and abundance of nirS-nosZ genes. DMPP efficiency in reducing nitrification rates was dependent on N addition but not affected by the two typologies of zeolites tested. The outcomes of this study indicated the good compatibility of both natural and NH4+-enriched chabazite zeolite with DMPP. In particular, the application of NH4 +-enriched zeolites with DMPP is recommended to mitigate short-term N losses

Effect of the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) on N-turnover, the N2_{2}O reductase-gene nosZ and N2_{2}O:N2_{2} partitioning from agricultural soils

Nitrification inhibitors (NIs) have been shown to reduce emissions of the greenhouse gas nitrous oxide (N$_{2}$O) from agricultural soils. However, their N$_{2}$O reduction efficacy varies widely across different agro-ecosystems, and underlying mechanisms remain poorly understood. To investigate effects of the NI 3,4-dimethylpyrazole-phosphate (DMPP) on N-turnover from a pasture and a horticultural soil, we combined the quantification of N$_{2}$ and N$_{2}$O emissions with $^{15}$N tracing analysis and the quantification of the N$_{2}$O-reductase gene (nosZ) in a soil microcosm study. Nitrogen fertilization suppressed nosZ abundance in both soils, showing that high nitrate availability and the preferential reduction of nitrate over N$_{2}$O is responsible for large pulses of N$_{2}$O after the fertilization of agricultural soils. DMPP attenuated this effect only in the horticultural soil, reducing nitrification while increasing nosZ abundance. DMPP reduced N$_{2}$O emissions from the horticultural soil by >50% but did not affect overall N$_{2}$ + N$_{2}$O losses, demonstrating the shift in the N$_{2}$O:N$_{2}$ ratio towards N$_{2}$ as a key mechanism of N$_{2}$O mitigation by NIs. Under non-limiting NO$_{3}$$^{-}$ availability, the efficacy of NIs to mitigate N$_{2}$O emissions therefore depends on their ability to reduce the suppression of the N$_{2}$O reductase by high NO$_{3}$$^{-}$ concentrations in the soil, enabling complete denitrification to N$_{2}$

Quicklime application instantly increases soil aggregate stability

Agricultural intensification, especially enhanced mechanisation of soil management, can lead to the deterioration of soil structure and to compaction. A possible amelioration strategy is the application of (structural) lime. In this study, we tested the effect of two different liming materials, ie limestone (CaCO3) and quicklime (CaO), on soil aggregate stability in a 3-month greenhouse pot experiment with three agricultural soils. The liming materials were applied in the form of pulverised additives at a rate of 2 000 kg ha1. Our results show a significant and instantaneous increase of stable aggregates after quicklime application whereas no effects were observed for limestone. Quicklime application seems to improve aggregate stability more efficiently in soils with high clay content and cation exchange capacity. In conclusion, quicklime application may be a feasible strategy for rapid improvement of aggregate stability of fine textured agricultural soils.(VLID)224292

Short-term effect of the nitrification inhibitor DMPP on N-turnover and denitrification losses from two agricultural soils in subtropical Australia

Intense wetting and drying cycles render agricultural soils in the subtropics prone to nitrogen (N) loss via denitrification, with large pulses of the greenhouse gas nitrous oxide (N2O) triggered by rainfall. The nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) proved to be effective under subtropical conditions, demonstrating substantial reductions of N2O emitted from cropping soils. However, DMPP has consistently failed to reduce N2O emissions from subtropical pasture soils. The aim of this study was therefore to investigate (a) the response of N-transformations and N2O emissions from a subtropical pasture and a vegetable soil to DMPP, and (b) if the abundance of nosZ, the gene encoding the N2O reductase, can explain N2O emissions as affected by DMPP. Soil microcosms were established in centrifuge tubes and fertilised with ammonium nitrate (35 μg g-1 soil) with or without DMPP. Labelling either ammonium (NH4+), or nitrate (NO3-) with 15N at 10 atom% excess enabled the quantification of gross N-transformations using 15N tracer and pool dilution methods. Soil microcosms were incubated at 75% WFPS over two days, and gas samples were taken each day. Gas samples were analysed for 15N2O to split N2O production into the ammonia oxidation pathway and denitrification. Soil was extracted before and after the incubation for DNA, quantifying the response of nosZ abundance to DMPP. Denitrification was the main source of N2O production in both soils. The pasture soil emitted more than 1.5 μg N-N2O g-1 soil over two days, exceeding N2O emissions of the vegetable soil by a factor of 10. This trend was consistent with the high N-transformation rates in the pasture soil, exceeding those of the vegetable soil by a factor >10. DMPP reduced gross nitrification by 12 and 60% for the pasture and vegetable soil, respectively. However, DMPP reduced cumulative N2O emissions from the vegetable soil only. Fertilisation decreased nosZ abundance in the pasture soil, regardless of the treatment. The same trend was observed for the fertiliser only treatment from the vegetable soil. DMPP however increased nosZ abundance compared to the fertiliser only treatment in the vegetable soil. Gross N transformation rates identified the pasture soil as the more productive soil regarding soil mineral N supply and demonstrate the magnitude of N2O emissions as a function of N-turnover. The reduction of nosZ abundance after fertilisation in both soils reflects the stimulating effect of fertiliser and water addition on N turnover. Increased NO3- production suppresses nosZ activity, limiting further reduction of N2O to dinitrogen (N2). This mechanism was mitigated by DMPP in the vegetable soil, explaining the significant reduction of N2O emissions by DMPP. The high N turnover in the pasture soil and the resulting NO3- concentration is likely to limit the short-term efficacy of DMPP. The relationship between N2O emissions and nosZ abundance identifies the shift in the N2:N2O ratio to N2 as a key mechanism of N2O reduction by DMPP. This shift is however driven and limited by soil-intrinsic N-turnover, explaining differences in N2O reduction by DMPP observed for different soil types in the field

Amplitude and frequency of wetting and drying cycles drive N2 and N2O emissions from a subtropical pasture

This study investigated the effects of irrigation frequency on N2 and N2O emissions from an intensively managed pasture in the subtropics. Irrigation volumes were estimated to replace evapotranspiration and were applied either once (low frequency) or split into four applications (high frequency). To test for legacy effects, a large rainfall event was simulated at the end of the experiment. Over 15 days, 7.9 ± 2.7 kg N2 + N2O-N ha−1 was emitted on average regardless of irrigation frequency, with N2O accounting for 25% of overall N2 + N2O. Repeated, small amounts of irrigation produced an equal amount of N2 + N2O losses as a single, large irrigation event. The increase in N2O emissions after the large rainfall event was smaller in the high-frequency treatment, shifting the N2O/(N2O + N2) ratio towards N2, indicating a treatment legacy effect. Cumulative losses of N2O and N2 did not differ between treatments, but higher CO2 emissions were observed in the high-frequency treatment. Our results suggest that the increase in microbial activity and related O2 consumption in response to small and repeated wetting events can offset the effects of increased soil gas diffusivity on denitrification, explaining the lack of treatment effect on cumulative N2O and N2 emissions and the abundance of N cycling marker genes. The observed legacy effect may be linked to increased mineralisation and subsequent increased dissolved organic carbon availability, suggesting that increased irrigation frequency can reduce the environmental impact (N2O), but not overall magnitude of N2O and N2 emissions from intensively managed pastures. </p

Gross Ammonification and Nitrification Rates in Soil Amended with Natural and NH4-Enriched Chabazite Zeolite and Nitrification Inhibitor DMPP

Using zeolite-rich tuffs for improving soil properties and crop N-use efficiency is becoming popular. However, the mechanistic understanding of their influence on soil N-processes is still poor. This paper aims to shed new light on how natural and NH4+-enriched chabazite zeolites alter short-term N-ammonification and nitrification rates with and without the use of nitrification inhibitor (DMPP). We employed the 15N pool dilution technique to determine short-term gross rates of ammonification and nitrification in a silty-clay soil amended with two typologies of chabazite-rich tuff: (1) at natural state and (2) enriched with NH4+-N from an animal slurry. Archaeal and bacterial amoA, nirS and nosZ genes, N2O-N and CO2-C emissions were also evaluated. The results showed modest short-term effects of chabazite at natural state only on nitrate production rates, which was slightly delayed compared to the unamended soil. On the other hand, the addition of NH4+-enriched chabazite stimulated NH4+-N production, N2O-N emissions, but reduced NO3−-N production and abundance of nirS-nosZ genes. DMPP efficiency in reducing nitrification rates was dependent on N addition but not affected by the two typologies of zeolites tested. The outcomes of this study indicated the good compatibility of both natural and NH4+-enriched chabazite zeolite with DMPP. In particular, the application of NH4+-enriched zeolites with DMPP is recommended to mitigate short-term N losses

Effect of the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) on N-turnover, the N2O reductase-gene nosZ and N2O:N2 partitioning from agricultural soils

Nitrification inhibitors (NIs) have been shown to reduce emissions of the greenhouse gas nitrous oxide (N2O) from agricultural soils. However, their N2O reduction efficacy varies widely across different agro-ecosystems, and underlying mechanisms remain poorly understood. To investigate effects of the NI 3,4-dimethylpyrazole-phosphate (DMPP) on N-turnover from a pasture and a horticultural soil, we combined the quantification of N2 and N2O emissions with 15N tracing analysis and the quantification of the N2O-reductase gene (nosZ) in a soil microcosm study. Nitrogen fertilization suppressed nosZ abundance in both soils, showing that high nitrate availability and the preferential reduction of nitrate over N2O is responsible for large pulses of N2O after the fertilization of agricultural soils. DMPP attenuated this effect only in the horticultural soil, reducing nitrification while increasing nosZ abundance. DMPP reduced N2O emissions from the horticultural soil by >50% but did not affect overall N2 + N2O losses, demonstrating the shift in the N2O:N2 ratio towards N2 as a key mechanism of N2O mitigation by NIs. Under non-limiting NO3 − availability, the efficacy of NIs to mitigate N2O emissions therefore depends on their ability to reduce the suppression of the N2O reductase by high NO3 − concentrations in the soil, enabling complete denitrification to N2.</p