There is an increasing need for accurate and readily available farm level data as environmental sustainability reporting becomes an embedded part of livestock supply chain activities. In this study, we aimed to understand the Australian beef industry’s contemporary approaches to measuring farm level sustainability and the challenges encountered with collecting and using farm level data. In-depth interviews with industry professionals and academic experts revealed systemic and practical challenges limiting the collection and usefulness of farm level data for supply chain sustainability reporting. These challenges were grouped into four main themes: data collection and quality; data coverage, comprehensibility and language; and governance challenges. We found systemic issues stemmed from governance challenges, namely barriers to investment in data collection initiatives upheld by industry competitiveness and a perception of a data free-riding phenomenon. Politicisation of the sustainability of beef production, and the lack of standards around how to measure environmental sustainability attributes has the potential to cause severe adverse outcomes for the industry’s sustainability measuring and reporting activities, although some industry players currently benefit from the lack of standards through product differentiation. To address practical challenges of data coverage and quality, we refer to the growing movement of using research infrastructure networks to collect high quality datasets of environmental attributes, including Australia’s Long-Term Agroecosystem Research Network. Our findings highlight the need for more structured sustainability standards and governance, to build clarity for the industry and ensure meaningful sustainability reporting is achieved.

Context Lower nitrogen (N) use efficiency and direct N losses are adversely affecting global cereal production. Yet, the exact fate of applied N in the soil and the interactions that occur are largely unknown. Aims We aimed to quantify the fate, recovery and magnitude of losses from applied N and compare the effectiveness of compost application on N recovery and yield. We hypothesised that high N losses and low N use efficiency from tropical soils can be combatted by integrated application of compost and synthetic N. Methods A randomised complete block design with two N rates and two compost rates (0 and 15 Mg ha−1) with four replicates was used. Isotopically (15N) labelled urea was applied to tropical maize and the 15N recovery, grain yield and dry matter were analyzed. Key results The combination of compost and urea increased N recovery (16% reduction in N loss), and significantly increased maize yield by 50% and stover yield by 33% in applied urea 150N (urea at 150 kg N ha−1) + compost treatment relative to the 150N only treatment, demonstrating that compost-derived N considerably increased crop N acquisition compared to urea alone. Compost addition significantly increased both apparent N recovery and mineralised N by 31% and 62%, respectively. Up to 71% N harvested was obtained from non-fertiliser sources, with 80–90% recovered in the surface 40 cm of soil. Application of urea and compost demonstrated the considerable potential to increase N recovery and enhance crop productivity of cereals. Conclusion Proving the hypothesis, beyond the effect of mineral N alone, additional organic N provided by compost significantly contributed to crop productivity and N retention in the soil. Compost is thus characterised as an ecologically balanced alternative to synthetic fertiliser, with potential decreases in losses of N, while enhancing N recovery in the plant–soil system. Implications As compost is unlikely to be commercially feasible at the rates applied and difficult to handle as a bulk, further studies should explore the most cost-effective and practical rates of compost application combined with optimised urea rates.

According to current global trends, there is little prospect of achieving either the IPCC’s target reduction of carbon emissions needed to hold temperature increases to both 1.5 and 2.0 degrees or the UN’s Sustainable Development Goal’s target of preserving 30

Nitrogen (N) is vital for mango yield and fruit quality, but finding the optimal amount is crucial to avoid the ‘stay green’ problem, which diminishes both fruit quality and profitability. This study aimed to assess the impact of N levels on the fruit quality and yield of ‘Kensington Pride’ (‘KP’) mangoes and determine the amount of N that triggers the ‘stay green’ effect in fruit. A field trial was conducted in a commercial orchard with N treatments (0, 12.5, 25, and 50 kg ha−1) and four replications during the 2018 and 2019 cropping seasons. Fruit yield was quantified, and post-harvest quality (skin color during ripening, sugar content [°Brix], and texture) as well as ethylene effects were assessed. Fruit yields did not vary among N levels over the two cropping seasons but were significantly lower in 2018 (20.0 t ha−1) compared to 2019 (38.5 t ha−1), illustrating the alternate year-bearing habit of ‘KP’ mangoes. In the 2018 harvest, fruit from trees receiving 25 kg N ha−1 appeared yellow–green compared to those with less N, while fruit from trees with 50 kg N ha−1 exhibited ‘stay green’ skin, indicating that applications of 25 and 50 kg N ha−1 were excessive. There was no ‘stay green’ skin observed in the 2019 harvest, indicating that the environment may also be a contributing factor. The texture of ripe fruit from untreated control trees had the highest flesh resistance. Moreover, ethylene-treated fruit ripened in nine days post-harvest and had significantly lower sugar content than untreated fruit, which ripened in 14 days. This study provides valuable insights into the complex interactions among N application, fruit quality, and yield of ‘KP’ mangoes, highlighting the importance of appropriate N management for a sustainable and environmentally friendly commercial mango production system.

Soil organic carbon dynamics are strongly influenced by soil and climate conditions, as well as management practices including grazing and cropping. Over the past two decades, biogeochemical models have been widely used for analysing the effect of different environmental and management variables on soil carbon, including potential change under hypothetical future climate and management scenarios. The DayCent model, which is a daily implementation of the Century model, considers the impacts of soil texture, climate, historical vegetation cover, and land management practices, including crop type, fertilizer additions, and cultivation events on soil carbon dynamics.In this study, we calibrate the DayCent model for two long-term (38-year) native pasture exclosures at one location in south-eastern Queensland. These sites have had similar management, being ungrazed and burnt or mown at the beginning of each pasture growing season but differ with respect to soil type (texture and depth) and species composition. One site is dominated by kangaroo grass (Themeda triandra), which represents the species composition prior to the introduction of tree clearing and grazing by cattle in the late 1800s. The other site is dominated by black spear grass (Heteropogon contortus) which has become the dominant species in the region since that time. To reflect the long-term species composition changes in the region, kangaroo grass crop parameters were used to run the model to equilibrium from year 1 AD to the year 1900 for both sites, and spear grass parameters were introduced in 1901 for the spear grass site.The model calibration concentrated on the key ‘crop’ parameters governing potential production, root to shoot ratio, and plant carbon to nitrogen ratio. The calibrated DayCent model accounted for only 21 percent of the observed year-to-year variability in end-of-season above-ground biomass at the kangaroo grass site and 58% at the spear grass site. The observed biomass production for the two sites was most strongly correlated with simulated evapotranspiration during the growing season (R2 = 0.43 and 0.58 for kangaroo grass and spear grass respectively) and we found a strong correlation between simulated and observed soil water content to a depth of 50 cm at both sites (R2 = 0.64 and 0.6 for kangaroo grass and speargrass respectively).Whilst year-to-year variability was not well simulated, the long-term average production of each site is the main driver of soil carbon. For both sites, the model overestimated the average observed above-ground biomass at the end of the growing season by approximately 15 percent. By this time of year, the plants have flowered and lost biomass through the detachment of seeds and seed heads as well as some dead leaves. The timing of this detachment process is difficult to simulate in DayCent and it is therefore likely that DayCent simulated the annual biomass production quite closely. It remains to validate the DayCent simulations against similar long-term production data at a further six long-term study sites at this location and to evaluate how well DayCent simulates observed soil carbon across soil types, both under grazed and ungrazed conditions.

Intensively managed pasture systems receive large inputs of nitrogen (N) in the form of fertiliser and through the deposition of ruminant urine, creating hot-spots for denitrification which results in variable amounts of nitrous oxide (N2O) and dinitrogen (N2) emitted. Here we investigated the potential of increased irrigation frequency to reduce N2O and N2 emissions from an intensively managed pasture in the subtropics after ruminant urine deposition. Irrigation volumes were estimated to replace evapotranspiration and were applied either once (Low-Frequency) or split into four applications (High-Frequency). This irrigation schedule was applied 3 times over the 60 day monitoring period, and fluxes of N2O and N2 were measured using the 15N gas flux method. In line with farming practice, simulated urine patches (equivalent of 80 g N m-2 applied) were also fertilised three times with 2 g urea N m-2 to show the combined effects of urinary and fertiliser N on N2O and N2 emissions. Highest N2O emissions of up to 60 mg N2O-N m-2 day-1 were observed briefly after urine deposition, decreasing thereafter, resulting in cumulative N2O losses of 169.9 mg N2O-N m-2 from the Low-Frequency treatment. Denitrification was dominated by N2, accounting for more than 89% of N2O+N2 emitted. Irrigation treatments had no effect on cumulative N2 losses of more than 2700 mg N2-N m-2. However, High frequency irrigation reduced cumulative N2O losses by 35%. Our findings suggest that under conditions of high N availability, increased irrigation frequency can reduce the environmental impact (N2O) of denitrification, but not overall N losses via this pathway. The response of N2O emissions may further indicate that less frequent, but more intense rainfall events will shift the product ratio of denitrification towards N2O, increasing environmentally harmful N losses from intensively managed pasture systems.

Soil organic carbon (SOC) plays an important role in sequestering CO2 and assists in reducing atmospheric greenhouse gases in addition plays a critical role in maintaining the sustainability of grasslands. The valuable roles of SOC, make its accurate measurement critical however temporal changes in SOC are small and spatially vary. Therefore, a large number of samples are required to detect the SOC changes which makes it a complex and costly task. Stratification is capable of improving the efficiency of sampling by reducing the number of samples and increasing the accuracy of SOC measurement. Stratification relies on assessing the relationship between SOC and environmental factors. Vegetation has the potential to be used as a proxy to spatially predict SOC.This experiment aimed to assess the relationship between SOC and vegetation characteristics as a key factor in small areas with uniform climate and soil type. The three study sites were located in southern Queensland with subtropical climate. Short-term data was collected using the BOTANAL method and biomass harvesting over two years period in different seasons which included biomass, pasture composition, and vegetation type. Long-term data was extracted from various satellite images for up to 30 years which indicate the long-term effect of vegetation on SOC. Remote sensing data contained vegetation and soil indices.The kriging method was applied to both soil and vegetation data to interpolate unsampled points for the study areas, then K-means clustering was used to cluster the data. Spearman rank-order correlation coefficient was used to assess the correlation between SOC clusters and vegetation factor clusters.While some of the vegetation parameters have a significant correlation with SOC, the correlation is not consistent between different sites and different seasons. It can be concluded from this study that vegetation factors are not capable of using landscape clustering for SOC sampling on small scale.

Soil carbon (C) sequestration by restoring degraded grasslands with adequate management practices offers significant opportunities for climate change mitigation while remaining highly uncertain. In this study, a combination of a biogeochemical model DayCent-CABBI and eddy covariance (EC) flux towers was applied to evaluate soil C sequestration potential (at a depth of 0-0.3 m) of management strategies in subtropical grasslands. DayCent-CABBI was calibrated for grasslands in northeast Australia using biomass and soil organic carbon (SOC) data from a long-term trial and then fine-tuned using EC flux tower data from seven sites in the region. The model was then validated with cumulative net ecosystem exchange, biomass, and SOC, resulting in root mean square errors of 1.16, 0.88, and 2.81 Mg C ha-1, respectively. The model was used to project long-term changes in SOC stocks under innovative management practices (time-controlled grazing and pasture legume incorporation), estimating soil C sequestration by 0.37-0.48 and 0.15-0.26 Mg C ha-1 year-1 toward 2050 with the respective practices. This study confirms the validity of the Measure, Model, and Verification (MMV) approach to estimate and project soil C sequestration for evaluating SOC methodologies by grassland management within a shorter period than soil sampling-measuring the baseline SOC, modeling the C dynamics with the calibrated DayCent-CABBI, and verifying the projected soil C sequestration with EC flux tower data.

Voluntary carbon offset markets play an important role in climate change mitigation by deploying technologies in order of lowest abatement cost. The objective of this study is to identify the key drivers of changes in the volume of carbon credits issued in voluntary registry offset markets from 2006 to 2020 using a decomposition analysis framework. The results show that the volume of issued carbon credits related to forestry and land use increased from 2006 to 2015 due to priority increases and scale expansions in REDD+ projects. In addition, the reasons for the priority changes in carbon credits issued varied according to the scale of carbon offset programs in each region. The comparison of scale effect and carbon offset program priority is a useful tool for understanding changes in carbon credits issued according to project technology and region. The very rapid increase in forestry carbon credits issued does however pose important policy implications given it has been accompanied by widespread indications of poor governance and questionable outcomes in terms of CO2 reduction. In light of the IPCC's reliance on carbon credits the need for thoroughgoing policy reform is underlined.

Shang et al. (2024) recently suggested to include nitrous oxide (N2O) emissions during the fallow period to better estimate N2O emission factors (EFs). We however highlighted several pitfalls of the proposed adjusted EFs for croplands in the specific case of dry subhumid, semiarid, and arid regions with dry fallow periods, these regions covering about 47% of the Earth's terrestrial area.

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Context Agricultural soils are a major source of emissions of the greenhouse gas nitrous oxide (N2O). Aim Quantify direct N2O emissions from Australian agricultural production systems receiving nitrogen (N) inputs from synthetic and organic fertilisers, crop residues, urine and dung. Method A meta-analysis of N2O emissions from Australian agriculture (2003–2021) identified 394 valid emission factors (EFs), including 102 EFs with enhanced efficiency fertilisers (EEFs). Key results The average EF from all N sources (excluding EEFs) was 0.57%. Industry-based EFs for synthetic N fertiliser (excluding EEFs) ranged from 0.17% (non-irrigated pasture) to 1.77% (sugar cane), with an average Australia-wide EF of 0.70%. Emission factors were independent of topsoil organic carbon content, bulk density and pH. The revised EF for the non-irrigated cropping (grains) industry is now 0.41%; however, geographically-defined EFs are recommended. Urea was the most common N source with an average EF of 0.72% compared to urine (0.20%), dung (0.06%) and organo-mineral mixtures (0.26%). The EF for synthetic N fertilisers in rainfed environments increased by 0.16% for every 100 mm over 300 mm mean annual rainfall. For each additional 50 kg N ha−1 of synthetic fertiliser, EFs increased by 0.13%, 0.31% and 0.38% for the horticulture, irrigated and high rainfall non-irrigated cropping industries, respectively. The use of 3,4 dimethylpyrazole-phosphate (DMPP) produced significant reductions in EFs of 55%, 80% and 84% for the horticulture, non-irrigated and irrigated cropping industries, respectively. Conclusions and implications Incorporation of the revised EFs into the 2020 National Greenhouse Accounts (NGA) produced a 12% increase in direct N2O emissions from the application of synthetic N fertilisers. The lack of country-specific crop residue decomposition data is a major deficiency in the NGA.

Denitrification is a key process in the global nitrogen (N) cycle, causing nitrous oxide (N2O) and dinitrogen (N-2) emissions. Biogeochemical models allow field-scale estimates of N2O and N-2, extrapolating important yet often limited experimental results. However, such predictions rely mostly on N2O data, and the lack of N-2 data hinders validating total denitrification, which remain a major uncertainty for N budgets. This study investigated denitrification losses and N budgets in two tropical sugarcane systems using the Agricultural Production Systems sIMulator (APSIM) and the LandscapeDNDC (LDNDC) simulation framework using a unique dataset of both N2O and N-2 emissions measured in the field over a complete growing season. Key soil N parameters influencing N2O and N-2 emissions in APSIM and LDNDC were identified via global sensitivity analysis, followed by generalised likelihood uncertainty estimation to determine their posterior distributions using (i) N2O data only and (ii) both N2O and N-2 data. The simulation of N2O emissions in APSIM and LDNDC were improved in both calibration approaches, resulting in 0.7-1.3 kg N ha(-1) of RMSE. However, simulated N-2 emissions increased and agreed better with the observed values only when calibrated with both N2O and N-2 (RMSE 30.1-45.0 kg N ha(-1) before calibration and 19.3-19.9 kg N ha(-1) after). The simulated N loss pathway shifted from leaching to N-2 emissions after calibration including N-2. The simulated N balance was larger when sugarcane residues were retained as compared to burning consistently across the different soil N parameter configurations. These findings indicate that biogeochemical models, when used with default soil N parameters or calibration limited to N2O data, are likely to underestimate denitrification losses (>50 %), leading to a bias in N budgets simulation. Accurate N loss estimates are essential for understanding the long-term management impacts on soil organic matter dynamics, as demonstrated by the improved N budgets from both simulation models denote N mining when sugarcane is burnt, and the potential to sequester N when cane residues are retained. These outcomes emphasise the importance of integrating in-situ measurements of N2O and N-2 in simulation exercises, ensuring more accurate N budget estimates across scales.

In 2023, the Australian Government issued similar to 250,000 soil carbon credits following a measurement period characterised by high rainfall (Decile 10). The inferred soil organic carbon (SOC) sequestration rates during this period, ranging from similar to 2 to 8 t C ha-(1) yr-(1), significantly exceed rates reported in Australian scientific studies (similar to 0.1 to 1.2 t C ha-(1) yr-(1)). Our analysis, incorporating SOC and biomass measurements alongside remote sensing of NDVI, reveals that these SOC gains were largely attributable to above-average rainfall rather than project interventions. Moreover, these gains were not sustained when rainfall returned to average levels, raising concerns about the durability of credited sequestration and its additionality beyond natural climatic variability. Our findings demonstrate that current safeguards within the Soil Carbon Method-such as withholding 25% of credits during the first measurement period-are likely insufficient to account for climatic variability. To strengthen the integrity of the carbon crediting system, we recommend extending the minimum measurement period for credit issuance to at least five years. Additionally, governments should establish science-based 'reasonable bounds' for expected long-term SOC gains from management practices to sense-check reported outcomes. These measures will ensure that credited SOC sequestration is more closely tied to management-driven outcomes rather than short-term climate-driven fluctuations.

Grasslands store approximately one-third of the global terrestrial carbon (C) stocks. However, intensified grassland management over the last decades has resulted in soil degradation and subsequent soil organic C (SOC) losses as well as enhanced greenhouse gas emissions. Restoring grassland soils with adequate management practices offers huge opportunities for climate change mitigation with the potential to globally sequester ~150 megatons of CO2 eq per year in the soil. Emerging C credit markets further stress the importance of effective grassland management practices to restore SOC stocks. Despite that several improved management practices have been tested, their efficacy on soil C sequestration largely varies depending on environmental conditions. Soil C sequestration potential of grassland management practices under climate change scenarios is therefore highly uncertain. To this end, biogeochemical models, such as DayCent, offer a powerful tool to investigate the efficacy of grassland management practices, simulating the complex interaction between management and environmental conditions. Furthermore, Eddy Covariance (EC) flux towers provide opportunities to calibrate and validate the model’s C cycling with its high-frequency C balance measurements accounting for high spatial heterogeneity in pasture systems. In this study, DayCent was calibrated for pasture systems in the Brigalow belt region in Australia using EC flux tower data. The model was then validated with SOC data and used to project SOC stocks under combinations of different management practices and climate change scenarios. The calibrated parameters on soil organic matter decomposition reflected the deeper soil depth boundary down to 30 cm and the higher ratio of mineral-associated organic matter observed in Australian pasture systems. The calibrated DayCent model showed the potential to sequester C for the long term under climate change scenarios by introducing deep rooting legume and time-controlled grazing, restoring the degraded pasture soils due to historic intensive management. These simulated C sequestration estimates strongly correlated with C inputs and thus were limited by rather rainfall, grass productivity or grazing management than clay content. This study suggests Measure, Model and Verify (MMV) approach to estimate and project soil C sequestration for evaluation of SOC methodologies by pasture management within a shorter period than soil sampling – measure the baseline SOC, model the C dynamics with the calibrated DayCent and verify the projected soil C sequestration with EC flux tower data.

Acid-sulphate sugarcane soils in the subtropics are known hot-spots for nitrous oxide (N 2 O) emissions, yet the reduction of reactive N 2 O to non-reactive dinitrogen (N 2 ) via specific pathways remains a major uncertainty for nitrogen (N) cycling and loss from these soils. This study investigated the magnitude and the N 2 O:N 2 partitioning of N 2 O and N 2 losses from a subtropical acid-sulphate soil under sugarcane production using the 15 N gas flux method, establishing the contribution of hybrid (co- and chemo-denitrification) and heterotrophic denitrification to N 2 O and N 2 losses. Soils were fertilised with potassium nitrate, equivalent to 25 and 50 kg N ha −1 , watered close to saturation then incubated over 30 days. An innovative, fully automated incubation system coupled to an isotope-ratio mass-spectrometer enabled real time analysis of 15 N 2 O and 15 N 2 at sub-diel resolution. Peak losses of N 2 O and N 2 reached 6.5 kg N ha −1 day −1 , totalling > 50 kg of N 2 O+N 2 -N ha −1 . Emissions were dominated by N 2 , accounting for more than 57% of N 2 O+N 2 losses, demonstrating that the reduction of N 2 O to N 2 proceeded even under highly acidic conditions. Over 40% of N 2 O, but only 2% of N 2 emissions, were produced via hybrid pathways. These findings demonstrate hybrid pathways are generally limited to N 2 O production, likely driven by high organic matter content and low soil pH, promoting both biotic, and abiotic nitrosation. Regardless of the underlying process, the magnitude of the N 2 O emissions demonstrates the environmental, but also the potential agronomic significance, of hybrid pathways of N 2 O formation for N loss from fertilised acid-sulphate soils.

Commercial mango growers commonly spray potassium nitrate (KNO3) solution to enhance flowering and fruit quality, yet there is limited information on the uptake efficiency of nitrogen (N) by mango cultivars through leaf cuticles. The study aimed to assess N uptake efficiency (NUpE) from foliar application of KNO3 solution and compare NUpE among mango varieties. Mango cultivars were ‘Kensington Pride’ (‘KP’), ‘B74’ (‘Calypso®’), and ‘NMBP 1201’ (‘AhHa!®’), ‘NMBP 1243’ (‘Yess!®’), and ‘NMBP 4069’ (‘Now®’) grafted onto ‘KP’ seedlings. Leaves of six-month-old seedlings were dipped in 15N-enriched KNO3 solution and analyzed for total N and 15N contents. A significant correlation was observed between the leaf area and the amount of solution retained after dipping the leaves in the KNO3 solution. Moreover, leaves treated with the KNO3 solution had higher 15N levels than the natural 15N abundance, indicating successful N uptake from the KNO3 solution. The NUpE ranged from 27% to 44% and varied with variety. Cultivar ‘NMBP 4069’ had the highest NUE (44%) which was comparable with that of ‘B74’ (40%). ‘NMBP 1201’ showed the lowest (27%) NUpE which was comparable with that of ‘NMBP 1243’ (30%) and ‘KP’ (33%). These data on 15N uptake through the mango leaf cuticle demonstrates the effectiveness of foliar application as a method of supplying N to mango trees, highlighting important varietal differences in foliar 15N uptake efficiency. Considering these differences in NUpE among mango varieties will help in making informed decisions about cultivar selection and N management strategies for sustainable mango production.

The livestock industry accounts for a considerable proportion of agricultural greenhouse gas emissions, and in response, the Australian red meat industry has committed to an aspirational target of net-zero emissions by 2030. Increasing soil carbon storage in grazing lands has been identified as one method to help achieve this, while also potentially improving production and provision of other ecosystem services. This review examined the effects of grazing management on soil carbon and factors that drive soil carbon sequestration in Australia. A systematic literature search and meta-analysis was used to compare effects of stocking intensity (stocking rate or utilisation) and stocking method (i.e, continuous, rotational or seasonal grazing systems) on soil organic carbon, pasture herbage mass, plant growth and ground cover. Impacts on below ground biomass, soil nitrogen and soil structure are also discussed. Overall, no significant impact of stocking intensity or method on soil carbon sequestration in Australia was found, although lower stocking intensity and incorporating periods of rest into grazing systems (rotational grazing) had positive effects on herbage mass and ground cover compared with higher stocking intensity or continuous grazing. Minimal impact of grazing management on pasture growth rate and below-ground biomass has been reported in Australia. However, these factors improved with grazing intensity or rotational grazing in some circumstances. While there is a lack of evidence in Australia that grazing management directly increases soil carbon, this meta-analysis indicated that grazing management practices have potential to benefit the drivers of soil carbon sequestration by increasing above and below-ground plant production, maintaining a higher residual biomass, and promoting productive perennial pasture species. Specific recommendations for future research and management are provided in the paper.

Purpose The reduction of the greenhouse gas nitrous oxide (N 2 O) to dinitrogen (N 2 ) via denitrification and N 2 O source partitioning between nitrification and denitrification remain major uncertainties in sugarcane systems. We therefore investigated magnitude and product stoichiometry of denitrification and production pathways of N 2 O from a tropical sugarcane soil in response to increasing soil nitrate (NO 3 − ) availability. Methods Microcosms were established using a tropical sugarcane soil (Qld, Australia) and emissions of N 2 O and N 2 were measured following fertilisation with 15 NO 3 − –N equivalent to 25, 50 and 100 μg N g −1 soil, simulating soil NO 3 − contents previously observed in situ, and mimicking flood irrigation by wetting the soil close to saturation. Results Cumulative N 2 O emissions increased exponentially with NO 3 − availability, while cumulative N 2 emissions followed an exponential increase to maximum. Average daily N 2 emissions exceeded 5 µg N 2 –N g soil −1 and accounted for > 99% of denitrification. The response of N 2 O suggests preferential NO 3 − reduction with increasing NO 3 − availability, increasing N 2 O even when NO 3 − levels had only a diminishing effect on the overall denitrification rate. The fraction of N 2 O emitted from denitrification increased with NO 3 − availability, and was a function of soil water, NO 3 − and heterotrophic soil respiration. Conclusions Our findings show the exponential increase of N 2 O driven by excess NO 3 − , even though the complete reduction to N 2 dominated denitrification. The low N 2 O/(N 2 O + N 2 ) product ratio questions the use of N 2 O as proxy for overall denitrification rates, highlighting the need for in-situ N 2 measurements to account for denitrification losses from sugarcane systems.