Search

Methane (CH4) is the second most important atmospheric greenhouse gas (GHG) and forest soils are a significant sink for atmospheric CH4. Uptake of CH4 by global forest soils is affected by nitrogen (N) deposition; clarifying the effect of N deposition helps to reduce uncertainties of the global CH4 budget. However, it remains an unsolved puzzle why N input stimulates soil CH4 uptake in some forests while suppressing it in others. Combining previous findings and data from N addition experiments conducted in global forests, we proposed and tested a "stimulating‐suppressing‐weakened effect" ("three stages") hypothesis on the changing responses of soil CH4 flux (RCH4) to N input. Specifically, we calculated the response factors (f) of RCH4 to N input for N‐limited and N‐saturated forests across biomes; the phased changes in f values supported our hypothesis. We also estimated the global forest soil CH4 uptake budget to be approximately 11.2 Tg yr−1. CH4 uptake hotspots were predominantly located in temperate forests. Furthermore, we quantified that the current level of N deposition reduced global forest soil CH4 uptake by ∼3%. This suppression effect was more pronounced in temperate forests than in tropical or boreal forests, likely due to differences in N status. The proposed "three stages" hypothesis in this study generalizes the diverse effects of N input on RCH4, which could help improve experimental design. Additionally, our findings imply that by regulating N pollution and reducing N deposition, soil CH4 uptake can be significantly increased in the N‐saturated forests in tropical and temperate biomes. Plain Language Summary: Methane is an important greenhouse gas. Forest soils can absorb methane from the atmosphere and mitigate its warming effect. Meanwhile, forests suffer from high atmospheric nitrogen deposition, yet the effect of nitrogen on the methane uptake by forest soils remains unclear. Using data from global nitrogen addition experiments, we validated a "stimulating‐suppressing‐weakened effect" ("three stages") hypothesis, which could explain the diverse responses of soil methane flux to nitrogen input observed in different forests. On this basis, we quantified that nitrogen deposition decreased global forest soil methane uptake by approximately 3%. Our findings also imply that by regulating nitrogen pollution, soil methane uptake can be significantly increased in the nitrogen‐saturated forests in tropical and temperate biomes, potentially mitigate global warming. Key Points: A "three stage hypothesis" was developed to generalize the diverse responses of forest soil CH4 flux to N inputCH4 uptake by global forest soils was estimated to be 11.2 Tg yr−1, with N deposition suppressing ∼3% of this uptakeEffective regulation to reduce N deposition would promote CH4 uptake by N‐saturated forests and mitigate global warming [ABSTRACT FROM AUTHOR]

Nitrogen oxides (NOx) play an important role for atmospheric chemistry and radiative forcing. However, NOx emissions from the vast northern circumpolar permafrost regions have not been studied in situ due to limitations of measurement techniques. Our goals were to validate the offline analytical technique, and based on this, to widely quantify in situ NOx emissions from peatlands in the southern Eurasian permafrost region. To this end, we conducted a comparison of online and offline flux measurements in 2018 and 2019 using the synthetic air flushing, steady‐state opaque chamber method. With differences in annual average and cumulative fluxes less than 0.1 μg N m−2 h−1 and 0.01 kg N ha−1 year−1, the online and offline fluxes were in good agreement, demonstrating the feasibility of conducting offline measurements in remote regions without power supply. The flux measurements over 2 years showed obvious NOx emissions of 0.05–0.14 and 0.13–0.30 kg N ha−1 year−1 in the hollow and hummock microtopography of permafrost peatlands, respectively. The rapid expansion of alder (Alnus sibirica) in the peatlands induced by permafrost degradation significantly increased soil mineral N contents and NOx emissions depending on the age of alder (0.64–1.74 and 1.44–2.20 kg N ha−1 year−1 from the alder forests with tree ages of 1–10 years and 11–20 years, respectively). Alder expansion also intensively altered the thermal state of permafrost including the sharp increases of soil temperatures during the non‐growing season from October to April and active layer thickness. This study provides the first in situ evidences of NOx emissions from the northern circumpolar permafrost regions and uncovers the well‐documented expansion of alders can substantially stimulate NOx emissions and thus, significantly affect air quality, radiative forcing, and ecosystem productivity in the pristine regions. [ABSTRACT FROM AUTHOR]

Restoration of drained peatlands through rewetting has recently emerged as a prevailing strategy to mitigate excessive greenhouse gas emissions and re-establish the vital carbon sequestration capacity of peatlands. Rewetting can help to restore vegetation communities and biodiversity, while still allowing for extensive agricultural management such as paludiculture. Belowground processes governing carbon fluxes and greenhouse gas dynamics are mediated by a complex network of microbial communities and processes. Our understanding of this complexity and its multi-factorial controls in rewetted peatlands is limited. Here, we summarize the research regarding the role of soil microbial communities and functions in driving carbon and nutrient cycling in rewetted peatlands including the use of molecular biology techniques in understanding biogeochemical processes linked to greenhouse gas fluxes. We emphasize that rapidly advancing molecular biology approaches, such as high-throughput sequencing, are powerful tools helping to elucidate the dynamics of key biogeochemical processes when combined with isotope tracing and greenhouse gas measuring techniques. Insights gained from the gathered studies can help inform efficient monitoring practices for rewetted peatlands and the development of climate-smart restoration and management strategies. [ABSTRACT FROM AUTHOR]

This document, titled "Editorial: Peatlands for climate change mitigation in agriculture," discusses the importance of peatlands in storing carbon and their role in climate change mitigation. Peatlands store a significant amount of carbon, but they have been extensively drained for agricultural purposes, leading to greenhouse gas emissions. Peatland restoration is seen as a key measure to reduce these emissions and restore carbon stocks. The document also highlights the need for more research and monitoring of peatlands to support conservation and restoration efforts. [Extracted from the article]

The assessment of cropland carbon and nitrogen (C and N) balances plays a key role in identifying cost-effective mitigation measures to combat climate change and reduce environmental pollution. In this paper, a biogeochemical modelling approach is adopted to assess all C and N fluxes in a regional cropland ecosystem of Thessaly, Greece. Additionally, the estimation and quantification of the modelling uncertainty in the regional inventory are realized through the propagation of parameter distributions through the model, leading to result distributions for modelling estimations. The model was applied to a regional dataset of approximately 1000 polygons, deploying model initializations and crop rotations for the five major crop cultivations and for a time span of 8 years. The full statistical analysis on modelling results (including the uncertainty ranges given as ± values) yields for the C balance carbon input fluxes into the soil of 12.4 ± 1.4 t C ha -1 yr -1 and output fluxes of 11.9 ± 1.3 t C ha -1 yr -1 , with a resulting average carbon sequestration of 0.5 ± 0.3 t C ha -1 yr -1. The averaged N influx was 212.3 ± 9.1 kg N ha -1 yr -1 , while outfluxes of 198.3 ± 11.2 kg N ha -1 yr -1 were estimated on average. The net N accumulation into the soil nitrogen pools was estimated to be 14.0 ± 2.1 kg N ha -1 yr -1. The N outflux consists of gaseous N fluxes composed of N 2 O emissions of 2.6 ± 0.8 kg N 2 O–N ha -1 yr -1 , NO emissions of 3.2 ± 1.5 kg NO–N ha -1 yr -1 , N 2 emissions of 15.5 ± 7.0 kg N 2 –N ha -1 yr -1 and NH 3 emissions of 34.0 ± 6.7 kg NH 3 –N ha -1 yr -1 , as well as aquatic N fluxes (only nitrate leaching into surface waters) of 14.1 ± 4.5 kg NO 3 –N ha -1 yr -1 and N fluxes of N removed from the fields in yields, straw and feed of 128.8 ± 8.5 kg N ha -1 yr -1. [ABSTRACT FROM AUTHOR]

Soil microbial nitrate (NO3−) immobilization plays a vital role in enhancing the nitrogen (N) retention in the subtropical montane agricultural landscapes. However, how and why the potential microbial NO3− immobilization and the relative contribution of fungi and bacteria vary across different land use types remain still unclear in the subtropical mosaic montane agricultural landscapes. Thus, in the present study, soil gross microbial NO3− immobilization rates as well as the respective contribution of fungi and bacteria were determined throughout the whole soil profiles for three land use types (woodland, orchard, and cropland) by using the 15N tracing and amino sugar–based stable isotope probing (Amino sugars-SIP) techniques. The soil gross microbial NO3− immobilization rates in woodland soils were significantly higher than those in cropland and orchard soils across different soil layers (p < 0.05), and those of topsoil were significantly higher than those for subsoils (e.g., 20–40 cm) across different land use types (p < 0.05). Soil microbial biomass C (MBC) and N (MBN), organic C (SOC), total N (TN), and dissolved organic C (DOC) contents and C/N ratios were closely associated to gross microbial NO3− immobilization rates. Fungi played a greater role than bacteria in immobilizing soil NO3− in woodland and orchard soils, but the opposite occurred in cropland soils that over 85% of the variations in fungal and bacterial NO3− immobilization rates could be explained by their respective phospholipid fatty acid–derived (PLFA-derived) biomass. The present study indicated that afforestation may be effective to enhance soil NO3− retention in alkaline soils, thereby likely decreasing the risk of NO3− losses in subtropical mosaic montane agricultural landscapes through enhancing the soil NO3− immobilization by both fungi and bacteria. [ABSTRACT FROM AUTHOR]

Denitrification plays a critical role in soil nitrogen (N) cycling, affecting N availability in agroecosystems. However, the challenges in direct measurement of denitrification products (NO, N2O, and N2) hinder our understanding of denitrification N losses patterns across the spatial scale. To address this gap, we constructed a data‐model fusion method to map the county‐scale denitrification N losses from China's rice fields over the past decade. The estimated denitrification N losses as a percentage of N application from 2009 to 2018 were 11.8 ± 4.0% for single rice, 12.4 ± 3.7% for early rice, and 11.6 ± 3.1% for late rice. The model results showed that the spatial heterogeneity of denitrification N losses is primarily driven by edaphic and climatic factors rather than by management practices. In particular, diffusion and production rates emerged as key contributors to the variation of denitrification N losses. These findings humanize a 38.9 ± 4.8 kg N ha−1 N loss by denitrification and challenge the common hypothesis that substrate availability drives the pattern of N losses by denitrification in rice fields. [ABSTRACT FROM AUTHOR]

Maintaining or even increasing crop yields while reducing nitrous oxide (N2O) emissions is necessary to reconcile food security and climate change, while the metric of yield‐scaled N2O emission (i.e., N2O emissions per unit of crop yield) is at present poorly understood. Here we conducted a global meta‐analysis with more than 6000 observations to explore the variation patterns and controlling factors of yield‐scaled N2O emissions for maize, wheat and rice and associated potential mitigation options. Our results showed that the average yield‐scaled N2O emissions across all available data followed the order wheat (322 g N Mg−1, with the 95% confidence interval [CI]: 301–346) > maize (211 g N Mg−1, CI: 198–225) > rice (153 g N Mg−1, CI: 144–163). Yield‐scaled N2O emissions for individual crops were generally higher in tropical or subtropical zones than in temperate zones, and also showed a trend towards lower intensities from low to high latitudes. This global variation was better explained by climatic and edaphic factors than by N fertilizer management, while their combined effect predicted more than 70% of the variance. Furthermore, our analysis showed a significant decrease in yield‐scaled N2O emissions with increasing N use efficiency or in N2O emissions for production systems with cereal yields >10 Mg ha−1 (maize), 6.6 Mg ha−1 (wheat) or 6.8 Mg ha−1 (rice), respectively. This highlights that N use efficiency indicators can be used as valuable proxies for reconciling trade‐offs between crop production and N2O mitigation. For all three major staple crops, reducing N fertilization by up to 30%, optimizing the timing and placement of fertilizer application or using enhanced‐efficiency N fertilizers significantly reduced yield‐scaled N2O emissions at similar or even higher cereal yields. Our data‐driven assessment provides some key guidance for developing effective and targeted mitigation and adaptation strategies for the sustainable intensification of cereal production. [ABSTRACT FROM AUTHOR]

Global food production faces challenges in balancing the need for increased yields with environmental sustainability. This study presents a six-year field experiment in the North China Plain, demonstrating the benefits of diversifying traditional cereal monoculture (wheat–maize) with cash crops (sweet potato) and legumes (peanut and soybean). The diversified rotations increase equivalent yield by up to 38%, reduce N2O emissions by 39%, and improve the system's greenhouse gas balance by 88%. Furthermore, including legumes in crop rotations stimulates soil microbial activities, increases soil organic carbon stocks by 8%, and enhances soil health (indexed with the selected soil physiochemical and biological properties) by 45%. The large-scale adoption of diversified cropping systems in the North China Plain could increase cereal production by 32% when wheat–maize follows alternative crops in rotation and farmer income by 20% while benefiting the environment. This study provides an example of sustainable food production practices, emphasizing the significance of crop diversification for long-term agricultural resilience and soil health. Food production systems need to balance yield and sustainability. Here, the authors conduct 6 years long crop diversification field experiments in the North China Plain, showing that diversifying cereal monocultures with cash crops and legumes cand improve yield and reduce GHG emissions. [ABSTRACT FROM AUTHOR]

Anthropogenic nitrogen (N) loading alters soil ammonia‐oxidizing archaea (AOA) and bacteria (AOB) abundances, likely leading to substantial changes in soil nitrification. However, the factors and mechanisms determining the responses of soil AOA:AOB and nitrification to N loading are still unclear, making it difficult to predict future changes in soil nitrification. Herein, we synthesize 68 field studies around the world to evaluate the impacts of N loading on soil ammonia oxidizers and nitrification. Across a wide range of biotic and abiotic factors, climate is the most important driver of the responses of AOA:AOB to N loading. Climate does not directly affect the N‐stimulation of nitrification, but does so via climate‐related shifts in AOA:AOB. Specifically, climate modulates the responses of AOA:AOB to N loading by affecting soil pH, N‐availability and moisture. AOB play a dominant role in affecting nitrification in dry climates, while the impacts from AOA can exceed AOB in humid climates. Together, these results suggest that climate‐related shifts in soil ammonia‐oxidizing community maintain the N‐stimulation of nitrification, highlighting the importance of microbial community composition in mediating the responses of the soil N cycle to N loading. [ABSTRACT FROM AUTHOR]

Upscaling chamber measurements of soil greenhouse gas (GHG) fluxes from point scale to landscape scale remain challenging due to the high variability in the fluxes in space and time. This study measured GHG fluxes and soil parameters at selected point locations (n=268), thereby implementing a stratified sampling approach on a mixed-land-use landscape (∼5.8 km2). Based on these field-based measurements and remotely sensed data on landscape and vegetation properties, we used random forest (RF) models to predict GHG fluxes at a landscape scale (1 m resolution) in summer and autumn. The RF models, combining field-measured soil parameters and remotely sensed data, outperformed those with field-measured predictors or remotely sensed data alone. Available satellite data products from Sentinel-2 on vegetation cover and water content played a more significant role than those attributes derived from a digital elevation model, possibly due to their ability to capture both spatial and seasonal changes in the ecosystem parameters within the landscape. Similar seasonal patterns of higher soil/ecosystem respiration (SR/ER– CO2) and nitrous oxide (N2O) fluxes in summer and higher methane (CH4) uptake in autumn were observed in both the measured and predicted landscape fluxes. Based on the upscaled fluxes, we also assessed the contribution of hot spots to the total landscape fluxes. The identified emission hot spots occupied a small landscape area (7 % to 16 %) but accounted for up to 42 % of the landscape GHG fluxes. Our study showed that combining remotely sensed data with chamber measurements and soil properties is a promising approach for identifying spatial patterns and hot spots of GHG fluxes across heterogeneous landscapes. Such information may be used to inform targeted mitigation strategies at the landscape scale. [ABSTRACT FROM AUTHOR]

Crop residues are important inputs of carbon (C) and nitrogen (N) to soils and thus directly and indirectly affect nitrous oxide (N2O) emissions. As the current inventory methodology considers N inputs by crop residues as the sole determining factor for N2O emissions, it fails to consider other underlying factors and processes. There is compelling evidence that emissions vary greatly between residues with different biochemical and physical characteristics, with the concentrations of mineralizable N and decomposable C in the residue biomass both enhancing the soil N2O production potential. High concentrations of these components are associated with immature residues (e.g., cover crops, grass, legumes, and vegetables) as opposed to mature residues (e.g., straw). A more accurate estimation of the short‐term (months) effects of the crop residues on N2O could involve distinguishing mature and immature crop residues with distinctly different emission factors. The medium‐term (years) and long‐term (decades) effects relate to the effects of residue management on soil N fertility and soil physical and chemical properties, considering that these are affected by local climatic and soil conditions as well as land use and management. More targeted mitigation efforts for N2O emissions, after addition of crop residues to the soil, are urgently needed and require an improved methodology for emission accounting. This work needs to be underpinned by research to (1) develop and validate N2O emission factors for mature and immature crop residues, (2) assess emissions from belowground residues of terminated crops, (3) improve activity data on management of different residue types, in particular immature residues, and (4) evaluate long‐term effects of residue addition on N2O emissions. [ABSTRACT FROM AUTHOR]

Soil nitrogen mineralization (Nmin) is a key process that converts organic N into mineral N that controls soil N availability to plants. However, regional assessments of soil Nmin in cropland and its affecting factors are lacking, especially in relation to variation in elevation. In this study, a 4-week incubation experiment was implemented to measure net soil Nmin rate, gross nitrification (Nit) rate and corresponding soil abiotic properties in five field soils (A-C, maize; D, flue-cured tobacco; and E, vegetables; with elevation decreasing from A to E) from different altitudes in a typical intensive agricultural area in Dali City, Yunnan Province, China. The results showed that soil Nmin rate ranged from 0.10 to 0.17 mg·kg-1·d-1 N, with the highest value observed in field E, followed by fields D, C, B, and A, which indicated that soil Nmin and Nit rates varied between fields, decreasing with elevation. The soil Nit rate ranged from 434.2 to 827.1 µg·kg-1·h-1 N, with the highest value determined in field D, followed by those in fields E, C, B, and A. The rates of soil Nmin and Nit were positively correlated with several key soil parameters, including total soil N, dissolved organic carbon and dissolved inorganic N across all fields, which indicated that soil variables regulated soil Nmin and Nit in cropland fields. In addition, a strong positive relationship was observed between soil Nmin and Nit. These findings provide a greater understanding of the response of soil Nmin among cropland fields related to spatial variation. It is suggested that the soil Nmin from cropland should be considered in the evaluation of the N transformations at the regional scale. [ABSTRACT FROM AUTHOR]

Arable soil continues to be the dominant anthropogenic source of nitrous oxide (N2O) emissions owing to application of nitrogen (N) fertilizers and manures across the world. Using laboratory and in situ studies to elucidate the key factors controlling soil N2O emissions remains challenging due to the potential importance of multiple complex processes. We examined soil surface N2O fluxes in an arable soil, combined with in situ high‐frequency measurements of soil matrix oxygen (O2) and N2O concentrations, in situ 15N labeling, and N2O 15N site preference (SP). The in situ O2 concentration and further microcosm visualized spatiotemporal distribution of O2 both suggested that O2 dynamics were the proximal determining factor to matrix N2O concentration and fluxes due to quick O2 depletion after N fertilization. Further SP analysis and in situ 15N labeling experiment revealed that the main source for N2O emissions was bacterial denitrification during the hot‐wet summer with lower soil O2 concentration, while nitrification or fungal denitrification contributed about 50.0% to total emissions during the cold‐dry winter with higher soil O2 concentration. The robust positive correlation between O2 concentration and SP values underpinned that the O2 dynamics were the key factor to differentiate the composite processes of N2O production in in situ structured soil. Our findings deciphered the complexity of N2O production processes in real field conditions, and suggest that O2 dynamics rather than stimulation of functional gene abundances play a key role in controlling soil N2O production processes in undisturbed structure soils. Our results help to develop targeted N2O mitigation measures and to improve process models for constraining global N2O budget. [ABSTRACT FROM AUTHOR]

Anthropogenic activities increase the contributions of inland waters to global greenhouse gas (GHG; CO 2 , CH 4 , and N 2 O) budgets, yet the mechanisms driving these increases are still not well constrained. In this study, we quantified year-long GHG concentrations, fluxes, and water physico-chemical variables from 28 sites contrasted by land use across five headwater catchments in Germany. Based on linear mixed-effects models, we showed that land use was more significant than seasonality in controlling the intra-annual variability of the GHGs. Streams in agriculture-dominated catchments or with wastewater inflows had up to 10 times higher daily CO 2 , CH 4 , and N 2 O emissions and were also more temporally variable (CV > 55 %) than forested streams. Our findings also suggested that nutrient, labile carbon, and dissolved GHG inputs from the agricultural and settlement areas may have supported these hotspots and hot-moments of fluvial GHG emissions. Overall, the annual emission from anthropogenic-influenced streams in CO 2 equivalents was up to 20 times higher (∼ 71 kg CO 2 m -2 yr -1) than from natural streams (∼ 3 kg CO 2 m -2 yr -1), with CO 2 accounting for up to 81 % of these annual emissions, while N 2 O and CH 4 accounted for up to 18 % and 7 %, respectively. The positive influence of anthropogenic activities on fluvial GHG emissions also resulted in a breakdown of the expected declining trends of fluvial GHG emissions with stream size. Therefore, future studies should focus on anthropogenically perturbed streams, as their GHG emissions are much more variable in space and time and can potentially introduce the largest uncertainties to fluvial GHG estimates. [ABSTRACT FROM AUTHOR]

Upscaling chamber measurements of soil greenhouse gas (GHG) fluxes from points to landscape scales remain challenging due to high variability of fluxes in space and time. This study measured GHG fluxes and soil parameters at selected point locations (n=268), thereby implementing a stratified sampling approach on a mixed land-use landscape (~5.8 km2). Based on these field-based measurements and remotely-sensed data on landscape and vegetation properties, we used Random Forest models to predict GHG fluxes at a landscape scale (1 m resolution) in summer and autumn. The results showed improved GHG flux prediction performance when combining field25 measured soil parameters with remotely-sensed data. Available satellite data products from Sentinel-2 on vegetation cover and water content played a more significant role than attributes derived from a digital elevation model, possibly due to their ability to capture both spatial and seasonal changes of ecosystem parameters within the landscape. Similar seasonal patterns of higher soil/ecosystem respiration (SR/ER-CO2) and nitrous oxide (N2O) fluxes in summer and higher methane (CH4) uptake in autumn were observed in both the measured and predicted landscape fluxes. Based on the upscaled fluxes, we also assessed the contribution of hot spots to total landscape fluxes. The identified emission hot spots occupied a small landscape area (7 to 16%) but accounted for up to 42% of the landscape GHG fluxes. Our study showed that combining remotely-sensed data with chamber measurements and soil properties is a promising approach for identifying spatial patterns and hot spots of GHG fluxes across heterogeneous landscapes. Such information may be used to inform targeted mitigation strategies at landscape-scale. [ABSTRACT FROM AUTHOR]

Urban land‐use change has the potential to affect local to global biogeochemical carbon (C) and nitrogen (N) cycles and associated greenhouse gas (GHG) fluxes. We conducted a meta‐analysis to (1) assess the effects of urbanization‐induced land‐use conversion on soil nitrous oxide (N2O) and methane (CH4) fluxes, (2) quantify direct N2O emission factors (EFd) of fertilized urban soils used, for example, as lawns or forests, and (3) identify the key drivers leading to flux changes associated with urbanization. On average, urbanization increases soil N2O emissions by 153%, to 3.0 kg N ha−1 year−1, while rates of soil CH4 uptake are reduced by 50%, to 2.0 kg C ha−1 year−1. The global mean annual N2O EFd of fertilized lawns and urban forests is 1.4%, suggesting that urban soils can be regional hotspots of N2O emissions. On a global basis, conversion of land to urban greenspaces has increased soil N2O emission by 0.46 Tg N2O‐N year−1 and decreased soil CH4 uptake by 0.58 Tg CH4‐C year−1. Urbanization driven changes in soil N2O emission and CH4 uptake are associated with changes in soil properties (bulk density, pH, total N content, and C/N ratio), increased temperature, and management practices, especially fertilizer use. Overall, our meta‐analysis shows that urbanization increases soil N2O emissions and reduces the role of soils as a sink for atmospheric CH4. These effects can be mitigated by avoiding soil compaction, reducing fertilization of lawns, and by restoring native ecosystems in urban landscapes. [ABSTRACT FROM AUTHOR]

Anthropogenic activities increase the contributions of inland waters to global greenhouse gas (GHG; CO2, CH4, and N2O) budgets, yet the mechanisms driving these increases are still not well constrained. In this study, we quantified year-long GHG concentrations and fluxes, as well as water physico-chemical variables from 23 streams, 3 ditches, and 2 wastewater inflow sites across five headwater catchments in Germany contrasted by land use. Using mixed-effects models, we determined the overall impact of land use and seasonality on the intra-annual variabilities of these parameters. We found that land use was more significant than seasonality in controlling the intra-annual variability of GHG concentrations and fluxes. Agricultural land use and wastewater inflows in settlement areas resulted in up to 10 times higher daily riverine CO2, CH4, and N2O emissions than forested areas, as substrate inputs by these sources appeared to favor in situ GHG production processes. Dissolved GHG inputs directly from agricultural runoff and waste-water inputs also contributed substantially to the annual emissions from these sites. Drainage ditches were hotspots for CO2 and CH4 fluxes due to high dissolved organic matter concentrations, which appeared to favor in situ production via respiration and methanogensis. Overall, the annual emission from anthropogenic-influenced streams in CO2-equivalents was up to 20 times higher (~71 kg CO2 m-2 yr-1) than from natural streams (~3 kg CO2 m-2 yr-1). Future studies aiming to estimate the contribution of lotic ecosystems to GHG emissions should therefore focus on anthropogenically perturbed streams, as their GHG emission are much more variable in space and time. [ABSTRACT FROM AUTHOR]

The assessment of cropland carbon and nitrogen (C & N) balances play a key role to identify cost effective mitigation measures to combat climate change and reduce environmental pollution. In this paper, a biogeochemical modelling approach is adopted to assess all C & N fluxes in a regional cropland ecosystem of Thessaly, Greece. Additionally, the estimation and quantification of the modelling uncertainty in the regional inventory are realized through the propagation of parameter distributions through the model leading to result distributions for modelling estimations. The model was applied on a regional dataset of approximately 1000 polygons deploying model initializations and crop rotations for the 5 major crop cultivations and for a timespan of 8 years. The full statistical analysis on modelling results yields for the C balance carbon input fluxes into the soil of 12.4 ± 1.4 tons C ha-1 yr-1 and output fluxes of 11.9 ± 1.3 tons C ha-1 yr-1, with a resulting average carbon sequestration of 0.5 ± 0.3 tons C ha-1 yr-1. The averaged N influx was 212.3 ± 9.1 kg N ha-1 yr-1 while outfluxes were estimated on average of 198.3 ± 11.2 kg N ha-1 yr-1. The net N accumulation into the soil nitrogen pools was estimated to 14.0 ± 2.1 kg N ha-1 yr-1. The N outflux consist of gaseous N fluxes composed by N2O emissions 2.6 ± 0.8 kg N2O-N ha-1 yr-1, NO emissions of 3.2 ± 1.5 kg NO-N ha-1 yr-1, N2 emissions 15.5 ± 7.0 kg N2-N ha-1 yr-1 and NH3 emissions of 34.0 ± 6.7 kg NH3-N ha-1 yr-1, as well as aquatic N fluxes (only nitrate leaching into surface waters) of 14.± 4.5 kg NO3-N ha-1 yr-1, N fluxes of N removed from the fields in yields, straw and feed of 128.8 ± 8.5 kg N ha-1 yr-1. [ABSTRACT FROM AUTHOR]

Background: Arbuscular mycorrhizal fungi (AMF) are key soil organisms and their extensive hyphae create a unique hyphosphere associated with microbes actively involved in N cycling. However, the underlying mechanisms how AMF and hyphae-associated microbes may cooperate to influence N2O emissions from "hot spot" residue patches remain unclear. Here we explored the key microbes in the hyphosphere involved in N2O production and consumption using amplicon and shotgun metagenomic sequencing. Chemotaxis, growth and N2O emissions of isolated N2O-reducing bacteria in response to hyphal exudates were tested using in vitro cultures and inoculation experiments. Results: AMF hyphae reduced denitrification-derived N2O emission (max. 63%) in C- and N-rich residue patches. AMF consistently enhanced the abundance and expression of clade I nosZ gene, and inconsistently increased that of nirS and nirK genes. The reduction of N2O emissions in the hyphosphere was linked to N2O-reducing Pseudomonas specifically enriched by AMF, concurring with the increase in the relative abundance of the key genes involved in bacterial citrate cycle. Phenotypic characterization of the isolated complete denitrifying P. fluorescens strain JL1 (possessing clade I nosZ) indicated that the decline of net N2O emission was a result of upregulated nosZ expression in P. fluorescens following hyphal exudation (e.g. carboxylates). These findings were further validated by re-inoculating sterilized residue patches with P. fluorescens and by an 11-year-long field experiment showing significant positive correlation between hyphal length density with the abundance of clade I nosZ gene. Conclusions: The cooperation between AMF and the N2O-reducing Pseudomonas residing on hyphae significantly reduce N2O emissions in the microsites. Carboxylates exuded by hyphae act as attractants in recruiting P. fluorescens and also as stimulants triggering nosZ gene expression. Our discovery indicates that reinforcing synergies between AMF and hyphosphere microbiome may provide unexplored opportunities to stimulate N2O consumption in nutrient-enriched microsites, and consequently reduce N2O emissions from soils. This knowledge opens novel avenues to exploit cross-kingdom microbial interactions for sustainable agriculture and for climate change mitigation. C1gn2zbPQXat79TnoeAsNQ Video Abstract [ABSTRACT FROM AUTHOR]

Excessive water and fertiliser inputs, as well as long-term monocropping, not only cause resource waste and environmental pollution but also drive soil degradation and the occurrence of soil-borne diseases. Anaerobic soil disinfestation (ASD) is a widely used technique in greenhouse vegetable production to replace the use of agrochemicals in disinfestation and improve product quality. While the short-term effects of ASD on the soil microbial community have been well documented in the past 15 years, only a few studies have investigated the multiseason effects of ASD, particularly on the soil microbial community composition and stability, as well as on pathogens and antagonistic microorganisms. Field experiments were conducted in three adjacent greenhouses used for tomato production for at least 20 years. Three treatments were included: CK (control: no irrigation, no plastic film covering, incorporation of chicken manure), ASD (irrigation, plastic film covering, and incorporation of rice husks), and ASD+M (ASD plus incorporation of chicken manure). Results showed that (1) ASD significantly reduced the diversity of soil bacteria and fungi and improved the complexity and stability of the soil bacterial community at the end of the ASD, but the soil microbial diversity recovered to the level before the experiment after 1.5 years. (2) Compared with CK, ASD significantly increased the relative abundance of antagonistic bacteria Bacillus, Paenibacillus and Streptomyces, decreased the relative abundance of pathogens Fusarium and the quantity of nematodes and could still effectively eliminate soil pathogens after 1.5 years. (3) Chicken manure application did not increase the pathogenic microorganisms Fusarium and nematodes, but it significantly decreased the relative abundance of antagonistic bacteria. Our results highlight that ASD not only showed an inhibitory effect on soil-borne diseases after 1.5 years but also significantly increased the relative abundance of antagonistic bacteria. However, the additional incorporation of chicken manure for ASD should be avoided due to its negative effects on the abundance of antagonistic bacteria and its contribution to environmental pollution due to N leaching and increased emissions of GHG N2O. [ABSTRACT FROM AUTHOR]

Tropical montane forests store high amounts of soil organic carbon (SOC). However, global warming may affect these stocks via enhanced soil respiration. Improved insight into the temperature response of SOC respiration can be obtained from in and ex situ warming studies. In situ warming via the translocation of intact soil mesocosms was carried out along an elevation gradient ranging between ca. 1250 m in the Kibale Forest to ca. 3000 m in the Rwenzori Mountains in Uganda. Samples from the same transect were also warmed ex situ. Ex situ results revealed that, following the elevation gradient, which represents a natural climate gradient, specific heterotrophic CO2 respiration decreased linearly by 1.01 ± 0.12 µgCh-1g-1 of SOC per 100 m of elevation increase. The coefficient of temperature sensitivity increased from 1.50 ± 0.13 in the lowest- to 2.68 ± 0.25 in the highest-elevation cluster, showing a linear increase of 0.09 ± 0.03 per 100 m of elevation increase. Additionally, respired CO2 was more depleted in 13C in the warmer lower elevations as compared to colder higher elevations, with a linear decrease of 0.23 ‰ ± 0.04 ‰ per 100 m of elevation increase. Furthermore, the microbial community structure indicated a weak trend along the elevation gradient, with higher elevations more dominated by fungi relative to bacteria. The results indicate an increased recalcitrance and decreased mineralisation of SOC, with elevation likely driven by decreasing soil temperature and pH. Subsequently, after 2 years of in situ warming (0.9 to 2.8 ∘C), specific heterotrophic SOC respiration tended to be lower for warmed soil compared to control soil. Furthermore, in warmed soils, δ13 C values and SOC content tended to increase and decrease, respectively. Collectively, this points towards the increased mineralisation and depletion of readily available C during 2 years of warming. In conclusion, our results suggest that climate warming may trigger enhanced losses of SOC from tropical montane forests due to a combination of a higher temperature sensitivity of mineralisation and higher SOC content at higher elevations. [ABSTRACT FROM AUTHOR]

Background: Globally, rice systems are a major source of atmospheric CH4 and for major rice‐producing countries, such as Vietnam, CH4 as well as N2O emissions from agricultural land used for rice production may represent about one‐fourth of total national anthropogenic greenhouse gas (GHG) emissions. However, national‐scale estimates of GHG emissions from rice systems are uncertain with regard to its magnitude, spatial distribution, and seasonality. Aims: Here, we used the biogeochemical model LandscapeDNDC to calculate emissions of CH4 and N2O from rice systems in Vietnam (Tier 3 IPCC approach). Our objectives were to identify hotspot regions of emissions and to assess the contribution of N2O to the total non‐CO2 (CH4+N2O) GHG balance of rice systems as well as the seasonal and interannual variability of fluxes in dependence of uncertain input data on field management. Methods: The biogeochemical model LandscapeDNDC model was linked to publicly available information on climate, soils, and land management (fertilization, irrigation, crop rotation) for calculating a national inventory in daily time steps of CH4 and N2O emissions from rice systems at a spatial resolution of 0.083° × 0.083°. Uncertainty in management practices related to fertilization, use of harvest residues or irrigation water, and its effects on simulated CH4 and N2O fluxes was accounted for by Latin Hypercube Sampling of probability distribution functions. Results: Our study shows that CH4 and N2O fluxes from rice systems in Vietnam are highly seasonal, with national CH4 and N2O emissions totaling to about 2600 Gg CH4 year–1 and 42 Gg N2O year–1, respectively. Highest emissions were simulated for double and triple rice cropping systems in the Mekong Delta region. Yield‐scaled emissions varied largely in a range of 300–3000 kg CO2‐eq Mg–1 year–1, with CH4 emissions during the rice season(s) dominating (>82%) the total annual non‐CO2 GHG balance of rice systems. In our study, uncertainty in field management information (nitrogen fertilization, ratio synthetic to organic fertilization, residue management, availability of irrigation water) were major drivers of uncertainty of the national CH4 and N2O emission inventory. Conclusions: Our study shows that Tier 3 approaches, that is, process‐oriented model approaches combined with GIS databases, for estimating national‐scale GHG emissions from rice systems are ready to be applied at national scale. Generally, this approach is powerful as it allows to identify regions with elevated emissions, thereby accounting not only for CH4, but as well for N2O emissions. However, our study also shows that specifically better information on land management is required to narrowing uncertainties. [ABSTRACT FROM AUTHOR]

Livestock are an important source of livelihoods in agricultural systems in sub-Saharan Africa (SSA), while also being the largest source of national greenhouse gas (GHG) emissions in most African countries. As a consequence, there is a critical need for data on livestock GHG sources and sinks to develop national inventories, as well as conduct baseline measurements and intervention testing to mitigate GHG emissions and meet ambitious national climate goals. Our objective was to review studies on GHG emissions from livestock systems in SSA, as well as soil carbon storage in livestock-dominated systems (i.e., grasslands and rangelands), to evaluate best current data and suggest future research priorities. To this end, we compiled studies from SSA that determined emission factors (EFs) for enteric methane and manure emissions, along with studies on soil organic carbon (SOC) stocks in SSA. We found that there has been limited research on livestock GHG emissions and SOC relative to national ambitions for climate change mitigation in SSA. Enteric methane emission factors (EFs) in low productivity cattle systems may be lower than IPCC Tier 1 default EFs, whereas small ruminants (i.e. sheep and goats) had higher EFs compared to IPCC Tier 1 EFs. Manure EFs were equal to or lower than IPCC Tier 1 EFs for deposited manure (while grazing), manure applied as fertilizer, and manure management. SOC stocks for grasslands and rangelands in SSA show broad agreement with IPCC estimates, but there was a strong geographic bias and many studies did not report soil type, bulk density, or SOC stocks at >30 cm depth. In general, the largest data gaps included information for manure (quantity, quality, management), small ruminants, agropastoral/pastoralist systems, and in general from West Africa. Future research should focus on filling major data gaps on locally appropriate mitigation interventions and improving livestock activity data for developing Tier 2 GHG inventories in SSA. At the science-policy interface, all parties would benefit from enhanced coordination within the research community and between researchers and African governments to improve Tier 2 inventories and harmonize measurement for mitigation in livestock systems in SSA. [ABSTRACT FROM AUTHOR]

Greenhouse gas fluxes (CO2, CH4, and N2O) from African streams and rivers are under‐represented in global datasets, resulting in uncertainties in their contributions to regional and global budgets. We conducted year‐long sampling of 59 sites in a nested‐catchment design in the Mara River, Kenya in which fluxes were quantified and their underlying controls assessed. We estimated annual basin‐scale greenhouse gas emissions from measured in‐stream gas concentrations, modeled gas transfer velocities, and determined the sensitivity of up‐scaling to discharge. Based on the total annual CO2‐equivalent emissions calculated from global warming potentials (GWP), the Mara basin was a net greenhouse gas source (294 ± 35 Gg CO2 eq yr−1). Lower‐order streams (1–3) contributed 81% of the total fluxes, and higher stream orders (4–8) contributed 19%. Cropland‐draining streams also exhibited higher fluxes compared to forested streams. Seasonality in stream discharge affected stream widths (and stream area) and gas exchange rates, strongly influencing the basin‐wide annual flux, which was 10 times higher during the high and medium discharge periods than the low discharge period. The basin‐wide estimate was underestimated by up to 36% if discharge was ignored, and up to 37% for lower stream orders. Future research should therefore include seasonality in stream surface areas in upscaling procedures to better constrain basin‐wide fluxes. Given that agricultural activities are a major factor increasing riverine greenhouse gas fluxes in the study region, increased conversion of forests and agricultural intensification has the possibility of increasing the contribution of the African continent to global greenhouse gas sources. [ABSTRACT FROM AUTHOR]

Nitrogen (N) fertilizer application to agricultural soils results in substantial emissions of nitric oxide (NO), a key substance in tropospheric chemistry involved in climate forcing and air pollution. However, the estimates of global cropland NO emissions remain uncertain due to a lack of information on direct NO emission factors (EFds) of applied N for various cropping systems at seasonal or annual scales. Here we quantified the crop-specific seasonal and annual-scale NO EFds through synthesizing 1094 measurements from 125 field-based studies worldwide. The global mean crop-specific seasonal EFd was 0.53%, with the highest for vegetables (0.75%). Among cereal crops, the EFd of maize (0.45%) or wheat (0.47%) was about three times higher than for rice (0.12%). At annual scale, the mean EFd across all cropping systems was 0.58%, with tea plantations having the highest (1.54%). For other cropping systems, the annual-scale EFds ranged from 0.02% to 1.07%. Besides crop type, also soil organic carbon, total N, and pH as well as N fertilizer type were the main factors explaining the variations of NO EFds. Based on obtained specific EFds for each crop type, we estimated that NO emissions due to the use of synthetic fertilizers from global croplands are about 0.42-0.62 Tg N year-1. Our budgets are relatively lower if compared to estimates derived by the use of IPCC defaults for NO emissions (0.72-1.66 Tg N year-1) or reported elsewhere (0.67-1.04 Tg N year-1). In our estimates, cash crops (vegetable, tea and orchard), which cover only 9% of the world cropland area, contributed about 31% to total NO emissions from global fertilized croplands. Overall, our meta-analysis provides improved crop-specific NO EFds reflecting current stage of knowledge. The work also highlights the relative importance of cash crop production as sources for atmospheric NO, that is, agricultural systems on which mitigation efforts may focus. [ABSTRACT FROM AUTHOR]

Drip fertigation with reduced fertilizer and water inputs has been widely used in greenhouse vegetable production in China. However, farmers usually do not apply additional organic material with a high carbon content, although soil organic carbon (SOC) concentrations are mostly below the optimum level for vegetable production. Returning straw or biochar to fields is an effective strategy for sustainability and environmental friendliness. We tested whether drip fertigation, (DIF) combined with maize straw (DIF+S) or biochar (DIF+BC), is a suitable option to improve SOC sequestration over eight growing seasons, and how these options affect soil N2O emissions and yields or partial factor productivity of applied N (PFPN) of crops over three growing seasons. During the winter–spring growing season, DIF+BC significantly reduced soil N2O emission by 61.2% and yield-scaled N2O emission by 62.4%, while increasing the tomato yield and PFPN compared with DIF. Straw incorporation had similar trends but without significant effects. Conversely, straw and biochar incorporation increased N2O emission during the autumn–winter season. The structural equation model indicated N2O emission was dominantly driven by soil NH4+-N concentration, temperature and moisture. The N2O emission factor decreased significantly with increased PFPN. Moreover, the contribution of biochar to the increased SOC was approximately 78%, which was four times higher than that of straw incorporation. Overall, the results highlighted the potential of drip fertigation with biochar incorporation to mitigate N2O emissions, improve PFPN and significantly increase SOC storage, which could all contribute to maintaining environmental sustainability and soil quality of greenhouse vegetable production. [ABSTRACT FROM AUTHOR]

Worldwide, rice production contributes about 10% of total greenhouse gas (GHG) emissions from the agricultural sector, mainly due to CH4 emissions from continuously flooded fields. Alternate Wetting and Drying (AWD) is a promising crop technology for mitigating CH4 emissions and reducing the irrigation water currently being applied in many of the world's top rice‐producing countries. However, decreased emissions of CH4 may be partially counterbalanced by increased N2O emissions. In this case study for the Philippines, the national mitigation potential of AWD is explored using the process‐based biogeochemical model LandscapeDNDC. Simulated mean annual CH4 emissions under conventional rice production for the time period 2000–2011 are estimated as 1,180 ± 163 Gg CH4 yr−1. During the cropping season, this is about +16% higher than a former estimate using emission factors. Scenario simulations of nationwide introduction of AWD in irrigated landscapes suggest a considerable decrease in CH4 emissions by −23%, while N2O emissions are only increased by +8%. Irrespective of field management, at national scale, the radiative forcing of irrigated rice production is always dominated by CH4 (>95%). The reduction potential of GHG emissions depends on, for example, number of crops per year, residue management, amount of applied irrigation water, and sand content. Seasonal weather conditions also play an important role since the mitigation potential of AWD is almost double as high in dry as compared to wet seasons. Furthermore, this study demonstrates the importance of temporal continuity, considering off‐season emissions and the long‐term development of GHG emissions across multiple years. Plain Language Summary: Worldwide, rice production contributes to about 10% of total greenhouse gas emissions of the agricultural sector mainly due to CH4 emissions from fields that are continuously flooded. Alternate Wetting and Drying (AWD) is an alternative cropping practice where fields are irrigated a few days after the disappearance of the ponded water. This study explores the mitigation potential of nationwide introduction of AWD in the Philippines. Results from the application of a process‐based model suggest a considerable decrease in CH4 emissions by −23%. Compared to N2O, CH4 is responsible for more than 95% of the total radiative forcing under conventional or AWD field management. Key Points: Nationwide, Alternate Wetting and Drying (AWD) reduces CH4 emissions by −23%N2O emissions contribute to less than 5% to the total radiative forcing under conventional or AWD field managementMitigation of AWD depends on, for example, seasonal weather conditions, cropping intensity, irrigation, residue management, and soil texture [ABSTRACT FROM AUTHOR]

The flux calculation schemes (FCSs) and gas sampling schemes (GSSs) determine the accuracy and representativeness of non‐steady‐state chamber measurements. The study aimed to provide guidelines on FCSs and GSSs to improve cumulative flux estimations of the non‐steady‐state chamber method. Based on a dataset obtained from automated chamber measurements in a permafrost‐affected wetland in northeast China, we evaluated the effects of FCSs and GSSs on cumulative methane and nitrous oxide flux estimates at the field scale. The evolution of chamber headspace gas concentrations was classified into five patterns, presenting the measurement disturbance and variation of non‐steady‐state chamber method. Three FCSs, that is, the sole use of linear model and hybrid use of linear with empirical quadratic and theoretical exponential models, were established on the basis of evolution patterns of chamber headspace gas concentrations. The hybrid FCSs were more robust for cumulative flux estimates than the sole FCS of the linear model. The flux dataset with the high spatiotemporal resolution was subsampled to simulate datasets obtained with different GSSs. The subsampling of flux dataset proved optimization of GSSs by allocating limited measurement resources to preferentially promote the spatial representativeness of measurements (e.g., with more replicate chambers and stratified chamber placement according to microtopographies), characterize the small‐scale spatiotemporal variability of fluxes (e.g., diurnal variation and spatial heterogeneity due to microtopographies), and capture the evolution pattern of chamber headspace gas concentrations, could effectively improve cumulative flux estimates at the field scale. Our guidelines on FCSs and GSSs can serve to the improvement of non‐steady‐state chamber methodology. Plain Language Summary: Ecosystems may mitigate or intensify global warming depending on the ecosystem−atmosphere greenhouse gas exchanges. Quantification of greenhouse gas exchanges at a field scale involves a high degree of uncertainty due to the error of flux measurements and spatiotemporal variability of fluxes. The greenhouse gas fluxes are usually measured with the non‐steady‐state chamber method, that is, placing a bottomless chamber on an accessional base frame in soils and measuring the change rate of gas concentrations in the chamber headspace. Minimizing the bias and uncertainty of non‐steady‐state chamber measurements is crucial for assessing the role of ecosystems on global warming. This study evaluated the effects of non‐steady‐state chamber methodology on estimating cumulative methane and nitrous oxide emissions from a typical wetland in the permafrost region of northeast China. The optimization of measurement schemes, for example, flux calculation and gas sampling schemes, can effectively improve cumulative flux estimates at the field scale. The findings respond to the question of how to allocate the limited observation resources to minimize the bias and uncertainty of quantifying greenhouse gas exchanges over a field scale. Key Points: Optimized flux calculation schemes were established based on the evolution pattern of chamber headspace gas concentrationsOptimization of flux calculation and gas sampling schemes can effectively improve cumulative flux estimates at the field scaleCapturing small‐scale spatiotemporal variabilities of fluxes deserves the top priority in the allocation of the measurement resource [ABSTRACT FROM AUTHOR]

Tropical montane forest store high amounts of soil organic carbon. However, global warming may affect these carbon stocks by enhancing soil organic carbon respiration. Better insight into temperature response of soil organic carbon respiration can be obtained from in and ex situ warming studies. In situ warming via translocation of intact soil mesocosms was carried out along an elevational transect ranging between ca. 1250 m a.s.l. in the Kibale Forest to ca. 3000 m a.s.l. in the Rwenzori Mountains. Samples from the same transect were also warmed ex situ to determine temperature sensitivity. The ex situ results revealed that along the natural climate gradient in the elevational transect, specific heterotrophic CO2 respiration decreased linearly by 1.01 ± 0.12 μg C h−1 g−1 SOC per 100 m of elevation increase. Similarly, the temperature sensitivity increased from 1.50 ± 0.13 in the lowest elevation clusters to 2.68 ± 0.25 in the highest elevation cluster, showing a linear decrease of 0.09 ± 0.03 per 100 m of elevation increase. Additionally, the 13C depletion factor of the respired CO2 decreased linearly by 0.23 ± 0.04 ‰ per 100 m of elevation increase. The results indicate an increased recalcitrance and decreased mineralisation of soil organic carbon with elevation driven by decreasing soil temperature and pH. Subsequently, after two years of in situ warming (0.9 to 2.8 °C), specific heterotrophic soil organic carbon respiration tends to be lower for warmed as compared to control soil. Further, in warmed soils, 13C and content of soil organic carbon relatively increased and decreased, respectively. This indicates increased mineralisation and depletion of readily available carbon during two years of warming. In conclusion, our results suggest that climate warming may trigger enhanced losses of soil organic carbon from tropical montane forests, due to a combination of a higher temperature sensitivity of mineralisation and soil organic carbon content. [ABSTRACT FROM AUTHOR]

Background: About 30 % of vegetables in China are produced in intensively managed greenhouses comprising flood irrigation and extreme rates of nitrogen fertilizers. Little is known about denitrification N losses. Methods: Soil denitrification rates were measured by the acetylene inhibition technique applied to anaerobically incubated soil samples. Four different greenhouse management systems were differentiated: Conventional flood irrigation and over-fertilization (CIF, 800 kg N ha−1, 460 mm); CIF plus straw incorporation (CIF+S, 889 kg N ha−1, 460 mm); Drip fertigation with reduced fertilizer application rates (DIF, 314 kg N ha−1, 190 mm); DIF plus straw incorporation (DIF+S, 403 kg N ha−1, 190 mm). Soil denitrification was measured on nine sampling dates during the growing season (Feb 2019-May 2019) for the top-/ subsoil (0 – 20/ 20- 40 cm) and on three sampling dates for deep soils (40-60/ 80-100 cm). Data was used to constrain N-input-output balances of the different vegetable production systems. Results: Rates of denitrification were at least one magnitude higher in topsoil than in sub- and deep soils. Total seasonal denitrification N losses for the 0 – 40 cm soil layer ranged from 76 (DIF) to 422 kg N ha−1 (CIF+S). Straw addition stimulated soil denitrification in top- and subsoil, but not in deep soil layers. Integrating our denitrification data (0-100 cm) with additional data on N leaching, N2O emissions, plant N uptake, and NH3 volatilization showed, that on average 50 % of added N fertilizers are lost due to denitrification. Conclusions: Denitrification is likely the dominant environmental N loss pathway in greenhouse vegetable production systems. Reducing irrigation and fertilizer application rates while incorporating straw in soils allows the reduction of accumulated nitrate. [ABSTRACT FROM AUTHOR]

Background: Reductions of ammonia volatilization resulting from slurry applications to intensively managed grassland may be achieved via slurry acidification. However, it remains uncertain if this may result in pollution swapping, that is, due to reduced ammonia volatilization and increased soil N availability, emission of nitrous oxide from soils may increase. Aims: In this study, we compared control (no fertilizer) and slurry fertilized grassland treatments [not acidified (S) and acidified (AS)] to assess whether slurry acidification results in changes of soil N availability, denitrification potential and activity as well as soil fluxes of nitrous oxide. Methods: The study was carried out in a montane grassland system in southern Germany, and parameters were followed over a 43‐days period with continuous measurements of soil GHG fluxes and biweekly measurements of microbial and soil parameters preceding and following two fertilizing events. Results: Over the entire observation period cumulative N2O emissions were significantly elevated for treatments receiving slurry applications, with differences between acidified and non‐acidified slurry treatments being overall insignificant. Transcripts of the nirK type nitrite reductase showed significantly higher numbers in soils of the AS treatment. While soil potential denitrification rates (PDR) did not differ between treatments, there was a strong tendency of increased PDRs for the AS treatment. Conclusions: Against expectation, we did not find that application of AS affects PDR or soil N2O emissions significantly, though in tendency higher rates of soil N2O emissions as well as higher potential denitrification rates were found in treatments receiving acidified slurry as compared to the slurry only treatment. Our results indicate that longer observation periods and given the significant spatial variability, higher numbers of replicates are needed, to finally assess if slurry application indeed results in increased soil denitrification activity, soil N2O production and soil‐atmosphere N2O emissions. [ABSTRACT FROM AUTHOR]

We applied the process-based model, LandscapeDNDC, to estimate feed availability in the Sahelian and Sudanian agro-ecological zones of West Africa as a basis for calculating the regional Livestock Carrying Capacity (LCC). Comparison of the energy supply (S) from feed resources, including natural pasture, browse, and crop residues, with energy demand (D) of the livestock population for the period 1981–2020 allowed us to assess regional surpluses (S > D) or deficits (S < D) in feed availability. We show that in the last 40 years a large-scale shift from surplus to deficit has occurred. While during 1981–1990 only 27% of the area exceeded the LCC, it was 72% for the period 2011–2020. This was caused by a reduction in the total feed supply of ~ 8% and an increase in feed demand of ~ 37% per-decade, driven by climate change and increased livestock population, respectively. Overall, the S/D decreased from ~ 2.6 (surplus) in 1981 to ~ 0.5 (deficit) in 2019, with a north–south gradient of increasing S/D. As climate change continues and feed availability may likely further shrink, pastoralists either need to source external feed or significantly reduce livestock numbers to avoid overgrazing, land degradation, and any further conflicts for resources. [ABSTRACT FROM AUTHOR]

Climate warming and management will likely affect carbon (C) fluxes of montane grassland ecosystems. In this study, we assessed the effect of simultaneous warming (+2°C) and decreased precipitation (−25%) on carbon exchange of montane grasslands in S‐Germany by translocating large intact plant‐soil cores from a high altitude to a low altitude site. Cores received two common grassland management regimes: intensive (4–5 cuts and slurry application) and extensive (1–2 cuts and slurry application). Diurnal patterns of net ecosystem exchange (NEE) and total ecosystem respiration (Reco) were measured over 1.5 years in 2–3 weeks intervals during the snow free period. Additional data on environmental controls, that is, photosynthetic active radiation, grass height and soil moisture and temperature, were used to develop empirical models to estimate daily and annual fluxes of gross primary production (GPP) and Reco. Considering the 2 years period (2014 and 2015), we found that, under warmer and slightly drier conditions, both GPP and Reco significantly (p < 0.01) increased (up to 20%) but with a higher temperature sensitivity of Reco, particularly in intensive managed grassland. The higher temperature sensitivity of Reco reduced the NEE by 0.7 t C ha−1 yr−1 for both extensive and intensive management, respectively. Considering additional carbon inputs via slurry and exports via harvest (i.e., annual net ecosystem carbon budget), our results showed that managed grasslands are already a source of C under current climate conditions (1.7–1.8 t ha−1 yr−1) which significantly (p < 0.05) increased under climate warming (2.3–2.9 t ha−1 yr−1). Key Points: Climate change can accelerate depletion of montane grassland C stocksUnder warmer conditions gross primary production and ecosystem respiration (Reco) increase, but Reco with a higher temperature sensitivityAdaptation of grassland cutting and manure management regimes can likely reduce ecosystem carbon losses [ABSTRACT FROM AUTHOR]

Aims: Root exudates are known to shape microbial activities in the rhizosphere and to be of fundamental importance for plant-soil-microbe-carbon–nitrogen interactions. However, it remains unclear how and to what extent the amount and composition of root exudation affects rhizosphere denitrification. Methods: In this study root exudation patterns and rhizosphere denitrification enzyme activity of three different grass species grown on two agricultural soils under two different soil water contents were investigated under controlled conditions. Results: We found that root exudation of primary metabolites largely depends on plant species, soil type, soil moisture and root exudation medium. In dependence of soil properties and soil moisture levels, plants largely controlled amount and quality of root exudation. Exudates affected denitrification activity and plant–microbe competition for nitrate. Specifically, exudation of organic acids stimulated denitrifying activity while the sugar lyxose exhibited an inhibitory effect. Conclusion: We show that interactive effects of physicochemical soil properties and species-specific effects of plant metabolism on root exudation act as a dominant control of rhizosphere denitrification, thereby explaining more than half of its variance. [ABSTRACT FROM AUTHOR]

Pastoral systems are the dominant livestock production system in arid and semiarid regions of sub‐Saharan Africa (SSA). They are often the only form of agriculture that can be practiced due to unfavorable climate and soil fertility levels that prevent crop cultivation. Pastoralism can have negative impacts on the environment, including land degradation, greenhouse gas emissions and other gases to the atmosphere, soil erosion, water pollution and biodiversity loss. Here, we review the current knowledge on nitrogen (N) cycling, storage, and loss pathways, with an emphasis on identification of N emission hotspots. Our review reports a large uncertainty in the amount of N lost as ammonia from excreta and manure storage, as well as N losses via nitrate and DON leaching. We also found that another major N loss pathway (18%), soil N2 emissions, has not yet been measured. In order to summarize the available information, we use a virtual pastoral farm, with characteristics and management practices obtained from a real farm, Kapiti Research Station in Kenya. For outlining N flows at this virtual farm, we used published data, data from global studies, satellite imagery and geographic information system (GIS) tools. Our results show that N inputs in pastoral systems are dominated by atmospheric N deposition (˜80%), while inputs due to biological nitrogen fixation seems to play a smaller role. A major N loss pathway is nitrogen leaching (nitrate > DON) from pastures (33%). Cattle enclosures (bomas), where animals are kept during night, represent N emissions hotspots, representing 16% of the total N losses from the system. N losses via ammonia volatilization and N2O were four and three orders of magnitude higher from bomas than from the pasture, respectively. Based on our results, we further identify future research requirements and highlight the urgent need for experimental data collection to quantify nitrogen losses from manure in animal congregation areas. Such information is needed to improve our understanding on N cycling in pastoral systems in semiarid regions and to provide practical recommendations for managers that can help with decision‐making on management strategies in pastoral systems in semiarid savannas. [ABSTRACT FROM AUTHOR]

Aim: The effects of residue type and distribution, soil moisture and NO3− availability were investigated in 43 days laboratory incubations (15 °C) on emissions of N2O, CO2, and for some treatments NO and NH3. Methods: Two crop residues were considered (red clover, RC, and winter wheat, WW), and they were either mixed with topsoil, placed as a discrete layer in soil, or no addition. Soil NO3− was either at ambient level or increased. Water filled pore space (WFPS) was adjusted to either 40 or 60%. All treatments were analysed for mineral N, N2O and CO2 with manual sampling and gas chromatography. Selected treatments were analysed with a continuous-flow method of N2O and CO2 by laser spectroscopy, NO by photoluminescence and NH3 by acid traps. Results: The NH3 and NO emissions was higher in mixed RC than control and WW treatment. The N2O emission was many-fold higher with mixed than layered distribution, but only with high soil NO3− availability and high soil moisture. Emissions of N2O from WW were an order of magnitude lower compared to RC, and decomposition was slower. Both batch and continuous-flow incubations resulted in similar emissions. Disregarding the extreme emissions in the high WFPS and NO3− treatment, the N2O emission factors averaged 0.3 and 0.6% of residue N for WW and RC, respectively. Conclusion: Residue decomposition was enhanced by mixing, and N2O emissions by higher soil water and NO3− content. The results show the importance of residue distribution and soil condition on estimating N2O emission factors for crops. [ABSTRACT FROM AUTHOR]

Globally, about 50% of all arable soils are classified as acidic. As crop and plant growth are significantly hampered under acidic soil conditions, many farmers, but increasingly as well forest managers, apply lime to raise the soil pH. Besides its direct effect on soil pH, liming also affects soil C and nutrient cycles and associated greenhouse gas (GHG) fluxes. In this meta‐analysis, we reviewed 1570 observations reported in 121 field‐based studies worldwide, to assess liming effects on soil GHG fluxes and plant productivity. We found that liming significantly increases crop yield by 36.3%. Also, soil organic C (SOC) stocks were found to increase by 4.51% annually, though soil respiration is stimulated too (7.57%). Moreover, liming was found to reduce soil N2O emission by 21.3%, yield‐scaled N2O emission by 21.5%, and CH4 emission and yield‐scaled CH4 emission from rice paddies by 19.0% and 12.4%, respectively. Assuming that all acid agricultural soils are limed periodically, liming results in a total GHG balance benefit of 633−749 Tg CO2‐eq year−1 due to reductions in soil N2O emissions (0.60−0.67 Tg N2O‐N year−1) and paddy soil CH4 emissions (1.75−2.21 Tg CH4 year−1) and increases in SOC stocks (65.7–110 Tg C year−1). However, this comes at the cost of an additional CO2 release (c. 624–656 Tg CO2 year−1) deriving from lime mining, transport and application, and lime dissolution, so that the overall GHG balance is likely neutral. Nevertheless, liming of acid agricultural soils will increase yields by at least 6.64 × 108 Mg year−1, covering the food supply of 876 million people. Overall, our study shows for the first time that a general strategy of liming of acid agricultural soils is likely to result in an increasing sustainability of global agricultural production, indicating the potential benefit of liming acid soils for climate change mitigation and food security. [ABSTRACT FROM AUTHOR]

West African Sahelian and Sudanian ecosystems provide essential services to people and also play a significant role within the global carbon cycle. However, climate and land use are dynamically changing, and uncertainty remains with respect to how these changes will affect the potential of these regions to provide food and fodder resources or how they will affect the biosphere–atmosphere exchange of CO 2. In this study, we investigate the capacity of a process-based biogeochemical model, LandscapeDNDC, to simulate net ecosystem exchange (NEE) and aboveground biomass of typical managed and natural Sahelian and Sudanian savanna ecosystems. In order to improve the simulation of phenology, we introduced soil-water availability as a common driver of foliage development and productivity for all of these systems. The new approach was tested by using a sample of sites (calibration sites) that provided NEE from flux tower observations as well as leaf area index data from satellite images (MODIS, MODerate resolution Imaging Spectroradiometer). For assessing the simulation accuracy, we applied the calibrated model to 42 additional sites (validation sites) across West Africa for which measured aboveground biomass data were available. The model showed good performance regarding biomass of crops, grass, or trees, yielding correlation coefficients of 0.82, 0.94, and 0.77 and root-mean-square errors of 0.15, 0.22, and 0.12 kg m -2 , respectively. The simulations indicate aboveground carbon stocks of up to 0.17, 0.33, and 0.54 kg C ha -1 m -2 for agricultural, savanna grasslands, and savanna mixed tree–grassland sites, respectively. Carbon stocks and exchange rates were particularly correlated with the abundance of trees, and grass biomass and crop yields were higher under more humid climatic conditions. Our study shows the capability of LandscapeDNDC to accurately simulate carbon balances in natural and agricultural ecosystems in semiarid West Africa under a wide range of conditions; thus, the model could be used to assess the impact of land-use and climate change on the regional biomass productivity. [ABSTRACT FROM AUTHOR]

West African Sahelian and Sudanian ecosystems are providing essential services to people and also play a significant role within the global carbon cycle. However, climate and land use are dynamically changing and it remains uncertain how these changes will affect the potential of these regions for providing food and fodder resources or the biosphere-atmosphere exchange of CO2. In this study, we investigate the capacity of a process-based biogeochemical model, LandscapeDNDC, to simulate net ecosystem exchange (NEE) and aboveground biomass of typical managed and natural Sahelian and Sudanian savanna ecosystems. We tested the model for various sites with different proportions of trees and grasses, as well as for the most typical arable cropping systems of the region. In order to describe the phenological development with a common parameterization across all ecosystem types, we introduced soil-water availability in addition to temperature as a driver as seasonal soil water-shortage is a common feature for all these systems. The new approach was tested by using a sample of sites (calibration sites) that provided NEE from flux tower observations and leaf area index data from satellite images (MODIS). For assessing the simulation accuracy, we applied the calibrated model to 42 additional sites (validation sites) across West Africa for which measured aboveground biomass data were available. The model showed a good performance regarding simulated biomass development. Overall, the comparison of simulated and observed biomass at sites with a dominating land cover of crops, grass or trees yielded correlation coefficients of 0.82, 0.94, and 0.77 and the Root Mean Square Error of 0.15, 0.22, and 0.12 kg m-2, respectively. In absolute terms, the model results indicate above-ground carbon stocks up to 1733, 3291, and 5377 kg C ha-1 yr-1 for agricultural, savanna grasslands, and savanna mixed tree-grassland sites. Carbon stocks as well as exchange rates correlated in particular with the abundance of trees. The simulations indicate higher grass biomass and crop yields under more humid climatic conditions as can be found in the Sudanian savanna region. Our study shows the capability of LandscapeDNDC to accurately simulate carbon balances in natural and agricultural ecosystems in semi-arid West Africa under a wide range of conditions, so that it might be used to assess the impact of land-use and climate change on the regional biomass productivity. [ABSTRACT FROM AUTHOR]

Increasing levels of atmospheric CO2 are expected to enhance crop yields and alter soil greenhouse gas fluxes from rice paddies. While elevated CO2 (ECO2) effects on CH4 emissions from rice paddies have been studied in some detail, little is known how ECO2 might affect N2O fluxes or yield-scaled emissions. Here, we report on a multi-site, multi-year in-situ FACE (free-air CO2 enrichment) study, aiming to determine N2O fluxes and crop yields from Chinese subtropical rice systems as affected by ECO2. In this study, we tested various N fertilization and residue addition treatments, with rice being grown under either ECO2 (+200 µmol/mol) or ambient control. Across the six site-years, rice straw and grain yields under ECO2 were increased by 9%-40% for treatments fertilized with =150 kg N/ha, while seasonal N2O emissions were decreased by 23%-73%. Consequently, yield-scaled N2O emissions were significantly lower under ECO2. For treatments receiving insufficient fertilization (=125 kg N/ha), however, no significant ECO2 effects on N2O emissions were observed. The mitigating effect of ECO2 upon N2O emissions is closely associated with plant N uptake and a reduction of soil N availability. Nevertheless, increases in yield-scaled N2O emissions with increasing N surplus suggests that N surplus is a useful indicator for assessing N2O emissions from rice paddies. Our findings indicate that with rising atmospheric CO2 soil N2O emissions from rice paddies will decrease, given that the farmers' N fertilization is usually sufficient for crop growth. The expected decrease in N2O emissions was calculated to compensate 24% of the simultaneously observed increase in CH4 emissions under ECO2. This shows that for an agronomic and environmental assessment of ECO2 effects on rice systems, not only CH4 emissions, but also N2O fluxes and yield-scaled emissions need to be considered for identifying most climatefriendly and economically viable options for future rice production. [ABSTRACT FROM AUTHOR]

Short-lived pulses of soil nitrous oxide (N2O) emissions during freeze-thaw periods can dominate annual cumulative N2O fluxes from temperate managed and natural soils. However, the effects of freeze thaw cycles (FTCs) on dinitrogen (N2) emissions, i.e., the dominant terminal product of the denitrification process, and ratios of N2/N2O emissions have remained largely unknown because methodological difficulties were so far hampering detailed studies. Here, we quantified both N2 and N2O emissions of montane grassland soils exposed to three subsequent FTCs under two different soil moisture levels (40 and 80% WFPS) and under manure addition at 80% WFPS. In addition, we also quantified abundance and expression of functional genes involved in nitrification and denitrification to better understand microbial drivers of gaseous N losses. Our study shows that each freeze thaw cycle was associated with pulse emissions of both N2O and N2, with soil N2 emissions exceeding N2O emissions by a factor of 5–30. Increasing soil moisture from 40 to 80% WFPS and addition of cow slurry increased the cumulative FTC N2 emissions by 102% and 77%, respectively. For N2O, increasing soil moisture from 40 to 80% WFPS and addition of slurry increased the cumulative emissions by 147% and 42%, respectively. Denitrification gene cnorB and nosZ clade I transcript levels showed high explanatory power for N2O and N2 emissions, thereby reflecting both N gas flux dynamics due to FTC and effects of different water availability and fertilizer addition. In agreement with several other studies for various ecosystems, we show here for mountainous grassland soils that pulse emissions of N2O were observed during freeze-thaw. More importantly, this study shows that the freeze-thaw N2 pulse emissions strongly exceeded those of N2O in magnitude, which indicates that N2 emissions during FTCs could represent an important N loss pathway within the grassland N mass balances. However, their actual significance needs to be assessed under field conditions using intact plant-soil systems. [ABSTRACT FROM AUTHOR]

This study focuses on heat stress conditions for dairy cattle production in West Africa under current and future climatic conditions. After testing the accuracy of the dynamically downscaled climate datasets for simulating the historical daily maximum temperature (Tmax) and relative humidity (RH) in West Africa for 50 meteorological stations, we used the dataset for calculating the temperature-humidity index (THI), i.e., an index indicating heat stress for dairy cattle on a daily scale. Calculations were made for the historical period (1981–2010) using the ERA-Interim reanalysis dataset, and for two future periods (2021–2050 and 2071–2100) using climate predictions of the GFDL-ESM2M, HadGEM2-ES, and MPI-ESM-MR Global Circulation Models (GCMs) under the RCP4.5 emission scenario. Here, we show that during the period from 1981 to 2010 for > 1/5 of the region of West Africa, the frequency of severe/danger heat events per year, i.e., events that result in significant decreases in productive and reproductive performances, increased from 11 to 29–38 days (significant at 95% confidence level). Most obvious changes were observed for the eastern and southeastern parts. Under future climate conditions periods with severe/danger heat stress events will increase further as compared with the historical period by 5–22% depending on the GCM used. Moreover, the average length of periods with severe/danger heat stress is expected to increase from ~ 3 days in the historical period to ~ 4–7 days by 2021–2050 and even to up to 10 days by 2071–2100. Based on the average results of three GCMs, by 2071–2100, around 22% of dairy cattle population currently living in this area is expected to experience around 70 days more of severe/danger heat stress (compare with the historical period), especially in the southern half of West Africa. The result is alarming, as it shows that dairy production systems in West Africa are jeopardized at large scale by climate change and that depending on the GCM used, milk production might decrease by 200–400 kg/year by 2071–2100 in around 1, 7, or 11%. Our study calls for the development of improved dairy cattle production systems with higher adaptive capacity in order to deal with expected future heat stress conditions. [ABSTRACT FROM AUTHOR]

Solar vegetable greenhouse soils show low soil organic carbon content and thus also low rates of soil respiration. Processing vegetable residues to biochar and mixing biochar with maize straw might improve soil respiration and increase soil organic carbon stocks, while preventing the spread of soil‐borne diseases carried by vegetable residues. In an incubation experiment, we tested how additions of maize straw (S) and biochar (B) added in varying ratios (100S, 75S25B, 50S50B, 25S75B, 100B and 0S0B (control)) affect soil respiration and fraction of added C remaining in soil. Daily CO2 emissions were measured over 60 days incubation, the natural abundance of 13C in soil and in the added biochar and maize straw were analysed. Our result shows that (a) soil CO2 emissions were significantly increased compared to soil without the straw additions, while addition of biochar only decreased soil respiration; (b) cumulative CO2 emissions decreased with increasing ratio of added biochar to maize straw; (c) the abundance of soil 13C was significant positively correlated with cumulative CO2 emissions, and thus with the ratio of straw addition. Our results indicate that incorporation of maize straw in greenhouse soils is a meaningful measure to increase soil respiration and to facilitate greenhouse atmosphere CO2 limitation while producing vegetables. On the other hand, additions of biochar from vegetable residues will increase soil organic carbon concentration. Therefore, the simultaneous application of maize straw and biochar obtained from vegetable residues is an effective option to maintain essential soil functions for vegetable production in sunken solar greenhouses. [ABSTRACT FROM AUTHOR]

Isotopic composition of soil‐emitted nitrous oxide (N2O), especially the intramolecular distribution of 15N in N2O known as site preference (SP), can be used to track the two major N2O emitting soil‐processes nitrification and denitrification. Online analysis of SP in ambient air has been achieved recently, yet those approaches only allowed addressing large areas (footprints) on the basis of strong changes in surface atmospheric N2O concentrations. Here, we combined laser spectroscopy with automated static flux chambers to measure, for the first time, SP of low N2O fluxes with high sensitivity and temporal resolution and to explore its spatial variability. The measurements were then used to test the N2O isotope module SIMONE in combination with the biogeochemical model LandscapeDNDC to identify N2O source processes. End‐member mixing analysis of the data revealed denitrification as the predominant N2O source. This finding was independent of the soil water content close to the soil surface, suggesting that N2O production in the subsoil under high water‐filled pore space conditions outweighed the potential production of N2O by nitrification closer to the surface. Applying the SIMONE‐LandscapeDNDC model framework to our field site showed that the modeled SP was on average 4.2‰ lower than the observed values. This indicates that the model parameterization reflects the dominant N2O production pathways but overestimates the contribution of denitrification by 6%. Applying the stable isotope‐based model framework at other sites and comparing with other models will help identifying model shortcomings and improve our capability to support N2O mitigation from agricultural ecosystems. Plain Language Summary: Between August and December 2017 the concentration and isotopic composition of soil emitted nitrous oxide (N2O) was measured above a grassland site in Central Switzerland. Automated flux chambers were coupled to a custom‐built preconcentration and laser spectroscopy‐based online measurement method. The obtained results were used to validate a recently developed isotope submodule (SIMONE) for a biogeochemical model (LandscapeDNDC), to simulate fluxes of trace gases. Our results show a clear predominance of denitrification as the primary N2O emitting source process. In contrast to previous studies, this dominance led to stable N2O site preference values throughout the measurement campaign, a feature that was also represented by SIMONE. These findings will bridge current shortcomings in our model understanding and thereby help developing targeted N2O mitigation strategies. Key Points: Spatial allocation and high instrumental sensitivity was achieved by combining automated flux chambers and laser spectroscopy with preconcentrationWe report on the first quasi‐continuous analysis of the intramolecular 15N distribution (known as site preference, SP) of soil‐emitted N2O over a 3 months periodMeasurements and biogeochemical modeling revealed that denitrification was the dominant N2O production pathway in the managed grassland [ABSTRACT FROM AUTHOR]

Aims: Decomposition of manure deposited onto pasture from grazing animals represents an important process for carbon (C) and nitrogen (N) cycles in grassland systems. However, studies investigating manure decomposition are scarce; especially in sub-Saharan Africa (SSA). Methods: In this study, we measured decomposition of three types of animal manure (cattle, sheep, goat) over >1 year using litter bags at four climatically different sites across Kenya. Results Manure dry matter, total C, total N and ammonium concentrations decreased exponentially, with the most rapid decrease occurring during the first few weeks following application, followed by slower changes during the following 2–3 months. Rates of N mineralization were lower than those for C mineralization, resulting in decreasing C/N ratios over time. Generally, cattle manure decomposed faster than sheep or goat manure despite having a higher initial C/N ratio and lower N concentration, with decomposition rates for dry matter ranging from 0.200 to 0.989 k year−1. Cellulose decomposed first, while lignin concentrations increased among all manure types and at all sites. Conclusions: We found that total manure decomposition rates were positively correlated with cumulative precipitation and aridity index, but negatively correlated with mean temperature. Our results show much slower decomposition rates of manures in semi-arid tropical environments of East Africa as compared to the few previous studies in temperate climates. [ABSTRACT FROM AUTHOR]

Gaseous nitrogen (N) emissions, especially emissions of dinitrogen (N2) and ammonia (NH3), have long been considered as the major pathways of N loss from flooded rice paddies. However, no studies have simultaneously evaluated the overall response of gaseous N losses to improved N fertilization practices due to the difficulties to directly measure N2 emissions from paddy soils. We simultaneously quantified emissions of N2 (using membrane inlet mass spectrometry), NH3 and nitrous oxide (N2O) from a flooded paddy field in southern China over an entire rice‐growing season. Our field experiment included three treatments: a control treatment (no N addition) and two N fertilizer (220 kg N/ha) application methods, the traditional surface application of N fertilizer and the incorporation of N fertilizer into the soil. Our results show that over the rice‐growing season, the cumulative gaseous N losses from the surface application treatment accounted for 13.5% (N2), 19.1% (NH3), 0.2% (N2O) and 32.8% (total gaseous N loss) of the applied N fertilizer. Compared with the surface application treatment, the incorporation of N fertilizer into the soil decreased the emissions of NH3, N2 and N2O by 14.2%, 13.3% and 42.5%, respectively. Overall, the incorporation of N fertilizer into the soil significantly reduced the total gaseous N loss by 13.8%, improved the fertilizer N use efficiency by 14.4%, increased the rice yield by 13.9% and reduced the gaseous N loss intensity (gaseous N loss/rice yield) by 24.3%. Our results indicate that the incorporation of N fertilizer into the soil is an effective agricultural management practice in ensuring food security and environmental sustainability in flooded paddy ecosystems. [ABSTRACT FROM AUTHOR]