Mohammad Ibrahim Khalil

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• BScAg(Hons), MSc, MS, PhD
• Senior Research Fellow at University College Dublin

Forests can play a key role in the mitigation of climate change, although there have been limited regional scale assessments that account for variations in soil type and tree species. Most of the focus has been on their ability to sequester atmospheric CO2, while there is less information on the two other major greenhouse gases (GHGs), N2O and CH4....

Biogeochemical models are essential for the prediction and management of nitrogen (N) cycling in agroecosystems, but the accuracy of the denitrification and decomposition sub-modules is critical. Current models were developed before suitable soil N2 flux data were available, which may have led to inaccuracies in how denitrification was described. N...

Description, carbon and other benefits, drawbacks and barriers of grassland-related practices. Chapters: 30. Conservation of permanent grassland 31. Grassland diversification 32. Restoration of degraded grassland 33. Conversion of cropland to grassland 34. Improved pasture management 35. Grazing exclusion and rotational grazing 36. Pastoralism Book...

Understanding the functioning of different forest ecosystems is important due to their key role in strategies for climate change mitigation, especially through soil C sequestration. In controlled laboratory conditions, we conducted a preliminary study on six different forest soils (two coniferous, two deciduous, and two mixed sites comprising trees...

Biogeochemical models are useful for the prediction of nitrogen (N) cycling processes, but accurate description of the denitrification and decomposition sub-modules is critical. Current models were developed before suitable soil N2 flux data were available; new measurement techniques have enabled the collection of improved N2 data. We use measured...

Citation: Walkiewicz, A.; Bulak, P.; Brzezińska, M.; Khalil, M.I.; Osborne, B. Variations in Soil Properties and CO 2 Emissions of a Temperate Forest Gully Soil along a Topographical Gradient. Forests 2021, 12, 226. https://doi.

We are listed contributors in an FAO-authored book: FAO. 2020. A protocol for measurement, monitoring, reporting and verification of soil organic carbon in agricultural landscapes – GSOC-MRV Protocol. Rome. DOI: 10.4060/cb0509en This document provides a conceptual framework and standard methodologies for the monitoring, reporting and verificatio...

Full text available upon request. The accurate assessment of agricultural greenhouse gas emissions (GHGs) for accounting and mitigation options is still a key concern. An extensive body of data is available, but limitations of the different measuring approaches have often been ignored. Despite some constraints, chamber-based approaches have dominat...

Agricultural soils may act as either a source or a sink for atmospheric methane (CH4) depending on soil type, aeration, water regimes, nutrient availability and environmental variables. The interaction between CH4 and nitrogen (N) has been identified as one of the major gaps in the global carbon (C) and N cycles. Methane is being considered as a lo...

The adoption and use of improved methodologies including models that reflect more robust emissions accounting procedures and the identification of specific mitigation options for agricultural greenhouse gases are a global concern. In Ireland, country-specific N2O emission factors (EFs) are constrained primarily by short-term measurements and limite...

Understanding management-induced C sequestration potential in soils under agriculture, forestry, and other land use systems and their quantification to offset increasing greenhouse gases are of global concern. This chapter reviews management-induced changes in C storage in soils of grazing grassland systems, their impacts on ecosystem functions, an...

Understanding management-induced C sequestration potential in soils under agriculture, forestry, and other land use systems and their quantification to offset increasing greenhouse gases are of global concern. This chapter reviews management-induced changes in C storage in soils of grazing grassland systems, their impacts on ecosystem functions, an...

Ammonia (NH 3) and Nitrogen Oxides (NO x = NO + NO 2) emissions from soils and vegetation, and their subsequent deposition are key factors in global Nitrogen (N) cycling and have important functions in atmospheric and ecosystem degradation processes. To better understand their contribution, NH 3 and NO x gases were simultaneously measured from diff...

Reduction of greenhouse gas (GHG) assessment uncertainties and improvement in the quantification of sinks and offsetting mechanisms are a global necessity for the development of appropriate mitigation measures aimed at keeping global temperature <2oC. In order to meet these objectives precise, verifiable estimations of soil organic carbon (SOC) and...

Reduction of greenhouse gas (GHG) assessment uncertainties and improvement in the quantification of sinks and offsetting mechanisms are required to develop appropriate mitigation measures aimed at keeping global temperature <2oC. The key factors that are needed to fulfil these objectives are a precise, verifiable estimation of soil organic carbon (...

A field experiment was carried out in a non-calcareous sandy loam soil of subtropics using crop residue and root biomass of preceding rainfed rice to study the soil organic carbon (SOC) storage and nutrient uptake by succeeding irrigated rice. Decomposition of incorporated biomass was rapid initially and the residue-amended plots showed higher peak...

The Paris Agreement emphasises the need for enhanced greenhouse gas (GHG) mitigation measures, a reduction in assessment uncertainties, better quantified sinks, and the tailored use of different offsetting mechanisms to keep global temperature <2°C. A precise, verifiable estimation of soil organic carbon (SOC), and its variation at field scales has...

The nitrite reductase (nirS and nirK) and nitrous oxide reductase-encoding (nosZ) genes of denitrifying populations present in an agricultural grassland soil were quantified using real-time polymerase chain reaction (PCR) assays. Samples from three separate pedological depths at the chosen site were investigated: horizon A (0–10 cm), horizon B (45–...

Globally a large number of process-based models have been assessed for quantification of agricultural greenhouse gas (GHG) emissions. Modelling approaches minimize the presence of spatial variability of biogeochemical processes, leading to improved estimates of GHGs as well as identifying mitigation and policy options. The comparative performance o...

h i g h l i g h t s ECOSSE model simulated N 2 O fluxes from arable field well with EF (0.53 AE 0.03%). Predicted R H (3149 kg C ha À1 yr À1) was within the uncertainty ranges of croplands. Simulated CH 4 showed a sink (26.61e31.37 g C ha À1 yr À1), decreased with N fertilizer. Simulated SOC suggest a loss (516 kg C ha À1 yr À1) and within the unce...

Understanding denitrification rates in groundwater ecosystems can help predict where agricultural reactive nitrogen (N) contributes to environmental degradation. In situ groundwater denitrification rates were determined in subsoil, at the bedrock interface and in bedrock at two sites, grassland and arable, using an in situ ‘push–pull’ method with 1...

Nitrate (NO3−) loss from agriculture to shallow groundwater and transferral to sensitive aquatic ecosystems is of global concern. Denitrifying bioreactor technology, where a solid carbon (C) reactive media intercepts contaminated groundwater, has been successfully used to convert NO3− to di-nitrogen (N2) gas. One of the challenges of groundwater re...

Substitution of the Intergovernmental Panel on Climate Change (IPCC) default methodology by country-specific activity data is recommended for improved estimation of baseline soil organic carbon (SOC) stocks and their changes. In the Republic of Ireland (ROI), previous studies focused either predominantly on grassland or on all land cover types but...

Estimating losses of dissolved carbon (C) and nitrogen (N) via groundwater in an agricultural system provides insights into reducing uncertainties in the terrestrial C and N balances. In addition, quantification of dissolved nitrous oxide (N2O), carbon dioxide (CO2) and methane (CH4) in groundwaters beneath agricultural systems is important for glo...

Nitrate (NO3--N) contamination of groundwater and associated surface waters is an increasingly important global issue with multiple impacts on terrestrial, aquatic and atmospheric environments. Investigation of the distribution of hydrogeochemical variables and their connection with the occurrence of NO3--N provides better insights into the predict...

Understanding subsurface denitrification potential will give greater insights into landscape nitrate (NO3−) delivery to groundwater and indirect nitrous oxide (N2O) emissions to the atmosphere. Potential denitrification rates and ratios of N2O/(N2O+N2) were investigated in intact soil cores collected from 0–0.10, 0.45–0.55 and 1.20–1.30m depths rep...

Estimating losses of dissolved carbon (C) and nitrogen (N) via groundwater in an agricultural system provides insights into reducing uncertainties in the terrestrial C and N balances. In addition, quantification of dissolved nitrous oxide (N2O), carbon dioxide (CO2) and methane (CH4) in groundwaters beneath agricultural systems is important for glo...

Agriculture and associated land-use changes contribute a significant portion to global greenhouse gas (GHG) emissions; mainly as N2O, CO2 and CH4. Improved modelling of soil processes will greatly enhance the value of national inventories, both in terms of more accurate reporting and better mitigation policy options. In Ireland, Agriculture and Lan...

Due to well established global warming concerns, technological attempts have been made to decrease reactive nitrogen (N) species emitted from the application of urea fertilizer to agricultural soils. This chapter summarizes previous work which investigates the mitigation potential for ammonia (NH 3), nitrogen oxides (NOx) and nitrous oxide (N 2O),...

The importance of subsoil denitrification on the fate of agriculturally derived nitrate (NO3) leached to groundwater is crucial for budgeting N in an ecosystem and for identifying areas where the risk of excess NO3 is reduced. However, the high atmospheric background of di-nitrogen (N2) causes difficulties in assessing denitrification enzyme activi...

The impact of urea prills (1–2 mm) versus urea supergranules (USGs, 10 mm), placed at different depths, on the growth and nitrogen (N) use efficiency of spring wheat was investigated under greenhouse conditions. The amount of fertilizer 15N derived from either form was 50% greater in the top soil than at lower depths. The comparatively slower relea...

Dissolved organic C Dissolved oxygen Redox-potential SO 2À 4 Nitrate retention s u m m a r y Nitrate (NO À 3 —N) contamination of groundwater and associated surface waters is an increasingly important global issue with multiple impacts on terrestrial, aquatic and atmospheric environments. Investigation of the distribution of hydrogeochemical variab...

The growing industrialisation of agriculture has led to a dramatic increase in organic and inorganic nitrogen (N) fertiliser inputs to agro-ecosystems. This increase has had negative effects on the quality of water ecosystems and greenhouse gas emissions.The study objective was to quantify denitrification and denitrifying microorganisms, using real...

Biological denitrification is an important mechanism for the reduction of nitrate in the terrestrial and aquatic environments and contributing to the global nitrogen balance. This study focuses on the abundance of denitrifier functional genes and dissolved gases (N2O and denitrified N2, called excess N2) in groundwater. Multilevel piezometers (36)...

Irish agricultural N2O emissions accounted for 9.9% of the country’s total ghg emissions and 37% of agricultural emissions in 2007. Fortunately, the prospects for reducing those emissions are much better than those of cutting methane. As the following section shows, significant reductions of around 20% nationally can be made immediately via • full...

Assessing groundwater denitrification under two contrasting land uses in South-East Ireland - Volume 1 Issue 1 - M M R Jahangir, P Johnston, M I Khalil, K G Richards

Application of cattle slurry to grassland can lead to gaseous losses of nitrogen (N). The dynamics of ammonia (NH3) emissions are well documented, but emissions of nitrous oxide (N2O) and other trace gases from land application of cattle slurry, are not as well understood. Nitrification inhibitors such as dicyandiamide (DCD) help to retain soil N i...

Urea fertilizer-induced N2O emissions from soils might be reduced by the addition of urease and nitrification inhibitors. Here, we investigated the effect of urea granule (2–3 mm) added with a new urease inhibitor, a nitrification inhibitor, and with a combined urease inhibitor and nitrification inhibitor on N2O emissions. For comparison, the urea...

Globally identifying mitigation options for the emission of reactive N gases from agricultural soils is a research priority. We investigated the effect of urea size and placement depth on sources and emissions of N gases from a Cambisol cropped to spring wheat (Triticum aestivum L.). In Exp. 1, wheat received either prilled urea (PU) mixed within t...

Groundwater contamination was characterised using a methodology which combines shallow groundwater geochemistry data from 17 piezometers over a 2 yr period in a statistical framework and hydrogeological techniques. Nitrate-N (NO3-N) contaminant mass flux was calculated across three control planes (rows of piezometers) in six isolated plots. Results...

The superiority of mixing and deep placement of prilled urea (PU) or urea supergranules (USG) over surface‐broadcast application for reducing nitrogen (N) loss from lowland rice is well established. In upland agricultural systems, rainfall and/or the application and loss of irrigation water from soil systems may regulate urea N transformations and...

Denitrifier population size and potential activity combined with the relevant environmental factors regulate the rates of denitrification in terrestrial and aquatic ecosystems. Due to the high atmospheric background of di-nitrogen (N2), denitrification enzyme activity (DEA) in soils is traditionally measured using the acetylene block or stable isot...

Dissolved organic C Dissolved oxygen Redox-potential SO 2À 4 Nitrate retention s u m m a r y Nitrate (NO À 3 —N) contamination of groundwater and associated surface waters is an increasingly important global issue with multiple impacts on terrestrial, aquatic and atmospheric environments. Investigation of the distribution of hydrogeochemical variab...

The challenge for sustainable grassland production is to integrate economically profitable farming systems with environmental protection. The Water Framework Directive aims to attain at least “good status” for all waters by 2015, to be achieved through the introduction of measures across all sectors of society. Historically, the impact of grassland...

Global warming potential (GWP) of sandy paddy soils may be reduced by trade-offs between N2O, CH4 and CO2 emissions. Laboratory experiments using either rice straw (1% or 0.5%) or together with urea-N (25 or 50 mg N kg−1 soil) at various levels of soil water were carried out for 30 days each, to test this assumption. Waterlogging combined with urea...

A 90-day laboratory incubation study was carried out using six contrasting subtropical soils (calcareous, peat, saline, noncalcareous, terrace, and acid sulfate) from Bangladesh. A control treatment without nitrogen (N) application was compared with treatments where urea, ammonium sulfate (AS), and ammonium nitrate (AN) were applied at a rate of 10...

We examined the influence of various urea granule sizes (<2, 7.0, 9.9 and 12.7 mm) applied into a silt loam soil (experiment 1) and soil types (sandy, silt and clay loam) treated with the largest granule (experiment 2) on gaseous N loss (except N 2) at field capacity. The prilled urea (PU) was mixed into the soil whereas the urea granules were poin...

Nitrous oxide (N2O) contributes to global climate change, and its emission from soil-crop systems depend on soil, environmental, and anthropogenic factors. Thus, we evaluated the variability of N2O emissions measured by microchambers (cross section: 184 cm2) from a groundnut-fallow-maize-fallow cropping system of the humid tropics. The crops receiv...

We examined the influence of various urea granule sizes (< 2, 7.0, 9.9 and 12.7 mm) applied into a silt loam soil (experiment 1) and soil types (sandy, silt and clay loam) treated with the largest granule (experiment 2) on gaseous N loss (except N2) at field capacity. The prilled urea (PU) was mixed into the soil whereas the urea granules were poin...

Emission of N2O and CH4 oxidation rates were measured from soils of contrasting (30–75%) water-filled pore space (WFPS). Oxidation rates of 13C–CH4 were determined after application of 10 μl 13C–CH4 l−1 (10 at. % excess 13C) to soil headspace and comparisons made with estimates from changes in net CH4 emission in these treatments and under ambient...

Use and management of organic waste/residues is currently an important global issue for attaining sustainability in agricultural production. However, knowledge about the decomposition characteristics and nutrient release pattern of added organic materials in subtropical soils and their interaction with inherent soil properties are lacking. Thus, la...

Recycling of organic manure/waste is an important global issue to improve soil productivity for sustaining agricultural production as well as to preserve the environment. In Asia, rearing of poultry especially chicken is becoming one of the key industrial sectors and the wastes from clean-out operations may contribute largely to plant nutrients. Th...

Nitrous oxide (N2O) is formed mainly during nitrification and denitrification. Inherent soil properties strongly influence the magnitude of N2O formation and vary with soil types. A laboratory study was carried out using eight humid tropic soils of Malaysia to monitor NH4 + and NO3 – dynamics and N2O production. The soils were treated with NH4NO3 (...

To investigate the impact of different N sources and moisture regimes on N2O production, laboratory incubations using a Bungor series soil (Typic Paleudults) were carried out for a period of 25 days. A maximum N2O flux was detected upon application of chicken manure (2,379낥 g N2O-N kg-1 soil day-1) at 60% water-filled pore space (WFPS). Application...

Nitrous oxide (N20) contributes to global climate change and agricultural soils seem to be the major source. Lack of information led to this study on the influence of different amounts and sources of nitrogen on N2O emission from a maize (Zea mays L.)-groundnut (Arachis hypogae L.) crop rotation in an Ultisol of the humid tropics. The treatments we...

Development of appropriate land management techniques to attain sustainability and increase the N use efficiency of crops in the tropics has been gaining momentum. The nitrous oxides (N2Os) affect global climate change and its contribution from N and C management systems is of great significance. Thus, N transformations and N2O emission during maiz...

Laboratory studies were carried out to investigate the nitrogen (N) transformation processes of three Malaysian acid soils (pHH2O ranged from 3.74–4.44) belonging to Aeric Tropic Fluvaquent and Xanthic Hapludox. The soils, amended with inorganic and organic N sources, were incubated at 25°C separately under aerobic and anaerobic conditions. The N m...

Potentials of three Malaysian acid soils on nitrous oxide (N2O) and methane (CH4) emission were studied. The soils were incubated during 15 days under two moisture regimes and amended with organic and inorganic nitrogen (N) sources. Soil type, moisture content and NO3 availability influenced the N2O production. Under aerobic conditions, N2O flux wa...

soils is a research priority. We investigated the effect of urea size and placement depth on sources and emissions of N gases from a Cambisol cropped to spring wheat (Triticum aestivum L.). In Exp. 1, wheat received either prilled urea (PU) mixed within the soil, urea super granule (USG; diam. 10.1 mm) point-placed at a soil-depth of 7.5 cm, or no...

A field experiment was carried out in a non-calcareous sandy loam soil of subtropics using crop resi- due and root biomass of preceding rainfed rice to study the soil organic carbon (SOC) storage and nutrient uptake by succeeding irrigated rice. Decomposition of incorporated biomass was rapid initially and the residue-amended plots showed higher pe...