Tim Clough

Lincoln University New Zealand · Department of Soil and Physical Sciences

Numerous studies have investigated the effects of nitrogen (N) addition on soil organic carbon (SOC) decomposition. However, most studies have focused on the shallow top soils <0.2 m (surface soil), with a few studies also examining the deeper soil depths of 0.5–1.0 m (subsoil). Studies investigating the effects of N addition on SOC decomposition i...

Soil density plays an important role in regulating the migration of greenhouse gases from terrestrial soils to the atmosphere. Soil moisture is one of the main soil physical controls determining the fate and transport of gases in soils. This study investigated the transport of methane (CH4) originating from a simulated CH4 source within a variably...

Soil-gas diffusivity and its variation with soil moisture plays a fundamental role in diffusion controlled migration of climate-impact gases from different terrestrial agroecosystems including cultivated soils and managed pasture systems. The wide contrast in soil texture and structure (e.g., density, soil aggregation) in agriculture topsoils (0-10...

The addition of carbon (C) substrate often modifies the rate of soil organic matter (SOM) decomposition. This is known as the priming effect. Nitrous oxide (N2O) emissions from soil are also linked to C substrate dynamics; however, the relationship between the priming effect and N2O emissions from soil is not understood. This study aimed to investi...

Intensification of grazed grasslands following conversion from dryland to irrigated farming has the potential to alter ecosystem carbon (C) cycling and affect components of carbon dioxide (CO2) exchange that could lead to either net accumulation or loss of soil C. While there are many studies on the effect of water availability on biomass productio...

Cattle grazing of pastures deposits urine onto the pasture soil at high nitrogen (N) rates that exceed the pasture's immediate N demands, increasing the risk of N loss. Nitrous oxide (N2O), a greenhouse gas, and dinitrogen (N2) are lost from the cattle urine patches. There is limited information on the in situ loss of N2 from grazed-pasture systems...

Enhancing dissimilatory nitrate reduction to ammonium (DNRA) is environmentally and agronomically beneficial due to DNRA improving nitrogen (N) retention in soil. However, the rate of DNRA is generally considerably lower than that of denitrification because DNRA requires more electron donors than denitrification. Biochar has been increasingly repor...

Nitrogen (N) inputs to agricultural systems contribute substantially to soil nitrate (NO 3 −) concentrations, which increase NO 3 − leaching and contamination of groundwater. The influence of soil microbes in regulating NO 3 − concentrations in the topsoil are well studied but it is often assumed that microbial regulation of NO 3 − concentrations i...

Nitrous oxide (N2O) is a potent greenhouse gas generated in agricultural soils by microbial processes that vary according to soil redox. Soil oxygen (O2) supply and demand strongly influence soil redox. Migration of O2 into the soil primarily occurs via gas diffusion, expressed as relative gas diffusivity (Dp/Do), and is influenced by soil structur...

Poorly crystalline iron (Fe) oxides are commonly deposited on the surface of rice roots, forming an Fe plaque. This Fe plaque is an important area for Fe redox reactions because the poorly crystalline Fe is available for microbial transformations. However, it remains unclear what the mechanisms are that cause the root Fe plaque to affect CO2 emissi...

Nitrous oxide (N2O) is a greenhouse gas emitted from grazed pasture systems. The influence of phosphorus (P) fertility on these emissions is not understood. This study examined if fertiliser P affected N2O emissions following nitrate application to soil from the Winchmore long-term P fertiliser trial. We hypothesised increasing P fertility would en...

Grazed pastures can be introduced as a dominant source of nitrous oxide (N2O), a high potent greenhouse gas. Although past studies have examined N2O emissions in relation to soil physical properties, linking emissions with soil gas diffusivity (Dp/Do) and its dependency on soil physical properties and soil moisture are lacking. This study to empiri...

Grazed pastures can be introduced as a dominant source of nitrous oxide (N2O), a high potent greenhouse gas. Although past studies have examined N2O emissions in relation to soil physical properties, linking emissions with soil gas diffusivity (Dp/Do) and its dependency on soil physical properties and soil moisture are lacking. This study to empiri...

Soil N2O emission potential is commonly investigated under idealized denitrifying conditions (e.g. nitrate-N supplied and anaerobic soil), with pH commonly identified as a major determinant of N2O emission potential. However, under urine patch conditions in grazed pastures soils a more complex series of abiotic and biotic factors may influence emis...

Full manuscript available: https://www.essoar.org/doi/abs/10.1002/essoar.10507536.1

Dicyandiamide (DCD) is a nitrification inhibitor (NI) used to reduce reactive nitrogen (N) losses from soils. While commonly used, its effectiveness varies widely. Few studies have measured DCD and temperature effects on a complete set of soil N variables, including nitrite (NO2⁻) measured separately from nitrate (NO3⁻). Here the DCD reduction effi...

Pastures require year-round access to water and in some locations rely on irrigation during dry periods. Currently, there is a dearth of knowledge about the potential for using irrigation to mitigate N2O emissions. This study aimed to mitigate N2O losses from intensely managed pastures by adjusting irrigation frequency using soil gas diffusivity (D...

Biochars containing abundant and diverse functional groups can influence soil nitrous oxide (N2O) emissions. It remains unclear how these functional groups alter soil N2O emissions and which specific functional groups are responsible. In this study, biochars containing differing functional group compositions were initially screened for their abilit...

Carbon (C) substrates are critical for regulating denitrification, a process that results in nitrous oxide (N2O) and dinitrogen (N2) emissions from soil. However, the impacts of C substrates on concomitant soil emissions of carbon dioxide (CO2) and N2O under varying soil types and soil water contents are not well studied. Three repacked Pallic gras...

Nitrous oxide (N2O) produced from dissolved nitrogen (N) compounds in agricultural runoff water must be accounted for when reporting N2O budgets from agricultural industries. Constructed (‘artificial’) water bodies within the farm landscape are the first aquatic systems that receive field N losses, yet emission accounting for these systems remains...

Ruminant urine patches in grazed grasslands significantly change the chemical and biological properties of the affected soils due to the predominance of urea within ruminant urine and the high rates deposited onto pastures. The net result is the loss of reactive N (Nr) but little is known about the gross N transformation rates leading to Nr losses...

Nitrous oxide (N2O) is a strong greenhouse gas produced by biotic/abiotic processes directly linked to both fungal and prokaryotic communities that produce, consume or create conditions leading to its emission. In soils exposed to nitrogen (N) in the form of urea, an ecological succession is triggered resulting in a dynamic turnover of microbial po...

Micrometeorological techniques are useful if greenhouse gas (GHG) emissions from larger areas (i.e. entire fields) should be integrated. The theory and the various techniques such as flux-gradient, aerodynamic, and Bowen ratio as well as Eddy correlation methods are described and discussed. Alternative methods also used are Eddy correlation, mass b...

Agricultural lands make up approximately 37% of the global land surface, and agriculture is a significant source of greenhouse gas (GHG) emissions, including carbon dioxide (CO 2 ), methane (CH 4 ) and nitrous oxide (N 2 O). Those GHGs are responsible for the majority of the anthropogenic global warming effect. Agricultural GHG emissions are associ...

Methods Method and techniques are described for automatedAutomation, automated measurements of greenhouse gasesGreenhouse Gases (GHGs) (GHGsGreenhouse Gases (GHGs)) in both the laboratory and the field. Robotic systems are currently available to measure the entire range of gases evolved from soils including dinitrogenDinitrogen (N2) (N2). These sys...

Several approaches exist for measuring greenhouse gases (GHGs), mainly CO 2 , N 2 O, and CH 4 , from soil surfaces. The principle methods that are used to measure GHG from agricultural sites are chamber-based techniques. Both open and closed chamber techniques are in use; however, the majority of field applications use closed chambers. The advantag...

GHGemissions are usually the result of several simultaneous processes. Furthermore, some gases such as N 2 are very difficult to quantify and require special techniques. Therefore, in this chapter, the focus is on stable isotopemethods. Both natural abundance techniques and enrichment techniques are used. Especially in the last decade, a number of...

Soils harbour diverse soil faunaSoil faunaandFungi a wide range of soil microorganisms. These fauna and microorganisms directly contribute to soil greenhouse gasGreenhouse Gases (GHGs) (GHGGreenhouse Gases (GHGs)) fluxes via their respiratory and metabolic activities and indirectly by changing the physical, chemical and biological properties of soi...

Agriculture is a significant source of GHGsglobally and ruminant livestock animals are one of the largest contributors to these emissions, responsible for an estimated 14% of GHGs (CH 4 and N 2 O combined) worldwide. A large portion of GHG fluxes from agricultural activities is related to CH 4 emissions from ruminants. Both direct and indirect meth...

The rapidly changing global climate due to increased emission of anthropogenic greenhouse gases (GHGs) is leading to an increased occurrence of extreme weather events such as droughts, floods, and heatwaves. The three major GHGs are carbon dioxide (CO 2 ), methane (CH 4 ), and nitrous oxide (N 2 O). The major natural sources of CO 2 include ocean–a...

Despite optimising fertiliser practice and nitrogen (N) use efficiency nitrous oxide N2O generation from ruminant-urine deposition prevails due to the concentration of N in the urine excreted. Development and application of mitigation strategies to reduce N2O emissions from grazed pasture systems requires knowledge of production and consumption pat...

Across landscape and field scales, nitrogen (N) transformation rates are enhanced in hot spots (HS) and transient hot moments (HM), leading to losses of environmentally reactive N. Nitrous oxide (N2O) emission trends follow these spatial and temporal patterns. Consequently, landscape features can accelerate N2O emissions, and significant fractions...

Denitrification, a significant pathway of reactive N-loss from terrestrial soils, impacts on agricultural production and the environment. Net production and emission of the denitrification product nitrous oxide (N2O) is readily quantifiable, but measuring denitrification's final product, dinitrogen (N2), against a high atmospheric background remain...

Multispecies grasslands can alter nitrogen (N) cycling processes. A mesocosm experiment was performed comparing bare soil, soil planted with perennial ryegrass (Lolium perenne), white clover (Trifolium repens), plantain (Plantago lanceolata), and a mixed sward with all three species. We aimed to assess the plant effects on: ruminant urine-induced d...

Soil organic carbon (SOC) is both a source and sink of atmospheric carbon dioxide (CO2), with important implications for global climate change. Irrigation of grazed pastures has reportedly increased, reduced or made no difference to SOC stocks relative to dryland management. This study examined, over an annual plant growth cycle, the persistence of...

Grazed pastures rich in nitrogen (N) from ruminant urine and fertilizer inputs are significant sources of nitrous oxide (N2O), a highly potent greenhouse gas. Diffusion-controlled emission of N2O from pasture systems can be described by soil-gas diffusivity (Dp/Do), and its dependency on soil physical properties and soil moisture dynamics. But stud...

Nitrous oxide (N2O), a greenhouse gas, contributes to stratospheric ozone depletion. Agricultural fertiliser use and animal excreta dominate anthropogenic N2O emissions. Soil relative gas diffusivity (Dp/Do) has been used to predict the likelihood of soil N2O emissions, but limited information exists about how soil N2O emissions vary with soil type...

Source determination of N2O has often been performed using stable isotope incubation experiments. In situ experiments with isotopic tracers are an important next step. However, the challenge is to distribute the tracers in the field as homogeneously as possible. To examine this, a bromide solution was applied as a stand‐in tracer using either a wat...

Denitrification is an important mechanism for mitigating groundwater nitrate (NO3⁻) pollution. Our previous results showed that electric potential application (−0.5 V versus standard hydrogen electrode) accelerated subsoil NO3⁻ reduction efficiently, but nitrous oxide (N2O) emissions were also elevated with the application of the electric potential...

There are aspects in the collection, handling, storage and subsequent analysis of discrete air samples from non‐steady state flux chambers that are critical to generating accurate and unbiased estimates of N2O fluxes. The focus of this paper is on air sample collection and storage in small vials (<12 mL) primarily for Gas Chromatography (GC) analys...

Non‐steady state (NSS) chamber techniques have been used for decades to measure nitrous oxide (N2O) fluxes from agricultural soils. These techniques are widely used because they are relatively inexpensive, easy to adopt, versatile and adaptable to varying conditions. Much of our current understanding of the drivers of N2O emissions is based on stud...

Terrestrial ecosystems, both natural ecosystems and agroecosystems, generate greenhouse gases (GHG). The chamber method is the most common method to quantify GHG gas fluxes from soil‐plant systems, and to better understand factors affecting their generation and mitigation. The objective of this study was to review and synthesize literature on chamb...

Grazed pasture constitutes a major source of agriculturally derived nitrous oxide (N2O), which is a potent greenhouse gas. Soil texture and structure, soil moisture, and soil‐gas diffusivity are considered to be major soil physical drivers controlling pastoral N2O emissions. Research gaps exist regarding their combined roles on N2O emissions dynami...

Nitrite (NO2⁻) accumulation and associated production of nitric oxide (NO) and nitrous oxide (N2O) gases in soils amended with nitrogen (N) fertilizers are well documented, but there remains a poor understanding of their regulation and variation among soil types. We examined responses to urea inputs in two soils at five temperatures from 5 to 30 °C...

Long-term irrigation of temperate pastures has been reported to either increase or decrease soil organic carbon (SOC) stocks when compared with dryland systems. Understanding the short-term effects of irrigation on the fixation and partitioning of carbon (C) to plant and soil components may be important to explaining the observed differences. Conti...

Grazed pastures and cultivated fields are significant sources of greenhouse gas (GHG) emissions, in particular N2O emissions derived from fertilizer deposition and animal excreta. Net surface emissions rely on subsurface gas transfer controlled mainly by diffusion, expressed as the soil-gas diffusivity (Dp/Do). The value of Dp/Do is a function of s...

Livestock urine deposition onto grazed New Zealand pastures drives soil nitrous oxide (N2O) emissions. Urine patch N2O emissions can be reduced by inhibiting nitrification, a key urine patch nitrogen (N) transformation pathway. Aucubin, a secondary metabolite found in the pasture herb species plantain (Plantago lanceolata), is a potential nitrifica...

Acid organic soils drained for agriculture are hotspots for nitrous oxide (N O) emissions. Previous studies have indicated that water table (WT) depth and nitrogen (N) availability are important environmental controls, however, little is known about pathways leading to N O emission. We investigated a raised bog drained for agriculture (pH 4.6 to 5....

Organic soils drained for crop production or grazing land are agroecosystems with potentially high but variable emissions of nitrous oxide (N2O). The present study investigated the regulation of N2O emissions in a raised bog area drained for agriculture, which is classified as potentially acid sulfate soil. We hypothesised that pyrite (FeS2) oxidat...

Aggregated porous media are widely used as plant growth substrates due to its inherent structural properties and their distinctive mass transport characteristics. Soil-gas diffusivity (Dp/Do; where Dp and Do are gas diffusion coefficients for a given gas in porous medium and free air, respectively) characterizes the ability of the media to facilita...

Aggregated porous media are widely used as plant growth substrates due to its inherent structural properties and their distinctive mass transport characteristics. Soil-gas diffusivity (Dp/Do; where Dp and Do are gas diffusion coefficients for a given gas in porous medium and free air, respectively) characterizes the ability of the media to facilita...

Grazed pasture constitutes a major source of agriculturally derived nitrous oxide (N2O), a potent greenhouse gas. Soil texture and structure, soil moisture, and soil-gas diffusivity are considered to be major soil physical drivers controlling pastoral N2O emissions. Research gaps, however, still exist with regard to their combined roles on N2O emis...

Intensification of grazed grasslands following conversion from dryland to irrigated farming is a major land-use change in New Zealand. Such conversion has the potential to alter ecosystem carbon (C) cycling and affect components of the C balance that could lead to either net accumulation or loss of soil C. While there are many studies of the effect...

Drained agricultural peat soils are potential hot spots of nitrous oxide (N2O) emissions, but the biogeochemical basis for distinctively large emissions is still unclear. Incubation experiments with acidic bog peat, using nitrate (NO3⁻), nitrite (NO2⁻), synthetic iron monosulfide (FeS), and ground natural pyrite (FeS2), suggested that heterotrophic...

Ruminant urine patches on grazed grassland are a significant source of agricultural nitrous oxide (N2O) emissions. Of the many biotic and abiotic N2O production mechanisms initiated following urine-urea deposition, codenitrification resulting in the formation of hybrid N2O, is one of the least understood. Codenitrification forms hybrid N2O via biot...

Iron (Fe) plaque, defined as a film of poorly crystalline Fe oxides deposited on the surface of rice roots, potentially mediates paddy-soil N2O emissions. The aims of this study were to test if, and how, Fe plaque affects N2O production and reduction within a rice paddy soil. Rice seedlings were grown so that Fe plaque was either present or absent....

Worldwide there is an increasing awareness of the potential risks that pasture grazing systems pose to freshwater. Excess nutrient levels, predominately nitrate ( NO3−), result in reduced water quality. This study focused on further understanding how the presence or absence of perennial ryegrass (Lolium perenne L) and bovine urine (BU) influenced b...

Ruminant urine patches are nitrous oxide (N2O) emission hot-spots and compounds that inhibit nitrification in urine-affected soils, a key step in soil N2O production, can significantly reduce N2O emissions. Aucubin, a potential nitrification inhibitor found in plantain (Plantago lanceolata) was assessed in two field trials for its efficacy in reduc...

Grazed pasture has long been recognized as a dominant source of global nitrous oxide (N2O), a highly potent greenhouse gas. Among the main soil physical controls on N2O emissions, soil structure, moisture status, and soil-gas diffusivity play important and combined roles in controlling N2O emissions. A wide range of research has been conducted to i...

The functionality of biochar as an electron shuttle has been hypothesized to rationalize its suppressing effect on nitrous oxide (N2O) emissions from soil denitrification. However, this hypothesis has not yet been experimentally confirmed in soil matrices. In this study, we weakened biochar's function as an electron shuttle using a hydrogen peroxid...

Drained organic soils are extensively used for cereal and high-value cash crop production or as grazing land, but emissions of nitrous oxide (N2O) are enhanced by the drainage and cultivation. A study was conducted to investigate the regulation of N2O emissions in a raised bog area drained for agriculture. The area has been classified as potentiall...

Microbial strains and indigenous microbiota in soil slurries have been reported to use electrons from electrodes for nitrate (NO3−) reduction. However, there are few studies confirming this in a soil matrix hitherto. This study investigated if, and how, an electric potential affected NO3− reduction in a soil matrix. The results showed that, compare...

The acetylene inhibition technique (AIT) is the most widely used indirect method of determining denitrification fluxes. Although AIT bias has long been recognised, the contributions of soil denitrification-related parameters to this bias have not yet been well quantified. Using a direct-N2 method as a baseline, we determined the composition of AIT...

Denitrification is sensitive to changes in soil physical properties that affect solute transport, air content and gas diffusion. Using lysimeters, containing intact soil from intensively tilled (IT) and no-tilled (NT) soil used to grow forage crops, we examined how simulated animal treading at different moisture contents (above and below field capa...

Soil rewetting can induce a flush of organic matter mineralisation, but the factors underpinning this mineralisation response are poorly understood. We investigated the effects of antecedent soil water content, before rewetting, on the quantity, quality and biodegradability of dissolved organic matter present in the leachate pore volumes from a soi...

Atmospheric emissions of nitrogen (N) from New Zealand dairy farms are significant but have the potential to be affected by manure management prior to land application. The current work examined whether reducing cattle manure dry matter (DM) from 0.16 high DM (HDM) to 0.06 low DM (LDM), to enhance infiltration and reduce ammonia (NH 3 ) emissions w...

Density-induced soil structural changes may potentially alter both soil total porosity and soil pore size distribution, and thus change the soil’s water retention characteristics, gas diffusion and transport properties, and subsequent greenhouse emissions. In this study, we characterized and parameterized water retention, pore size distribution, ga...

Natural denitrification in groundwater systems has been recognised as an ecosystem service that reduces the impact of agriculturally-derived nitrate inputs to surface waters. Identification of this ecosystem service within the landscape would permit spatially differentiated land management and legislation. However, spatial variation in groundwater...

Nitrate isotopes (δ¹⁵N-NO3⁻ and δ¹⁸O-NO3⁻) are a potentially powerful tool for tracking the biological removal of reactive nitrogen (N) as it is transported from land to sea. However, uncertainties about, 1) the variability of the strength of biological isotopic fractionation during anaerobic benthic NO3⁻ reduction (the kinetic enrichment factor: ε...