Denitrification in pasture soils is mediated by microbial and physicochemical processes leading to nitrogen loss through the emission of N2O and N2. It is known that N2O reduction to N2 is impaired by low soil pH yet controversy remains as inconsistent use of soil pH measurement methods by researchers, and differences in analytical methods between studies, undermine direct comparison of results. In addition, the link between denitrification and N2O emissions in response to carbon (C) mineralization and pH in different pasture soils is still not well described. We hypothesized that potential denitrification rate and aerobic respiration rate would be positively associated with soils. This relationship was predicted to be more robust when a high resolution analysis is performed as opposed to a single time point comparison. We tested this by characterizing 13 different temperate pasture soils from northern and southern hemispheres sites (Ireland and New Zealand) using a fully automated-high-resolution GC detection system that allowed us to detect a wide range of gas emissions simultaneously. We also compared the impact of using different extractants for determining pH on our conclusions. In all pH measurements, soil pH was strongly and negatively associated with both N2O production index (IN2O) and N2O/(N2O+N2) product ratio. Furthermore, emission kinetics across all soils revealed that the denitrification rates under anoxic conditions (NO+N2O+N2 μmol N/h/vial) were significantly associated with C mineralization (CO2 μmol/h/vial) measured both under oxic (r2 = 0.62, p = 0.0015) and anoxic (r2 = 0.89, p<0.0001) conditions.

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The emissions of nitrous oxide (N 2 O) and leaching of nitrate (NO 3 ) from agricultural cropping systems have considerable negative impacts on climate and the environment. Although these environmental burdens are less per unit area in organic than in non-organic production on average, they are roughly similar per unit of product. If organic farming is to maintain its goal of being environmentally friendly, these loadings must be addressed. We discuss the impact of possible drivers of N 2 O emissions and NO 3 leaching within organic arable farming practice under European climatic conditions, and potential strategies to reduce these. Organic arable crop rotations are generally diverse with the frequent use of legumes, intercropping and organic fertilisers. The soil organic matter content and the share of active organic matter, soil structure, microbial and faunal activity are higher in such diverse rotations, and the yields are lower, than in non-organic arable cropping systems based on less diverse systems and inorganic fertilisers. Soil mineral nitrogen (SMN), N 2 O emissions and NO 3 leaching are low under growing crops, but there is the potential for SMN accumulation and losses after crop termination, harvest or senescence. The risk of high N 2 O fluxes increases when large amounts of herbage or organic fertilisers with readily available nitrogen (N) and degradable carbon are incorporated into the soil or left on the surface. Freezing/thawing, drying/rewetting, compacted and/or wet soil and mechanical mixing of crop residues into the soil further enhance the risk of high N 2 O fluxes. N derived from soil organic matter (background emissions) does, however, seem to be the most important driver for N 2 O emission from organic arable crop rotations, and the correlation between yearly total Ninput and N 2 O emissions is weak. Incorporation of N-rich plant residues or mechanical weeding followed by bare fallow conditions increases the risk of NO 3 leaching. In contrast, strategic use of deep-rooted crops with long growing seasons or effective cover crops in the rotation reduces NO 3 leaching risk. Enhanced recycling of herbage from green manures, crop residues and cover crops through biogas or com-Published by Copernicus Publications on behalf of the European Geosciences Union. 2796 S. Hansen et al.: Review of N 2 O emissions and NO 3 leaching from organic arable rotations posting may increase N efficiency and reduce N 2 O emissions and NO 3 leaching. Mixtures of legumes (e.g. clover or vetch)and non-legumes (e.g. grasses or Brassica species) are as efficient cover crops for reducing NO 3 leaching as monocultures of non-legume species. Continued regular use of cover crops has the potential to reduce NO 3 leaching and enhance soil organic matter but may enhance N 2 O emissions. There is a need to optimise the use of crops and cover crops to enhance the synchrony of mineralisation with crop N uptake to enhance crop productivity, and this will concurrently reduce the long-term risks of NO 3 leaching and N 2 O emissions.

This paper presents an investigation of drivers' response behaviors to intelligent transportation systems. It describes the results of a detailed survey and the results of an econometric model of route diversion behavior in response to real-time information provided by variable message signs (VMSs). The study location was Deerfoot Trail in Calgary, Canada. In case of major delays because of accidents on Deerfoot Trail, the City of Calgary uses 12 VMSs along Deerfoot Trail to divert drivers to alternative parallel arterials. A survey of 500 Deerfoot Trail commuters was conducted to examine the factors affecting drivers' compliance with VMSs. A latent discrete choice model was developed to model the responses of drivers to VMSs. This model introduces behavioral variables within a discrete choice model by endogenously estimating the latent variables. The primary finding of the study is that the en route information provided by VMSs convinces few drivers to change their trip destinations. Of the 500 respondents, 63.3% of drivers alter their trip plans in light of the information provided. However, 36.7% of drivers experience inertia by not altering their route, despite the excessive delays because of route blockage. The empirical model shows that driving experience, familiarity with alternative routes, trip purpose, trip time, trip length, and complementary information sources (e.g., the radio) are the most important factors influencing route-switching behavior in response to VMSs. In addition, drivers' attitudes toward VMSs were found to have the most significant impact on their responses to these systems.

Liming acidic soils is often found to reduce their N2O emission due to lowered N2O/(N2O + N2) product ratio of denitrification. Some field experiments have shown the opposite effect, however, and the reason for this could be that liming stimulates nitrification-driven N2O production by enhancing nitrification rates, and by favoring ammonia oxidizing bacteria (AOB) over ammonia oxidizing archaea (AOA). AOB produce more N2O than AOA, and high nitrification rates induce transient/local hypoxia, thereby stimulating heterotrophic denitrification. To study these phenomena, we investigated nitrification and denitrification kinetics and the abundance of AOB and AOA in soils sampled from a field experiment 2–3 years after liming. The field trial compared traditional liming (carbonates) with powdered siliceous rocks. As expected, the N2O/(N2O + N2) product ratio of heterotrophic denitrification declined with increasing pH, and the potential nitrification rate and its N2O yield (YN2O: N2O-N/NO3–-N), as measured in fully oxic soil slurries, increased with pH, and both correlated strongly with the AOB/AOA gene abundance ratio. Soil microcosm experiments were monitored for nitrification, its O2-consumption and N2O emissions, as induced by ammonium fertilization. Here we observed a conspicuous dependency on water filled pore space (WFPS): at 60 and 70% WFPS, YN2O was 0.03-0.06% and 0.06–0.15%, respectively, increasing with increasing pH, as in the aerobic soil slurries. At 85% WFPS, however, YN2O was more than two orders of magnitude higher, and decreased with increasing pH. A plausible interpretation is that O2 consumption by fertilizer-induced nitrification cause hypoxia in wet soils, hence induce heterotrophic nitrification, whose YN2O decline with increasing pH. We conclude that while low emissions from nitrification in well-drained soils may be enhanced by liming, the spikes of high N2O emission induced by ammonium fertilization at high soil moisture may be reduced by liming, because the heterotrophic N2O reduction is enhanced by high pH.