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Increasing tropospheric ozone (O3) and atmospheric nitrogen (N) deposition alter the structure and composition of pastures. These changes could affect N and C compounds in the soil that in turn can influence soil microbial activity and processes involved in the emission of N oxides, methane (CH4) and carbon dioxide (CO2), but these effects have been scarcely studied. Through an open top chamber (OTC) field experiment, the combined effects of both pollutants on soil gas emissions from an annual experimental Mediterranean community were assessed. Four O3 treatments and three different N input levels were considered. Fluxes of nitric (NO) and nitrous (N2O) oxide, CH4 and CO2 were analysed as well as soil mineral N and dissolved organic carbon. Belowground plant parameters like root biomass and root C and N content were also sampled. Ozone strongly increased soil N2O emissions, doubling the cumulative emission through the growing cycle in the highest O3 treatment, while N-inputs enhanced more slightly NO; CH4 and CO2 where not affected. Both N-gases had a clear seasonality, peaking at the start and at the end of the season when pasture physiological activity is minimal; thus, higher microorganism activity occurred when pasture had a low nutrient demand. The O3-induced peak of N2O under low N availability at the end of the growing season was counterbalanced by the high N inputs. These effects were related to the O3 x N significant interaction found for the root-N content in the grass and the enhanced senescence of the community. Results indicate the importance of the belowground processes, where competition between plants and microorganisms for the available soil N is a key factor, for understanding the ecosystem responses to O3 and N.

Drip-fertigated systems have variable distributions of water and nutrients in the soil, which influence soil microbial activity. Because there is a lack of data on greenhouse gas (GHG) fluxes for these systems, a field experiment comparing drip irrigation systems (fertigated and non-fertigated) was carried out in a melon crop. For the fertigated treatment, nitrogen (N) as NH4NO3 was dissolved in irrigation water and split into six applications (Fertigation treatment). In the non-fertigated soil (ANS treatment), granular NH4NO3 was incorporated homogeneously into the upper part of soil surface at planting. A control treatment without N fertilizer was also included. In order to evaluate the pattern of nitrous oxide (N2O) and methane (CH4), measurements were made at six different distances from the irrigation distributor point (dripper). An additional field experiment with N-15-labelled N fertilizer was carried out in parallel, with the aim of evaluating the contribution of nitrification and denitrification to the total N2O flux. Two different sources of N-15 were applied: (NH4NO3)-N-15 (20 at% excess N-15) ((NH4+)-N-15 treatment, TR1) and (NH4NO3)-N-15 (20 at% excess(15)N) ((NO3-)-N-15 treatment, TR2). Results indicated that both treatments (ANS and Fertigation) had small emission fluxes of N2O (< 0.1% of N applied). However, Fertigation produced larger emissions (175.3 g N2O-N ha(-1)) than ANS (90.1 g N2O N ha(-1)), with the pattern of N2O emission being strongly influenced by nitrification in both systems. Denitrification also contributed to emissions of (N2O)-N-15 but mainly on the day after fertilizer application in the Fertigation treatment. Methane fluxes were also affected by N fertilizer, with a decrease in the sink effect for CH4 when NH4+ was present in the soil.

Aims Agricultural soils in semiarid Mediterranean areas are characterized by low organic matter contents and low fertility levels. Application of crop residues and/or manures as amendments is a cost-effective and sustainable alternative to overcome this problem. However, these management practices may induce important changes in the nitrogen oxide emissions from these agroecosystems, with additional impacts on carbon dioxide emissions. In this context, a field experiment was carried out with a barley (Hordeum vulgare L.) crop under Mediterranean conditions to evaluate the effect of combining maize (Zea mays L.) residues and N fertilizer inputs (organic and/or mineral) on these emissions. Methods Crop yield and N uptake, soil mineral N concentrations, dissolved organic carbon (DOC), denitrification capacity, N2O, NO and CO2 fluxes were measured during the growing season. Results The incorporation of maize stover increased N2O emissions during the experimental period by c. 105 %. Conversely, NO emissions were significantly reduced in the plots amended with crop residues. The partial substitution of urea by pig slurry reduced net N2O emissions by 46 and 39 %, with and without the incorporation of crop residues respectively. Net emissions of NO were reduced 38 and 17 % for the same treatments. Molar DOC:NO 3 − ratio was found to be a robust predictor of N2O and NO fluxes. Conclusions The main effect of the interaction between crop residue and N fertilizer application occurred in the medium term (4–6 month after application), enhancing N2O emissions and decreasing NO emissions as consequence of residue incorporation. The substitution of urea by pig slurry can be considered a good management strategy since N2O and NO emissions were reduced by the use of the organic residue.

Urea has become the predominant source of synthetic nitrogen (N) fertilizer used throughout the world. Among the various available mitigation tools, urease inhibitors like NBPT have the most potential to improve efficiency of urea by reducing N losses, mainly via ammonia volatilization. However, there is a lack of information on the effect of N-(n-butyl) thiophosphoric triamide (NBPT) on other N losses such as gaseous emissions of N2O and NO and NO3− leaching. A two-year field experiment using irrigated maize (Zea mays) crop was carried out under Mediterranean conditions to evaluate the effectiveness of urea coated with NBPT (0.4%, w/w) alone and with both NBPT and nitrification inhibitor dicyandiamide (DCD) (0.4 and 3%, w/w, respectively) to mitigate N2O–N, NO–N and NO3−–N losses. The different treatments of U, U+NBPT and U+NBPT+DCD were applied to the maize crop in 2009 and then in 2010. The 2010 maize crop followed a fallow period, during which the 2009 crop residues were incorporated into the soil. Two different irrigation regimes were followed each year. In 2009, irrigation was controlled for the first 2 weeks following urea fertilization; whereas, the 2010 crop period was characterized by increased irrigation in the same period. After each treatment application, measurements of the changes in soil mineral N, gaseous emissions of N2O and NO, nitrate leaching and biomass production were made. N2O emissions were effectively abated by NBPT and NBPT+DCD and were reduced by 54 and 24%, respectively, in 2009. A reduction in nitrification rate by the inhibitors was also observed during 2009. In 2010 cropping period, NBPT reduced N2O emissions by 4%; while the combination of NBPT and DCD treatment reduced N2O emission by 43%. Yield-scaled N2O emissions were reduced by 50 and 18% by NBPT and the mixture of NBPT+DCD, respectively, in 2009. Applying inhibitors did not have any significant effect on yield-scaled N2O emissions in the 2010 crop period. Total NO losses from urea were 2.25 kg NO–N ha−1 in the 2009 crop period and 5 times lower in the following year; this may provide an indicator of the prevalence of nitrification as the main process in the production of N2O in the 2009 maize crop. Most of the NO3− was lost within the fallow period (i.e. 92, 81 and 75% of the total NO3− leached for U, U+NBPT and U+NBPT+DCD, respectively), so the incorporation of crop residues was not as effective as expected at reducing these N losses. Our study suggests that the effectiveness of NBPT and combination of NBPT+DCD in reducing N losses from applied urea is influenced by management practices, such as irrigation, and climatic conditions.

Fertilizer and irrigation management are two of the most important factors which directly influence nitrification and denitrification processes from agricultural soils and, therefore, emissions of nitrous oxide (N2O) and nitric oxide (NO). To date, the effect of combining organic fertilizer (applied before planting) with a drip irrigation system (DI) on the emissions of these nitrogen (N) oxides has not been evaluated. The different distribution and amount of water applied with this irrigation system should produce less favourable conditions for denitrification than other irrigation systems, such as furrow irrigation (FI), and this could be used to mitigate emissions of N2O, especially following organic fertilizer application. In order to test this hypothesis, a field experiment was carried out to compare the influence of FI and DI on N2O and NO emissions using digested pig slurry (DPS) as organic fertilizer during a melon crop (Cucumis melo L. cv. Sancho) season. Plots without any N fertilizer were used as a control (control). The irrigation system influenced the water distribution pattern, producing significantly higher ammonium-N (NH4+-N) and nitrate-N (NO3−-N) concentrations in the soil under DI than under FI. Moreover, the differences observed in water filled pore space (WFPS) and mineral N also favoured a different pattern of emissions of N oxides. Only one large pulse of N2O (106.9 mg N m−2 d−1) and NO (0.81 mg N m−2 d−1) were observed for FI after the first irrigation event while several pulses were observed for DI during the entire experimental period. As a consequence, nitrous oxide emissions were 75% and 28% lower from control and DPS, respectively under DI than under FI. In contrast, NO emissions were higher for DI on some sampling dates in both treatments, but without significant differences in the cumulative NO emissions between both irrigation systems. In conclusion, this work shows that combining drip irrigation with organic fertilizer for horticultural crops in semiarid climates could be a good management strategy for three reasons: it saves water; it re-uses organic residues and it mitigates N2O emissions.

Contradictory findings can be found in the literature regarding the effects of applying organic instead of mineral fertilizers on the associated emissions of nitrous oxide (N2O) and nitric oxide (NO). The main aim of this experiment was to study the effect on these emissions of applying mineral or organic fertilizers to a non-irrigated crop under Mediterranean conditions. A secondary aim was to determine whether application of the fertilizer had a residual effect on the N2O and NO pulses observed after the first rainfall events in autumn, and the magnitude of these fluxes. A field experiment was carried out with a barley crop (Hordeum vulgare L. cv Bornova). Untreated pig slurry (UPS), digested pig slurry (DPS), municipal solid waste (MSW) and composted crop residues mixed with sewage sludge (CCR + S) were applied to the soil. The resulting emissions were compared with those from a mineral fertilizer, urea (U), and a control treatment (C), in which no nitrogen was applied. Very low NO and N2O fluxes were measured during the entire experimental period in all treatments. The accumulated N2O emissions from the organic and inorganic fertilizers ranged from 266 to 345 g N2O-N ha−1 and did not show significant differences. Three of the four organic fertilizers had the positive effect of reducing NO emissions (28.82–44.48 g NO-N ha−1) compared with inorganic fertilizer (61.86 g NO-N ha−1). Nitrous oxide pulses were observed in autumn. Negative N2O fluxes were measured on several occasions. The emission factor relating N2O emissions to the N applied as fertilizer, ranged from 0.06 to 0.17% for MSW and DPS, respectively, which is much lower than the default factor proposed by the IPCC. The emission factor which relates N2O emissions to crop production ranged from 241 to 361 mg N2O-N kg−1 for DPS and U, respectively, suggesting that DPS should be promoted in order to reduce N2O emissions.

Irrigation management has an important influence on emissions of nitrous oxide (N 2 O) and nitric oxide (NO) from irrigated agricultural soils. In order to develop strategies to reduce the emission of these gases, a field experiment was carried out to compare the influence of different irrigation systems: furrow (FI) and drip-irrigation (DI), on N 2 O and NO emissions from a soil during the melon crop season. Two fertilizer treatments were evaluated for each irrigation regime: ammonium sulphate (AS) as a mineral N fertilizer, at a rate of 175 kg N ha −1 ; and a control without any N fertilizer (Control). On plots where the AS treatment was applied, drip irrigation reduced total N 2 O and NO emissions (by 70% and 33% respectively) with respect to values for furrow irrigation. This was probably due to the lower amount of water applied and the different soil wetting pattern associated with DI. Dry areas of the drip-irrigated plots emitted a similar amount of N 2 O to the wet areas (0.45 kg N 2 O-N ha −1 ) in the Control and greater quantities in the AS treatment (0.92 kg N 2 O-N ha −1 for dry and 0.70 kg N 2 O-N ha −1 for wet areas). We suggest that the N oxide pulses observed throughout the irrigation period on DI plots could have been the result of frequent increases in the soil wetting volume after the addition of water. Denitrification losses (from depths of 0–10 cm) were estimated at 11.44 kg N 2 O- N ha −1 for the AS treatment under FI and at 4.96 kg N 2 O-N ha −1 for DI. Under DI, nitrification was an important source of N 2 O, whereas denitrification was the most important source under FI. The addition of NH 4 + and the use of DI enhanced the N 2 O/N 2 ratio of gases produced through denitrification. The quantity of dissolved organic C (DOC) in the soil generally decreased with addition of NH 4 + . This work showed that, in comparison with furrow irrigation, drip irrigation is a method that can be used to save water and mitigate emissions of the atmospheric pollutants NO and N 2 O.

Nitrous oxide, nitric oxide and denitrification losses from an irrigated soil amended with organic fertilizers with different soluble organic carbon fractions and ammonium contents were studied in a field study covering the growing season of potato ( Solanum tuberosum ). Untreated pig slurry (IPS) with and without the nitrification inhibitor dicyandiamide (DCD), digested thin fraction of pig slurry (DTP), composted solid fraction of pig slurry (CP) and composted municipal solid waste (MSW) mixed with urea were applied at a rate of 175 kg available N ha −1 , and emissions were compared with those from urea (U) and a control treatment without any added N fertilizer (Control). The cumulative denitrification losses correlated significantly with the soluble carbohydrates, dissolved N and total C added. Added dissolved organic C (DOC) and dissolved N affected the N 2 O/N 2 ratio, and a lower ratio was observed for organic fertilizers than from urea or unfertilized controls. The proportion of N 2 O produced from nitrification was higher from urea than from organic fertilizers. Accumulated N 2 O losses during the crop season ranged from 3.69 to 7.31 kg N 2 O–N ha −1 for control and urea, respectively, whereas NO losses ranged from 0.005 to 0.24 kg NO–N ha −1 , respectively. Digested thin fraction of pig slurry compared to IPS mitigated the total N 2 O emission by 48% and the denitrification rate by 33%, but did not influence NO emissions. Composted pig slurry compared to untreated pig slurry increased the N 2 O emission by 40% and NO emission by 55%, but reduced the denitrification losses (34%). DCD partially inhibited nitrification rates and reduced N 2 O and NO emissions from pig slurry by at least 83% and 77%, respectively. MSW+U, with a C:N ratio higher than that of the composted pig slurry, produced the largest denitrification losses (33.3 kg N ha −1 ), although N 2 O and NO emissions were lower than for the U and CP treatments. This work has shown that for an irrigated clay loam soil additions of treated organic fertilizers can mitigate the emissions of the atmospheric pollutants NO and N 2 O in comparison with urea.

Nitrous oxide (N 2O), nitric oxide (NO), denitrification losses and NO−3 leaching from an irrigated sward were quantified under Mediterranean conditions. The effect of injected pig slurry (IPS) with and without the nitrification inhibitor dicyandiamide (DCD) was evaluated and also compared with that of a surface pig slurry application (SPS) and a control treatment (Control) without fertiliser. After application, fluxes of NO and N 2O peaked from SPS (3.06 mg NO-N m −2 d −1 and 108 mg N 2O-N m −2 d −1) and IPS (3.50 mg NO-N m −2 d −1 and 105 mg N 2O-N m −2 d −1). However, when irrigation was applied, N 2O and NO emissions declined. The total N 2O and denitrification losses were slightly large from IPS than from SPS, although the differences were not significant (P < 0.05). Emission of NO was not affected by the method of pig slurry application. DCD inhibited nitrification during the first 20–30 days and reduced N 2O and NO emissions from pig slurry by at least 46% and 37%, respectively. Considering the 215 days following pig slurry application, the emission factor of N 2O based on N fertiliser was 1.60% (SPS), 2.95% (IPS), and 0.50% (IPS + DCD). The emission factor for NO was 0.14% (SPS), 0.12% (IPS), and 0.02% (IPS + DCD). Environmental conditions of the crop favoured the denitrification process as the most important source of N 2O during the experimental period. The differences in the denitrification rate between treatments could be explained by the pattern of water soluble carbon (WSC), that was the highest value in injected pig slurry (with and without DCD). Due to low drainage (5% of water applied), leaching losses of NO 3 − were lower than those of denitrification from the upper soil layer (0–10 cm) in all treatments and especially with IPS + DCD, where the nitrification inhibitor was very efficient in reducing leaching losses.

Drip irrigation combined with split application of fertilizer nitrogen (N) dissolved in the irrigation water (i.e. drip fertigation) is commonly considered best management practice for water and nutrient efficiency. As a consequence, its use is becoming widespread. Some of the main factors (water-filled pore space, NH4+ and NO3−) regulating the emissions of greenhouse gases (i.e. N2O, CO2 and CH4) and NO from agroecosystems can easily be manipulated by drip fertigation without yield penalties. In this study, we tested management options to reduce these emissions in a field experiment with a melon (Cucumis melo L.) crop. Treatments included drip irrigation frequency (weekly/daily) and type of N fertilizer (urea/calcium nitrate) applied by fertigation. Crop yield, environmental parameters, soil mineral N concentrations and fluxes of N2O, NO, CH4 and CO2 were measured during 85 days. Fertigation with urea instead of calcium nitrate increased N2O and NO emissions by a factor of 2.4 and 2.9, respectively (P < 0.005). Daily irrigation reduced NO emissions by 42% (P < 0.005) but increased CO2 emissions by 21% (P < 0.05) compared with weekly irrigation. We found no relation between irrigation frequency and N2O emissions. Based on yield-scaled Global Warming Potential as well as NO cumulative emissions, we conclude that weekly fertigation with a NO3−-based fertilizer is the best option to combine agronomic productivity with environmental sustainability. Our study shows that adequate management of drip fertigation, while contributing to the attainment of water and food security, may provide an opportunity for climate change mitigation.

10 pages, figures, and tables statistics., Nitrous oxide (N2O) emissions and denitrification losses from an irrigated sandy loam soil amended with composted municipal solid waste (MSW), sheep manure (SM), surface applied pig slurry (SPS), incorporated pig slurry (IPS) or urea (U) were studied under Mediterranean conditions. We quantified emissions, in both the presence and absence of maize and N2O production, via denitrification and nitrification pathways using varying concentrations of acetylene. Discounting the N2O lost in the Control, the percentages of N2O lost in relation to the total N applied were greater for urea (1.80%) than for MSW (0.50%), SM (0.46%), SPS (1.02%) or IPS (1.27%). In general, plots treated with organic fertilisers emitted higher amounts of N2O when under maize than bare soil plots. On the other hand, greater denitrification losses were also recorded for plots in the absence of plants (between 9.7 and 29.3 kg N2O-N ha–1) than for areas with plants (between 7.1 and 24.1 kg N2ON ha–1). The proportion of N2O produced via denitrification was greater from fertiliser treatments than for the controls and also greater without plants (between 66 and 91 % of the N2O emitted) than with plants (between 48 and 81%)., The authors are grateful to the Spanish Commission of Science and Technology (Project AGL2000 1554–C02) for financing this research. It is also a pleasure to acknowledge Ana Muelas, Demetrio Gonza´lez and Asuncio´n de Diego for their technical assistance. We would like to thank Mark Theobald and Phil Nightingale for his useful comments.