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Sustainable irrigation expansion is pivotal to guarantee global food security. Fertigation techniques with surface or subsurface drip lines are among the most promising irrigation practices. Yet, the effect of surface versus subsurface drip fertigation on ecosystem respiration (CO 2) fluxes remains largely unknown while there is not available information regarding CH 4 emissions, even though this knowledge is essential to obtain a comprehensive overview of the carbon (C) footprint of these practices. To address this knowledge gap, a field experiment was set up in a maize (Zea mays L.) crop comparing surface and subsurface drip (buried at 30 cm depth) in combination with four fertilization treatments (unfertilized control, calcium nitrate and ammonium sulphate with or without the nitrification inhibitor DMPP). Our results showed that all fertilized treatments (except the unfertilized control) were net CH 4 sources (135–208 g C ha−1). Subsurface irrigation reduced cumulative CH 4 emissions compared to surface irrigation by 80% (P < 0.05). Moreover, subsurface irrigation also abated ecosystem respiration fluxes (by 41%, P < 0.05) relative to surface irrigation. Emission peaks of both C fluxes were observed after fertigation events. Our results demonstrate that subsurface irrigation is a water-saving strategy that can contribute to decreasing the net greenhouse gas emissions of irrigated croplands through the abatement of CH 4 and respiration fluxes. • Surface and subsurface drip fertigation tested in combination with several N sources. • All fertilizer treatments (except unfertilized control) were net CH 4 sources. • Subsurface drip decreased CH 4 emissions by 80%, compared to surface irrigation. • Subsurface drip decreased CO 2 emissions by 41%, compared to surface irrigation. [ABSTRACT FROM AUTHOR]

Crop rotation with legumes and conservation tillage systems are advisable practices in rainfed Mediterranean agro-ecosystems, since, in these areas, soils are broadly characterized by low organic matter contents and low fertility. These management practices can substantially modify the dynamics of soil greenhouse gas (GHG) emissions, carbon sequestration and carbon dioxide (CO 2 ) emissions derived from system inputs and farm operations. In this context, a field experiment was conducted under Mediterranean conditions to evaluate the effect of three long-term tillage systems (no tillage (NT), minimum tillage (MT) and conventional tillage (CT)) and two crops (vetch (V, Vicia sativa L.) versus barley (B, Hordeum vulgare L.)) on nitrous oxide (N 2 O), methane (CH 4 ) and CO 2 emissions during one year. Crop yields, soil mineral nitrogen concentrations, dissolved organic carbon and GHG fluxes were measured during the growing season. Soil organic carbon was measured in spring 2012 (18 years after the beginning of a long-term tillage experiment) and together with input and fuel consumption by farm machinery was used to compare the Global Warming Potential (GWP) of the different crop and tillage treatments. Cumulative fluxes of N 2 O ranged between 0.16 (B-MT) and 0.29 (V-MT) kg N 2 O-N ha −1 yr −1 , resulting in a lower impact on Net GWP than in previous studies. A significant ‘tillage × crop’ interaction was observed in cumulative N 2 O emissions (V resulted in higher N 2 O losses than barley in CT and MT, whereas similar fluxes were observed under NT), which was influenced by soil water-filled pore space, dissolved organic carbon content and denitrification losses, in spite of the presumable predominance of nitrification. Neither tillage nor crop influenced CH 4 or CO 2 emissions. Yield-scaled N 2 O emissions (YSNE) were low (<4 g N 2 O-N kg aboveground N uptake −1 ) and significantly higher in B than in V. The most sustainable crop and tillage treatments in terms of GWP were non-fertilized-V and NT, due to higher carbon sequestration and lower fuel consumption under NT and the absence of mineral N fertilizers in V. These crop and tillage treatments could be considered good management strategies in rainfed Mediterranean agro-ecosystems since they provide the best balance between soil emissions, YSNE and Net GWP. [ABSTRACT FROM AUTHOR]

No tillage management is being encouraged nowadays to prevent soil erosion and contribute to carbon (C) sequestration. However, N fertilizer should be managed properly to optimize N use efficiency and to avoid the side-effects of losses of gaseous nitrogen (N), particularly those of ammonia (NH 3), which are expected to increase due to the presence of residues in the topsoil. In this context, a non-tilled (two years after conversion from tillage) field experiment was set up in central Spain, in which urea treated with a combination of urease (N-butyl thiophosphorictriamide, NBPT) and nitrification (2-(3,4-dimethyl-1H-pyrazol-1-yl) succinic acid isomeric mixture, DMPSA) inhibitors was compared with the use of urea without inhibitors. Fluxes of NH 3 (using the integrated horizontal flux method with three replicates), nitrous oxide (N 2 O), methane (CH 4) and soil respiration were measured throughout the wheat (Triticum aestivum L.) cropping cycle under rainfed conditions, together with ancillary soil measurements (e.g., soil moisture and mineral N), yield and crop uptake of N. Gaseous N losses from urea without inhibitors accounted for 10.35% and 0.66% (for NH 3 and N 2 O, respectively) of total N applied. The use of the double inhibitor resulted in a significant mitigation of both losses (by 50.5% and 91.6% for NH 3 and N 2 O, respectively). The double inhibitor increased N use efficiency expressed as crop recovery efficiency and partial nutrient balance, and decreased N surplus, in comparison with urea without inhibitors. In spite of a similar grain yield, the unfertilized control had the lowest aboveground N uptake rate, due to the higher concentrations of grain and straw N for the fertilized treatments. Under the conditions of our study, NH 3 volatilization in a short-term no-till managed field can be minimized using a double (urease plus nitrification) inhibitor. This strategy had no negative side effects on N surplus, CH 4 uptake or N 2 O mitigation and led to a significant improvement of N use efficiency. [Display omitted] • The use of the DMPSA + NBPT inhibitor reduced NH 3 volatilization rates under rainfed no-till (short-term) conditions. • The double inhibitor decreased N 2 O losses by 91.6% in comparison with urea alone. • The double inhibitor tended to increase CH 4 uptake and temporarily decreased respiration fluxes. • Soil rewetting episodes were relevant for the N 2 O, CH 4 and CO 2 fluxes. • The double inhibitor significantly improved N use efficiency and mitigated N surplus. [ABSTRACT FROM AUTHOR]

• Several Zn sources (with or without N) were tested on an irrigated maize crop under semi-arid climate. • Zn fertilization increased N 2 O and respiration fluxes in comparison to urea alone. • Zinc fertilization produced a detrimental effect on nitrifying and denitrifying communities. • Greater effect of Zn sources on NosZ communities compared to other denitrifying genes was found. • The zinc sulphate but not the synthetic chelate increased Zn concentration in grain. Previous studies have shown that the use of zinc (Zn) chelate fertilizers combined with a nitrogen (N) fertilizer (urea) can lead to both agronomic (i.e., yields and Zn and N biofortification due to the synergies between both nutrients) and environmental (i.e., by reducing the emissions of nitrous oxide, N 2 O, derived from N fertilization) benefits under rainfed semi-arid conditions. However, little is known about the effect of Zn-N co-fertilization on greenhouse gas (GHG) emissions or soil microbial processes involved in N 2 O fluxes under non-flooded irrigated conditions (during the dry season). Under these conditions, water-filled pore space continuously fluctuates following a periodic pattern and soil temperatures are in the optimum range for soil microorganisms. In this context, a field experiment was conducted using a maize (Zea mays L.) crop treated with two N levels (no N application and 120 kg N ha−1 as urea), and three Zn sources (no Zn application, Zn sulphate, and Zn applied with a mixture of chelating compounds, DTPA-HEDTA-EDTA). Nitrous oxide, methane (CH 4) and carbon dioxide (CO 2) fluxes were measured using opaque chambers, as well as the total abundances of soil bacteria, archaea and nitrifier and denitrifier communities. Zn-N co-fertilization increased cumulative N 2 O emissions from 0.36 kg N-N 2 O ha−1 (for urea combined with Zn chelates) to 0.76 kg N-N 2 O ha−1 (for urea combined with Zn sulphate), with respect to urea without Zn application. The N 2 O emission factors were lower (0.34%–0.72%) than the IPCC default value of 1%. Total abundances of the nosZ denitrification gene, which is involved in the reduction in N 2 O to dinitrogen (N 2), were reduced by 75% on average in the plots that received Zn fertilizers. This reduction may explain the higher N 2 O emissions in these treatments. In contrast with the case with non-irrigated crops, Zn-N co-fertilization cannot be recommended as a strategy to mitigate N 2 O emissions in irrigated maize under semi-arid conditions, despite of the enhancement of Zn availability in soil. [ABSTRACT FROM AUTHOR]

The transition year from tillage to no tillage in semiarid areas and its effects on nitrous oxide (N 2 O) emissions and related microbial communities, as well as the potential interaction with N management, including enhanced-efficiency fertilisers, are not well studied despite their economic and environmental implications. In tilled and nontilled plots, the effectiveness of the double DMPSA + NBPT inhibitor (applied with urea at basal fertilisation) and that of DMPSA (applied with calcium ammonium nitrate at top-dressing) in the mitigation of N 2 O emissions were evaluated in a rainfed barley (Hordeum vulgare L.) crop in central Spain. Crop yield, nitrogen (N) uptake, the abundances of key genes involved in nitrification and denitrification processes and meteorological conditions and soil ancillary properties were monitored. In addition, the composition of bacterial communities was determined by sequencing the 16S rRNA gene. Fertilisers with inhibitors decreased cumulative N 2 O emissions and yield-scaled N 2 O emissions by 53% and 56%, respectively, with respect to those without inhibitors, which coincided with a trend of increasing grain and biomass yield and aboveground N uptake (by 11.3%, 9.2% and 7.2%, respectively). The highest N 2 O emissions were measured 49 days after harvest (immediately after a rainfall event that like reactivated soil microorganisms), reaching 15 mg N m−2 d−1 for the treatment with fertiliser without inhibitor combined with tillage. This peak was linked to a remarkable increase in the abundance of denitrifiers. The abundance of nitrifiers and denitrifiers successfully explained the N 2 O dynamics observed after basal fertilisation (i.e. an increase in the amoA / nosZ ratio in fertilised plots with inhibitors, where the highest emissions were observed). Our results also showed a reduction in the abundance of the phylum Nitrospirae throughout the cropping period in the plots that received inhibitors. No tillage led to a higher abundance of Cyanobacteria , Verrucomicrobia and Bacteroidetes and resulted in better implantation of the crop and higher plant density compared with tillage, thus increasing yields and N use efficiency and decreasing N 2 O emissions. Under the conditions of our study, shifting from conventional tillage to no tillage enhanced the balance between N use efficiency and yield-scaled N 2 O emissions in the first year of conversion, particularity with the use of the double inhibitor with urea at basal fertilisation and DMPSA with CAN at dressing. • We addressed the transition from tillage to no tillage (NT) under semiarid conditions. • The highest N 2 O pulse occurred after a rewetting episode after harvest. • Changes in the N-cycling microbiota were observed even under short-term NT management. • Inhibitor-based treatments caused a decrease in the abundance of Nitrospirae. • Double inhibitor was effective in reducing N 2 O through stimulation of nosZ. [ABSTRACT FROM AUTHOR]