Soil Water-filled Pore Space Research Articles

Characteristics of N2O and NOx Emissions from Purple Soil Under Different Fertilization Regimes

N2O and NOx emissions from a winter wheat-summer maize rotation system in purple soil were measured on a long-term fertilization platform of purple soil for two consecutive cropping years (from November 2014 to September 2016) by using a closed-chamber and gas chromatography-based system. Chemical fertilizer (NPK), pig manure (OM), incorporation of crop residues plus synthetic NPK fertilizer (RSDNPK), pig manure plus synthetic NPK fertilizer (OMNPK), and nitrification inhibitor with NPK fertilizer (DCDNPK) under the same rate of total nitrogen were involved in monitoring N2O and NOx emissions. Short-term fertilizer-free treatment (CK) was used as a control for emission coefficient calculation. The results showed that N2O emission peaks appeared in the early stage of fertilization and in the period of heavy rainfall for all fertilization regimes. The NOx emission process was similar to that of N2O, in that emission peaks appeared at the early stage of fertilization, yet no obvious emission peaks were observed during heavy rainfall. The annual cumulative emissions of N2O from NPK, OM, RSDNPK, OMNPK, and DCDNPK were 1.35, 4.38, 1.43, 2.46, and 0.92 kg·hm-2, respectively, and the emission coefficients were 0.33%, 1.41%, 0.36% 0.73%, and 0.18%. The annual emissions of NOx from NPK, OM, RSDNPK, OMNPK, and DCDNPK were 0.11, 0.38, 0.10, 0.27, and 0.04 kg·hm-2, respectively, and the cumulative emission coefficients were 0.03%, 0.13%, 0.03%, 0.09%, and 0.01%. Amendment of organic material was the main stimulator for N2O and NOx emissions, as they significantly increased 226% and 262% (for OM) and 83% and 157% (for OMNPK), respectively (P<0.01), compared with conventional synthetic fertilizers. The application of synthetic fertilizers combined with nitrification inhibitor (DCDNPK) significantly reduced N2O emissions 32% and NOx emissions 62% (P<0.01), whereas straw returning with NPK application increased N2O emissions 6% and reduced NOx emissions 5% (P>0.05). Furthermore, statistical analyses showed that soil inorganic N content was the main regulating factor of N2O and NOx emissions together, whereas soil water-filled pore space (WFPS) and temperature were the respective main regulating factors of N2O and NOx emissions individually.

The effect of nitrification inhibitor on N2O, NO and N2 emissions under different soil moisture levels in a permanent grassland soil

Emissions of gaseous forms of nitrogen from soil, such as nitrous oxide (N2O) and nitric oxide (NO), have shown great impact on global warming and atmospheric chemistry. Although in soil both nitrification and denitrification could cause N2O and NO emissions, most studies demonstrated that denitrification is the dominant process responsible for the increase of atmospheric N2O, while nitrification produces mostly NO. The use of nitrification inhibitors (NIs) has repeatedly been shown to reduce both N2O and NO emissions from agricultural soils; nevertheless, the efficiency of the mitigation effect varies greatly. It is generally assumed that nitrification inhibitors have no direct effect on denitrification. However, the indirect impact, due to the reduced substrate (nitrate) delivery to microsites where denitrification occurs, may have significant effects on denitrification product stoichiometry that may significantly lower soil-borne N2O emissions. Soil-water status is considered to have a remarkable effect on the relative fluxes of nitrogen gases. The effect and mechanism of NI on N2O, NO and N2 emission under different soil water-filled pore space (WFPS) is still not well explored. In the present study, we conducted a soil incubation experiment in an automated continuous-flow incubation system under a He/O2 atmosphere. Ammonium sulfate was applied with and without NI (DMPP) to a permanent UK grassland soil under three different soil moisture conditions (50, 65, and 80% WFPS). With every treatment, glucose was applied to supply enough available carbon for denitrification. Emissions of CO2, N2O, NO and N2 were investigated. Additionally, isotopic signatures of soil-emitted N2O were analyzed. Generally, higher WFPS led to higher N2O and NO emissions, while N2 emissions were only detected at high soil moisture condition (80% WFPS). Different processes were responsible for N2O and NO emission in different phases of the incubation period. The application of DMPP did significantly reduce both N2O and NO emissions at all three soil moisture conditions. Furthermore, DMPP application increased N2 emissions and decreased the N2O/(N2O + N2) product ratio at 80% WFPS.

Effects of Long-term Organic Amendments on Soil N2 O Emissions from Winter Wheat-maize Cropping Systems in the Guanzhong Plain

The primary aim of this study was to quantify the effects of long-term organic amendments on soil nitrous oxide (N2O) emissions. Using static chamber-gas chromatograph technique, we measured N2O fluxes from winter wheat-maize rotation system and related environmental factors in the Guanzhong Plain for one year (October 2014 to October 2015). Field experiments were based on the "Chinese National Loess Fertility and Fertilizer Effects Long-term Monitoring Experiment". Four treatments were control (CK, 0 kg·hm-2), NPK (NPK, 353 kg·hm-2), NPK combined with maize straw[NPKS, (353+40) kg·hm-2] and cattle waste[NPKM, (238+115) kg·hm-2]. During the experimental period, N2O fluxes from CK treatment were small[<2.9 g·(hm2·d)-1]; while emissions from fertilized treatments peaked after fertilization[up to 113.4 g·(hm2·d)-1 for NPKS] and irrigation[up to 495.0 g·(hm2·d)-1 for NPKM] during winter wheat and maize seasons, respectively. N2O flux was significantly correlated to soil water-filled pore space for all treatments (r>0.28,P<0.05). Annual N2O emissions were (0.1±0.0), (2.6±0.1), (3.4±0.7) and (2.9±0.3) kg·hm-2 for CK, NPK, NPKS and NPKM, respectively. The fertilized treatments released higher N2O emissions than CK treatment (P<0.05), indicating that fertilization stimulated N2O emissions. However, the differences in N2O emissions were not significant among the fertilized treatments (P=0.06), suggesting that organic amendments did not increase N2O emissions obviously. The direct emission factors were 0.72%, 0.83% and 0.80% for NPK, NPKS and NPKM, respectively, all of which were lower than the IPCC default of 1%. The yield-scaled N2O emission for NPKM was the lowest among the fertilized treatments.

Soil water content modulates the effect of the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) on nitrifying and denitrifying bacteria

In the last decades, intensive agriculture management and the application of nitrogen fertilizer have led to high nitrogen losses to the environment. Among these losses is the soil emission of the potent greenhouse gas nitrous oxide (N2O) which is mainly produced by the soil microbial processes of nitrification and denitrification. The use of nitrification inhibitors with ammonium based fertilizers can be an efficient mitigation strategy to decrease these nitrogen losses. Soil water content and temperature are major factors controlling N2O production and, so, also the efficiency of the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) to reduce these emissions. In this work we study the effect of soil water content and temperature on the abundance of soil bacteria, ammonia-oxidizing bacteria and denitrifying bacteria, and on the performance of DMPP modulating these different bacterial populations responsible for N2O production/consumption. The effect of DMPP on the abundance of the different bacterial populations was dependent on soil water content. Under 40% of soil water filled pore space (WFPS), the application of DMPP caused an expected decrease of the target amoA gene abundance while narG, nirK and nosZ gene abundances also decreased probably due to an indirect effect induced by the lack of substrate for denitrifiers. Under 80% of WFPS, while the application of DMPP did not induce any change in the amoA gene abundance, an unexpected increase in non-target denitrifying gene abundances (narG, nirK and nosZ) was observed at either 10°C or 20°C incubation temperatures. This finding opens a new gate of research in the use of DMPP, where nitrous oxide reductase enzyme gene (nosZ) abundance and expression should be studied in the future in order to better understand the performance of DMPP not only inhibiting nitrification, but also affecting the non-target denitrification process.

Annual methane uptake from different land uses in an agro-pastoral ecotone of northern China

The semi-arid grasslands in northern China are subjected to accelerating land use change due to population growth and food demand. Considerable uncertainty exists on annual methane (CH4) fluxes of different land uses because most measurements have only been conducted during the growing season. Using static chamber – gas chromatographic technique, we quantified and characterized annual CH4 fluxes (from 2012 to 2015) from four land uses common in an agro-pastoral ecotone of northern China: summer-grazed grassland (SumGrazed), winter-grazed grassland (WinGrazed), ungrazed grassland since 1997 (Ungrazed) and oat cropland (OatCrop). The soil at all land uses functioned exclusively as a sink for atmospheric CH4 through the entire three years. Annual CH4 uptake rates averaged 1.42, 2.36, 1.12 and 2.57kgCha−1 yr−1 for SumGrazed, WinGrazed, Ungrazed and OatCrop, respectively, during 2012–2015. Compared to Ungrazed, OatCrop and WinGrazed increased annual CH4 uptake by 129 and 111%, respectively. Non-growing season (October–April) contributed 28–43% of the annual CH4 uptake at all land uses. Across all four land uses, annual cumulative CH4 uptake decreased with increasing soil water-filled pore space (WFPS) explaining 81% of the variance in annual CH4 uptake. WFPS negatively correlated to CH4 uptake in the growing season (R2=0.16-0.35, P<0.001). CH4 uptake increased with soil temperature through the entire observed period (R2=0.38-0.63, P<0.001) and the non-growing season (R2=0.51–0.74, P<0.001). We conclude that grazing has the potential to increase CH4 uptake from the atmosphere and consequently, contribute positively to CH4 related part of C budget.

Season and location–specific nitrous oxide emissions in an almond orchard in California

Almonds are an important commodity in California and account for around 15% of the state’s fertilizer nitrogen (N) consumption. Motivated by strong correlations typically observed between fertilizer N inputs and emissions of the potent greenhouse gas and ozone depleting molecule nitrous oxide (N2O), this study aimed to characterize spatial and temporal patterns in N2O emissions in an almond orchard under typical agronomic management. N2O fluxes were measured for a total of 2.5 years, including 3 growing seasons and 2 dormant seasons. Measurements targeted two functional locations, defined as tree rows and tractor rows. In conjunction with the flux measurements, we determined driving variables including soil ammonium (NH4+) and nitrate (NO3−), dissolved organic carbon (DOC), soil water-filled pore space (WFPS), soil pH, air temperature and precipitation. Cumulative annual N2O emissions were low (0.65 ± 0.07 and 0.53 ± 0.19 kg N2O–N ha−1 year−1 in year 1 and 2, respectively), likely due to the coarse soil texture and microject sprinkler irrigation and fertigation system. Emission factors (EF), conservatively calculated as the ratio of N2O emitted to fertilizer N applied, were 0.25 ± 0.03% and 0.19 ± 0.07% for year 1 and 2, respectively, which is below the IPCC EF range of 0.3–3%. Correlation analyses between N2O and driving variables suggested that overall N2O production was limited by microbial activity and nitrification was likely the major source process, but specific drivers of N2O emissions varied between seasons and functional locations.

Nitrous oxide emissions from cattle urine deposited onto soil supporting a winter forage kale crop

ABSTRACTWintering cows on forage crops leads to urine being excreted onto wet, compacted soils, which can result in significant emissions of nitrous oxide (N2O). A field trial was conducted to determine the N2O emission factor (EF3; proportion of urine-N lost as N2O-N) for dairy cows wintered on a kale forage crop on a poorly drained soil. Urine was collected from non-lactating dairy cows on a forage kale diet and applied at 550 kg N ha−1 to artificially compacted soil to simulate trampling and non-compacted soil in a kale field. Cumulative N2O losses over four months were 7.38 and 2.64 kg N2O-N ha−1 from urine applied to, respectively, compacted and non-compacted soil. The corresponding EF3 values 0.75% and 0.30%, respectively, differed (P = .003) due to compaction. Combining our results with previous studies, where brassica-fed livestock urine was applied to soils supporting a forage brassica crop, suggested a significant relationship between soil water-filled pore space (WFPS) and brassica-derived urine EF3 (P = .005).

Effects of Long-Term Use of Compost on N2O and CO2 Fluxes in Greenhouse Vegetable Systems

ABSTRACTThis study was based on a long-term field trial of three different greenhouse vegetable growing systems which were started in March 2002. Fertilizer nitrogen and organic carbon inputs in three treatments in the spring of 2015 were as follows: (1) conventional system (CON): cow manure and dry chicken manure composts (about 146 kg N ha−1 and 1483 kg C ha−1) and urea (about 525 kg N ha−1); (2) low-input system (LOW): cow manure and dry chicken manure composts (about 325 kg N ha−1 and 3160 kg C ha−1) and urea (about 263 kg N ha−1); and (3) organic system (ORG): cow manure and dry chicken manure composts (about 651 kg N ha−1 and 5456 kg C ha−1). N2O and CO2 fluxes were monitored in the growing season of 2015 (from March to August) using static chamber and gas chromatography techniques. Results showed that: (1) The N2O and CO2 fluxes in three treatments all reached their peaks within 4 days and 8 days after irrigation, respectively. N2O emissions were positively correlated with soil temperature, soil water-filled pore space (WFPS), and NO3−-N contents, while strong association between CO2 emissions and soil temperature was observed. (2) Lower cumulative N2O emission and direct emission factor (p < 0.05) were observed in ORG than that from LOW and CON. (3) No significant differences of cumulative CO2 emissions were observed in three treatments, but CO2 emissions proportion of fertilizer carbon inputs and soil organic carbon stock in ORG was significantly lower (p < 0.05).

Management Practices of Miscanthus × giganteus Strongly Influence Soil Properties and N2O Emissions Over the Long Term

Cropping practices of Miscanthus × giganteus, a promising energy crop, can influence C and N cycles and therefore potentially affect N2O emissions. They may vary in harvesting date, either early (EH) or late harvest (LH), and the fertiliser form (NH4 or NO3). In this study, we combined a long-term field experiment and simulations with the STICS model to investigate the effect of these practices on soil parameters, N2O emissions and the contribution of nitrification and denitrification. Daily N2O fluxes and soil parameters were measured during the 4-month period following fertilisation in 2014 and 2015. Mean cumulative N2O emissions were markedly higher in LH than EH (4.21 vs. 0.89 kg N2O–N ha−1 year−1) but did not differ significantly between fertiliser forms or years. The difference was mainly attributed to the higher soil water-filled pore space (WFPS) observed in LH (80 vs. 56 % in EH) which resulted itself from the leaf mulch present in LH and not in EH. WFPS explained 67 % of the variance of N2O emissions. The large decrease in pH observed after NH4 fertilisation stimulated N2O emissions probably through less-efficient reduction of N2O to N2 as simulated by STICS. Model outputs suggest a large contribution of nitrification in EH and a dominant contribution of denitrification in LH. Our study highlights the crucial impact of management practises on N2O emissions in Miscanthus crops through changes in physico-chemical parameters and soil processes on the short and long term and brings knowledge required to maximise the benefits of bioenergy crops.

Fluxos de óxido nitroso e suas relações com atributos físicos e químicos do solo

Resumo O objetivo deste trabalho foi avaliar a dinâmica dos fluxos de óxido nitroso (N2O) em solo sob pastagem, em sistema de integração lavoura-pecuária, e sob cerrado nativo usado como referência, bem como identificar os atributos físicos e químicos do solo que influenciam esses fluxos. O estudo foi realizado na Fazenda Capivara, da Embrapa Arroz e Feijão, de 5 de fevereiro a 30 de setembro de 2013. As amostragens de gás foram realizadas com uso de câmaras estáticas manuais. O solo sob pastagem apresentou os maiores fluxos de N2O, com média de 14,12 ng m-2 s-1. Essa área também apresentou maior espaço poroso preenchido por água (EPPA), que, associado à temperatura e ao teor de nitrato no solo, influenciou a produção de N2O. Na época chuvosa, os fluxos apresentaram correlação positiva com o EPPA do solo e, na época seca, com seu teor de amônio e nitrato. A emissão total de N2O na área da pastagem foi de 1.644,19 gha1. No cerrado nativo, não houve emissão de N2O do solo para a atmosfera.

Soil Methane Uptake Increases under Continuous Throughfall Reduction in a Temperate Evergreen, Broadleaved Eucalypt Forest

Soils in temperate forests ecosystems are the greatest terrestrial CH4 sink globally. Global and regional circulation models predict decreased average rainfall, increased extreme rainfall events and increased temperatures for many temperate ecosystems. However, most studies of soil CH4 uptake have only considered extended periods of drought rather than an overall decrease in rainfall amount. We measured soil CH4 uptake from March 2010 to March 2012 after installing passive rainfall reduction systems to intercept approximately 40% of throughfall in a temperate broadleaf evergreen eucalypt forest in south-eastern Australia. Throughfall reduction caused an average reduction of 15.1 ± 6.4% (SE) in soil volumetric water content, a reduction of 19.8 ± 6.9% in soil water-filled pore space (%WFPS) and a 20.1 ± 6.8% increase in soil air-filled porosity. In response to these changes, soil CH4 uptake increased by 54.7 ± 19.3%. The increase in soil CH4 uptake could be explained by increased diffusivity in drier soils, whilst the activity of methanotrophs remained relatively unchanged. It is likely that soil CH4 uptake will increase if rainfall reduces in temperate broadleaf evergreen forests of Australia as a consequence of climate change.

Greenhouse gas fluxes from a grazed grassland soil after slurry injections and mineral fertilizer applications under the Atlantic climatic conditions of NW Spain

The number of studies that investigate how agricultural practices on dairy farms in the North West (NW) of Spain affect greenhouse gas (GHG) fluxes from soils is limited. Thus, the objective of this study was to quantify the effects of the application of mineral fertilizers and cattle slurry injections on GHG fluxes from a grassland soil with grazing dairy cattle, in Galicia (NW Spain). We also aimed to identify the type of fertilizer associated with high grass production and low GHG fluxes. To achieve this, fluxes of nitrous oxide (N2O), methane (CH4) and carbon dioxide (CO2), grass yields and soil mineral nitrogen (N) contents were monitored after three applications (in spring, summer and autumn) of surface broadcasted mineral fertilizer (MN) and injected cattle slurry (CS) and compared with no fertilization (zero N). Dry soil conditions (<60% water-filled pore space (WFPS)) were observed during the spring and summer, contrasting with the higher soil WFPS (>60%) in autumn due to the more frequent rainfall. Overall, total cumulative N2O fluxes from CS were similar than from MN (P>0.05), indicating that denitrification in this C-rich soil was not stimulated by slurry-carbon applications. Large losses of CH4 and CO2 were related to CS, but overall only total cumulative CH4 fluxes were larger with respect to MN (P<0.05). Dry weather conditions would have stimulated organic matter mineralization in this soil, which resulted in the low efficiency of both fertilizers to increase yields. As we obtained similar total CO2 equivalents to produce same yields with both types of fertilization (P>0.05), this study did not show a clear type of fertilization related to low GHG fluxes and high yields. We believe that longer-term studies are required to provide more robust estimations and conclusions about the effect of fertilizer applications on GHG fluxes from grassland soils in NW Spain.

Assessment of Gaseous Nitrogen (NH3 and N2O) Mitigation After the Application of a Range of New Nitrogen Fertilizers in Summer Maize Cultivation

In order to evaluate the potential of a range of new nitrogen fertilizers in comparison with the conventional fertilization to mitigate ammonia (NH3) and nitrous oxide (N2O) emissions, a field experiment was conducted to investigate NH3 volatilization and N2O emissions from the summer maize field and the relevant driving factors under the different nitrogen fertilizer treatments. Five new varieties of nitrogen fertilizers including the urea ammonium (UA), stability urea with dicyandiamide and hydroquinone (UHD), sulfur coated urea (SCU), urea formaldehyde compound fertilizer (UF) and organic fertilizer (OF) were applied in this experiment, and conventional fertilization (compound fertilizer + urea, CK) was used as the control. The nitrogen amount of 300 kg·hm-2 was applied in all treatments. Correlation analysis results showed that both NH3 volatilization and N2O emissions were influenced by environmental factors. They were negatively correlated with soil water-filled pore space (P<0.05). Moreover, N2O emissions were positively correlated with soil nitrate nitrogen (P<0.01). Regression analysis showed that N2O emissions were mainly determined by the soil nitrate content, while NH3 volatilization was mainly dependent on the values of soil ammonium nitrogen. Compared with CK, in addition to UA, other fertilizer treatments decreased the NH3 volatilization, especially the UF and OF treatments decreased NH3 volatilization by up to 37%-43%, while all treatments had no significant difference in N2O emissions. Considering the total gaseous nitrogen losses (NH3 volatilization + N2O emissions), in comparison with CK, the UHD, SCU, UF and OF were reduced by 9%, 5%, 30% and 23%, respectively, while the UA was increased by 3%. Therefore, considering environmental benefit under this experimental condition,urea formaldehyde compound fertilizer and organic fertilizer were more suitable for maize cultivation.

Soil CO2, CH4 and N2O emissions from production fields with planted and remnant hedgerows in the Fraser River Delta of British Columbia

Planting hedgerows on farm field edges can help mitigate greenhouse gas (GHG) emissions from agricultural landscapes by sequestering carbon (C) in woody biomass and in soil. Sequestration rates however, must be assessed in terms of their overall global warming potential (GWP) which must also consider GHG emissions. The objectives of this study were to (1) compare carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) emissions from two types of hedgerows and adjacent annual agricultural production fields, and 2) better understand how climate, soil properties and plant species configurations affect hedgerow GHG emissions. At eight study sites in the lower Fraser River delta of British Columbia, we measured emissions from soil in both planted (P-Hedgerow) and remnant hedgerows (R-Hedgerow), as well as in adjacent annual crop production fields over 1 year using a closed-static chamber method. CO2 emissions were 59 % higher in P-Hedgerow than R-Hedgerow, yet there were no significant differences of relative emissions of CH4 and N2O. The environmental variables that explained the variation in emissions differed for the three GHGs. CO2 emissions were significantly correlated with soil temperature. CH4 and N2O and emissions were marginally significantly correlated with soil organic carbon (SOC) and soil water-filled pore space (WFPS), respectively. Emissions were not significantly correlated with hedgerow plant species diversity. While hedgerows sequester carbon in their woody biomass, we demonstrated that it is critical to measure hedgerow emissions to accurately ascertain their overall GHG mitigation potential. Our results show that there are no CO2e emission differences between the management options that plant new diverse hedgerows or conserve existing hedgerows.

Effect of nitrogen fertilization and residue management practices on ammonia emissions from subtropical sugarcane production

Ammonia (NH3) emission from soil is a loss of nitrogen (N) nutrient for plant production as well as an issue of air quality, due to the fact that it is an active precursor of airborne particulate matters. Ammonia also acts as a secondary source of nitrous oxide (N2O) emission when present in the soil. In this study, the impacts of different sources of N fertilizers and harvest residue management schemes on NH3 emissions from sugarcane production were evaluated based on an active chamber method. The field experiment plots consisting of two sources of N fertilizer (urea and urea ammonium nitrate (UAN)) and two common residue management practices, namely residue retained (RR) and residue burned (RB), were established on a Commerce silt loam. The NH3 volatilized following N fertilizer application was collected in an impinger containing diluted citric acid and was subsequently analyzed using ion chromatography. The NH3 loss was primarily found within 3–4 weeks after N application. Average seasonal soil NH3 flux was significantly greater in urea plots with NH3-N emission factor (EF) twice or more than in UAN plots (2.4–5.6% vs. 1.2–1.7%). The RR residue management scheme had much higher NH3 volatilization than the RB treatment regardless of N fertilizer sources, corresponding to generally higher soil moisture levels in the former. Ammonia-N emissions in N fertilizer-treated sugarcane fields increased with increasing soil water-filled pore space (WFPS) up to 45–55% observed in the field. Both N fertilizer sources and residue management approaches significantly affected NH3 emissions.

CO2 and N2O emissions from Lou soils of greenhouse tomato fields under aerated irrigation

The change of O2 content in soil caused by aerated irrigation (AI) must inevitably affect the production and emissions of CO2 and N2O from soils. This paper described in-situ observation of CO2 and N2O emissions from AI soils with static chamber-GC technique, in order to reveal the effects of AI on CO2 and N2O emissions from soils of greenhouse tomato fields in autumn-winter season. CO2 and N2O emissions from AI soils mainly concentrated in the blooming and fruit setting period compared to other periods. AI increased cumulative emissions of CO2 and N2O by 11.8% (p = 0.394) and 10.0% (p = 0.480), respectively, compared to the control. The integrative global warming potential of CO2 and N2O on a 100-year horizon for the AI treatment was 6430.60 kg ha−1, increased by 11.7% compared with that for the control (p = 0.356). Both the emissions of CO2 and N2O from AI soils had the exponential positive correlation with soil water-filled pore space (WFPS). The highest peak of CO2 and N2O fluxes from AI soils was observed at 46.7% and 47.5% WFPS, with WFPS ranging from 43.3% to 51.5% and from 45.6% to 52.3% during the whole growth stage, respectively. In addition, the average yield for the AI treatment (34.52 t ha−1) was significantly greater (17.4%) compared with that of the control (p = 0.018). These results suggest that AI do not significantly increase the integrative greenhouse effect caused by CO2 and N2O from soils of greenhouse tomato fields, but significantly increase the tomato yield. The research results provide certain theoretical foundation and scientific basis for accurately evaluating the farmland ecological effect of AI technique.

Effect of tillage and crop (cereal versus legume) on greenhouse gas emissions and Global Warming Potential in a non-irrigated Mediterranean field

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 (CO2) 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 (N2O), methane (CH4) and CO2 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 N2O ranged between 0.16 (B-MT) and 0.29 (V-MT) kgN2O-Nha−1yr−1, resulting in a lower impact on Net GWP than in previous studies. A significant ‘tillage×crop’ interaction was observed in cumulative N2O emissions (V resulted in higher N2O 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 CH4 or CO2 emissions. Yield-scaled N2O emissions (YSNE) were low (<4gN2O-NkgabovegroundNuptake−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.

Nitrous Oxide Emissions from a Coal Mine Land Reclaimed with Stabilized Manure

AbstractMine‐soil treatment using stabilized manure rapidly sequesters large quantities of organic carbon and nutrients. However, the nutrient‐rich soil conditions may become highly conducive for production and emission of N2O. We examined this possibility in a Pennsylvania coal mine restored using poultry manure stabilized in two forms: composted (Comp) or mixed with paper mill sludge (Man + PMS) at C/N ratios of 14, 21, and 28 and compared those with the emissions from conventionally treated soil. The mine soil was extremely well drained with 59% coarse fragments. Soil–atmosphere exchange of N2O and CO2 was determined using a sampling campaign of ten measurements between 16 June and 14 September 2009 (90 days) and 13 measurements between 28 June and 9 November 2010 (134 days) using static vented chambers at ambient and increased moisture (water added) content. Potential denitrification was determined in a laboratory incubation experiment. While non‐amended mine soil did not have a measurable potential for denitrifying activity, the manure‐based amendments introduced the potential. Soil water filled pore space was less than 60% on most sampling days in both ambient and water‐added plots. Daily N2O‐N emissions ranged between 40 and 70 g N ha−1 with cumulative emissions of 2–4 kg N ha−1 from non‐amended, lime and fertilizer (L + F) and Comp, and 3–10 kg N ha−1 from Man + PMS treatments. The maximum emission obtained from Man + PMS represented &lt;1% loss of applied N. Although stabilized manure‐treated soil exhibits the potential for N2O production, the emission is limited when soils are excessively well drained and reducing conditions rarely develop. Copyright © 2015 John Wiley &amp; Sons, Ltd.

Effect of intensity and duration of freezing on soil microbial biomass, extractable C and N pools, and N2O and CO2 emissions from forest soils in cold temperate region

Freezing can increase the emissions of carbon dioxide (CO2) and nitrous oxide (N2O) and the release of labile carbon (C) and nitrogen (N) pools into the soil. However, there is limited knowledge about how both emissions respond differently to soil freezing and their relationships to soil properties. We evaluated the effect of intensity and duration of freezing on the emissions of CO2 and N2O, net N mineralization, microbial biomass, and extractable C and N pools in soils from a mature broadleaf and Korean pine mixed forest and an adjacent secondary white birch forest in northeastern China. These soils had different contents of microbial biomass and bulk density. Intact soil cores of 0–5 cm and 5–10 cm depth sampled from the two temperate forest floors were subjected to -8, -18, and -80°C freezing treatments for a short (10 d) and long (145 d) duration, and then respectively incubated at 10°C for 21 d. Soil cores, incubated at 10°C for 21 d without a pretreatment of freezing, served as control. Emissions of N2O and CO2 after thaw varied with forest type, soil depth, and freezing treatment. The difference could be induced by the soil water-filled pore space (WFPS) during incubation and availability of substrates for N2O and CO2 production, which are released by freezing. A maximum N2O emission following thawing of frozen soils was observed at approximately 80% WFPS, whereas CO2 emission from soils after thaw significantly increased with increasing WFPS. The soil dissolved organic C just after freezing treatment and CO2 emission increased with increase of freezing duration, which paralleled with a decrease in soil microbial biomass C. The cumulative net N mineralization and net ammonification after freezing treatment as well as N2O emission were significantly affected by freezing temperature. The N2O emission was negatively correlated to soil pH and bulk density, but positively correlated to soil K2SO4-extractable NO3 --N content and net ammonification. The CO2 emission was positively correlated to the cumulative net N mineralization and net ammonification. From the above results, it can be reasonably concluded that for a wide range of freezing temperature and freezing duration, N2O and CO2 emissions after thaw were associated mainly with the changes in soil net N mineralization and the availability of substrate liberated by freezing as well as other soil properties that influence porosity.

Gross Nitrification Rates and Nitrous Oxide Emissions in an Apple Orchard Soil in Northeast China

A better understanding of nitrogen (N) transformation in agricultural soils is crucial for the development of sustainable and environmental-friendly N fertilizer management and the proposal of effective N2O mitigation strategies. This study aimed: i) to elucidate the seasonal dynamic of gross nitrification rate and N2O emission, ii) to determine the influence of soil conditions on the gross nitrification, and iii) to confirm the relationship between gross nitrification and N2O emissions in the soil of an apple orchard in Yantai, Northeast China. The gross nitrification rates and N2O fluxes were examined from March to October in 2009, 2010, and 2011 using the barometric process separation (BaPS) technique and the static chamber method. During the wet seasons gross nitrification rates were 1.64 times higher than those under dry season conditions. Multiple regression analysis revealed that gross nitrification rates were significantly correlated with soil temperature and soil water-filled pore space (WFPS). The relationship between gross nitrification rates and soil WFPS followed an optimum curve peaking at 60% WFPS. Nitrous oxide fluxes varied widely from March to October and were stimulated by N fertilizer application. Statistically significant positive correlations were found between gross nitrification rates and soil N2O emissions. Further evaluation indicated that gross nitrification contributed significantly to N2O formation during the dry season (about 86%) but to a lesser degree during the wet season (about 51%). Therefore, gross nitrification is a key process for the formation of N2O in soils of apple orchard ecosystems of the geographical region.