Fluxes of CO2, CH4, and N2O in an alpine meadow affected by yak excreta on the Qinghai-Tibetan plateau during summer grazing periods

To assess the impacts of yak excreta patches on greenhouse gas (GHG) fluxes in the alpine meadow of the Qinghai-Tibetan plateau, methane (CH₄), carbon dioxide (CO₂), and nitrous oxide (N₂O) fluxes were measured for the first time from experimental excreta patches placed on the meadow during the summer grazing seasons in 2005 and 2006. Dung patches were CH₄ sources (average 586 μg m⁻² h⁻¹ in 2005 and 199 μg m⁻² h⁻¹ in 2006) during the investigation period of two years, while urine patches (average −31 μg m⁻² h⁻¹ in 2005 and −33 μg m⁻² h⁻¹ in 2006) and control plots (average −28 μg m⁻² h⁻¹ in 2005 and −30 μg m⁻² h⁻¹ in 2006) consumed CH₄. The cumulative CO₂ emission for dung patches was about 36-50% higher than control plots during the experimental period in 2005 and 2006. The cumulative N₂O emissions for both urine and dung patches were 2.1-3.7 and 1.8-3.5 times greater than control plots in 2005 and 2006, respectively. Soil water-filled pore space (WFPS) explained 35% and 36% of CH₄ flux variation for urine patches and control plots, respectively. Soil temperature explained 40-75% of temporal variation of CO₂ emissions for all treatments. Temporal N₂O flux variation in urine patches (34%), dung patches (48%), and control (56%) plots was mainly driven by the simultaneous effect of soil temperature and WFPS. Although yak excreta patches significantly affected GHG fluxes, their contributions to the whole grazing alpine meadow in terms of CO₂ equivalents are limited under the moderate grazing intensity (1.45 yak ha⁻¹). However, the contributions of excreta patches to N₂O emissions are not negligible when estimating N₂O emissions in the grazing meadow. In this study, the N₂O emission factor of yak excreta patches varied with year (about 0.9-1.0%, and 0.1-0.2% in 2005 and 2006, respectively), which was lower than IPCC default value of 2%.     

Effect of plantain on nitrous oxide emissions and soil nitrification rate in pasture soil under a simulated urine patch in Canterbury,New Zealand

Purpose

The aim of this research was to quantify the effect of plantain (Plantago lanceolata L.) on soil nitrification rate, functional gene abundance of soil ammonia oxidisers, and the concomitant effect on nitrous oxide emissions from urine patches in a shallow, free-draining soil in Canterbury during late autumn/winter season.

Materials and methods

Urine was collected from dairy cows grazing either ryegrass/white clover (RGWC), 30% plantain (P30) mixed in with RGWC or 100% plantain (P100) pasture, and applied at two rates (700 or 450 kg N ha^?1) to intact soil blocks growing either RGWC, P30 or P100 pasture.

Results and discussion

Results showed that increased plantain content reduced N-concentration in urine from 7.2 in RGWC urine to 4.5 and 3.7 g N L^?1 in P30 and P100 urine, respectively. Total N₂O emissions and emission factors (EF₃) from urine-treated pastures were low, <?2 kg N ha^?1 and <?0.22%, respectively. Urine application at the lower urine N-loading rate of 450 kg N ha^?1 (i.e. representative of that in a P30 urine patch) resulted in 30% lower N₂O emissions (P?<?0.01) and 35% lower soil nitrate concentrations (P?<?0.001) compared to those at the higher urine loading rate of 700 kg N ha^?1 (i.e. representative of that in a RGWC urine patch). Increasing plantain content in the pasture sward from 0 to 30% and 100% with urine N applied at the same loading rate did not reduce N₂O emissions or nitrification compared to the standard ryegrass-white clover pasture. Cow urine derived from the different pasture diets had no effect on N₂O emissions, N transformation or ammonia-oxidiser abundance in soil compared to the RGWC urine applied at the same rate.

Conclusions

The main effect of plantain in this study appears to be related to the reduction in urine N-loading rate, rather than factors related to urine properties or plantain-soil interactions.

     

Microbial pathways for nitrous oxide emissions from sheep urine and dung in a typical steppe grassland

The aim of this study was to determine the responses of nitrifiers and denitrifiers to understand microbial pathways of nitrous oxide (N₂O) emissions in grassland soils that received inputs of sheep excreta. Sheep dung and synthetic sheep urine were applied at three different rates, simulating a single, double, or triple overlapping of urine or dung depositions in the field. Quantitative PCR and high-throughput sequencing were combined with process-based modeling to understand effects of sheep excreta on microbial populations and on pathways for N₂O production. Results showed that emissions of N₂O from urine were significantly higher than from dung, ranging from 0.12 to 0.78 kg N₂O-N ha^?1 during the 3 months. The N₂O emissions were significantly related to the bacterial amoA (r?=?0.373, P?<?0.001) and nirK (r?=?0.614, P?<?0.001) gene abundances. It was autotrophic nitrification that dominated N₂O production in the low urine-N rate soils, whereas it was denitrification (including nitrifier denitrification and heterotrophic denitrification) that dominated N₂O production in the high urine-N rate soils. Nitrifier denitrification was responsible for most of the N₂O emissions in the dung-treated soils. This study suggests that nitrifier denitrification is indeed an important pathway for N₂O emissions in these low fertility and dry grazed grassland ecosystems.     

Contribution of nitrification and denitrification to N2O emissions from urine patches

Urine deposition by grazing livestock causes an immediate increase in nitrous oxide (N₂O) emissions, but the responsible mechanisms are not well understood. A nitrogen-15 (¹⁵N) labelling study was conducted in an organic grass-clover sward to examine the initial effect of urine on the rates and N₂O loss ratio of nitrification (i.e. moles of N₂O-N produced per moles of nitrate produced) and denitrification (i.e. moles of N₂O produced per moles of N₂O+N₂ produced). The effect of artificial urine (52.9 g N m⁻²) and ammonium solution (52.9 g N m⁻²) was examined in separate experiments at 45% and 35% water-filled pore space (WFPS), respectively, and in each experiment a water control was included. The N₂O loss derived from nitrification or denitrification was determined in the field immediately after application of ¹⁵N-labelled solutions. During the next 24 h, gross nitrification rates were measured in the field, whereas the denitrification rates were measured in soil cores in the laboratory. Compared with the water control, urine application increased the N₂O emission from 3.9 to 42.3 μg N₂O-N m⁻² h⁻¹, whereas application of ammonium increased the emission from 0.9 to 6.1 μg N₂O-N m⁻² h⁻¹. In the urine-affected soil, nitrification and denitrification contributed equally to the N₂O emission, and the increased N₂O loss resulted from a combination of higher rates and higher N₂O loss ratios of the processes. In the present study, an enhanced nitrification rate seemed to be the most important factor explaining the high initial N₂O emission from urine patches deposited on well-aerated soils.     

Influence of drip and furrow irrigation systems on nitrogen oxide emissions from a horticultural crop

Irrigation management has an important influence on emissions of nitrous oxide (N₂O) 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 N₂O 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 N₂O 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 N₂O to the wet areas (0.45 kg N₂O-N ha^?1) in the Control and greater quantities in the AS treatment (0.92 kg N₂O-N ha^?1 for dry and 0.70 kg N₂O-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 N₂O- N ha^?1 for the AS treatment under FI and at 4.96 kg N₂O-N ha^?1 for DI. Under DI, nitrification was an important source of N₂O, whereas denitrification was the most important source under FI. The addition of NH₄⁺ and the use of DI enhanced the N₂O/N₂ ratio of gases produced through denitrification. The quantity of dissolved organic C (DOC) in the soil generally decreased with addition of NH₄⁺.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 N₂O.     

N2O emissions from humid tropical agricultural soils: effects of soil moisture,texture and nitrogen availability

We studied soil moisture dynamics and nitrous oxide (N₂O) fluxes from agricultural soils in the humid tropics of Costa Rica. Using a split-plot design on two soils (clay, loam) we compared two crop types (annual, perennial) each unfertilized and fertilized. Both soils are of andic origin. Their properties include relatively low bulk density and high organic matter content, water retention capacity, and hydraulic conductivity. The top 2–3 cm of the soils consists of distinct small aggregates (dia. <0.5 cm). We measured a strong gradient of bulk density and moisture within the top 7 cm of the clay soil. Using automated sampling and analysis systems we measured N₂O emissions at 4.6 h intervals, meteorological variables, soil moisture, and temperature at 0.5 h intervals. Mean daily soil moisture content at 5 cm depth ranged from 46% water filled pore space (WFPS) on clay in April 1995 to near saturation on loam during a wet period in February 1996. On both soils the aggregated surface layer always remained unsaturated. Soils emitted N₂O throughout the year. Mean N₂O fluxes were 1.04±0.72 ng N₂O-N cm⁻² h⁻¹ (mean±standard deviation) from unfertilized loam under annual crops compared to 3.54±4.31 ng N₂O-N cm⁻² h⁻¹ from the fertilized plot (351 days measurement). Fertilization dominated the temporal variation of N₂O emissions. Generally fluxes peaked shortly after fertilization and were increased for up to 6 weeks (‘post fertilization flux’). Emissions continued at a lower rate (‘background flux’) after fertilization effects faded. Mean post-fertilization fluxes were 6.3±6.5 ng N₂O-N cm⁻² h⁻¹ while the background flux rate was 2.2±1.8 ng N₂O-N cm⁻² h⁻¹. Soil moisture dynamics affected N₂O emissions. Post fertilization fluxes were highest from wet soils; fluxes from relatively dry soils increased only after rain events. N₂O emissions were weakly affected by soil moisture during phases of low N availability. Statistical modeling confirmed N availability and soil moisture as the major controls on N₂O flux. Our data suggest that small-scale differences in soil structure and moisture content cause very different biogeochemical environments within the top 7 cm of soils, which is important for net N₂O fluxes from soils.     

No significant difference in N2O emission,fertilizer-induced N2O emission factor and CH4 absorption between anaerobically digested cattle slurry and chemical fertilizer applied timothy (Phleum pratense L.) sward in central Hokkaido,Japan

Abstract

Nitrous oxide (N₂O) and methane (CH₄) fluxes from a fertilized timothy (Phleum pratense L.) sward on the northern island of Japan were measured over 2?years using a randomized block design in the field. The objectives of the present study were to obtain annual N₂O and CH₄ emission rates and to elucidate the effect of the applied material (control [no nitrogen], anaerobically digested cattle slurry [ADCS] or chemical fertilizer [CF]) and the application season (autumn or spring) on the annual N₂O emission, fertilizer-induced N₂O emission factor (EF) and the annual CH₄ absorption. Ammonium sulfate was applied to the CF plots at the same application rate of NH₄-N to the ADCS plots. A three-way ANOVA was used to examine the significance of the factors (the applied material, the application season and the year). The ANOVA for the annual N₂O emission rates showed a significant effect with regard to the applied material (P?=?0.042). The annual N₂O emission rate from the control plots (0.398?kg N₂O-N ha^?1?year^?1) was significantly lower than that from the ADCS plots (0.708?kg N₂O-N ha^?1?year^?1) and the CF plots (0.636?kg N₂O-N ha^?1?year^?1). There was no significant difference in the annual N₂O emission rate between the ADCS and CF plots. The ANOVA for the EFs showed insignificance of all factors (P?>?0.05). The total mean?±?standard error of the EFs (fertilizer-induced N₂O-N emission/total applied N) was 0.0024?±?0.0007 (kg N₂O-N [kg N]^?1), which is similar to the reported EF (0.0032?±?0.0013) for well-drained uplands in Japan. The CH₄ absorption rates differed significantly between years (P?=?0.014). The CH₄ absorption rate in the first year (3.28?kg CH₄?ha^?1?year^?1) was higher than that in the second year (2.31?kg CH₄?ha^?1?year^?1), probably as a result of lower precipitation in the first year. In conclusion, under the same application rate of NH₄-N, differences in the applied materials (ADCS or CF) and the application season (autumn or spring) led to no significant differences in N₂O emission, fertilizer-induced N₂O EF and CH₄ absorption.     

Nitrous oxide emissions from a rainfed-cultivated black soil in Northeast China: effect of fertilization and maize crop

Nitrous oxide emission (N₂O) from applied fertilizer across the different agricultural landscapes especially those of rainfed area is extremely variable (both spatially and temporally), thus posing the greatest challenge to researchers, modelers, and policy makers to accurately predict N₂O emissions. Nitrous oxide emissions from a rainfed, maize-planted, black soil (Udic Mollisols) were monitored in the Harbin State Key Agroecological Experimental Station (Harbin, Heilongjiang Province, China). The four treatments were: a bare soil amended with no N (C0) or with 225?kg?N ha^?1 (CN), and maize (Zea mays L.)-planted soils fertilized with no N (P0) or with 225?kg?N ha^?1 (PN). Nitrous oxide emissions significantly (P?<?0.05) increased from 141?±?5?g N₂O-N?ha^?1 (C0) to 570?±?33?g N₂O-N?ha^?1 (CN) in unplanted soil, and from 209?±?29?g N₂O-N?ha^?1 (P0) to 884?±?45?g N₂O-N?ha^?1 (PN) in planted soil. Approximately 75?% of N₂O emissions were from fertilizer N applied and the emission factor (EF) of applied fertilizer N as N₂O in unplanted and planted soils was 0.19 and 0.30?%, respectively. The presence of maize crop significantly (P?<?0.05) increased the N₂O emission by 55?% in the N-fertilized soil but not in the N-unfertilized soil. There was a significant (P?<?0.05) interaction effect of fertilization?×?maize on N₂O emissions. Nitrous oxide fluxes were significantly affected by soil moisture and soil temperature (P?<?0.05), with the temperature sensitivity of 1.73–2.24, which together explained 62–76?% of seasonal variation in N₂O fluxes. Our results demonstrated that N₂O emissions from rainfed arable black soils in Northeast China primarily depended on the application of fertilizer N; however, the EF of fertilizer N as N₂O was low, probably due to low precipitation and soil moisture.     

Greenhouse gas diffusive fluxes at the sediment–water interface of sewage-draining rivers

Purpose

The purposes of this study were to analyse the spatiotemporal variations in greenhouse gas diffusive fluxes at the sediment–water interface of sewage-draining rivers and natural rivers, and investigate the factors responsible for the changes in greenhouse gas diffusive fluxes.

Materials and methods

Greenhouse gas diffusive fluxes at the sediment–water interface of rivers in Tianjin city (Haihe watershed) were investigated during July and October 2014, and January and April 2015 by laboratory incubation experiments. The influence of environmental variables on greenhouse gas diffusive fluxes was evaluated by Spearman’s correlation analysis and a multiple stepwise regression analysis.

Results and discussion

Sewage-draining rivers were more seriously polluted by human sewage discharge than natural rivers. The greenhouse gas diffusive fluxes at the sediment–water interface exhibited obvious spatiotemporal variations. The mean absolute value of the CO₂ diffusive fluxes was seasonally variable with spring>winter>fall>summer, while the mean absolute values of the CH₄ and N₂O diffusive fluxes were both higher in summer and winter, and lower in fall and spring. The annual mean values of the CO₂, CH₄ and N₂O diffusive fluxes at the sewage-draining river sediment–water interface were ??123.26?±?233.78 μmol m^?2 h^?1, 1.88?±?6.89 μmol m^?2 h^?1 and 1505.03?±?2388.46 nmol m^?2 h^?1, respectively, which were 1.22, 4.37 and 134.50 times those at the natural river sediment–water interface, respectively. The spatial variation of the N₂O diffusive fluxes in the sewage-draining rivers and the natural rivers was the most significant. As a general rule, the more serious the river pollution was, the greater the diffusive fluxes of the greenhouse gases were. On average for the whole year, the river sediment was the sink of CO₂ and the source of CH₄ and N₂O. There were positive correlations among the CO₂, CH₄ and N₂O diffusive fluxes. The main influencing factor for CO₂ and N₂O diffusive fluxes was the water temperature of the overlying water; however, the key factors for CH₄ diffusive fluxes were the Eh of the sediment and the NH₄⁺-N of the overlying water.

Conclusions

River sediment can be either a sink or a source of greenhouse gases, which varies in different levels of pollution and different seasons. Human sewage discharge has greatly affected the carbon and nitrogen cycling of urban rivers.

     

Nitrous oxide emissions from two dairy pasture soils as affected by different rates of a fine particle suspension nitrification inhibitor, dicyandiamide

In grazed pasture systems, a major source of N₂O is nitrogen (N) returned to the soil in animal urine. We report in this paper the effectiveness of a nitrification inhibitor, dicyandiamide (DCD), applied in a fine particle suspension (FPS) to reduce N₂O emissions from dairy cow urine patches in two different soils. The soils are Lismore stony silt loam (Udic Haplustept loamy skeletal) and Templeton fine sandy loam (Udic Haplustepts). The pasture on both soils was a mixture of perennial ryegrass (Lolium perenne) and white clover (Trifolium repens). Total N₂O emissions in the Lismore soil were 23.1–31.0 kg N₂O-N ha⁻¹ following the May (autumn) and August (late winter) urine applications, respectively, without DCD. These were reduced to 6.2–8.4 kg N₂O-N ha⁻¹ by the application of DCD FPS, equivalent to reductions of 65–73%. All three rates of DCD applied (7.5, 10 and 15 kg ha⁻¹) were effective in reducing N₂O emissions. In the Templeton soil, total N₂O emissions were reduced from 37.4 kg N₂O-N ha⁻¹ without DCD to 14.6–16.3 kg N₂O-N ha⁻¹ when DCD was applied either immediately or 10 days after the urine application. These reductions are similar to those in an earlier study where DCD was applied as a solution. Therefore, treating grazed pasture soils with an FPS of DCD is an effective technology to mitigate N₂O emissions from cow urine patch areas in grazed pasture soils.     

Nitrous oxide emissions from fertilized,irrigated cotton (Gossypium hirsutum L.) in the Aral Sea Basin,Uzbekistan: Influence of nitrogen applications and irrigation practices

Nitrous oxide emissions were monitored at three sites over a 2-year period in irrigated cotton fields in Khorezm, Uzbekistan, a region located in the arid deserts of the Aral Sea Basin. The fields were managed using different fertilizer management strategies and irrigation water regimes. N₂O emissions varied widely between years, within 1 year throughout the vegetation season, and between the sites. The amount of irrigation water applied, the amount and type of N fertilizer used, and topsoil temperature had the greatest effect on these emissions.Very high N₂O emissions of up to 3000 μg N₂O-N m^?2 h^?1 were measured in periods following N-fertilizer application in combination with irrigation events. These “emission pulses” accounted for 80–95% of the total N₂O emissions between April and September and varied from 0.9 to 6.5 kg N₂O-N ha^?1.. Emission factors (EF), uncorrected for background emission, ranged from 0.4% to 2.6% of total N applied, corresponding to an average EF of 1.48% of applied N fertilizer lost as N₂O-N. This is in line with the default global average value of 1.25% of applied N used in calculations of N₂O emissions by the Intergovernmental Panel on Climate Change.During the emission pulses, which were triggered by high soil moisture and high availability of mineral N, a clear diurnal pattern of N₂O emissions was observed, driven by daily changes in topsoil temperature. For these periods, air sampling from 8:00 to 10:00 and from 18:00 to 20:00 was found to best represent the mean daily N₂O flux rates. The wet topsoil conditions caused by irrigation favored the production of N₂O from NO₃^? fertilizers, but not from NH₄⁺ fertilizers, thus indicating that denitrification was the main process causing N₂O emissions. It is therefore argued that there is scope for reducing N₂O emission from irrigated cotton production; i.e. through the exclusive use of NH₄⁺ fertilizers. Advanced application and irrigation techniques such as subsurface fertilizer application, drip irrigation and fertigation may also minimize N₂O emission from this regionally dominant agro-ecosystem.     

Nutrient balance in Scots pine (Plnus sylvestris L.) forest. 3. Fluxes of N2O from lysimeter as influenced by nitrogen input

Forest soils may become an increasingly important source of N₂O, due to disturbances to the forest ecosystem (e.g. fertilization to increase growth, or atmospheric deposition of air-borre nitrogen compounds such as NH₃, NO₃ and NO_x). A lysimeter experiment was used to study the effects of different amounts of N input [0 (control), 30 kg (Medium) and 90 kg (High) N ha^?1 y^?1 as NH₄NO₃] on fluxes of N₂O, measured by the close chamber method. The estimated annual N₂O flux were about 0.4 kg N₂O-N ha^?1 for control, 0.9 kg N₂O-N ha^?1 for medium N and 1.8 kg N₂O-N ha^?1 for high N treatments. The relation between the estimated annual N₂O flux and fertilizer dose showed an almost perfect proportionality between fertilizer dose and the increase in N₂O flux. This is important, since one crucial question is wether we can extrapolate results from high N-doses to situations with low amounts of N inputs prevailing in forests exposed to moderate input of N. The increase in N₂O fluxes from the control to the fertilised treatments corresponds to 1.7% of the annual N input in the medium N treatments and 1.6% of the annual input in the high N treatment.     

Fluxes of nitrous oxide and nitric oxide from experimental excreta patches in boreal agricultural soil

Nitric oxide (NO) and nitrous oxide (N₂O) emissions were measured from experimental dung and urine patches placed on boreal pasture soil during two growing seasons and one autumn period until soil freezing. N₂O emissions in situ were studied by a static chamber method. NO was measured with a dynamic chamber method using a NO analyser in situ. Mean emissions from the control plots were 47.6±4.5 μg N₂ON m⁻² h⁻¹ and 12.6±1.6 μg NON m⁻² h⁻¹. N₂O and NO emissions from urine plots (132±21.2 μg N₂ON m⁻² h⁻¹ and 51.9±7.6 μg NON m⁻² h⁻¹) were higher than those from dung plots (110.0±20.1 μg N₂ON m⁻² h⁻¹ and 14.7±2.1 μg NON m⁻² h⁻¹). There was a large temporal variation in N₂O and NO emissions. Maximum N₂O emissions were measured a few weeks after dung or urine application, whereas the maximum NO emissions were detected the following year. NO was responsible on average 14% (autumn) and 34% (summer) of total (NO+N₂O)N emissions from the pasture soil. NO emissions increased with increasing soil temperature and with decreasing soil moisture. N₂O emissions increased with increasing soil moisture, but did not correlate with soil temperature. Therefore we propose that N₂O and NO were produced mainly during different microbial processes, i.e., nitrification and denitrification, respectively. The results show that the overall conditions and mechanism especially for emissions of NO are still poorly understood but that there are differences in the mechanisms regulating N₂O and NO production.     

The Effect of N Deposition on Nitrous Oxide and Nitric Oxide Emissions from Temperate Forest Soils

Long-term and short-term N deposition effects on N₂O and NO emissions from forest soils were compared. Long-term NH₃ deposition (> 20 years) from a poultry farm to a downwind woodland (decreasing from 73 to 18 kg N ha^-1 y^-1, 30 to 110 m downwind of the farm) resulted in the re-emission of 6% and 14% of NH₃-N deposited as N₂O-N and NO-N, respectively. However, when in short-term (2-3 years) field experiments the atmospheric N deposition to mature conifer plantations was raised by fumigation with NH₃ to 15 kg N ha^-1 y^-1 or by acid mist to 48 and 96 kg N ha^-1 y^-1 the N deposited was immobilised. In the acid mist experiment more than 2 years of acid mist (48 and 96 kg N ha-1 y^-1) were required to significantly increase N₂O emissions from -0.3 μg N₂O-N m^-2 h^-1 (control) to 0.5 and 5.7 μg N₂O-N m^-2 h^-1, respectively. This suggests, that N deposition simulation studies in soil ecosystems, which have previously not been exposed to high rates of N (by deposition or fertilisation), need to be long-term. Also, measurements of N₂O and/or NO may be a non-destructive, quick indicator of the N status of the soil.     

Impact of nitrogen fertilization and tillage practices on nitrous oxide emission from a summer rice ecosystem

ABSTRACT

Identification of the combination of tillage and N fertilization practices that reduce agricultural Nitrous oxide (N₂O) emissions while maintaining productivity is strongly required in the Indian subcontinent. This study investigated the effects of tillage in combination with different levels of nitrogen fertilizer on N₂O emissions from a rice paddy for two consecutive seasons (2013–2014 and 2014–2015). The experiment consisted of two tillage practices, i.e., conventional (CT) and reduced tillage (RT), and four levels of nitrogen fertilizer, i.e., 0 kg N ha^–1 (F1), 45 kg N ha^–1 (F2), 60 kg N ha^–1 (F3) and 75 kg N ha^–1 (F4). Both tillage and fertilizer rate significantly affected cumulative N₂O emissions (p < 0.05). Fertilizer at 45 and 60 kg N ha^–1 in RT resulted in higher N₂O emissions over than did the CT. Compared with the recommended level of 60 kg N ha^?1, a 25% reduction in the fertilizer to 45 kg N ha^?1 in both CT and RT increased nitrogen use efficiency (NUE) and maintained grain yield, resulting in the lowest yield-scaled N₂O-N emission. The application of 45 kg N ha^?1 reduced the cumulative emission by 6.08% and 6% in CT and RT practices, respectively, without compromising productivity.     

Nitrous oxide emission as affected by alternate anaerobic and aerobic conditions from soil suspensions enriched with ammonium sulfate

The effect of several anaerobic and aerobic cycles of varying duration on N₂O emission and labelled N loss was investigated in (¹⁵NH₄)₂SO₄ amended soil suspensions. No N₂O was evolved from the continuously-anaerobic treatment. The continuously-aerobic treatment produced approximately 0.8 μg N₂O-N g^?1 dry soil in 56 days. Alternate anaerobic-aerobic cycles increased the net N₂O evolution with 7.2 μg N₂O-N g^?1 dry soil produced in 56 days from the 7-day anaerobic, 7-day aerobic treatment. The net N₂O evolution increased further when the duration of the anaerobic and aerobic periods was increased from 7-7 days to 14-14 days (15.7μg N₂O-N g^?1 dry soil in 56 days), although the total ¹⁵N loss from the system was approximately the same for the two treatments. The results of this study show that N₂O evolution from soils is likely to be greater under fluctuating moisture conditions than under either continuously well-aerated conditions, or continuously excess-moisture conditions.     

Biochar amendment of chromium-polluted paddy soil suppresses greenhouse gas emissions and decreases chromium uptake by rice grain

Purpose

Soil chromium (Cr) pollution has received substantial attention owing to related food chain health risks and possible promotion of greenhouse gas (GHG) emissions. The aim of the present study was to develop a promising remediation technology to alleviate Cr bioavailability and decrease GHG emissions in Cr-polluted paddy soil.

Materials and methods

We investigated the potential role of biochar amendment in decreasing soil CO₂, CH₄, and N₂O emissions, as well in reducing Cr uptake by rice grains at application rates of 0 t ha^?1 (CK), 20 t ha^?1 (BC20), and 40 t ha^?1 (BC40) in Cr-polluted paddy soil in southeastern China. In addition, the soil aggregate size distribution, soil organic carbon (SOC) concentration of soil aggregates, soil available Cr concentration, and rice yield were analyzed after harvesting.

Results and discussion

Biochar amendment significantly reduced CO₂, CH₄, and N₂O emission fluxes. Compared to CK, total C emissions in the BC20 and BC40 treatments decreased by 9.94% and 17.13% for CO₂-C, by 30.46% and 37.10% for CH₄-C, and by 34.24% and 37.49% for N₂O-N, respectively. Biochar amendment increased the proportion of both the 2000–200 μm and 200–20 μm size fractions in the soil aggregate distribution. Accordingly, the organic carbon concentration of these fractions increased, which increased the total SOC. Moreover, biochar amendment significantly decreased soil available Cr concentration and total Cr content of the rice grains by 33.6% and 14.81% in BC20 and 48.1% and 33.33% in BC40, respectively. Rice yield did not differ significantly between biochar amendment treatment and that of CK.

Conclusions

Biochar application reduced GHG emissions in paddy soil, which was attributed to its comprehensive effect on the soil properties, soil microbial community, and soil aggregates, as well as on the mobility of Cr. Overall, the present study demonstrates that biochar has a great potential to enhance soil carbon sequestration while reducing Cr accumulation in rice grains from Cr-polluted rice paddies.

     

Tillage effects on N2O emissions as influenced by a winter cover crop

Conservation tillage practices are widely used to protect against soil erosion and soil C losses, whereas winter cover crops are used mainly to protect against N losses during autumn and winter. For the greenhouse gas balance of a cropping system the effect of reduced tillage and cover crops on N₂O emissions may be more important than the effect on soil C. This study monitored emissions of N₂O between September 2008 and May 2009 in three tillage treatments, i.e., conventional tillage (CT), reduced tillage (RT) and direct drilling (DD), all with (+CC) or without (−CC) fodder radish as a winter cover crop. Cover crop growth, soil mineral N dynamics, and other soil characteristics were recorded. Furthermore, soil concentrations of N₂O were determined eight times during the monitoring period using permanently installed needles. There was little evidence for effects of the cover crop on soil mineral N. Following spring tillage and slurry application soil mineral N was dominated by the input from slurry. Nitrous oxide emissions during autumn, winter and early spring remained low, although higher emissions from +CC treatments were indicated after freezing events. Following spring tillage and slurry application by direct injection N₂O emissions were stimulated in all tillage treatments, reaching 250-400 μg N m⁻² h⁻¹ except in the CT + CC treatment, where emissions peaked at 900 μg N m⁻² h⁻¹. Accumulated emissions ranged from 1.6 to 3.9 kg N₂O ha⁻¹. A strong positive interaction between cover crop and tillage was observed. Soil concentration profiles of N₂O showed a significant accumulation of N₂O in CT relative to RT and DD treatments after spring tillage and slurry application, and a positive interaction between slurry and cover crop residues. A comparison in early May of N₂O emissions with flux estimates based on soil concentration profiles indicated that much of the N₂O emitted was produced near the soil surface.     

Dinitrogen emissions and the N2:N2O emission ratio of a Rendzic Leptosol as influenced by pH and forest thinning

Reduction of nitrous oxide (N₂O) to dinitrogen (N₂) by denitrification in soils is of outstanding ecological significance since it is the prevailing natural process converting reactive nitrogen back into inert molecular dinitrogen. Furthermore, the extent to which N₂O is reduced to N₂ via denitrification is a major regulating factor affecting the magnitude of N₂O emission from soils. However, due to methodological problems in the past, extremely little information is available on N₂ emission and the N₂:N₂O emission ratio for soils of terrestrial ecosystems. In this study, we simultaneously determined N₂ and N₂O emissions from intact soil cores taken from a mountainous beech forest ecosystem. The soil cores were taken from plots with distinct differences in microclimate (warm-dry versus cool-moist) and silvicultural treatment (untreated control versus heavy thinning). Due to different microclimates, the plots showed pronounced differences in pH values (range: 6.3–7.3). N₂O emission from the soil cores was generally very low (2.0 ± 0.5–6.3 ± 3.8 μg N m⁻² h⁻¹ at the warm-dry site and 7.1 ± 3.1–57.4 ± 28.5 μg N m⁻² h⁻¹ at the cool-moist site), thus confirming results from field measurements. However, N₂ emission exceeded N₂O emission by a factor of 21 ± 6–220 ± 122 at the investigated plots. This illustrates that the dominant end product of denitrification at our plots and under the given environmental conditions is N₂ rather than N₂O. N₂ emission showed a huge variability (range: 161 ± 64–1070 ± 499 μg N m⁻² h⁻¹), so that potential effects of microclimate or silvicultural treatment on N₂ emission could not be identified with certainty. However, there was a significant effect of microclimate on the magnitude of N₂O emission as well as on the mean N₂:N₂O emission ratio. N₂:N₂O emission ratios were higher and N₂O emissions were lower for soil cores taken from the plots with warm-dry microclimate as compared to soil cores taken from the cool-moist microclimate plots. We hypothesize that the increase in the N₂:N₂O emission ratio at the warm-dry site was due to higher N₂O reductase activity provoked by the higher soil pH value of this site. Overall, the results of this study show that the N₂:N₂O emission ratio is crucial for understanding the regulation of N₂O fluxes of the investigated soil and that reliable estimates of N₂ emissions are an indispensable prerequisite for accurately calculating total N gas budgets for the investigated ecosystem and very likely for many other terrestrial upland ecosystems as well.     

Effects of 3,4-dimethylpyrazole phosphate (DMPP) on the abundance of ammonia oxidizers and denitrifiers in two different intensive vegetable cultivation soils

Purpose

Nitrification and denitrification in the N cycle are affected by various ammonia oxidizers and denitrifying microbes in intensive vegetable cultivation soils, but our current understanding of the effect these microbes have on N₂O emissions is limited. The nitrification inhibitor, 3,4-dimethylpyrazole phosphate (DMPP), acts by slowing nitrification and is used to improve fertilizer use efficiency and reduce N losses from agricultural systems; however, its effects on nitrifier and denitrifier activities in intensive vegetable cultivation soils are unknown.

Materials and methods

In this study, we measured the impacts of DMPP on N₂O emissions, ammonia oxidizers, and denitrifying microbes in two intensive vegetable cultivation soils: one that had been cultivated for a short term (1 year) and one that had been cultivated over a longer term (29 years). The quantitative PCR technique was used in this study. Three treatments, including control (no fertilizer), urea alone, and urea with DMPP, were included for each soil. The application rates of urea and DMPP were 1800 kg ha^?1 and 0.5% of the urea-N application rate.

Results and discussion

The application of N significantly increased N₂O emissions in both soils. The abundance of ammonia-oxidizing bacteria (AOB) increased significantly with high rate of N fertilizer application in both soils. Conversely, there was no change in the growth rate of ammonia-oxidizing archaea (AOA) in response to the applied urea despite the presence of larger numbers of AOA in these soils. This suggests AOB may play a greater role than AOA in the nitrification process, and N₂O emission in intensive vegetable cultivation soils. The application of DMPP significantly reduced soil NO₃^?-N content and N₂O emission, and delayed ammonia oxidation. It greatly reduced AOB abundance, but not AOA abundance. Moreover, the presence of DMPP was correlated with a significant decrease in the abundance of nitrite reductase (nirS and nirK) genes.

Conclusions

Long-term intensive vegetable cultivation with heavy N fertilization altered AOB and nirS abundance. In vegetable cultivation soils with high N levels, DMPP can be effective in mitigating N₂O emissions by directly inhibiting both ammonia oxidizing and denitrifying microbes.