Food production systems associated with livestock management are significant sources of greenhouse gases (GHGs). Livestock excreta are one of the primary sources of GHG emissions from grazing livestock. Against this context, a field experiment was established in a UK grassland to establish the extent of soil methane (CH4), carbon dioxide (CO2), andN2O fluxes upon the deposition of (i) cattle urine (U), (ii) urine + dicyandiamide (DCD) (U + DCD), (iii) artificial urine (AU), and dung (D), and compared with a (iv) control, where neither urine nor dung was applied. Excreta applications were made at three experimental periods during the grazing season: early-, mid-, and late-season. Soil N2O emissions data have been published already by co-authors; hence, this paper summarizes the emissions of soil-borne CH4 and CO2 emissions, and explores in particular, the effects of the addition of DCD, a nitrification inhibitor used to reduce direct and indirect N2O emissions from urine patches, on these (carbon) C-GHGs. Soil moisture (p = 0.47), soil temperature (p = 0.51), and nitrate (NO3−) (p = 0.049) and ammonium (NH4+) (p = 0.66) availability, and C (p = 0.54) addition were key controls of both soil CH4 and CO2 emissions. The dung treatment stimulated the production and subsequent emissions of soil CH4 and CO2, a significantly high net CH4 and CO2-based global warming potential (GWP). The findings of the current study lay a foundation for an in-depth understanding of the magnitude and dynamics of soil-borne CH4 and CO2 upon urine and dung deposition during three different seasons. This study implies that the use of DCD may have the potential to reduce carbon-based GHGs from the urine and dung of grazing animals.

Riparian buffers are expedient interventions for water quality functions in agricultural landscapes. However, the choice of vegetation and management affects soil microbial communities, which in turn affect nutrient cycling and the production and emission of gases such as nitric oxide (NO), nitrous oxide (N2O), nitrogen gas (N-2) and carbon dioxide (CO2). To investigate the potential fluxes of the above-mentioned gases, soil samples were collected from a cropland and downslope grass, willow and woodland riparian buffers from a replicated plot scale experimental facility. The soils were re-packed into cores and to investigate their potential to produce the aforementioned gases via potential denitrification, a potassium nitrate (KNO3-) and glucose (labile carbon)-containing amendment, was added prior to incubation in a specialized laboratory DENItrification System (DENIS). The resulting NO, N2O, N-2 and CO2 emissions were measured simultaneously, with the most NO (2.9 & PLUSMN; 0.31 mg NO m(-2)) and N2O (1413.4 & PLUSMN; 448.3 mg N2O m(-2)) generated by the grass riparian buffer and the most N-2 (698.1 & PLUSMN; 270.3 mg N-2 m(-2)) and CO2 (27,558.3 & PLUSMN; 128.9 mg CO2 m(-2)) produced by the willow riparian buffer. Thus, the results show that grass riparian buffer soils have a greater NO3- removal capacity, evidenced by their large potential denitrification rates, while the willow riparian buffers may be an effective riparian buffer as its soils potentially promote complete denitrification to N-2, especially in areas with similar conditions to the current study.

Abstract Riparian buffers are expedient interventions for water quality functions in agricultural landscapes. However, the choice of their vegetation and management affects soil microbial communities, which in turn affect nutrient cycling and the production and emission of gases such as nitric oxide (NO), nitrous oxide (N 2 O), nitrogen gas (N 2 ), and carbon dioxide (CO 2 ). To investigate the potential fluxes of the above-mentioned gases, soil samples were collected from a cropland and downslope grass, willow, and woodland riparian buffers from a replicated plot scale experimental facility. The soils were re-packed into cores, and to investigate their potential to produce the aforementioned gases, a potassium nitrate (KNO 3 − ) and glucose (labile carbon)-containing amendment, was added prior to incubation in a specialized laboratory DENItrification System (DENIS). The resulting NO, N 2 O, N 2, and CO 2 emissions were measured simultaneously, with the highest NO (2.9 ± 0.31 mg NO m − 2 ), and N 2 O (1413.4 ± 448.3 mg N 2 O m − 2 ) generated by the grass riparian buffer and the highest N 2 (698.1 ± 270.3 mg N 2 m − 2 ) and CO 2 (27558.3 ± 128.9 mg CO 2 m − 2 ) produced by the willow riparian buffer. Thus, the results show that soils developed under grass and willow riparian buffers may potentially increase greenhouse gas fluxes, especially in areas with similar conditions to the current study.

BackgroundRiparian buffers are primarily implemented for their water quality functions in agroecosystems. Their location in the agricultural landscape allows them to intercept and process pollutants from immediately adjacent agricultural land. Vegetated riparian buffers recycle soil organic matter, which elevates soil carbon (C), which upon processing, processes and releases carbon dioxide (CO2). The elevated soil C and seasonally anoxic environments associated with riparian buffers promote denitrification and fermentation, further increasing soil CO2 production. AimAgainst this context, a replicated plot-scale experiment was established at North Wyke, UK, to measure the extent of soil CO2 emissions in permanent pasture served by grass, willow, and woodland riparian buffers, as well as a no-buffer control. MethodsSoil CO2 was measured using the static chamber technique in conjunction with soil and environmental variables between June 2018 and February 2019. ResultsCumulative soil CO2 fluxes were in the descending order: woodland riparian buffer; 11,927.8 +/- 1987.9 kg CO2 ha(-1) > no-buffer control; 11,101.3 +/- 3700.4 kg CO2 ha(-1) > grass riparian buffer; 10,826.4 +/- 2551.8 kg CO2 ha(-1) > upslope pasture; 10,554.6 +/- 879.5 kg CO2 ha(-1) > willow riparian buffer; 9294.9 +/- 1549.2 5 kg CO2 ha(-1). There was, however, no evidence of significant differences among all treatments of the current study. ConclusionsDespite the lack of significant differences, the results from our short-term study show that the woodland riparian buffer had relatively larger soil CO2 emissions than the remainder of the other riparian buffers and the upslope pasture it serves. Our short-term findings may be useful in developing soil CO2 mitigation strategies through careful selection of riparian buffer vegetation and may be useful in calibrating mechanistic models for simulating such emissions from similar agro systems.

Animal manures are important sources of nutrients for crop production, yet the effects of slurry carbon (C) components on soil nitrogen gaseous emissions are poorly understood. Six experiments were conducted in a He/O 2 atmosphere aiming to determine the effects of cattle slurry and some of its C components on soil nitrous oxide (N 2 O) and dinitrogen (N 2 ) emissions. The treatments were: 1) NO 3 − ; 2) NO 3 − + glucose (experiments 1 to 4) or NO 3 − + NH 4 + (experiments 5 and 6); and 3) NO 3 − + C source (this was either vanillin, cellulose, glucosamine, butyric acid, fresh cattle slurry or aged cattle slurry, experiments 1 to 6). Results showed that the reactivity order of individual C sources on total N 2 O-N + N 2 -N emissions was: glucose > glucosamine > butyric acid > vanillin > aged slurry > cellulose > fresh slurry. Aged cattle slurry generated relatively higher soil total N 2 O-N + N 2 -N emissions, but also further reduction to N 2 than fresh cattle slurry after incorporation into the soil. In addition, the N 2 O/N 2 ratio was relatively higher in the NO 3 − + NH 4 + treatments (experiments 5 and 6), as well as in the NO 3 − + glucosamine treatment, due to the additional N application. We concluded that the availability/degradability of C in slurry is an important control of subsequent denitrification rates and the production and emission of N 2 O when applied to land suggesting that slurry management, i.e. storage period, can be optimised to influence C availability in cattle slurry, leading to a reduced risk of N 2 O production.

Vegetated land areas play a significant role in determining the fate of carbon (C) in the global C cycle. Riparian buffer vegetation is primarily implemented for water quality purposes as they attenuate pollutants from immediately adjacent croplands before reaching freashwater systems. However, their prevailing conditions may sometimes promote the production and subsequent emissions of soil carbon dioxide (CO2). Despite this, the understanding of soil CO2 emissions from riparian buffer vegetation and a direct comparison with adjacent croplands they serve remain elusive. In order to quantify the extent of CO2 emissions in such an agro system, we measured CO2 emissions simultaneously with soil and environmental variables for six months in a replicated plot-scale facility comprising of maize cropping served by three vegetated riparian buffers, namely: (i) a novel grass riparian buffer; (ii) a willow riparian buffer, and; (iii) a woodland riparian buffer. These buffered treatments were compared with a no-buffer control. The woodland (322.9 ± 3.1 kg ha− 1) and grass (285 ± 2.7 kg ha− 1) riparian buffer treatments (not significant to each other) generated significantly (p = < 0.0001) the largest CO2 compared to the remainder of the treatments. Our results suggest that during maize production in general, the woodland and grass riparian buffers serving a maize crop pose a CO2 threat. The results of the current study point to the need to consider the benefits for gaseous emissions of mitigation measures conventionally implemented for improving the sustainability of water resources.

Riparian buffer strips can have a significant role in reducing nitrogen (N) transfers from agricultural land to freshwater primarily via denitrification and plant uptake processes, but an unintended trade-off can be elevated nitrous oxide (N2O) production rates. Against this context, our replicated bounded plot scale study investigated N2O emissions from un-grazed ryegrass pasture served by three types of riparian buffer strips with different vegetation, comprising: (i) grass riparian buffer with novel deep-rooting species, (ii) willow (young trees at establishment phase) riparian buffer, and (iii) deciduous woodland (also young trees at establishment phase) riparian buffer. The experimental control was ryegrass pasture with no buffer strip. N2O emissions were measured at the same time as total oxidized N in run-off, and soil and environmental characteristics in the riparian buffer strips and upslope pasture between 2018 and 2019. During most of the sampling days, the no-buffer control treatment showed significantly (P < 0.05) greater N2O fluxes and cumulative N2O emissions compared to the remainder of the treatments. Our results also showed that the grass riparian buffer strip is a sink of N2O equivalent to - 2310.2 g N2O-N ha(-1) day(-1) (95% confidence interval:-535.5 to 492). Event-based water quality results obtained during storms (12 November 2018 and 11 February 2019) showed that the willow riparian buffer treatment had the highest flow-weighted mean N concentrations (N-FWMC) of 0.041 +/- 0.022 and 0.031 +/- 0.015 mg N L-1, when compared to the other treatments. Our 9-month experiment therefore, shows that riparian buffer strips with novel deep-rooting grass can therefore potentially address emissions to both water and air. The results imply that over a shorter timeline similar to the current study, the grass riparian buffer strip can potentially address N emission to both air and water, particularly when serving a permanent pasture in similar settings as the current experiment.

Methane (CH4) has a global warming potential (GWP) 28-times that of carbon dioxide (CO2) over a 100-year horizon. Riparian buffers strips are widely implemented for their water quality protection functions along agricultural land, but conditions prevailing within them may increase the emissions of greenhouse gases (GHGs), including CH4. However, only small amount of information is available regarding the dynamics of unintended emissions of soil CH4 in these commonplace features of agroecosystems and how the dynamics compare to those for agricultural land not containing buffer strips. To understand the dynamics of soil CH4 fluxes from a permanent upslope pasture and contiguous riparian buffer strips with different (grass, willow, and woodland) vegetation as well as controls with no buffer vegetation, field measurements were carried out using the static chamber technique on a replicated plot-scale facility. Gas fluxes were measured periodically with soil and environmental variables between June 2018 and February 2019 at Rothamsted Research, North Wyke, United Kingdom. Soils under all treatments were sinks of soil CH4 with the willow riparian buffer (-2555 ± 318.7 g CH4 ha-1) having the lowest soil CH4 flux followed by the grass riparian buffer (-2532 ± 318.7 g CH4 ha-1), woodland riparian buffer (-2318.0 ± 246.4 g CH4 ha-1), no-buffer control (-1938.0 ± 374.4 g CH4 ha-1), and lastly, the upslope pasture (-1328.0 ± 89.0 g CH4 ha-1) which had a higher flux. The three vegetated riparian buffers were more substantial soil CH4 sinks, suggesting that they may help reduce soil CH4 fluxes into the atmosphere in similar agroecosystems.

Nitrous oxide (N2O) and methane (CH4) are some of the most important greenhouse gases in the atmosphere of the 21st century. Vegetated riparian buffers are primarily implemented for their water quality functions in agroecosystems. Their location in agricultural landscapes allows them to intercept and process pollutants from adjacent agricultural land. They recycle organic matter, which increases soil carbon (C), intercept nitrogen (N)-rich runoff from adjacent croplands, and are seasonally anoxic. Thus processes producing environmentally harmful gases including N2O and CH4 are promoted. Against this context, the study quantified atmospheric losses between a cropland and vegetated riparian buffers that serve it. Environmental variables and simultaneous N2O and CH4 emissions were measured for a 6-month period in a replicated plot-scale facility comprising maize (Zea mays L.). A static chamber was used to measure gas emissions. The cropping was served by three vegetated riparian buffers, namely: (i) grass riparian buffer; (ii) willow riparian buffer and; (iii) woodland riparian buffer, which were compared with a no-buffer control. The no-buffer control generated the largest cumulative N2O emissions of 18.9 kg ha− 1 (95% confidence interval: 0.5–63.6) whilst the maize crop upslope generated the largest cumulative CH4 emissions (5.1 ± 0.88 kg ha− 1). Soil N2O and CH4-based global warming potential (GWP) were lower in the willow (1223.5 ± 362.0 and 134.7 ± 74.0 kg CO2-eq. ha− 1 year− 1, respectively) and woodland (1771.3 ± 800.5 and 3.4 ± 35.9 kg CO2-eq. ha− 1 year− 1, respectively) riparian buffers. Our results suggest that in maize production and where no riparian buffer vegetation is introduced for water quality purposes (no buffer control), atmospheric CH4 and N2O concerns may result.

Organic carbon (C) plays an essential role in the denitrification process as it supplies energy for N2O, N(2)and CO(2)producing reactions. The objectives of this study were to: (i) rank the reactivity of different C compounds found in manures based on their availability for denitrification and (ii) explore C-quality in different C sources based on their capacity to promote denitrification. Evaluation of different C-sources in promoting denitrification was conducted based on the molar ratio of CO(2)production to NO(3)(-)reduction after incubation. Results of the first experiment (a 12-day investigation) showed that glucose and glucosamine were highly reactive C compounds with all applied NO(3)(-)being exhausted by day 3, and glucosamine had significantly high amount of NH4+-N present at end of the experiment. The glucose and glucosamine treatments resulted in significantly greater cumulative CO(2)production, compared to the other treatments. In the second experiment (a 9-day investigation), all NO(3)(-)had been depleted by day 6 and 9 from acetic acid and glucose, respectively, and the greatest cumulative CO(2)production was from acetic acid. The CO(2)appearance to NO(3)(-)molar ratios revealed that glucose and glucosamine were compounds with highly available C in the first experiment. In the second experiment, the pig slurry and acetic acid were found to be C-sources that promoted potential denitrification. The application of slurry to soil results in the promotion of denitrification and this depends on the availability of the C compounds it contains. Understanding the relationship between C availability and denitrification potential is useful for developing denitrification mitigation strategies for organic soil amendments.