Effect of the application of cattle urine with or without the nitrification inhibitor DCD, and dung on greenhouse gas emissions from a UK grassland soil

Divergent responses of the native grassland soil microbiome to heavy grazing between spring and fall

Grasslands are estimated to cover about 40% of the earth's land area and are primarily used for grazing. Despite their importance globally, there is a paucity of information on long-term grazing effects on the soil microbiome. We used a 68-year-old grazing experiment to determine differences in the soil permanganate-oxidizable C (POXC), microbial biomass C (MBC), the soil prokaryotic (bacterial and archaeal) community composition and enzyme activities between no-grazing, light grazing and heavy grazing, i.e. 0, 1.2 and 2.4 animal unit months (AUM) ha-1. The grazing effects were determined in spring and fall grazing. Light grazing had little effect on soil MBC and the composition and diversity of prokaryotic communities in either grazing season, but the effects of heavy grazing depended on the grazing season. In spring, heavy grazing increased the relative abundances of copiotrophic phyla Actinomycetota, Bacillota and Nitrososphaerota, along with soil POXC contents but decreased those of oligotrophic phyla Acidobacteriota, Verrucomicrobiota and Nitrospirota. This difference in responses was not observed in fall, when grazing reduced soil POXC, MBC and the relative abundances of most phyla. The β-diversity analysis showed that the prokaryotic community structure under heavy grazing was different from those in the control and light grazing treatments, and α-diversity indices (except the Shannon index) were highest under heavy grazing in both grazing seasons. The activities of P-mobilizing and S-mobilizing soil enzymes decreased with increasing cattle stocking rate in both seasons, but the activities of the enzymes that mediate C and N cycling decreased only in the fall. The genus RB41 (phylum Acidobacteriota) was one of two core bacterial genera, and its relative abundance was positively correlated with the activity of the S-mobilizing enzyme. Therefore, light grazing is recommended to reduce negative effects on the grassland soil microbiome and its activity, and the grazing season should be considered when evaluating such grazing effects.

N2O emission factors for cattle urine: effect of patch characteristics and environmental drivers

Urine patches from grazing cattle are hotspots of nitrous oxide (N2O) emissions. The default IPCC emission factor for urine patches (EFurine) is 0.77% for wet climates and 0.32% for dry climates. However, literature reports a considerable range of cattle urine EF values and urine characteristics used in experimental studies, revealing contrary results on the effects of urine patch characteristics and seasonal pattern. Therefore, we examined N2O emissions and corresponding EFurine values in relation to urine patch characteristics (urine N concentration, urine volume, patch area, urine composition) and environmental drivers (precipitation, water filled pore space, soil temperature). Ten artificial urine application experiments were performed from July 2020 to June 2022 on a pasture located in Eastern Switzerland. Urine N concentration, patch area, volume and urine N composition showed no significant effects on the EFurine value (p > 0.05). EFurine varied, however, strongly over time (0.17-2.05%). A large part of the variation could be predicted either by cumulative precipitation 20 days after urine application using a second order polynomial model (Adj. R2 = 0.60) or average WFPS 30 days after urine application using a linear model (Adj. R2 = 0.45). The derived precipitation model was used to simulate EFurine weekly over the last 20 years showing no significant differences between the seasons of a year. The resulting overall average EFurine was 0.67%. More field studies are needed across sites/regions differing in climate and soil properties to implement a country-specific EF3 for Switzerland and to improve the quantification of N2O emissions at the national scales.

Effects of grazing and nitrogen application on greenhouse gas emissions in alpine meadow

Overgrazing and injudicious nitrogen applications have increased emissions of greenhouse gases from grassland ecosystems. To explore the effects and potential mechanisms of grazing, nitrogen application, and their interaction with greenhouse gas (GHG) emissions, field experiments were conducted on the Qinghai-Tibet Plateau for three consecutive years. Alpine meadow plots were subjected to light (8 sheep ha^-1) and heavy (16 sheep ha^-1) stocking rates, with or without ammonium nitrate (NH₄NO₃) (90 kg N ha^-1 yr^-1) treatment to simulate soil nitrogen deposition. During early warm growth season (May-June), peak growth season (July-September), and early cold season (October-November), static-chamber gas chromatography was used to analyze the soil's greenhouse gas emissions (CO₂, N₂O, and CH₄). Results indicated that light stocking rate (LG) led to an increase in cumulative CO₂ and N₂O emissions, while also promoting CH₄ uptake. Conversely, heavy stocking rate (HG) produced contrasting outcomes. Additionally, nitrogen applications significantly increased the short-term CO₂ and N₂O fluxes peaks. Combined treatment of nitrogen application and light stocking rate (LG + N) resulted in increased CO₂ and N₂O emissions while decreased CH₄ uptake, consequently leading to a significant increase in global warming potential. According to the structural equation model, we discovered that nitrogen application and grazing affected GHG fluxes both directly and indirectly through their impact on the environmental factors. Our findings suggest that in the context of increasing nitrogen deposition in the Qinghai-Tibet Plateau, a moderate increase in stocking rate is more effective than reducing grazing intensity for mitigating global warming potential in alpine meadow.

Response of soil health indicators to dung, urine and mineral fertilizer application in temperate pastures

Healthy soils are key to sustainability and food security. In temperate grasslands, not many studies have focused on soil health comparisons between contrasting pasture systems under different management strategies and treatment applications (e.g. manures and inorganic fertilisers). The aim of this study was to assess the responses of soil health indicators to dung, urine and inorganic N fertiliser in three temperate swards: permanent pasture not ploughed for at least 20 years (PP), high sugar ryegrass with white clover targeted at 30% coverage reseeded in 2013 (WC), and high sugar ryegrass reseeded in 2014 (HG). This study was conducted on the North Wyke Farm Platform (UK) from April 2017 to October 2017. Soil health indicators including soil organic carbon (SOC, measured by loss of ignition and elemental analyser), dissolved organic carbon (DOC), total nitrogen (TN), C:N ratio, soil C and N bulk isotopes, pH, bulk density (BD), aggregate stability, ergosterol concentration (as a proxy for fungi biomass), and earthworms (abundance, mass and density) were measured and analysed before and after application of dung and N fertilizer, urine and N fertiliser, and only N fertiliser. The highest SOC, TN, DOC, ergosterol concentration and earthworms as well as the lowest BD were found in PP, likely due to the lack of ploughing. Differences among treatments were observed due to the application of dung, resulting in an improvement in chemical indicators of soil health after 50 days of its application. Ergosterol concentration was significantly higher before treatment applications than at the end of the experiment. No changes were detected in BD and aggregate stability after treatment applications. We conclude that not enough time had passed for the soil to recover after the ploughing and reseeding of the permanent pasture, independently of the sward composition (HG or WC). Our results highlight the strong influence of the soil management legacy in temperate pasture and the positive effects of dung application on soil health over the short term. In addition, we point out the relevance of using standardised methods to report soil health indicators and some methodological limitations.

Revisiting sampling duration to estimate N2O emission factors for manure application and cattle excreta deposition for the UK and Ireland

According to the available guidelines, good practices for calculating nitrous oxide (N₂O) emission factors (EFs) for livestock excreta and manure application include that sampling duration should be of at least one year after the nitrogen (N) application or deposition. However, the available experimental data suggest that in many cases most emissions are concentrated in the first months following N application. Therefore resources could be better deployed by measuring more intensively during a shorter period. This study aimed to assess the contribution of the N₂O flux in the period directly after N application to the annual net emission. We used a database of 100 year-long plot experiments from different excreted-N sources (dung, urine, farmyard manure and slurry) used to derive EFs for the UK and Ireland. We explored different shorter potential measurement periods that could be used as proxies for cumulative annual emissions. The analysis showed that the majority of emissions occur in the first months after application, especially in experiments that i) had urine as the N source, ii) had spring N application, iii) were conducted on fine-textured soils, or iv) showed high annual emissions magnitude. Experiments that showed a smaller percentage of emissions in the first months also had a low magnitude of annual net emissions (below 370 gN₂O-N ha^-1 year^-1), so the impact of measuring during a shorter period would not greatly influence the calculated EF. Accurate EF estimations were obtained by measuring for at least 60 days for urine (underestimation: 7.1%), 120 days for dung and slurry (4.7 and 5.1%) and 180 days for FYM (1.4%). At least in temperate climates, these results are promising in terms of being able to estimate annual N₂O fluxes accurately by collecting data for less than 12 months, with significant resource-saving when conducting experiments towards developing country-specific EFs.

CO2 fluxes from three different temperate grazed pastures using Eddy covariance measurements

Grasslands cover around 25% of the global ice-free land surface, they are used predominantly for forage and livestock production and are considered to contribute significantly to soil carbon (C) sequestration. Recent investigations into using 'nature-based solutions' to limit warming to <2 °C suggest up to 25% of GHG mitigation might be achieved through changes to grassland management. In this study we evaluate pasture management interventions at the Rothamsted Research North Wyke Farm Platform, under commercial farming conditions, over two years and consider their impacts on net CO₂ exchange. We investigate if our permanent pasture system (PP) is, in the short-term, a net sink for CO₂ and whether reseeding this with deep-rooting, high-sugar grass (HS) or a mix of high-sugar grass and clover (HSC) might increase the net removal of atmospheric CO₂. In general CO₂ fluxes were less variable in 2018 than in 2017 while overall we found that net CO₂ fluxes for the PP treatment changed from a sink in 2017 (-5.40 t CO₂ ha^-1 y^-1) to a source in 2018 (6.17 t CO₂ ha^-1 y^-1), resulting in an overall small source of 0.76 t CO₂ ha^-1 over the two years for this treatment. HS showed a similar trend, changing from a net sink in 2017 (-4.82 t CO₂ ha^-1 y^-1) to a net source in 2018 (3.91 t CO₂ ha^-1 y^-1) whilst the HSC field was a net source in both years (3.92 and 4.10 t CO₂ ha^-1 y^-1, respectively). These results suggested that pasture type has an influence in the atmospheric CO₂ balance and our regression modelling supported this conclusion, with pasture type and time of the year (and their interaction) being significant factors in predicting fluxes.

Transfer of Nitrogen and Phosphorus From Cattle Manure to Soil and Oats Under Simulative Cattle Manure Deposition

Simulated cattle manure deposition was used to estimate nutrient transfer to soil and oats and to investigate changes in microbial community composition and functional groups in oat rhizospheres. Nutrient absorption and return efficiency were calculated as a series of standard calculation formulas, and total nutrient transfer efficiency was nutrient absorption efficiency plus nutrient return efficiency. In total, 74.83% of nitrogen (N) and 59.30% of phosphorus (P) in cattle manure were transferred to soil and oats, with 11.79% of N and 7.89% of P in cattle manure absorbed by oats, and the remainder sequestered in the soil for 80 days after sowing. Cattle manure increased oat root length, surface, and volume under 0.2 mm diameter, and improved relative abundance of the microbiome known to be beneficial. In response to cattle manure, several bacteria known to be beneficial, such as Proteobacteria, Bacteroidota, and Firmicutes at phyla the level and Pseudoxanthomonas, Pseudomonas, and Sphingomonas at the genus level, were positively related to oat biomass and nutrient accumulation. For fungal communities, the relative abundance of Ascomycota is the predominant phylum, which varied in a larger range in the control treatment (81.0–63.3%) than the cattle manure deposition treatment (37.0–42.9%) as plant growing days extend. The relevant abundance of Basidiomycota known as decomposer was higher in cattle manure deposition treatment compared to that in control treatment at 15 days after sowing. More importantly, cattle manure deposition inhibited trophic mode within pathotroph like Alternaria and Fusarium fungal genus and promoted saprotroph and symbiotroph.

Reactive nitrogen releases and nitrogen footprint during intensive vegetable production affected by partial human manure substitution

Evaluating the sustainability of vegetable production is crucial to secure future food supply. A 2-year field study of four different vegetable crops was performed to investigate the effects of inorganic fertilizer and human manure at different ratios on vegetable yields, reactive gaseous nitrogen emissions (GNrEs), reactive nitrogen (Nr) footprint, and net ecosystem economic income (NEEI) by using life cycle analysis. Four fertilization strategies were studied, including CK (no fertilization); CF (inorganic fertilization); CHF1 (human manure /inorganic fertilizer, N ratio = 1:7); and CHF2 (human manure /inorganic fertilizer, N ratio = 1:3). Results showed that compared with CF treatment, both CHF1 and CHF2 treatments increased the N₂O + NO emissions by 11.8% and 32.4% on average, while decreased the vegetable yields by 6.7% and 7.4%, respectively. Moreover, the addition of human manure increased the proportions of Nr footprint by 6.6% (CHF1) and 2.9% (CHF2) in comparison with CF treatment. However, although CHF2 treatment significantly increased the values of GNrEs and reactive gaseous nitrogen intensity (GNrI) by 8.4% and 12.5%, respectively, in relation to those in CF treatment, it still increased farmers' income by 16,404 CNY ha^-1. These findings suggest that although human manure incorporation could not mitigate Nr releases, the appropriate ratio of inorganic fertilizer and human manure (CHF2) is able to improve net economic income (NEI) and NEEI during intensive vegetable production. Nevertheless, it should be further explored about the relationship between combinatorial treatment of inorganic fertilizer and human manure on Nr release mitigation in intensive vegetable production.

Cattle wastewater as a low-cost supplement augmenting microalgal biomass under batch and fed-batch conditions

The utilization of costly chemical fertilizers and large freshwater requirements make the microalgae cultivation process uneconomical and highly unsustainable. To address this challenge, the present study aimed to integrate cattle wastewater (CW) (alternate for fertilizers) with domestic sewage wastewater (DSW) (substitute for freshwater) to cultivate Chlorella thermophile. To maximize the biomass yield, in-depth nutrient consumption patterns in both batch and fed-batch cultivation conditions were analyzed. Out of the eight (1%-4.5%) different CW feed concentrations tested during the batch cultivation, 2.5% CW set gave the highest biomass yield (2.17 g L^-1), which was almost double the yield obtained using Bold Basal Medium (1.24 g L^-1) and DSW without any CW addition (1.22 g L^-1). However, the biomass yield declined with CW> 2.5%, and the ammonium (NH₄⁺) inhibitory effect was observed. To address the (NH₄⁺) toxicity challenge and further enhance the biomass yield, fed-batch experiments were designed with an intermittent CW feeding based on nutrient (NH₄⁺) consumption pattern. The fed-batch cultivation resulted in twofold increased biomass yield (4.52 g L^-1) in comparison to the batch process. The nutrient consumption pattern inferred that the (NH₄⁺) concentration greater than 600 mg L^-1 during the logarithmic phase was inhibitory for Chlorella thermophila cells. On biomass characterization, a significant improvement in protein content with CW addition was observed. The FAME analysis of the derived lipid stated its competitive biofuel quality with up-gradation of C:16 and C:18 groups. Based on the obtained results, projection analysis for an integrated rural model demonstrated the technology's potential for sustainable water management with valuable resource recovery.

Greenhouse gas emissions from cattle dung depositions in two Urochloa forage fields with contrasting biological nitrification inhibition (BNI) capacity

Grazing-based production systems are a source of soil greenhouse gas (GHG) emissions triggered by excreta depositions. The adoption of Urochloa forages (formerly known as Brachiaria) with biological nitrification inhibition (BNI) capacity is a promising alternative to reduce nitrous oxide (N₂O) emissions from excreta patches. However, how this forage affects methane (CH₄) or carbon dioxide (CO₂) emissions from excreta patches remains unclear. This study investigated the potential effect of soils under two Urochloa forages with contrasting BNI capacity on GHG emissions from cattle dung deposits. Additionally, the N₂O and CH₄ emission factors (EF) for cattle dung under tropical conditions were determined. Dung from cattle grazing star grass (without BNI) was deposited on both forage plots: Urochloa hybrid cv. Mulato and Urochloa humidicola cv. Tully, with a respectively low and high BNI capacity. Two trials were conducted for GHG monitoring using the static chamber technique. Soil and dung properties and GHG emissions were monitored in trial 1. In trial 2, water was added to simulate rainfall and evaluate GHG emissions under wetter conditions. Our results showed that beneath dung patches, the forage genotype influenced daily CO₂ and cumulative CH₄ emissions during the driest conditions. However, no significant effect of the forage genotype was found on mitigating N₂O emissions from dung. We attribute the absence of a significant BNI effect on N₂O emissions to the limited incorporation of dung-N into the soil and rhizosphere where the BNI effect occurs. The average N₂O EFs was 0.14%, close to the IPCC 2019 uncertainty range (0.01-0.13% at 95% confidence level). Moreover, CH₄ EFs per unit of volatile solid (VS) averaged 0.31 g CH₄ kgVS^-1, slightly lower than the 0.6 g CH₄ kgVS^-1 developed by the IPCC. This implies the need to invest in studies to develop more region-specific Tier 2 EFs, including farm-level studies with animals consuming Urochloa forages to consider the complete implications of forage selection on animal excreta based GHG emissions.

Soil N2O and CH4 emissions from fodder maize production with and without riparian buffer strips of differing vegetation

PURPOSE

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.

METHODS

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.

RESULTS

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.

CONCLUSIONS

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.

Management and implications of using nitrification inhibitors to reduce nitrous oxide emissions from urine patches on grazed pasture soils - A review

Livestock urine patches are the main source of nitrous oxide (N₂O) emissions in pastoral system, and nitrification inhibitors (NIs) have been widely investigated as a N₂O mitigation strategy. This study reviews the current understanding of the effect of NIs use on N₂O emissions from urine patches, including the factors that affect their efficacy, as well as the unintended consequences of NIs use. It brings together the fundamental aspects of targeted management of urine patches for reducing N₂O emissions involving inhibitors. The available literature of 196 datasets indicates that dicyandiamide (DCD), 3,4-dimethylpyrazole phosphate (DMPP), and 2-chloro-6-(trichloromethyl) pyridine (nitrapyrin) reduced N₂O emissions from urine patches by 44 ± 2%, 28 ± 38% and 28 ± 5%, (average ± s.e.), respectively. DCD also increased pasture dry matter and nitrogen (N) uptake by 13 ± 2% and 15 ± 3%, (average ± s.e.), respectively. The effect of DMPP and nitrapyrin on pasture dry matter and N uptake, assessed in only one study, was not significant. It also suggests that harmonizing the timing of inhibitor use with urine-N transformation increase the efficacy of NIs. No negative impacts on non-targeted soil and aquatic organisms have been reported with the recommended rate of DCD applied to urine and recommended applications of DMPP and nitrapyrin for treated mineral fertilisers and manures. However, there was evidence of the presence of small amounts of DCD residues in milk products as a result of its use on livestock grazed pasture. DMPP and nitrapyrin can also enter the food chain via grazing livestock. The study concludes that for the use of NIs in livestock grazed systems, research is needed to establish acceptable maximum residue level (MRL) of NIs in soil, plant, and animal products, and develop technologies that optimise physical mixing between NIs and urine patches.

Nitrous oxide emissions from cow urine patches in an intensively managed grassland: Influence of nitrogen loading under contrasting soil moisture

In dairy grazing systems, livestock urine patches are hotspots that contribute to global warming, both directly through nitrous oxide (N₂O) emissions, and indirectly, through nitrate leaching. However, under warm-dry temperate environments, N₂O emission factors (EFs) have not been thoroughly evaluated, accounting for the influence of urinary nitrogen (N) concentration and urine volume, and emissions measurement approach through different urine application methods. Here we quantified and compared N₂O emissions and EFs on a moderately well-drained sandy loam soil from urine patches established in naturally expanding effective area (NEEA), representing urine volumes of 2, 3 and 4 L m^-2 (equivalent to urine -N loadings of 141, 211 and 282 kg N ha^-1), and using the uniformly wetted area (UWA) with urine applied at 10 L m^-2 (709 kg N ha^-1), under two different soil moistures (below field capacity, BFC; field capacity, FC). The results showed that cumulative N₂O emissions in the NEEA urine patches were 0.36-0.52 kg N₂O-N ha^-1 over 146 days (early-winter to late-spring). In the UWA urine patches, cumulative N₂O emissions were 2.3 times higher at FC (1.96 kg N₂O-N ha^-1) than BFC (0.87 kg N₂O-N ha^-1). The EFs were similar between UWA (0.09%) and NEEA (0.07-0.10%) at BFC but were significantly higher (P < 0.05-0.1) in UWA (0.26%) than NEEA (0.09-0.16%) at FC. The EFs in NEEA were not affected by urine-N loadings under BFC and FC, ranging between 0.07 and 0.16%. The relatively high versus low urine-N loadings in NEEA enhanced pasture herbage and N-uptake responses under both soil moistures. However, there were no differences in apparent N-use efficiency (ranging from 27 to 39%) across the treatments. The EFs observed in this study are much lower than the existing Australian cattle urine annual EF of 0.4%, and further examination to determine a more accurate EF for the industry is required.

Elucidating three-way interactions between soil, pasture and animals that regulate nitrous oxide emissions from temperate grazing systems

Pasture-based livestock farming contributes considerably to global emissions of nitrous oxide (N2O), a powerful greenhouse gas approximately 265 times more potent than carbon dioxide. Traditionally, the estimation of N2O emissions from grasslands is carried out by means of plot-scale experiments, where externally sourced animal excreta are applied to soils to simulate grazing conditions. This approach, however, fails to account for the impact of different sward types on the composition of excreta and thus the functionality of soil microbiomes, creating unrealistic situations that are seldom observed under commercial agriculture. Using three farming systems under contrasting pasture management strategies at the North Wyke Farm Platform, an instrumented ruminant grazing trial in Devon, UK, this study measured N2O emissions from soils treated with cattle urine and dung collected within each system as well as standard synthetic urine shared across all systems, and compared these values against those from two forms of controls with and without inorganic nitrogen fertiliser applications. Soil microbial activity was regularly monitored through gene abundance to evaluate interactions between sward types, soil amendments, soil microbiomes and, ultimately, N2O production. Across all systems, N2O emissions attributable to cattle urine and standard synthetic urine were found to be inconsistent with one another due to discrepancy in nitrogen content. Despite previous findings that grasses with elevated levels of water-soluble carbohydrates tend to generate lower levels of N2O, the soil under high sugar grass monoculture in this study recorded higher emissions when receiving excreta from cattle fed the same grass. Combined together, our results demonstrate the importance of evaluating environmental impacts of agriculture at a system scale, so that the feedback mechanisms linking soil, pasture, animals and microbiomes are appropriately considered.

Does Brachiaria humidicola and dicyandiamide reduce nitrous oxide and ammonia emissions from cattle urine patches in the subtropics?

Nitrous oxide (N₂O) emissions from pasture-based livestock systems represent 34% of Brazil's agricultural greenhouse gas emissions. The forage species Brachiaria humidicola is known for its biological nitrification inhibition (BNI) capacity and N₂O emissions reduction ability from urine patches under tropical conditions. However, there is little information about the effect of BNI on N₂O emission and ammonia (NH₃) volatilisation in the subtropics. This study aimed to: (i) evaluate the potential of Brachiaria humidicola, compared with Panicum maximum (Jacq. cv. Áries; guinea grass), a broadly used grass (with no BNI capacity), to reduce N₂O emissions under subtropical conditions; (ii) determine the efficacy of nitrification inhibitor dicyandiamide (DCD) to decrease N₂O emissions; and (iii) determine the effect of brachiaria and DCD application on NH₃ volatilisation. A field experiment was carried out using a Cambisol, where cattle urine ± DCD was applied to brachiaria and guinea grass. Over the 67-day measurement period, cumulative N₂O emissions were 20% lower from urine patches in the brachiaria treatment (1138 mg N m^-2, Emission factor = 1.06%) compared to guinea grass (1436 mg N m^-2, Emission factor = 1.33%) (P < .10). A greenhouse experiment, using pots with the same treatments as in the field experiment, suggested that this could have been due to lower soil nitrate levels under brachiaria forage compared to guinea grass, indicating that BNI could be a possible mechanism for lower N₂O emissions from brachiaria. The DCD application was effective in both forage species, decreasing N₂O emissions by 40-50% (P < .10) compared with the urine only treatment. Approximately 25% of the urine applied N was lost via NH₃ volatilisation, however the NH₃ loss was not affected by forage species or DCD application (P > .10). Overall, the results demonstrated that brachiaria and DCD use are strategies that can reduce N₂O emissions from urine patches.

Meta-analysis of global livestock urine-derived nitrous oxide emissions from agricultural soils

Nitrous oxide (N2 O) is an air pollutant of major environmental concern, with agriculture representing 60% of anthropogenic global N2 O emissions. Much of the N2 O emissions from livestock production systems result from transformation of N deposited to soil within animal excreta. There exists a substantial body of literature on urine patch N2 O dynamics, we aimed to identify key controlling factors influencing N2 O emissions and to aid understanding of knowledge gaps to improve GHG reporting and prioritize future research. We conducted an extensive literature review and random effect meta-analysis (using REML) of results to identify key relationships between multiple potential independent factors and global N2 O emissions factors (EFs) from urine patches. Mean air temperature, soil pH and ruminant animal species (sheep or cow) were significant factors influencing the EFs reviewed. However, several factors that are known to influence N2 O emissions, such as animal diet and urine composition, could not be considered due to the lack of reported data. The review highlighted a widespread tendency for inadequate metadata and uncertainty reporting in the published studies, as well as the limited geographical extent of investigations, which are more often conducted in temperate regions thus far. Therefore, here we give recommendations for factors that are likely to affect the EFs and should be included in all future studies, these include the following: soil pH and texture; experimental set-up; direct measurement of soil moisture and temperature during the study period; amount and composition of urine applied; animal type and diet; N2 O emissions with a measure of uncertainty; data from a control with zero-N application and meteorological data.

Nitrification represents the bottle-neck of sheep urine patch N2O emissions from extensively grazed organic soils

Extensively grazed grasslands are understudied in terms of their contribution to greenhouse gas (GHG) emissions from livestock production. Mountains, moorlands and heath occupy 18% of the UK land area, however, in situ studies providing high frequency N₂O emissions from sheep urine deposited to such areas are lacking. Organic soils typical of these regions may provide substrates for denitrification-related N₂O emissions, however, acidic and anoxic conditions may inhibit nitrification (and associated emissions from nitrification and denitrification). We hypothesised urine N₂O-N emission factors (EFs) would be lower than the UK country-specific and IPCC default value for urine, which is based on lowland measurements. Using automated GHG sampling chambers, N₂O emissions were determined from real sheep urine (930 kg N ha^-1) and artificial urine (920 kg N ha^-1) applied in summer, and from an artificial urine treatment (1120 kg N ha^-1) and a combined NO₃^- and glucose treatment (106 kg N ha^-1; 213 kg C ha^-1) in autumn. The latter treatment provided an assessment of the soils capacity for denitrification under non-substrate limiting conditions. The artificial urine-N₂O EF was 0.01 ± 0.00% of the N applied in summer and 0.00 ± 0.00% of the N applied in autumn. The N₂O EF for real sheep urine applied in summer was 0.01 ± 0.02%. A higher flux was observed in only one replicate of the real urine treatment, relating to one chamber where an increase in soil solution NO₃^- was observed. No lag phase in N₂O emission was evident following application of the NO₃^- and glucose treatment, which emitted 0.69 ± 0.15% of the N applied. This indicates nitrification rates are the bottle-neck for N₂O emissions in upland organic soils. We calculated the potential impact of using hill-grazing specific urine N₂O EFs on the UK inventory of N₂O emissions from sheep excreta, and found a reduction of ca. 43% in comparison to the use of a country-specific excretal EF.

The efficacy of Plantago lanceolata for mitigating nitrous oxide emissions from cattle urine patches

Urine deposited by grazing animals is the main source of nitrous oxide (N₂O) emissions in New Zealand. Recent studies have suggested that certain pasture plants, for example plantain (Plantago lanceolata), can curb N₂O emissions from livestock systems. This study aimed to i) evaluate the potential of plantain for reducing N₂O emissions from cattle urine patches; ii) determine the effect of including plantain in animal diets on urine-N loading and its influence on N₂O emissions; and, iii) evaluate whether any effects on N₂O emissions reduction could be attributed to a 'urine' or a 'plant' effect. A static chamber method was used to measure N₂O fluxes from urine collected from cows fed a 0, 15, 30 or 45% plantain mixed with "standard" ryegrass/clover (Lolium perenne/Trifolium repens) diet and applied to plots with the corresponding percentage of plantain in the sward. In addition, we measured N₂O emissions from different proportions of plantain in the sward (0, 30, 60 and 100%) that received urine collected from cows fed on ryegrass/clover. The urine N loading rates of animals fed plantain, significantly reduced with increasing proportions of plantain in the diet (r² = 0.987, P < 0.01). There was a trend of lower N₂O emissions with an increasing proportion of plantain in the diet (r² = 0.830, P < 0.08). However, there was no significantly difference in the N₂O emission factors (P > 0.10). Following applications of standard urine, total N₂O emissions and emission factor reduced linearly as the proportion of plantain in the sward increased (r² = 0.969, P < 0.05 and 0.974, P < 0.05, respectively). The results suggest that the efficacy of plantain as a N₂O mitigation option is due to both a reduction in urinary N excretion and a plant effect. The latter could be due to biological nitrification inhibition (BNI) caused by the release of root exudates and/or changes in the soil microclimate.

Nitrogen use efficiency and nitrous oxide emissions from five UK fertilised grasslands

Intensification of grasslands is necessary to meet the increasing demand of livestock products. The application of nitrogen (N) on grasslands affects the N balance therefore the nitrogen use efficiency (NUE). Emissions of nitrous oxide (N₂O) are produced due to N fertilisation and low NUE. These emissions depend on the type and rates of N applied. In this study we have compiled data from 5 UK N fertilised grassland sites (Crichton, Drayton, North Wyke, Hillsborough and Pwllpeiran) covering a range of soil types and climates. The experiments evaluated the effect of increasing rates of inorganic N fertiliser provided as ammonium nitrate (AN) or calcium ammonium nitrate (CAN). The following fertiliser strategies were also explored for a rate of 320 kg N ha^-1: using the nitrification inhibitor dicyandiamide (DCD), changing to urea as an N source and splitting fertiliser applications. We measured N₂O emissions for a full year in each experiment, as well as soil mineral N, climate data, pasture yield and N offtake. N₂O emissions were greater at Crichton and North Wyke whereas Drayton, Hillsborough and Pwllpeiran had the smallest emissions. The resulting average emission factor (EF) of 1.12% total N applied showed a range of values for all the sites between 0.6 and 2.08%. NUE depended on the site and for an application rate of 320 kg N ha^-1, N surplus was on average higher than 80 kg N ha^-1, which is proposed as a maximum by the EU Nitrogen Expert Panel. N₂O emissions tended to be lower when urea was applied instead of AN or CAN, and were particularly reduced when using urea with DCD. Finally, correlations between the factors studied showed that total N input was related to Nofftake and Nexcess; while cumulative emissions and EF were related to yield scaled emissions.

The contribution of cattle urine and dung to nitrous oxide emissions: Quantification of country specific emission factors and implications for national inventories

Urine patches and dung pats from grazing livestock create hotspots for production and emission of the greenhouse gas, nitrous oxide (N₂O), and represent a large proportion of total N₂O emissions in many national agricultural greenhouse gas inventories. As such, there is much interest in developing country specific N₂O emission factors (EFs) for excretal nitrogen (EF_3, pasture, range and paddock) deposited during gazing. The aims of this study were to generate separate N₂O emissions data for cattle derived urine and dung, to provide an evidence base for the generation of a country specific EF for the UK from this nitrogen source. The experiments were also designed to determine the effects of site and timing of application on emissions, and the efficacy of the nitrification inhibitor, dicyandiamide (DCD) on N₂O losses. This co-ordinated set of 15 plot-scale, year-long field experiments using static chambers was conducted at five grassland sites, typical of the soil and climatic zones of grazed grassland in the UK. We show that the average urine and dung N₂O EFs were 0.69% and 0.19%, respectively, resulting in a combined excretal N₂O EF (EF₃), of 0.49%, which is <25% of the IPCC default EF₃ for excretal returns from grazing cattle. Regression analysis suggests that urine N₂O EFs were controlled more by composition than was the case for dung, whilst dung N₂O EFs were more related to soil and environmental factors. The urine N₂O EF was significantly greater from the site in SW England, and significantly greater from the early grazing season urine application than later applications. Dycandiamide reduced the N₂O EF from urine patches by an average of 46%. The significantly lower excretal EF₃ than the IPCC default has implications for the UK's national inventory and for subsequent carbon footprinting of UK ruminant livestock products.

Feeding dicyandiamide (DCD) to cattle: An effective method to reduce N2O emissions from urine patches in a heavy-textured soil under temperate climatic conditions

Nitrate (NO₃^-) leaching and nitrous oxide (N₂O) emission from urine patches in grazed pastures are key sources of water and air pollution, respectively. Broadcast spraying of the nitrification inhibitor dicyandiamide (DCD) has been shown to reduce these losses, but it is expensive. As an alternative, it had been demonstrated that feeding DCD to cattle (after manual mixing with supplementary feeds) was a practical, effective and cheaper method to deliver high DCD rates within urine patches. This two-year study carried out on simulated urine patches in three application seasons (spring, summer, autumn) explored the efficacy of DCD feeding to cattle to reduce N losses from grazed pasture soil in a heavy-textured soil under temperate climatic conditions. In each application season, DCD fed to cows, then excreted with urine and applied at a rate of 30kgDCDha^-1 (treatment U+DCD³⁰-f) was as effective as powdered DCD mixed with normal urine and applied at the same rate (treatment U+DCD³⁰) at reducing cumulative N₂O-N emissions and the N₂O-N emission factor (EF3, expressed as % of N applied). Increasing DCD loading within urine patches from 10 to 30kgDCDha^-1 improved efficacy by significantly reducing the EF3 from 34% to 64%, which highlights that under local conditions, 10kgDCDha^-1 (the recommended rate for commercial use in New Zealand) was not the optimum DCD rate to curb N₂O emissions. The modelling of EF3 in this study also suggests that N mitigation should be given more attention when soil moisture is going to be high, which can be predicted with short-term weather forecasting. DCD feeding, for instance in autumn when cows are not lactating and the risk of N losses is high, could then be reduced by focusing mainly on those forecasted wet periods.

Using alternative forage species to reduce emissions of the greenhouse gas nitrous oxide from cattle urine deposited onto soil

Grazed pastures are a major contributor to emissions of the greenhouse gas nitrous oxide (N₂O), and urine deposition from grazing animals is the main source of the emissions. Incorporating alternative forages into grazing systems could be an approach for reducing N₂O emissions through mechanisms such as release of biological nitrification inhibitors from roots and increased root depth. Field plot and lysimeter (intact soil column) trials were conducted in a free draining Horotiu silt loam soil to test whether two alternative forage species, plantain (Plantago lanceolate L.) and lucerne (Medicago sativa L.), could reduce N₂O emissions relative to traditional pasture species, white clover (Trifolium repens L.) and perennial ryegrass (Lolium perenne L.). The amounts of N₂O emitted from the soil below each forage species, which all received the same cow urine at the same rates, was measured using an established static chamber method. Total N₂O emissions from the plantain, lucerne and perennial ryegrass controls (without urine application) were generally very low, but emissions from the white clover control were significantly higher. When urine was applied in autumn or winter N₂O emissions from plantain were lower compared with those from perennial ryegrass or white clover, but this difference was not found when urine was applied in summer. Lucerne had lower emissions in winter but not in other seasons. Incorporation of plantain into grazed pasture could be an approach to reduce N₂O emissions. However, further work is required to understand the mechanisms for the reduced emissions and the effects of environmental conditions in different seasons.

Nutrient Losses during Winter and Summer Storage of Separated and Unseparated Digested Cattle Slurry

Management factors affect nutrient loss during animal manure slurry storage in different ways. We conducted a pilot-scale study to evaluate carbon (C) and nitrogen (N) losses from unseparated and digested dairy slurry during winter and summer storage. In addition to season, treatments included mechanical separation of digestate into liquid and solid fractions and bimonthly mixing. Chemical analyses were performed every 2 wk for the mixed materials and at the start and end of storage for unmixed materials. The parameters examined allowed us to estimate C and N losses and examine the factors that determine these losses as well as emission patterns. Gas measurements were done every 2 wk to determine the main forms in which gaseous losses occurred. To evaluate the effect of separation, measured losses and emissions of separated liquid and solid fractions were mathematically combined using the mass separation efficiency of the mechanical separator. Nutrient losses were mainly affected by climatic conditions. Losses of C (up to 23%) from unseparated, unmixed digestate and of N (38% from combined separated fractions and from unseparated digestate) were much greater in summer than in winter, when C and N losses were <7%. Mixing tended to significantly increase N losses ( < 0.1) only in winter. Mechanical separation resulted in lower GHG emissions from combined separated fractions than from unseparated digestate. Results indicate that to maximize the fertilizer value of digested slurry, dairy farmers must carefully choose management practices, especially in summer. For separated digestates, practices should focus on storage of the liquid fraction, the major contributor of C and N losses (up to 64 and 90% of total losses, respectively) in summer. Moreover, management practices should limit NH, the main form of N losses (up to 99.5%).