Ruminant Urine Patches Research Articles

Gross N transformations vary with soil moisture and time following urea deposition to a pasture soil

Ruminant urine patches in grazed grasslands significantly change the chemical and biological properties of the affected soils due to the predominance of urea within ruminant urine and the high rates deposited onto pastures. The net result is the loss of reactive N (Nr) but little is known about the gross N transformation rates leading to Nr losses or the long-term fate of urine-N in pasture soils. Using data from a previous incubation study, that simulated ruminant urine application by applying 15N-urea, we investigated the effects of differing soil moisture regimes on gross soil N transformation rates, including urea hydrolysis and ammonia (NH3) formation. Gross transformation rates were quantified using a 15N tracing tool ‘NtraceBasic’ that was extended with a urea submodel. The new model (NtraceUrea) matched the measured data well (NH4+, NO3− concentrations and their respective 15N enrichments over time). Soil moisture affected urea hydrolysis dynamics and was postulated to regulate the magnitude of the NH3 dynamics due to constraints on gas diffusion under wetter (−1 kPa) soil conditions. Under drier soil conditions (−10 kPa) sorption and release of NH4+, the movement of NH4+ into and out of the soil labile N pool, the movement of NO3− into and out of the soil recalcitrant N pool, and the mineralisation of the recalcitrant N pool were all enhanced relative to −1 kPa, as were the gross N transformation rates in general due to the high urea N rate applied. This study shows that the time required for soils to re-establish equilibrium following urea deposition is substantial, and provides an explanation for the long-term 15N recoveries observed under ruminant urine patches in soils. The results highlight future research directions including the need to understand the potential role of NH3 in contributing to the recalcitrant N pool.

Sheep urination frequency, volume, N excretion and chemical composition: Implications for subsequent agricultural N losses

Ruminant urine patches are potential sites of reactive nitrogen (N) loss to the environment. Quantification of N losses from grazed grasslands requires measurement of the frequency of urine deposition, as well as its volume and chemical composition. However, studies to date are typically restricted to analyses of few replicate animals and urination events, especially for sheep. Here, we present data on urine frequency, volume, chemical composition (n = 193 events from n = 6 sheep) and metabolomic profile (n = 4–5 events from n = 4–5 sheep) from penned sheep. Differences in urine parameters and chemical composition data were compared seasonally and between two sites (improved and semi-improved pasture). Sheep urinated 8–11 times d−1, assuming time within pens represented a 24 h period. The mean urine event volume recorded was 289 ± 14 mL, from which we estimated a daily urine production value of 2.77 ± 0.15 L urine sheep−1 d−1. Daily urine N excretion and individual urine N concentrations were greater from sheep in improved pasture (26.7 ± 2.3 g N sheep−1 d−1; 7.0 ± 0.2 g N L−1) compared to those in semi-improved pasture (16.7 ± 1.2 g N sheep−1 d−1; 5.5 ± 0.4 g N L−1), but this did not equate to greater individual urine patch N loadings due to site differences in the urine-to-soil surface area influenced (17.5 L m-2 at the semi-improved site and 8.9 L m-2 at the improved site). Urine chemical composition varied seasonally and by site. Site- and season-specific urine should, therefore, be used in studies assessing N losses from urine patches. Based on the urine chemical composition data, we provide an updated artificial sheep urine ‘recipe’ which could be utilised to replicate natural sheep urine. The urine metabolomic profile clustered according to pasture quality, while clustering according to season was less evident. Our results provide important information for experimental and modelling studies assessing the scale and nature of N pollution arising from sheep-grazed pastures.

Nitrite accumulation and nitrogen gas production increase with decreasing temperature in urea-amended soils: Experiments and modeling

Nitrite (NO2−) accumulation and associated production of nitric oxide (NO) and nitrous oxide (N2O) gases in soils amended with nitrogen (N) fertilizers are well documented, but there remains a poor understanding of their regulation and variation among soil types. We examined responses to urea inputs in two soils at five temperatures from 5 to 30 °C and developed a process-driven model to describe the dynamics. A microcosm system was used to measure ammonia gas (NH3), ammonium (NH4+), NO2−, nitrate (NO3−), NO, N2O and pH over 12 weeks. Unexpectedly, NO2−, NO and N2O production tended to increase as soil temperature declined in both soils. The maximum NO2− concentration, or compensation point (CP), differed by soil type but the time required to reach CP decreased exponentially with increasing temperature in both soils. A two-step nitrification model (’2SN’) accounted for interactions of ammonia-oxidation (AmO), nitrite oxidation (NiO), urea hydrolysis, NH4+ sorption, N gas production and pH dynamics. Both steps of nitrification (AmO and NiO) were modeled using NH3 inhibition kinetics. The model adequately simulated the observed dynamics and temperature responses and showed that increased uncoupling of AmO and NiO at colder temperatures resulted from their differential temperature responses. The dynamics observed here may be important following high-rate and banded N fertilizer applications and in ruminant urine patches. The results may help explain elevated N2O emissions observed under cold temperatures. The 2SN model can account for interactions among multiple processes and may be useful for studying the effects of management practices and climate factors, including climate change scenarios, on soil N cycling.

Impact of nitrogen compounds on fungal and bacterial contributions to codenitrification in a pasture soil

Ruminant urine patches on grazed grassland are a significant source of agricultural nitrous oxide (N2O) emissions. Of the many biotic and abiotic N2O production mechanisms initiated following urine-urea deposition, codenitrification resulting in the formation of hybrid N2O, is one of the least understood. Codenitrification forms hybrid N2O via biotic N-nitrosation, co-metabolising organic and inorganic N compounds (N substrates) to produce N2O. The objective of this study was to assess the relative significance of different N substrates on codenitrification and to determine the contributions of fungi and bacteria to codenitrification. 15N-labelled ammonium, hydroxylamine (NH2OH) and two amino acids (phenylalanine or glycine) were applied, separately, to sieved soil mesocosms eight days after a simulated urine event, in the absence or presence of bacterial and fungal inhibitors. Soil chemical variables and N2O fluxes were monitored and the codenitrified N2O fluxes determined. Fungal inhibition decreased N2O fluxes by ca. 40% for both amino acid treatments, while bacterial inhibition only decreased the N2O flux of the glycine treatment, by 14%. Hydroxylamine (NH2OH) generated the highest N2O fluxes which declined with either fungal or bacterial inhibition alone, while combined inhibition resulted in a 60% decrease in the N2O flux. All the N substrates examined participated to some extent in codenitrification. Trends for codenitrification under the NH2OH substrate treatment followed those of total N2O fluxes (85.7% of total N2O flux). Codenitrification fluxes under non-NH2OH substrate treatments (0.7–1.2% of total N2O flux) were two orders of magnitude lower, and significant decreases in these treatments only occurred with fungal inhibition in the amino acid substrate treatments. These results demonstrate that in situ studies are required to better understand the dynamics of codenitrification substrates in grazed pasture soils and the associated role that fungi have with respect to codenitrification.

DMPP is ineffective at mitigating N 2 O emissions from sheep urine patches in a UK grassland under summer conditions

Abstract Nitrification inhibitors are a potential technology to mitigate N 2 O emissions from the urine patches of grazing animals. At present, there is limited information regarding the efficacy of the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) in reducing N 2 O emissions from ruminant urine patches, as opposed to the well-studied nitrification inhibitor, dicyandiamide. In practical terms, urine patches would be deposited to soil at various times following the application of a nitrification inhibitor to soil. We hypothesised that the effectiveness of DMPP in reducing cumulative N 2 O emissions would decrease the longer the time since DMPP application. This study utilised an automated closed chamber technique, to monitor fluxes of N 2 O from sheep urine patches (725 kg N ha −1 ; 150 ml; 300 cm 2 ) deposited to a Eutric Cambisol, where DMPP was applied (1 kg ha −1 ) on the same day, 2 weeks before and 4 weeks before urine application. Fluxes were monitored continuously from 4 weeks before, to 9 weeks after, urine application. DMPP was found to be ineffective at reducing cumulative N 2 O emissions and 9-week urine-N 2 O emission factors when applied at the same time as the sheep urine, although a low number of replicates were used in this study. Some effect of DMPP in delaying the accumulation of soil NO 3 − was observed, with effects being greater the shorter the time since DMPP application. The temporal dynamics of N 2 O fluxes were also altered where DMPP was applied on the same day as the urine. Heterogeneity in soil conditions were deemed responsible for the large spatial variability of N 2 O emissions observed in this study. The use of Rhizon samplers were useful for detecting spatial variability within the soil solution directly beneath the urine patches (within the flux chambers), which may not have been detected within duplicate urine patches (outside the chambers), where soil sampling was conducted. Further work is required to determine the loading rate and duration of efficacy of DMPP to reduce emissions from urine patches under temperate summer conditions.

15N recoveries from ruminant urine patches on three forage types

15Nitrogen balances are useful tools to increase our understanding of soil N processes and the efficiency of plants in taking up animal urine-N. This study aimed to investigate the effect of forage type on the fate of autumn-applied urine-N (700 kg N ha−1). In a 17-month lysimeter study the recoveries of 15N in herbage, leachate, nitrous oxide, and soil + roots (at the end of the trial) were determined for three forage types: perennial ryegrass-white clover (RGWC, Lolium perenne L.-Trifolium repens L.), Italian ryegrass (Italian RG, Lolium multiflorum Lam.), and lucerne (Medicago sativa L.) under simulated autumn grazing. We recovered 81.5–85.5% of the 15N applied in the urine. Italian RG had the greatest amount of urine-15N recovered in the herbage (49.5%) and the least recovered in leachate (16.8%) making it the most efficient of the three forages for utilizing urine-N. For RGWC, herbage and leachate recoveries were 40.1% and 23.7%, respectively. Lucerne was the least efficient with recoveries of 15N in herbage and leachate equaling 18.4% and 52.5%, respectively. This study demonstrates that Italian ryegrass could offer benefits in reducing urine-N leaching losses through its ability to take up more urine-N over winter.

Nitrous Oxide Fluxes, Soil Oxygen, and Denitrification Potential of Urine- and Non-Urine-Treated Soil under Different Irrigation Frequencies.

Despite increased use of irrigation to improve forage quality and quantity for grazing cattle ( Linnaeus), there is a lack of data that assess how irrigation practices influence nitrous oxide (NO) emissions from urine-affected soils. Irrigation effects on soil oxygen (O) availability, a primary controller of NO fluxes, is poorly understood. It was hypothesized that increased irrigation frequency would result in lower NO emissions by increasing soil moisture and decreasing soil O concentrations. This would favor more NO reduction to dinitrogen (N). We examined effects of high (3-d) versus low (6-d) irrigation frequency with and without bovine urine addition to pasture. Nitrous oxide fluxes were measured daily for 35 d. Soil O, temperature, and water content were continuously measured at multiple depths. Inorganic nitrogen, organic carbon, and soil pH were measured at 6-d intervals. Measurements of denitrification enzyme activity with and without acetylene inhibition were used to infer the NO/(NO + N) ratio. The NO/(NO + N) ratio was lower under high- compared with low-frequency irrigation, suggesting greater potential for NO reduction to N with more frequent irrigation. Although NO fluxes were increased by urine addition, they were not affected by irrigation frequency. Soil O decreased temporarily after urine deposition, but O dynamics did not explain NO dynamics. Relative soil gas diffusivity (/) was a better predictor of NO fluxes than O concentration. On a free-draining soil, increasing irrigation frequency while providing the same total water volume did not enhance NO emissions under ruminant urine patches in a grazed pasture.

Increasing soil aeration reduces mitigation efficacy of dicyandiamide when targeted at ruminant urine-derived N2O emissions

Soil aeration effects on the efficacy of dicyandiamide (DCD) at reducing reactive nitrous oxide (N2O) fluxes from ruminant urine patches have not been assessed. We tested the null hypothesis that increasing soil aeration and dissolved organic carbon (DOC) levels, following ruminant urine deposition, would reduce DCD efficacy, as determined from measurements of N2O fluxes. Soil aeration was controlled (−1 or −10 kPa, the former being wetter and less aerated) within a factorial experiment that also included DCD and ruminant urine (700 kg N ha−1) treatments, destructively sampled over 40 days. Increased soil aeration corresponded with a decrease in DCD efficacy. However, contrary to the null hypothesis, increasing soil DOC concentrations following urine application did not correspond with greater DCD degradation rates. In fact, at −1 kPa applying urine increased the DCD half-life from 23.5 (±3.0) to 53.3 (±7.5) days, while at −10 kPa the DCD half-life was not affected by urine application (14.9 [±2.9] and 16.7 [±2.7] days, with or without urine, respectively). The efficacy of DCD at mitigating urine-induced cumulative N2O fluxes was 95% at −1 kPa and 57% at −10 kPa. This study confirms that the degradation of DCD is slower, and thus its efficacy is better, in wet soils compared with well-aerated soils.

In situ N2O emissions are not mitigated by hippuric and benzoic acids under denitrifying conditions

Ruminant urine patches deposited onto pasture are a significant source of greenhouse gas nitrous oxide (N2O) from livestock agriculture. Increasing food demand is predicted to lead to a rise in ruminant numbers globally, which, in turn will result in elevated levels of urine-derived N2O. Therefore mitigation strategies are urgently needed. Urine contains hippuric acid and together with one of its breakdown products, benzoic acid, has previously been linked to mitigating N2O emissions from urine patches in laboratory studies. However, the sole field study to date found no effect of hippuric and benzoic acid concentration on N2O emissions. Therefore the aim of this study was to investigate the in situ effect of these urine constituents on N2O emissions under conditions conducive to denitrification losses. Unadulterated bovine urine (0mM of hippuric acid, U) was applied, as well as urine amended with either benzoic acid (96mM, U+BA) or varying rates of hippuric acid (8 and 82mM, U+HA1, U+HA2). Soil inorganic nitrogen (N) and N2O fluxes were monitored over a 66day period. Urine application resulted in elevated N2O flux for 44days. The largest N2O fluxes accounting for between 13% (U) and 26% (U+HA1) of total loss were observed on the day of urine application. Between 0.9 and 1.3% of urine-N was lost as N2O. Cumulative N2O loss from the control was 0.3kgN2O–Nha−1 compared with 11, 9, 12, and 10kgN2O–Nha−1 for the U, U+HA1, U+HA2, and U+BA treatments, respectively. Incremental increases in urine HA or increase in BA concentrations had no effect on N2O emissions. Although simulation of dietary manipulation to reduce N2O emissions through altering individual urine constituents appears to have no effect, there may be other manipulations such as reducing N content or inclusion of synthetic inhibitory products that warrant further investigation.

Biochar does not affect soil N-transformations or microbial community structure under ruminant urine patches but does alter relative proportions of nitrogen cycling bacteria

Nitrogen (N) cycling, especially denitrification, can be significantly altered when biochar is used as a soil conditioner. These alterations in N-cycling have been attributed to a combination of physicochemical change, alterations in microbial community ecology and pervading climatic conditions. This study investigated seasonal bacterial community change over two years in combination with a short-term winter study of N-transformations under bovine urine patches. A silt-loam pastoral soil in Canterbury, New Zealand was amended with either 0, 15 or 30tha−1 of Pinus radiata biochar (pyrolysed at ∼450°C) and bovine urine was added to patches within the 0 and 30tha−1 biochar amended plots (designated as 0U and 30U treatments, where U indicates ‘urine’).No discernible differences in bacterial community structure were observed during the two year study or the short term N-transformation study when comparing non-amended and biochar-amended soil. Differences in bacterial community structure were only evident when comparing seasons, with data pertaining to each season from successive years clustering together. During the short-term N-transformation study, bacterial communities formed 3 distinct clusters corresponding to elevated levels of urine derived NH4+-N (days 0–10), increases in NO3−-N and N2O (days 10–22) and a decline in NO3−-N and N2O (day 20 onward). Biochar amendment did increase the relative abundance of up to 50% of individual operational taxonomic units (OTUs or ‘species’), including key nitrite oxidisers and nitrate reducers. Biochar amendment did not affect the concentrations of inorganic-N compounds.The nirS (nitrite reductase) gene became elevated in the 30U treatment relative to the 0U treatment ∼10 days after the initial urine application. The nosZ (nitrous oxide reductase) gene became elevated in the 30U plots during the latter part of the experiment.Conclusions:•Biochar did not have a significant impact on the microbial community structure in pastoral soil over the course of two years.•The relative proportion of nitrifiers and denitrifiers increased in biochar amended soils subjected to large influxes of urine derived N.•Differences in N-transformation dynamics in the presence of biochar during the winter months were not statistically significant.

Influence of soil bulk density and matric potential on microbial dynamics, inorganic N transformations, N2O and N2 fluxes following urea deposition

Transformation of ruminant urine-nitrogen (N) can contribute to negative environmental outcomes such as nitrate leaching which leads to eutrophication of waterways and production of nitrous oxide (N2O), a greenhouse gas. Although abiotic factors influencing urine-N processing have been well studied, detailed studies of the soil microbial community dynamics following urine application are required to improve mitigation strategies for reducing harmful N fluxes from urine deposition. A factorial laboratory experiment using packed silt-loam soil cores with two levels each of urea (±), soil matric potential (ψ −6.0 or −0.2 kPa) and soil bulk density (ρb 1.1 or 1.5 g cm−3) was performed to study the interaction of urea and soil physical conditions on both soil inorganic N transformations and the abundance of ammonia-oxidizers and denitrifiers. Soil ψ and ρb treatments had an immediate impact on soil pH, dissolved organic carbon, inorganic N pools and emissions of N2O and N2 following urea deposition, and microorganisms carrying the nosZ gene were present in lower numbers in the most aerobic soil (−6.0 kPa and 1.1 g cm−3) from day 7. In all treatments, both bacterial amoA and denitrifier nirS, nirK and nosZ gene copy numbers increased within 1 day following urea application. Dynamics in the NH4+ concentrations were significantly correlated with cumulative changes in the abundance of the ammonia-oxidizers, but no relation was found between cumulative changes in the denitrifier nirS, nirK and nosZ gene copy numbers and the dynamics in soil inorganic N, N2O or N2 emissions. Throughout most of the study period the specific soil conditions, induced by the ψ and ρb treatments, determined nitrifier and denitrifier activity rather than the size of the microbial communities involved. However, by day 35 soil ψ and ρb treatments exerted large treatment effects on bacterial amoA, nirS and nirK gene copy numbers. Thus, although nitrate concentrations and N2O emissions following urea deposition were determined by the soil ψ and ρb conditions in the short-term, our results indicate that changes in the population sizes of denitrifiers and AOB in ruminant urine patches may influence environmental N fluxes in the long-term.

Influence of photosynthetically active radiation on diurnal N2O emissions under ruminant urine patches

Nitrous oxide (N2O) is a greenhouse gas and is also recognized as the single most important ozone depleting emission. Static chambers are commonly used to measure N2O fluxes from agricultural soils with fluxes measured over approximately 1 hour typically extrapolated to a daily flux, thus assuming a constant flux over 24 h. Diurnal variation in soil N2O fluxes may lead to inaccurate inventory calculations. The aim of this study was to assess the effect of diurnal changes in photosynthetically active radiation (PAR) on N2O emissions from planted and non-planted soil exposed to bovine urine. The effects of varying PAR, over a 16 h day length, on N2O emissions were observed in a split-split plot factorial experiment conducted in the New Zealand Biotron under constant soil and air temperatures. Treatments included absence or presence of both bovine urine and a 1-month-old perennial ryegrass (Lolium perenne) sward. Diurnal N2O fluxes were determined every 1.5 h on days 6 and 19 after urine deposition when ammonium (NH4 +) and nitrate (NO3 −) were expected to dominate the soil inorganic-N pool, respectively. On day 6, NH4 + dominated the soil inorganic-N pool and N2O-N fluxes were relatively low with diurnal amplitudes of 0.5–3.4. By day 19, the soil NO3 − pool had increased as did N2O-N fluxes along with diurnal amplitudes (2.1–41.7). The highest N2O-N fluxes occurred in the soil plus urine treatment as a consequence of PAR altering soil temperature and not as a direct consequence of PAR effects on grass. Diurnal fluxes of N2O-N following ruminant urine deposition to pasture did not occur as a direct result of diurnal PAR cycles potentially affecting root exudation. It is assumed that other sources of C, such as solubilized organic matter, dominated as a microbial C source for denitrifiers.

Biochar Incorporation into Pasture Soil Suppresses in situ Nitrous Oxide Emissions from Ruminant Urine Patches

Nitrous oxide (N2O) emissions from grazing animal excreta are estimated to be responsible for 1.5 Tg of the total 6.7 Tg of anthropogenic N2O emissions. This study was conducted to determine the in situ effect of incorporating biochar, into soil, on N2O emissions from bovine urine patches and associated pasture uptake of N. The effects of biochar rate (0-30 t ha(-1)), following soil incorporation, were investigated on ruminant urine-derived N2O fluxes, N uptake by pasture, and pasture yield. During an 86-d spring-summer period, where irrigation and rainfall occurred, the N2O fluxes from 15N labeled ruminant urine patches were reduced by >50%, after incorporating 30 t ha(-1) of biochar. Taking into account the N2O emissions from the control plots, 30 t ha(-1) ofbiochar reduced the N2O emission factor from urine by 70%. The atom% 15N enrichment of the N2O emitted was lower in the 30 t ha(-1) biochar treatment, indicating less urine-N contributed to the N2O flux. Soil NO3- -N concentrations were lower with increasing biochar rate during the first 30 d following urine deposition. No differences occurred, due to biochar addition, with respect to dry matter yields, herbage N content, or recovery of 15N applied in herbage. Incorporating biochar into the soil can significantly diminish ruminant urine-derived N2O emissions. Further work is required to determine the persistence of the observed effect and to fully understand the mechanism(s) of the observed reduction in N2O fluxes.

Unweathered Wood Biochar Impact on Nitrous Oxide Emissions from a Bovine‐Urine‐Amended Pasture Soil

Low‐temperature pyrolysis of biomass produces a product known as biochar The incorporation of this material into the soil has been advocated as a C sequestration method. Biochar also has the potential to influence the soil N cycle by altering nitrification rates and by adsorbing or NH3 Biochar can be incorporated into the soil during renovation of intensively managed pasture soils. These managed pastures are a significant source of N2O, a greenhouse gas, produced in ruminant urine patches. We hypothesized that biochar effects on the N cycle could reduce the soil inorganic‐N pool available for N2O‐producing mechanisms. A laboratory study was performed to examine the effect of biochar incorporation into soil (20 Mg ha−1) on N2O‐N and NH3–N fluxes, and inorganic‐N transformations, following the application of bovine urine (760 kg N ha−1). Treatments included controls (soil only and soil plus biochar), and two urine treatments (soil plus urine and soil plus biochar plus urine). Fluxes of N2O from the biochar plus urine treatment were generally higher than from urine alone during the first 30 d, but after 50 d there was no significant difference (P = 0.11) in terms of cumulative N2O‐N emitted as a percentage of the urine N applied during the 53‐d period; however, NH3–N fluxes were enhanced by approximately 3% of the N applied in the biochar plus urine treatment compared with the urine‐only treatment after 17 d. Soil inorganic‐N pools differed between treatments, with higher concentrations in the presence of biochar, indicative of lower rates of nitrification. The inorganic‐N pool available for N2O‐producing mechanisms was not reduced, however, by adding biochar.