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

Nitrous oxide (N2O) is an air pollutant of major environmental concern, with agriculture representing 60% of anthropogenic global N2O emissions. Much of the N2O 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 N2O dynamics, we aimed to identify key controlling factors influencing N2O emissions and to aid understanding of knowledge gaps to improve GHG reporting and prioritise 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 N2O 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 N2O 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: 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; N2O emissions with a measure of uncertainty; data from a control with zero-N application and meteorological data

The short-lived inhibitory effect of Brachiaria humidicola on nitrous oxide emissions following sheep urine application in a highly nitrifying soil

Background: Brachiaria humidicola (Bh) has the ability to produce biological nitrification inhibitors (NIs) and release NIs from the root to the soil. Aims: To compare the effects of growing Bh with Brachiaria ruziziensis (Br, which is not able to produceNIs) on soil nitrogen (N) dynamics,Ngases and carbon dioxide (CO2) emissions and nitrifiers and denitrifiers following sheep urine application, a laboratory incubation was conducted in a He/O2 continuous flow denitrification system (DENIS). This incubation was conducted in the absence of light. Hence themeasured effects of Bh and Br on N cycling were the residual effect of biological NIs released into the soil prior to the incubation and released via root death. Methods: The treatmentswere: (1) Bhwith water application (Bh+W); (2) Bh with sheep urine (Bh + U); (3) Br with water application (Br + W); (4) Br with sheep urine (Br + U). Results: Results showed that soil NO3– concentration increased significantly in the soil with sheep urine application after the incubation. Soil nitrous oxide (N2O) and nitric oxide (NO) emissions increased immediately after the sheep urine application and peaked twice during the incubation. Cumulative emissions for the first peak were significantly lower from the Bh + U treatment (0.054 kg N ha–1) compared with the Br + U treatment (0.111 kg N ha–1), but no significant differences were observed in the total cumulative N2O and NO emissions between the Bh + U and Br + U treatment at the end of the incubation. Sheep urine addition did not affect the AOA, nirS and nosZ gene copies, but significantly increased the AOB gene copies after the incubation. Conclusions: We conclude that the residual effect of Bh to mitigate N2O emissions in a highly nitrifying soil is short-lived

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

Soil nitrous oxide emissions from grassland: potential inhibitor effect of hippuric acid

In grassland systems, cattle and sheep urine patches are recognized as nitrous oxide (N2O) emission hot spots due to the high urinary nitrogen (N) concentrations. Hippuric acid (HA) is one of the constituents of ruminant urine that has been reported as a natural inhibitor of soil N2O emissions. The aim of this study was to examine the potential for elevated ruminant urine HA concentrations to reduce N2O emissions, in situ, on an acidic heavy clay soil under poorly drained conditions (WFPS > 85%). A randomized complete block design experiment with three replications and four treatments was conducted using the closed-static-flux chamber methodology. The four treatments were applied inside the chambers: control with no artificial urine application (C), control artificial urine (U), and enriched artificial urine containing two rates of HA (55.8 and 90 mM, U+HA1, U+HA2). Soil inorganic-N, soil dissolved organic carbon (DOC), soil pH as well as N2O and methane (CH4) fluxes were monitored over a 79-day period. Although N2O emissions were not affected by the HA enriched urine treatments, U+HA2 positively affected the retention of N as NH4+ until day 3, when the soil pH dropped to values <5. Subsequently, as a consequence of rainfall events and soil acidification, it is likely that leaching or sorption onto clay reduced the efficacy of HA, masking any treatment differential effect on N2O emissions. Moreover, CH4 fluxes as well as DOC results reflected the soil anaerobic conditions which did not favour nitrification processes. Further research is needed to determine the fate of HA into the soil which might clarify the lack of an in situ effect of this compoun

The effect of tillage management on microbial functions in a maize crop at different slope positions

Determining whether agricultural soils act as sinks or sources of greenhouse gases (GHGs) requires the quantification of variations in the pools and fluxes of soil organic carbon (SOC) and nutrients, e.g. nitrogen (N), as well as the associated soil microbial responses. In this study, soil was collected from experimental plots of maize (Zea mays) under conventional, minimum or strip tillage treatments established in a sloping field (~10%) of loamy soil in SW England, UK, where maize had been cultivated conventionally for 12 years. Topsoil (0–10 cm) cores were collected from the top, mid, bottom and foot slope positions to investigate soil C, N and microbial properties. The impact of conventional management on potential GHG emissions was assessed by incubating soils collected from the top, mid and bottom slope positions from the conventional treatment. Contents of SOC and total N were greatest at the top slope position and soil mineral N (NO3\u100000 -N and NH4+-N) concentrations were greater at the bottom and foot slope positions in all treatments. Biomarker phospholipid fatty acids (PLFA) for Gram positive bacteria and fungi were relatively 13C-enriched at each slope position regardless of treatment, indicating preferential utilization of organic matter from maize (C4) rather than SOC (C3). Around 70% of carbon incorporated into total PLFA was derived from C3-SOC at the slope foot, indicating that more SOC older than 12 years was being mineralized at the depositional position. Effluxes of N2O and CO2, and total GHG emission were greatest from the incubated soils sampled from the bottom slope position, suggesting that conditions in depositional positions of regularly ploughed sloping arable fields may have increased the potential for mineralization and denitrification. We conclude that the C sink potential of the depositional positions of slopes may be diminished by coincidental GHG emission

Atmospheric ammonia concentration modulates soil enzyme and microbial activity in an oak forest affecting soil microbial biomass

The present work was carried out to assess the effect of atmospheric ammonia (NH3) on soil physicochemical properties, soil enzymatic activities (β-glucosidase -β-GLU-, nitrate reductase –NR-, urease –UR-, protease –PRO-,acid phosphatase –PHO-, dehydrogenase –DHA-), soil microbial biomass and soil respiration. The study was conducted along a NH3 gradient in a Q. pubescens Milld. forest in the vicinity of two livestock farms. Because of NHy (NHy: NH3 and NH4+) deposition, N saturation was detected up to 330 m from the farms. This excess of N led to a decrease in soil C:N and an increase in soil nitrification processes, which resulted in an accumulation of the heavy N isotope (15N) in the soil. N saturation was also reflected in the activity of NR enzyme, which was inhibited. On the other hand, while UR enzyme was inhibited close to the farms possibly due to the high amount of N-NH4+ resulting from the hydrolysis of NH3, PRO activity was stimulated by the presence of organic nitrogen compounds and the need of soil organisms to meet the C demand. In addition, the activity of PHO and β-GLU enzymes was regulated by the relative amount of C and P that organisms need. Regarding biological variables,enhanced NH3 reduced soil microbial biomass and biomass respiratory efficiency. Finally, soil enzyme activities and soil microbial biomass have proved to be good biological indicators of soil qualit