Interactive effects of dung deposited onto urine patches on greenhouse gas fluxes from tropical pastures in Kenya

Influence of soil properties on N2O and CO2 emissions from excreta deposited on tropical pastures in Kenya

To improve estimates of agricultural greenhouse gas emissions in sub‐Saharan Africa, we measured over six individual periods of 25–29 days fluxes of methane (CH4), carbon dioxide (CO2), and nitrous oxide (N2O) with subdaily time resolution from dung patches of different quality (C/N ratio: 23–41) and quantity (0.5 and 1.0 kg) on a Kenyan rangeland during dry and wet seasons. Methane emissions peaked following dung application, whereas N2O and CO2 fluxes from dung patches were similar to fluxes from rangeland soils receiving no N additions. Greenhouse gas emissions scaled linearly with dung quantity during both seasons. Dung with a low (23) C/N ratio produced up to 10 times more CH4 than dung with a high (41) C/N ratio. Overall, CH4 emission factors (EFs) ranged from 0.001 to 0.042%, lower than those derived in temperate regions. Cumulative CO2 and N2O emissions were similar for all treatments across the different seasons. The N2O EF ranged from 0 to 0.01%, less than 1% of the Intergovernmental Panel on Climate Change Tier 1 default EF (2%) for N2O emissions from dung and urine patches, likely because of the low dung N content (9.7–16.5 g N kg−1 dry matter). However, these results were consistent with the updated cattle dung EF (0.2%) developed for Kenya in 2016/2017 (EF database ID# 422665). In view of the wide range of climates, soils, and management practices across sub‐Saharan Africa, development of robust GHG EFs from dung patches for SSA requires additional studies.

Core Ideas Limited data are available about mitigating N 2 O emissions from urine patches on semiarid pasture. Nitrapyrin reduced cumulative N 2 O emissions by 39% in a dry season. Nitrapyrin reduced cumulative N 2 O emissions by 58% in normal precipitation season. NBPT and NBPT plus DCD did not limit N 2 O emissions compared with untreated urine patches. N 2 O emission factors ranged from 0.03 to 0.21% over two grazing seasons Urease and/or nitrification inhibitors applied to urine patches or pastures may increase N retention in the soil–plant system, but how N 2 O emissions respond to these N stabilizers in semiarid regions is poorly understood. The objectives of this research were (i) to quantify N 2 O emissions and the associated emission factors, based on the percentage of applied urine‐N emitted as N 2 O–N, from beef cattle urine patches (urine) and (ii) to test the N 2 O reduction potential of three N stabilizers [2‐chloro‐6(trichloromethyl) pyridine (nitrapyrin), N‐(n‐butyl)‐thiophosphoric triamide (NBPT), and NBPT plus dicyandiamide (DCD)] on a semiarid tame pasture over two grazing seasons in western Canada. A deionized water control was also included. Nitrapyrin reduced cumulative N 2 O emissions by 39% and the N 2 O emission factor by 50% compared with untreated urine in a dry grazing season and reduced cumulative N 2 O emissions by 58% and the N 2 O emission factor by 68% compared with untreated urine in a grazing season with normal precipitation. The NBPT and NBPT + DCD had similar cumulative N 2 O emissions compared with untreated urine patches. The N 2 O emission factors ranged from 0.03 to 0.08% over 103 d in 2015 and from 0.06 to 0.21% over 119 d in 2016, all lower than the 2% Intergovernmental Panel on Climate Change default 365‐d value. Extrapolating over 1‐yr periods, N 2 O emission factors ranged from 0.11 to 0.64%. Based on the N stabilizers tested, nitrapyrin most effectively reduced N 2 O emissions from beef cattle urine patches on a tame pasture in a nonirrigated semiarid region of Canada.

Greenhouse gas emissions from excreta patches of grazing animals and their mitigation strategies

The intensification of pasture production has increased the use of N fertilizers—a practice that can alter soil greenhouse gas (GHG) fluxes. The objective of the present study was to evaluate the fluxes of CH4, CO2, and N2O in the soil of Urochloa brizantha ‘Marandu’ pastures fertilized with different sources and doses of N. Two field experiments were conducted to evaluate GHG fluxes following N fertilization with urea, ammonium nitrate, and ammonium sulfate at doses of 0, 90, 180, and 270 kg N ha−1. GHG fluxes were quantified using the static chamber technique and gas chromatography. In both experiments, the sources and doses of N did not significantly affect cumulative GHG emissions, while N fertilization significantly affected cumulative N2O and CO2 emissions compared to the control treatment. The N2O emission factor following fertilization with urea, ammonium nitrate, and ammonium sulfate was lower than the United Nations’ Intergovernmental Panel on Climate Change standard (0.35%, 0.24%, and 0.21%, respectively, with fractionation fertilization and 1.00%, 0.83%, and 1.03%, respectively, with single fertilization). These findings are important for integrating national inventories and improving GHG estimation in tropical regions.

During grazing, some of the nutrients ingested by cattle are returned to grassland as urine and dung patches and can be lost as greenhouse gases. Sites where cattle congregate are more likely to have overlapping excreta patches favouring enhanced nitrous oxide (N2O) emissions. However, there is no consensus about the magnitude of these or simultaneous methane (CH4) emissions or potential mitigation options. This study investigated the effect of combined cattle dung and urine depositions on N2O and CH4 emissions, compared with emissions from separate depositions, under different weather conditions. Local emission factors (EFs) were then calculated for both gases. A quantitative assessment of published studies was also performed to search for N2O emissions drivers. Two field experiments were performed during two 98-day trials under dry and wet conditions in Tandil, Argentina. Treatments included fresh excreta patches of urine (0.75 L), dung (2.50 kg), dung + urine (2.50 kg + 0.75 L) from Holstein dairy cows, and a control (without excreta). Soil and excreta properties were analysed, and N2O and CH4 fluxes from the patches were measured using the static chamber technique. Patches containing dung were shown to be localised CH4 hotspots. Urine applied to soil, and the addition of urine to dung patches had a negligible effect on CH4 fluxes. Urine, dung and combined patches were found to be localised N2O sources. Adding urine to dung patches under wet weather had a significant synergetic effect (threefold increase) on cumulative N2O emissions compared with the theoretical sum of separate excreta patches. Adding urine to dung patches under dry conditions gave an additive effect on N2O. These findings suggest that preventing overlapping excreta patches under wet conditions can help mitigate N2O emissions from temperate managed grazed pastures. The effect of combining excreta patches was also evident in the EF values obtained. That for CH4 was consistent with the default IPCC value (0.75 g CH4 kg−1 VS), while N2O (EF = 0.03–0.39%) was lower than the updated IPCC 2019 value of 0.6%.

Fluxes of CO 2, CH 4, and N 2O in an alpine meadow affected by yak excreta on the Qinghai-Tibetan plateau during summer grazing periods

Nitrous oxide emission factors for urine and dung patches in a subtropical Brazilian pastureland

Seasonal effects on ammonia, nitrous oxide, and methane emissions for beef cattle excreta and urea fertilizer applied to a tropical pasture

Effect of variety and harvesting management on the concentration of tannins and alkaloids in tagasaste ( Chamaecytisus palmensis)

This study was conducted on lake Ehuikro, located in Bongouanou (Côte d’Ivoire) from April 2017 to March 2018. Each month, the physico-chemical parameters of the water were measured at three (3) identified stations. In order to analyse its ecological status, the following equipment was used: Conductivity meter Model Sx713; Model Sx711 pH meter; Model Sx716 oximeter and Secchi disk, which made it possible to determine the annual average values: The dissolved solids rate was 154.13 ± 1.22 mg/L (long dry season) and 181.67 ± 3.78 mg/L (short dry season). Conductivity 250 ± 3.07 Ms/cm (short rainy season) and 297.75 ± 2.66 MS/cm (long dry season). Hydrogen potential 7.35 ± 0.13 (long dry season) and 8.09 ± 0.55 (short rainy season). Temperature 27.06 ± 0.67 °C (main rainy season) and 28.45 ± 0.05 °C (main dry season). Oxygen saturation level 42.67 ± 3.77% (minor dry season) and 67.93 ± 6.96% (long dry season). The dissolved oxygen level was 3.07 ± 0.64 mg/l (short dry season) and 5.24 ± 0.45 mg/l (long dry season). The phosphorus concentration was 0.03 ± 0.01 mg/l (short rainy season) and 0.06 ± 0.01 mg/l (long rainy season). The nitrate concentration was 0.01 ± 0.1 mg/L (long dry season) and 0.02 ± 0.1 mg/L (main rainy season). Transparency 0.44 ± 0.02 cm (main rainy season) and 0.68 ± 0.05 cm (minor dry season). Depth 2.71 ± 0.36 m (main dry season) and 4.20 ± 0.51 m (main rainy season). The results obtained reveal that certain physico-chemical parameters show signs of disturbance probably linked to local anthropogenic activities.

Animal production systems are important sources of greenhouse gases (GHGs), especially methane (CH4) and nitrous oxide (N2O). GHG emissions from urine patches have been extensively studied in temperate climates, with few studies under tropical conditions. Here we examined the driving factors of N2O and CH4 emission from urine patches in the tropics, as well as the role of the nitrification inhibitor DCD (dicyandiamide) in mitigating emissions. We hypothesized that the high temperature and periodical rainfall can increase GHG emissions from urine patches through accelerating mineralization of urine-N. We measured CH4 and N2O emissions from beef cattle urine (360 kg N ha−1) in Rondonia state (Brazil, tropical climate), during two different seasons (winter and summer), with and without the application of DCD (10 kg ha−1). No effects of DCD on cumulative N2O emissions were detected in summer, but DCD retarded the main emission peak. During winter DCD increased N2O emissions from 10.8 to 39.2 mg N–N2O m−2 (p ≤ 0.05). Emission factors averaged 0.4 % for summer and 0.1 % for winter, which is significantly lower than the IPCC default value of 1 %. The climate, associated with soil (acidic pH, WFPS and low N content) and plant properties (biological nitrification inhibition) resulted in a low emission factor. We concluded that the IPCC default emission factor for tropical systems may be reduced, and that the application of DCD is not recommended in such systems.

A study was conducted for two consecutive years (1998-1999) to determine the seasonal patterns of strongyle infection in working donkeys of Ethiopia. For the purpose 2385 donkeys from midland and lowland areas were examined for the presence of parasitic ova. A hundred percent prevalence of strongyle infection with similar seasonal pattern of strongyle faecal worm egg output was obtained in all study areas. However, seasonal variations in the number of strongyle faecal worm egg output were observed in all areas. The highest mean faecal worm egg outputs were recorded during the main rainy season (June to October) in both years in all areas. Although an increase in the mean strongyle faecal egg output was obtained in the short rainy season (March-April) followed by a drop in the short dry season (May), there was no statistically significant difference between the short rainy season and long dry season (Nov-Feb) (P > 0.05). A statistically significant difference however, was obtained between the main rainy season and short rainy season, and between the main rainy season and dry season (P < 0.05). Based on the results obtained it is suggested that the most economical and effective control of strongyles can be achieved by strategic deworming programme during the hot dry pre-main rainy season (May), when the herbage coverage is scarce and helminthologically 'sterile', and the arrested development of the parasites is suppose to be terminating. This could insure the greatest proportion of the existing worm population to be exposed to anthelmintic and also reduces pasture contamination and further infection in the subsequent wet season.

Greenhouse gas emissions from sheep excreta deposited onto tropical pastures in Kenya

Carbon (C) substrates are critical for regulating denitrification, a process that results in nitrous oxide (N 2 O) and dinitrogen (N 2 ) emissions from soil. However, the impacts of C substrates on concomitant soil emissions of carbon dioxide (CO 2 ) and N 2 O under varying soil types and soil water contents are not well studied. Three repacked Pallic grassland soils, varying in texture and phosphorus (P) status, containing NO 3 − ‐ 15 N were held at three levels of matric potential ( ψ , −3, −5 and −7 kPa), while receiving daily substrate additions (acetate, glucose and water control) for 14 days. The CO 2 and N 2 O emissions were measured daily. Additionally, the N 2 O:(N 2 + N 2 O) ratios were determined using 15 N on days 3 and 14. Results showed that N 2 O emissions increased exponentially as soil gas diffusivity declined, and N 2 O peak emissions were higher with glucose than with acetate addition, with a range (± standard deviation) of 0.1 ± 0.0 to 42.7 ± 2.1 mg N m −2 h −1 . The highest cumulative N 2 O emission (2.5 ± 0.2 g N m −2 ) was measured following glucose addition with a soil ψ of −3 kPa. In comparison with added glucose, acetate resulted in a twofold increase in N 2 emissions in soils with relatively low gas diffusivities. The N 2 O:(N 2 O + N 2 ) emissions ratios varied with substrate (glucose, 0.91; acetate, 0.81) on day 3, and had declined by day 14 under substrate addition (≤0.10). Cumulative CO 2 emissions were enhanced with increasing soil gas diffusivity and were higher for soils amended with glucose (ranging from 22.5 ± 1.3 to 36.6 ± 1.8, g C m −2 ) than for those amended with acetate. Collectively, the results demonstrate that the increase of N 2 O, N 2 and CO 2 emissions and changes in the N 2 O:(N 2 + N 2 O) ratio vary over time in response to C substrate type and soil gas diffusivity. Highlights Co‐regulation of CO 2 and N 2 O emissions was assessed for varying soil types and C substrates. Soil diffusivity explained concurrently cumulative N 2 O and CO 2 emissions. Acetate enhanced N 2 O reduction to N 2 in three grassland soils more than glucose. C substrate effects on soil N 2 O, N 2 and CO 2 emissions were soil type specific.