Soil Carbon Dioxide Emissions Research Articles

Soil greenhouse gas emissions from different land utilization types in Western Kenya

IntroductionThere is a vast data gap for the national and regional greenhouse gas (GHG) budget from different smallholder land utilization types in Kenya and sub-Saharan Africa (SSA) at large. Quantifying soil GHG, i.e., methane (CH4), carbon dioxide (CO2), and nitrous oxide (N2O) emissions from smallholder land utilization types, is essential in filling the data gap.MethodsWe quantified soil GHG emissions from different land utilization types in Western Kenya. We conducted a 26-soil GHG sampling campaign from the different land utilization types. The five land utilization types include 1) agroforestry M (agroforestry Markhamia lutea and sorghum), 2) sole sorghum (sorghum monocrop), 3) agroforestry L (Sorghum and Leucaena leucocephala), 4) sole maize (maize monocrop), and 5) grazing land.Results and discussionThe soil GHG fluxes varied across the land utilization types for all three GHGs (p ≤ 0.0001). We observed the lowest CH4 uptake under grazing land (−0.35 kg CH4–C ha−1) and the highest under sole maize (−1.05 kg CH4–C ha−1). We recorded the lowest soil CO2 emissions under sole maize at 6,509.86 kg CO2–Cha−1 and the highest under grazing land at 14,400.75 kg CO2–Cha−1. The results showed the lowest soil N2O fluxes under grazing land at 0.69 kg N2O–N ha−1 and the highest under agroforestry L at 2.48 kg N2O–N ha−1. The main drivers of soil GHG fluxes were soil bulk density, soil organic carbon, soil moisture, clay content, and root production. The yield-scale N2O fluxes ranged from 0.35 g N2O–N kg−1 under sole maize to 4.90 g N2O–N kg−1 grain yields under agroforestry L. Nevertheless, our findings on the influence of land utilization types on soil GHG fluxes and yield-scaled N2O emissions are within previous studies in SSA, including Kenya, thus fundamental in filling the national and regional data of emissions budget. The findings are pivotal to policymakers in developing low-carbon development across land utilization types for smallholders farming systems.

Responses of Soil N2O and CO2 Emissions and Their Global Warming Potentials to Irrigation Water Salinity

Irrigation using marginal quality water (brackish, saline, or treated wastewater, with a salinity of 2–8 g L−1) instead of fresh water alters the soil carbon and nitrogen cycle, and thus, soil greenhouse gas emissions. To reveal the responses of soil nitrous oxide (N2O) and carbon dioxide (CO2) emissions and their global warming potentials (GWPs) to irrigation water salinity, a pot experiment was conducted at three levels (2, 5, and 8 g L−1, namely S2, S5, and S8). The results show that the cumulative soil CO2 emissions were reduced with increases in the irrigation water salinity and were 11.6–28.1% lower than those from the fresh water-irrigated treatment (CK). The cumulative N2O emissions from S2 and S8 decreased by 22.7% and 39.6% (p < 0.05), respectively, in comparison to CK, whereas those from S5 increased by 87.7% (p < 0.05). The cumulative GWPs from S2 and S8 were 19.6% and 44.1% lower than those from CK, while those from S5 were significantly higher (p < 0.05). These findings indicate that reducing the salinity of brackish water from 5 to 2 g L−1 before using it for irrigation is a potential strategy to mitigate soil GHGs and solve water resource scarcity. The response of soil greenhouse gas (GHG) emissions to salinity may be significantly different among irrigation water salinity ranges. The results have an important guiding significance for exploring greenhouse gas emission reduction measures, and sustainable utilization models of water and soil resources.

Influence of Pig Slurry Application Techniques on Soil CO2, N2O, and NH3 Emissions

Greenhouse gas (GHG) emissions from agricultural soils can accelerate climate change, therefore, different soil fertilization techniques should be assessed before application to reduce GHG emissions. Pig slurry applications can greatly influence soil carbon dioxide (CO2), nitrous oxide (N2O), and ammonia (NH3) emissions of arable fields; thus, it is important to find site-specific techniques to lessen any negative environmental impacts. In this study, we examined the short-term effect of pig slurry application techniques of spreading and injection on soil greenhouse gas and NH3 emissions under different irrigation amounts. We used the dynamic chamber method with in-situ gas analyzers. Our study showed that there were elevated emissions during the first week after slurry application; however, the difference between GHG emissions of spreading and injection treatments were not significant. Elevated GHG emissions (213–338% and 250–594% in the case of CO2 and N2O emissions, respectively) were observed under dry circumstances compared to irrigated treatments, as well as significantly higher NH3 emissions occurred for surface spreading under non-irrigated (dry) circumstances compared to other treatments. There were no statistically significant differences between the soil chemistry of different application techniques. However, pig slurry increased the available nitrogen forms (ammonium- and nitrate-nitrogen), which caused N2O and NH3 peaks regardless of treatment type. Leachate chemistry was more affected by irrigation strategies than application techniques. Our study highlights the importance of soil conditions at the time of application, rather than the application technique for fertilization using pig slurry.

Comparative Assessment of Soil Carbon Sequestration and Carbon Dioxide Emissions from Agroforestry Systems in Kogi East Nigeria

This study was conducted to assess the below ground carbon sequestration (soil carbon stock per unit land area) and carbon dioxide (CO2) emissions from agroforestry systems (AFSs) in Kogi East (Ankpa, Dekina, Ofu, Olamaboro, and Omala local government areas) Nigeria. Stratified random sampling was used to select study locations of the agroforestry systems in Kogi East, Nigeria. Four AFSs were selected in each local government area (LGA) - this consisted majorly of smallholder farmer’s farm with silvoarable systems in the region (4 communities per LGA, total of 20 communities). The selection criteria for AFS was based on farm size not less than 1 hectare. The results from the analysis revealed that highest soil carbon stock [C stock (Mg Cha-1)] was recorded from AFSs in Dekina (334.43 Mg Cha-1) while no significant difference in carbon stock was observed from the soils of AFSs in Ankpa, Ofu, Olamaboro, and Omala LGAs (69.01, 159.21, 142.58, 117.33 Mg Cha-1 respectively). Nonetheless, the soils from AFSs in Dekina LGA had highest CO2 emissions followed by Ofu LGA (186.23 and 159.40 gCO2 emitted/50g wet soil slice respectively) while the lowest CO2 emissions (104.15 and 88.88 gCO2 emitted/50g wet soil slice) were recorded from Ankpa and Omala LGAs respectively. The highest carbon sequestration recorded from soils of AFSs in Dekina LGA may depend on the soil C input and soil stabilization processes including tree species and density and again highest CO2 emissions from the same Dekina LGA can be attributed to the coarse texture of the soils as coarse soils are considerably more susceptible to releasing their carbon. On the other hand, the absence of variation in CO2 emission levels in some of the locations studied can be attributed to similar land management practices like tillage, bush burning and soil fertility management.

Which are the most favourable conditions for reducing soil CO2 emissions with no-tillage? Results from a meta-analysis

No-tillage practices have a recognised beneficial impact on soil and water conservation while reducing erosion processes and enhancing soil organic matter content. However, scientists continue to debate the effectiveness of no-tillage in reducing soil carbon dioxide (CO2) emissions from farming. Following the same line of inquiry pursued by the authors who reviewed the impact of conservative practices on direct CO2 emissions, we applied meta-analytic and machine learning techniques to unravel the effect of no-tillage under contrasting pedo-environmental conditions and agricultural management. We analysed fifty-six experimental studies investigating direct soil CO2 emissions from no-tillage and conventional tillage practices (102 paired observations), considering pedological (soil texture, soil organic carbon content), environmental (climate type), and management (crop rotation, experiment duration) factors. We estimated the effect of different practices on the daily amount of soil CO2 emissions, and the impact of tillage in the period immediately following the event. The main insights of this study are: (i) the conditions leading to the highest reduction of CO2 emissions due to no-tillage were long-term experiments (standardised mean difference βˆ = 0.64) conducted in arid environments (βˆ = 0.76) and clay soils (βˆ = 0.81), with low organic carbon content (βˆ = 0.79) where crop rotations (βˆ = 0.65) were performed; (ii) the same conditions were associated with the lowest absolute CO2 emissions, irrespective of soil management; (iii) the highest contribution to the variability of absolute soil CO2 emissions was associated with soil texture (mean decrease in accuracy of Random Forest models, MDA = 4.57), rotation (MDA = 3.07), experiment duration (MDA = 2.93) and soil organic carbon content (MDA = 2.24), rather than to tillage practices; (iv) soil CO2 emissions almost doubled in the first day after a tillage event, consistently across studies (p = 0.001). This meta-analysis offers quantitative figures on the impact of tillage practices on soil CO2 emissions and releases data for informing policies aimed at promoting climate change mitigation.

Interactive effects of microplastics, biochar, and earthworms on CO2 and N2O emissions and microbial functional genes in vegetable-growing soil

Soil carbon dioxide (CO2) and nitrous oxide (N2O) emissions are two main greenhouse gases that play important roles in global warming. Studies have shown that microplastics, biochar, and earthworms can significantly affect soil greenhouse gas emissions. However, few studies have explored how their interactions affect soil CO2 and N2O emissions. A mesocosm experiment was conducted to investigate their interactive effects on soil greenhouse gases and soil microbial functional genes in vegetable-growing soil under different incubation times. Biochar alone or combined with microplastics significantly decreased soil CO2 emissions but had no effect on soil N2O emissions. Microplastics and biochar inhibited CO2 emissions and promoted N2O emissions in the soil with earthworms. The addition of microplastics, biochar, and earthworms had significant effects on soil chemical properties, including dissolved organic carbon, ammonia nitrogen, nitrate nitrogen, total nitrogen, and pH. Microplastics and earthworms selectively influenced microbial abundances and led to a fungi-prevalent soil microbial community, while biochar led to a bacteria-prevalent microbial community. The interactions of microplastics, biochar, and earthworms could alleviate the reduction of the bacteria-to-fungi ratio and the abundance of microbial functional genes caused by microplastics and earthworms alone. Microplastics significantly inhibited microorganisms as well as C and N cycling functional genes in earthworm guts, while biochar obviously stimulated them. The influence of the addition of exogenous material on soil greenhouse gas emissions, soil chemical properties, and functional microbes differed markedly with soil incubation time. Our results indicated that biochar is a promising amendment for soil with microplastics or earthworms to simultaneously mitigate CO2 emissions and regulate soil microbial community composition and function. These findings contribute to a better understanding of the interaction effects of microplastics, biochar, and earthworms on soil carbon and nitrogen cycles, which could be used to help conduct sustainable environmental management of soil.

Responses of CO2 emissions and soil microbial community structures to organic amendment in two contrasting soils in Zambia

In sub-Saharan Africa, efforts have been made to increase soil carbon (C) content in agricultural ecosystems due to severe soil degradation. The use of organic materials is a feasible method for recovering soil organic C; however, the effects of organic amendments on soil microbial communities and C cycles under C-limited soil conditions are still unknown. In this study, we conducted field experiments in Zambia using organic amendments at two sites with contrasting C content. At both sites, temporal changes in soil carbon dioxide (CO2) emissions and prokaryotic community structures were monitored during the crop growing season (126 days). The organic amendments increased CO2 emissions and prokaryotic abundance at the Kabwe site, whereas no direct impacts were observed at the Lusaka site. We also observed a larger temporal variability in the soil microbial community structure at Kabwe than that at Lusaka. These contrasting results between the two soils may be due to the microbial community stability differences between each site. However, as organic amendments have considerable potential to enhance microbial abundance and consequently sequester C at the Kabwe site, site-specific strategies are required to address the issues of soil C depletion in drylands.

Polyethylene microplastics alter the microbial functional gene abundances and increase nitrous oxide emissions from paddy soils

The accumulation of microplastics (MPs) in terrestrial ecosystems can affect greenhouse gases (GHGs) production by changing soil structure and microbial functions. In this study, microcosm experiments were conducted to investigate the impact of polyethylene (PE) MP addition on soil carbon dioxide (CO2) and nitrous oxide (N2O) emissions from paddy soils and their associated microbial functional genes. Methane was not considered due to the negligible emissions throughout the incubation. The amendment of both virgin and aged PE MPs did not significantly (p > 0.05) affect soil CO2 emissions, but significantly (p < 0.05) increased the abundances of microbial functional genes encoding enzymes involved in hemicellulose (abfA) and lignin (mnp) decomposition, indicating plastic particle has potential to stimulate soil organic carbon decomposition. The presence of PE MP significantly increased N2O emissions by 3.7-fold, which was probably due to PE MP increased the abundances of nirS gene involved in nitrite reductase. In addition, compared with virgin PE MP treatment, artificially aged PE MP did not significantly (p > 0.05) influence soil CO2 and N2O emissions. Our results provide evidence that PE MP likely cause a high risk of N2O emission from paddy soils, this factor should be considered in future estimates of GHGs emissions from rice fields.

Assessment of the Short-Term Impact of Anaerobic Digestate on Soil C Stock and CO2 Emissions in Shallow Water Table Conditions

Anaerobic digestion has been recently proposed as a more sustainable energy supply chain able to strengthen the existing security of supply provisions. Anaerobic digestate (AD) is the by-product of the anaerobic digestion process and presents organic fertilizer characteristics, but its agronomic usage has been hindered by both agronomic and environmental concerns. In this study, the impact of agricultural liquid (LD) and solid (SD) AD and beef manure (Man) was evaluated on some agro-environmental characteristics. First, the AD fractions functional groups were characterized by FT-IR, and then LD and SD performances were evaluated on soil organic carbon (SOC) stock and carbon dioxide (CO2) emissions and compared to beef manure (Man). The fertilizer impact was also considered with the presence or absence of a shallow water table. Results showed that SD increased of ca. 3 t ha−1 the SOC stock in the 0–20 cm soil profile with respect to LD, while it was comparable to Man despite the lower C input (6.7 vs. 8.7 t C ha−1), due to the presence of more stable compounds (e.g., lignin). The CO2 fluxes were affected by both fertilizer type and water table level. In the absence of a water table, the CO2 emissions (5.5 g CO2 m2 d−1) were driven by carbon content and quality in the fertilizer, while the presence of a shallower water table hindered mineralization of stable SOC and, in turn, reduced emissions (4.4 g CO2 m2 d−1). AD can be considered a beneficial solution to both maintain soil fertility and, at the same time, give new insight into a circular economy model, although further investigation on GHG emissions is required.

Different pipe burial depths associated with subsurface drip irrigation significantly affected soil gas emissions

AbstractEfforts are needed to reduce soil greenhouse gas emissions from irrigated croplands. Thus, in this study, patterns of soil carbon dioxide (CO2) and nitrous oxide (N2O) emissions in the root zone of tomato plants grown under subsurface drip irrigation (SDI) involving different pipe burial depths were studied, with surface drip irrigation (DI) used as a control (CK). The soil CO2 and N2O emission curves under DI and SDI with pipe burial depths of 10 and 20 cm tended to be similar. In contrast, SDI with a pipe depth of 30 cm resulted in peak CO2 and N2O emissions occurring at different times. The different pipe burial depths led to significantly different spatial distributions of soil water‐filled pore space, which indirectly affected root–soil interactions and soil gas emissions through direct effects on total tomato root fork numbers and microbial community composition. The SDI treatments involving 10‐ and 20‐cm pipe burial depths increased the number of root forks to 1.85 and 2.77 times that in the DI treatment, respectively, and increased the Shannon index of the fungal community by 11.9 and 7.29% compared with that in the DI treatment, respectively. The SDI treatment involving the 30‐cm pipe burial depth resulted in 2.22 times the number of root forks compared with that in the DI treatment; however, the Shannon index of the fungal community decreased by 13.6% compared with that in the DI treatment. As a result, the total soil CO2 emissions and total soil N2O emissions in the SDI treatment involving the 10‐cm pipe burial depth were 1.37 and 2.03 times those in the DI treatment, and those in the SDI treatment involving the 20‐cm pipe burial depth were 1.33 and 2.17 times those in the DI treatment, respectively. In the SDI treatment involving the 30‐cm pipe burial depth, the total amount of soil CO2 emissions was similar to that in the DI treatment; however, the total amount of soil N2O emissions was 28.98% lower than that in the DI treatment. Therefore, soil gas emissions can be reduced by increasing the burial depth of irrigation pipes. These results provide insights into the control of soil gas emissions in agroecosystems.

Warming-induced greenhouse gas fluxes from global croplands modified by agricultural practices: A meta-analysis

Climate warming increases the emissions of soil greenhouse gases (GHGs) by stimulating carbon (C) and nitrogen (N) processes in terrestrial ecosystems, contributing to climate change. However, the responses of soil GHG fluxes to warming from global agricultural ecosystems remain unknown. Here, we evaluate the effects of warming on soil GHG fluxes from global croplands under different agro-ecosystems, cropping systems, crop species, and N fertilizer levels, and determine the potential mechanisms through a meta-analysis of field observations. The results showed that warming (+2.0 °C on average) significantly enhanced soil carbon dioxide (CO2) emissions (i.e., soil respiration) by 14.7% and nitrous oxide (N2O) fluxes by 12.6% across croplands and increased soil methane (CH4) uptake by 21.8% in uplands and CH4 release by 23.4% in paddy fields. The responses of C gas fluxes to warming were regulated by initial C substrates, initial wetness, and changes in temperature in croplands. The responses of N2O fluxes to warming were mainly associated with changed NH4+-N and NO3−-N as well as initial wetness and N fertilizer in croplands. The responses of soil GHG fluxes to warming were generally comparable among different crop species and N fertilizer levels, respectively. However, the responses of CO2 emissions and CH4 release to warming were significantly higher in upland-paddy fields than in uplands and paddy fields; the warming-induced changes in CH4 release was significantly greater in rotation cropping systems than in single- and double-cropping systems. This synthesis highlights the important role of climate warming in increasing soil GHG fluxes from croplands, underscoring the critical need for agricultural practice adjustment to mitigate climate change in the future.

Impact of environmental and soil factors in the prediction of soil carbon dioxide emissions under different tillage systems

Understanding the roles of natural drivers in greenhouse gas (GHG) emissions of arable fields is crucial for adequate agricultural management. This study investigated the combined effect of two tillage treatments (NT - no-tillage; CT - tillage with mouldboard ploughing) and environmental (air pressure, air temperature) and soil factors (total organic carbon, gravimetric water content and soil penetration resistance) on soil carbon dioxide (CO2) emissions in maize in 2020 and 2021. The soil tubes required for the laboratory measurement were derived from three different altitudes of the two differently cultivated fields from Fejér county, Hungary. The typical soil type was Chernozem in both fields. At the time of soil sampling, soil penetration resistance was measured with a 06.15SA Penetrologger in 10 repetitions. To preserve the moisture content of the soil columns during the investigation, moisture replenishment was performed equal to the degree of weekly theoretical evapotranspiration. Emissions measurements of soil columns were performed by close chamber technique for five weeks from sampling, 15 times, in 3 repetitions in laboratory conditions. The data were evaluated by two-way ANOVA, followed by the Tukey HSD multiple comparison test and two-tailed Student’s T-test at a significance level of p&lt;0.05. The combined effect of environmental factors on soil carbon dioxide emissions was investigated using stepwise multiple linear regression. It has been proved that the observed difference between soil penetration resistance and soil carbon dioxide emissions was significant between CT and NT cultivation at different stages of the growing season. The analysis of the interaction of the experimental factors revealed that the combined effect of soil penetration resistance, total organic carbon and moisture content in tillage system (adjusted R2=0.92 at a significance level of p=0.05) in 2020, while the combined effect of moisture content and air temperature in the no-tillage system (adjusted R2=0.79 at a significance level of p=0.085) has the most significant effect on soil CO2 emissions in 2020. In 2021, the air temperature for the tillage system (adjusted R2=0.74 at a significance level of p=0.05) and the combined effect of air temperature and pressure for no-tillage systems (adjusted R2=0.69 at a significance level of p=0.1) played an important role in soil CO2 emissions. These observations highlight that different soil and environmental factors of different tillage significantly impact the soil carbon dioxide emissions in different years.

Biochar amendments increase soil organic carbon storage and decrease global warming potentials of soil CH4 and N2O under N addition in a subtropical Moso bamboo plantation

Nitrogen (N) deposition affects soil greenhouse gas (GHG) emissions, while biochar application reduces GHG emissions in agricultural soils. However, it remains unclear whether biochar amendment can alleviate the promoting effects of N input on GHG emissions in forest soils. Here, we quantify the separate and combined effects of biochar amendment (0, 20, and 40 ​t·ha −1 ) and N addition (0, 30, 60, and 90 ​kg ​N·ha −1 ·yr −1 ) on soil GHG fluxes in a long-term field experiment at a Moso bamboo ( Phyllostachys edulis ) plantation. Low and moderate N inputs (≤60 ​kg ​N·ha −1 ·yr −1 ) significantly increase mean annual soil carbon dioxide (CO 2 ) and nitrous oxide (N 2 O) emissions by 17.0%–25.4% and 29.8%–31.2%, respectively, while decreasing methane (CH 4 ) uptake by 12.4%–15.9%, leading to increases in the global warming potential (GWP) of soil CH 4 and N 2 O fluxes by 32.4%–44.0%. Moreover, N addition reduces soil organic carbon (C; SOC) storage by 0.2%–6.5%. Compared to the control treatment, biochar amendment increases mean annual soil CO 2 emissions, CH 4 uptake, and SOC storage by 18.4%–25.4%, 7.6%–15.8%, and 7.1%–13.4%, respectively, while decreasing N 2 O emissions by 17.6%–19.2%, leading to a GWP decrease of 18.4%–21.4%. Biochar amendments significantly enhance the promoting effects of N addition on soil CO 2 emissions, while substantially offsetting the promotion of N 2 O emissions, inhibition of CH 4 uptake, and decreased SOC storage, resulting in a GWP decrease of 9.1%–30.3%. Additionally, soil CO 2 and CH 4 fluxes are significantly and positively correlated with soil microbial biomass C (MBC) and pH. Meanwhile, N 2 O emissions have a significant and positive correlation with soil MBC and a negative correlation with pH. Biochar amendment can increase SOC storage and offset the enhanced GWP mediated by elevated N deposition and is, thus, a potential strategy for increasing soil C sinks and decreasing GWPs of soil CH 4 and N 2 O under increasing atmospheric N deposition in Moso bamboo plantations. 1. N additions significantly increased CO 2 and N 2 O emissions but decreased CH 4 uptake 2. Biochar amendment increased CO 2 emission and CH 4 uptake but decreased N 2 O emission 3. Biochar amendment suppressed the increase of global warming potential by N deposition 4. Biochar amendment increased soil organic carbon storage under N deposition 5. Soil pH played a key role in influencing greenhouse gases fluxes

Lagged Wetland CH4 Flux Response in a Historically Wet Year

AbstractWhile a stimulating effect of plant primary productivity on soil carbon dioxide (CO2) emissions has been well documented, links between gross primary productivity (GPP) and wetland methane (CH4) emissions are less well investigated. Determination of the influence of primary productivity on wetland CH4 emissions (FCH4) is complicated by confounding influences of water table level and temperature on CH4 production, which also vary seasonally. Here, we evaluate the link between preceding GPP and subsequent FCH4 at two fens in Wisconsin using eddy covariance flux towers, Lost Creek (US‐Los) and Allequash Creek (US‐ALQ). Both wetlands are mosaics of forested and shrub wetlands, with US‐Los being larger in scale and having a more open canopy. Co‐located sites with multi‐year observations of flux, hydrology, and meteorology provide an opportunity to measure and compare lag effects on FCH4 without interference due to differing climate. Daily average FCH4 from US‐Los reached a maximum of 47.7 ηmol CH4 m−2 s−1 during the study period, while US‐ALQ was more than double at 117.9 ηmol CH4 m−2 s−1. The lagged influence of GPP on temperature‐normalized FCH4 (Tair‐FCH4) was weaker and more delayed in a year with anomalously high precipitation than a following drier year at both sites. FCH4 at US‐ALQ was lower coincident with higher stream discharge in the wet year (2019), potentially due to soil gas flushing during high precipitation events and lower water temperatures. Better understanding of the lagged influence of GPP on FCH4 due to this study has implications for climate modeling and more accurate carbon budgeting.

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

AbstractBackgroundBrachiaria humidicola (Bh) has the ability to produce biological nitrification inhibitors (NIs) and release NIs from the root to the soil.AimsTo compare the effects of growing Bh with Brachiaria ruziziensis (Br, which is not able to produce NIs) on soil nitrogen (N) dynamics, N gases 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 the measured 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.MethodsThe treatments were: (1) Bh with 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).ResultsResults 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.ConclusionsWe conclude that the residual effect of Bh to mitigate N2O emissions in a highly nitrifying soil is short‐lived.

Effects of microplastics on soil carbon dioxide emissions and the microbial functional genes involved in organic carbon decomposition in agricultural soil

The accumulation of microplastics (MPs) in agricultural fields can not only disguise soil organic carbon (SOC) storage but also affect the production of carbon dioxide (CO2) by microbial decomposition. However, little is known about the impact of this emerging pollutant on soil CO2 emissions and the functional genes related to SOC degradation. In the present study, a short-term (30-day) microcosm experiment was performed to investigate the effects of virgin and aged low-density polyethylene (LDPE) MPs on soil CO2 emissions. We also measured functional gene abundances related to starch (sga), hemicellulose (abfA, manB and xylA), cellulose (cex) and lignin (lig and mnp) degradation through a high-throughput quantitative-PCR-based chip. Compared with the soils without MPs, low doses (0.01% and 0.1%) of both virgin and aged MPs had negligible effects on SOC decomposition, whereas a high dose (1.0%) of these two MPs significantly (p < 0.05) accelerated the production of CO2 in soils by 15–17%, showing a dose-dependent effect. The presence of MPs did not significantly affect soil dissolved organic carbon or microbial biomass carbon. A higher metabolic quotient at 1.0% MP concentration indicated that the microbes were stressed and needed more substrates and energy during their metabolic process, which could likely explain the increase in CO2 emission induced by this dose of MPs. Exposure to virgin MPs significantly reduced the functional genes related to hemicellulose (abfA and manB) degradation, whereas increasing the aged MPs concentrations significantly decreased the abundances of functional genes encoding starch (sga), hemicellulose (abfA, manB and xylA), and cellulose (cex) hydrolysis. Overall, we conclude that the low dose (<0.1%) of MPs in the soils has a negligible effect on the production of CO2, but this factor should be considered in evaluating the global C budget in future research as this contaminant reaches a certain threshold (1.0%).

Greenhouse Gas Emissions and Crop Yields From Winter Oilseed Rape Cropping Systems are Unaffected by Management Practices

Winter oilseed rape is traditionally established via plough-based soil cultivation and conventional sowing methods. Whilst there is potential to adopt lower cost, and less intensive establishment systems, the impact of these on greenhouse gas emissions have not been evaluated. To address this, field experiments were conducted in 2014/2015 and 2015/2016 to investigate the effects of 1) crop establishment method and 2) sowing method on soil greenhouse gas emissions from a winter oilseed rape crop grown in Ireland. Soil carbon dioxide, nitrous oxide and methane emission measurements were carried out using the static chamber method. Yield (t seed ha−1) and the yield-scaled global warming potential (kg CO2-eq. kg−1 seed) were also determined for each management practice. During crop establishment, conventional tillage induced an initially rapid loss of carbon dioxide (2.34 g C m−2 hr−1) compared to strip tillage (0.94 g C m−2 hr−1) or minimum tillage (0.16 g C m−2 hr−1) (p &amp;lt; 0.05), although this decreased to background values within a few hours. In the crop establishment trial, the cumulative greenhouse gas emissions were, apart from methane, unaffected by tillage management when sown at a conventional (125 mm) or wide (600 mm) row spacing. In the sowing method trial, cumulative carbon dioxide emissions were also 21% higher when plants were sown at 10 seeds m−2 compared to 60 seeds m−2 (p &amp;lt; 0.05). Row spacing width (125 and 750 mm) and variety (conventional and semi-dwarf) were found to have little effect on greenhouse gas emissions and differences in seed yield between the sowing treatments were small. Overall, management practices had no consistent effect on soil greenhouse gas emissions and modifications in seed yield per plant countered differences in planting density.

Effects of Different Biochar Amendments on Soil Enzyme Activities and Carbondioxide Emission

ABSTRACT Biochar production from organic waste offers an important alternative for waste management, also improves soil properties (bio-physico-chemical) and reduces heavy metal pollution risk caused by the excessive use of chemical fertilizers applied directly to the soils. Biochar is also proposed as an important management strategy to mitigate the negative impacts of greenhouse gases, which are among the most important causes of global climate change. This study aimed to investigate the effects of biochars produced from six different plant wastes on soil enzyme activity, CO2–C emission, total nitrogen (Nt), and nitrate (NO3–N) concentrations. Almond shell (AS), tobacco waste (TW), pomegranate peel (PP), cotton waste (CW), orange peel (OP), and wheat straw (WS) biochars were applied to the soil at the rates of 0.5, 1.0, and 1.5%, and the biochar amended soils were incubated in the laboratory environment (25 ± 2) for 37 weeks. The highest CO2 ̶ C emission was recorded in OP biochar treatment, while the lowest emission was measured in PP treatment, indicating that OP biochar addition tended to decrease C mineralization in the soil. The addition of AS biochar significantly increased the dehydrogenase and urease enzyme activities, while urease activity did not show a significant increase. The results can be attributed to the differences in composition and properties (C: N ratio, pH) of the biochars applied as well as the nature of the feedstocks used in biochar production. Biochar applications increased the Nt and NO3–N concentrations of the soils, and the highest increase was obtained in the WS treatment. The results of the study revealed that PP biochar can be recommended to reduce CO2–C emission from soils, AS biochar has a significant effect on urease and dehydrogenase enzyme activities, and the effect of WS biochar on Nt and NO3–N concentrations of soils were higher than the other five biochar types.

Environmental controls and influences of Pinus roxburghii Sarg. (Chir pine) plantation on temporal variation in soil carbon dioxide emission and soil organic carbon stock under humid subtropical region.

Soil carbon dioxide emission is a major component of ecosystem respiration, responsible for organic carbon losses from the ecosystem. In Pinus roxburghii Sarg. plantations, higher CO2 emission coincided with maximum soil moisture and soil temperature during the rainy season (4.23µmol CO2m-2s-1) followed by summer season (1.69µmol CO2m-2s-1) and winter season (1.35µmol CO2m-2s-1). The soil CO2 emission rates recorded during the rainy season differed significantly from other seasons (p < 0.05). Multiple linear regression revealed that rainfall was the main dominant factor affecting the soil CO2 emission. A significant positive correlation with minimum air temperature and average air temperature during the lag period, i.e., preceding 15days of data, was recorded. A significant positive correlation was also observed between annual soil CO2 emission rates with soil temperature, soil moisture, air temperature, and rainfall (p < 0.05). Vapor pressure and relative humidity at 14.19h also emerged as additional scientific variables affecting soil CO2 emission with significant positive correlations. Annual soil CO2 emission rates and soil properties were not significantly correlated but were positively correlated with organic carbon, exchangeable potassium and negatively correlated with available nitrogen and phosphorous (p > 0.05). Higher annual average carbon stock, 95.05 t ha-1 in P. roxburghii plantations than the yearly soil CO2 emission, 33.23 t ha-1 indicates that plantations sequester more carbon than the emissions.

Effect of mulch, no-tillage and no-fertiliser as sustainable practices on soil organic carbon and carbon dioxide emission

The study seeks to investigate the compounding effects of various practices such as mulch, no-tillage, tillage and nitrogen based fertilizer on CO2 emission and soil organic carbon (SOC) in three successive crop cycles in the region of Vacoas, Mauritius. Nitrogen based fertilizer (ammonium sulphate) was applied at 120 kg/ha to its corresponding treatment, and maize mulch was applied as full coverage (24 t/ha). Three treatments: Mulch (M), Fertilizer (F), Tillage (T), were tested at 2 levels each, and replicated 3 times. The 2 levels were mulch-no mulch, fertilizer-no fertilizer and tillage-no tillage. Results have shown a correlation between CO2 and pH, where increase in CO2 flux was due to addition of fertilizer. Furthermore, application of mulch did not increase SOC in the short term. A negative correlation was equally found between available phosphorous and temperature which was attributed to the interactions that exist between temperature, photosynthesis and nutrient availability. The present study revealed that reduction in CO2 emission and increase in soil fertility can be achieved at farmer level by adopting mulching and no-till. These practices are both economical and farmer friendly. This is a first study of such kind in the soils of Mauritius, a volcanic Island in the Indian Ocean latitude 20° 17′ 53″ South and longitude 57° 28′ 42″ East.