Ongoing conversion of forests in Sumatra to agricultural lands might affect the biodiversity of soil fauna, such as termites, and emissions of nitrous oxide (N2O), methane (CH4) and carbon dioxide (CO2). To assess the impact of such forest conversions, this study was conducted in Jambi, Sumatra in an undisturbed forest (FR), a disturbed forest (DF), a one year old rubber plantation (RB1), a twenty year old rubber plantation (RB20) and an oil palm plantation (OP). The plantations belonged to smallholders and were not usually fertilized. The effect of fertilizer was assessed by applying N fertilizer and taking a series of intensive measurements. The N2O, CH4 and CO2 fluxes were measured using static chamber methods and termite species richness was assessed using a standard semi quantitative transect method. Forest conversion to smallholder plantations did not significantly affect the N2O, CH4 and CO2 fluxes, but the diversity and relative abundance of termites was decreased. this implies that the ecosystem services regulated by termites might decline. The application of N fertilizer at the conventional rate (141 kg N ha-1 y-1), with an emission factor of 3.1 % in the oil palm plantation, increased N2O emissions to twice as high as that in the undisturbed forest. The annual N2O and CH4 fluxes from termites amounted to 0.14, 0.21, 0.88, 2.47 and – 0.56 kg ha-1 y-1 N2O-N and 0.85, 1.65, 3.80, 0.97 and 2.30 kg ha-1 y-1 CH4-C in the FR, DF, RB1, RB20 and OP, respectively. Further research is needed to understand the interannual variability of the N2O, CH4 and CO2 fluxes from soils and termites. Understanding the key drivers and underlying processes which regulate them would help to control the biodiversity loss and the change of N2O, CH4 and CO2 fluxes from soils and termites.
Tag: nitrous oxide
Conversion of degraded forests to oil palm plantations in the Peruvian Amazonia: Shifts in soil and ecosystem-level greenhouse gas fluxes
The expansion of oil palm (OP) plantations and associated forest clearance can significantly impact greenhouse gas (GHG) fluxes. This study examined carbon stocks and soil GHG emissions (N₂O, CO₂, CH₄) in a degraded forest and a neighboring 17-year-old OP plantation in Peruvian Amazonia, where three nitrogen (N) fertilizer treatments were applied: 0 kg (OPN0), 84 kg (OPN1), and 168 kg (OPN2) per hectare per year. Carbon stocks were measured across different pools, and GHG fluxes and environmental parameters were monitored monthly over 11 months and (bi)daily during fertilizer application, with measurements taken near and far from trees/palms. Ecosystem-scale CO₂ equivalent losses were calculated by balancing carbon stock losses against N₂O emission changes. Findings showed that: (1) N₂O emissions (kg N ha⁻¹ y⁻¹) were highest in the degraded forest (6.7 ± 1.2), where litterfall N inputs were substantial (213 kg N ha⁻¹ y⁻¹). Emissions in OP plantations were significantly lower: OPN0 (0.6 ± 0.2), OPN1 (1.4 ± 0.2), OPN2 (2.3 ± 0.3). (2) Soil respiration (Mg C ha⁻¹ y⁻¹) was 1.4 times higher in the forest (9.1 ± 0.6) compared to OP plantation treatments (OPN0: 7.3 ± 1, OPN1: 5.5 ± 0.5, OPN2: 6.5 ± 0.3). (3) The forest acted as a CH₄ sink (-1.5 ± 0.3 kg C ha⁻¹ y⁻¹), whereas all OP treatments were sources (OPN0: 0.2 ± 0.3, OPN1: 0.7 ± 0.5, OPN2: 0.2 ± 0.4). (4) Carbon stock losses from forest-to-OP conversion were significant (196.8 ± 44.0 Mg CO₂ ha⁻¹ over 15 years) but were partially offset (14–20%) by reduced N₂O emissions. These findings highlight the complex GHG trade-offs associated with OP expansion, reinforcing the need for complementary studies to enhance global GHG assessments.
Through their eyes: Indigenous film making in western China
Arbuscular mycorrhiza fungi spore density and root colonization in a dry Afromontane forest in northern Ethiopia
Ammonia and nitrous oxide emissions from a field Ultisol amended with tithonia green manure, urea, and biochar
Short-term mitigation of ammonia (NH3) and nitrous oxide (N2O) emissions by biochar soil amendments has been reported, but limited knowledge of the mechanisms, particularly those associated with long term changes, remain relatively unknown. In order to investigate potential mechanisms and residual effect of biochar on NH3 and N2O emission, a 3-year field trial was set up on an Ultisol in western Kenya with a three-replicate full factorial treatment structure. The factors investigated include the following: biochar (from eucalyptus wood, pyrolyzed at 550 °C, applied once before the start of the experiment at either 0 or 2.5 t ha−1); tithonia green manure applied at the start of each season at either 0, 2.5, or 5.0 t ha−1; mineral nitrogen (N) (as urea applied each season at either 0 or 120 kg N ha−1). NH3 as well as N2O emission and water-filled pore space (WFPS) were monitored throughout the 3 years. In the third year, soil mineral nitrogen (exchangeable NH4+ and NO3−) contents were measured. Biochar reduced cumulative emissions of NH3 and N2O by 47 ± 5 and 22% ± 3, respectively, over the 3 years. Over the 3 years, the effect size of biochar was reduced by 53 and 59% for NH3 and N2O, respectively, indicating that the residual effect of biochar on NH3 and N2O persists at least up to 3 years under field conditions. Tithonia and urea additions increased both gas emissions by 13–68% compared to the control. Combination of the three amendments reduced cumulative NH3 emissions by 18 ± 3%, but had no effect on cumulative N2O. Our results show that biochar can influence emissions of NH3 and N2O longer than most previous studies have reported but is not explained by N dynamics. Other mechanisms such as direct interactions with oxidized biochar surfaces could be more likely to account for the residual effect of biochar on NH3 and N2O in agricultural soils.
Greenhouse gas fluxes from agricultural soils of Kenya and Tanzania
Knowledge of greenhouse gas (GHG) fluxes in soils is a prerequisite to constrain national, continental, and global GHG budgets. However, data characterizing fluxes from agricultural soils of Africa are markedly limited. We measured carbon dioxide (CO2), nitrous oxide (N2O), and methane (CH4) fluxes at 10 farmer-managed sites of six crop types for 1 year in Kenya and Tanzania using static chambers and gas chromatography. Cumulative emissions ranged between 3.5–15.9 Mg CO2-C ha−1 yr−1, 0.4–3.9 kg N2O-N ha−1 yr−1, and −1.2–10.1 kg CH4-C ha−1 yr−1, depending on crop type, environmental conditions, and management. Manure inputs increased CO2 (p = 0.03), but not N2O or CH4, emissions. Soil cultivation had no discernable effect on emissions of any of the three gases. Fluxes of CO2 and N2O were 54–208% greater (p < 0.05) during the wet versus the dry seasons for some, but not all, crop types. The heterogeneity and seasonality of fluxes suggest that the available data describing soil fluxes in Africa, based on measurements of limited duration of only a few crop types and agroecological zones, are inadequate to use as a basis for estimating the impact of agricultural soils on GHG budgets. A targeted effort to understand the magnitude and mechanisms underlying African agricultural soil fluxes is necessary to accurately estimate the influence of this source on the global climate system and for determining mitigation strategies.
Unexpected results of a pilot throughfall exclusion experiment on soil emissions of CO2, CH4, N2O, and NO in eastern Amazonia
The eastern Amazon Basin may become drier as a result of less regional recirculation of water in a largely deforested landscape and because of increased frequency and intensity of El Niño events induced by global warming. Drier conditions may affect several plant and soil microbial processes, including soil emissions of CO2, CH4, NO, and N2O. We report here unanticipated results of a pilot study that was initiated to test the feasibility of a larger-scale throughfall exclusion experiment. In particular, soil drying caused a switch from net consumption of atmospheric CH4 by soils in the control plot to net CH4 emission from soils in the experimentally dried plot. This result is surprising because production of CH4 requires anaerobic microsites, which are uncommon in dry soil. A plausible explanation for increased CH4 emissions in the dried plot is that dry soil conditions favor termite activity and increased coarse root mortality provides them with a substrate. Another surprise was that both NO and N2O fluxes were elevated several years after initiation of the drying experiment. Apparently, a pulse of N availability caused by experimental drying persisted for at least 3 years. As expected, CO2 emissions were lower in the dried plots, which is consistent with lower rates of root growth observed in root in-growth cores placed in the dried plots. More work is needed to test these explanations and to confirm these phenomena, but these results demonstrate that changes in climate could have unanticipated effects on biogeochemical processes in soils that we do not adequately understand.
Effect of improved fallow on crop productivity, soil fertility and climate-forcing gas emissions in semi-arid conditions
The impacts of fallow on soil fertility, crop production and climate-forcing gas emissions were determined in two contrasting legumes, Gliricidia sepium and Acacia colei, in comparison with traditional unamended fallow and continuous cultivation systems. After 2 years, the amount of foliar material produced did not differ between the two improved fallow species; however, grain yield was significantly elevated by 55% in the first and second cropping season after G. sepium compared with traditional fallow. By contrast, relative to the unamended fallow, a drop in grain yield was observed in the first cropping season after A. colei, followed by no improvement in the second. G. sepium had higher foliar N, K and Mg, while A. colei had lower foliar N but higher lignin and polyphenols. In the third year after fallow improvement, a simulated rainfall experiment was performed on soils to compare efflux of N2O and CO2. Improved fallow effects on soil nutrient composition and microbial activity were demonstrated through elevated N2O and CO2 efflux from soils in G. sepium fallows compared with other treatments. N2O emissions were around six times higher from this nitrogen-fixing soil treatment, evolving 69.9 ngN2O–N g1soil h1 after a simulated rainfall event, compared with only 8.5 and 4.8 ngN2O–N g1soil h1 from soil under traditional fallow and continuous cultivation, respectively. The findings indicate that selection of improved fallows for short-term fertility enhancement has implications for regional N2O emissions for dry land regions.
Testing a Conceptual Model of Soil Emissions of Nitrous and Nitric Oxides: Using two functions based on soil nitrogen availability and soil water content, the hole-in-the-pipe model characterizes a large fraction of the observed variation of nitric oxide and nitrous oxide emissions from soils
In this article, we briefly review the disciplinary researchon soil emissions of N2O and NO. We describe a mechani s ti c a lly based con ceptual model—the “h o l e – i n – t h e -pipe” (HIP) model (Firestone and Davidson 1989)—thatintegrates the results of these disciplinary studies and thatrelates emissions of both nitrogen oxides to common soilprocesses. We then test the model predictions, using datafrom our recent studies in Costa Rica (Veldkamp et al.1999), Brazil (Verchot et al.1999),and Puerto Rico (Erickson,etal. in press) and additional data from the literaturefor forest ecosystems throughout the world.
Management intensity controls soil N2O fluxes in an Afromontane ecosystem
Studies that quantify nitrous oxide (N2O) fluxes from African tropical forests and adjacent managed land uses are scarce. The expansion of smallholder agriculture and commercial agriculture into the Mau forest, the largest montane forest in Kenya, has caused large-scale land use change over the last decades. We measured annual soil N2O fluxes between August 2015 and July 2016 from natural forests and compared them to the N2O fluxes from land either managed by smallholder farmers for grazing and tea production, or commercial tea and eucalyptus plantations (n = 18). Air samples from 5 pooled static chambers were collected between 8:00 am and 11:30 am and used within each plot to calculate the gas flux rates. Annual soil N2O fluxes ranged between 0.2 and 2.9 kg N ha- 1 yr- 1 at smallholder sites and 0.6–1.7 kg N ha- 1 yr- 1 at the commercial agriculture sites, with no difference between land uses (p = 0.98 and p = 0.18, respectively). There was marked variation within land uses and, in particular, within those managed by smallholder farmers where management was also highly variable. Plots receiving fertilizer applications and those with high densities of livestock showed the highest N2O fluxes (1.6 ± 0.3 kg N2O-N ha- 1 yr- 1, n = 7) followed by natural forests (1.1 ± 0.1 kg N2O-N ha- 1 yr- 1, n = 6); although these were not significantly different (p = 0.19). Significantly lower fluxes (0.5 ± 0.1 kg N ha- 1 yr- 1, p < 0.01, n = 5) were found on plots that received little or no inputs. Daily soil N2O flux rates were not correlated with concurrent measurements of water filled pore space (WFPS), soil temperature or inorganic nitrogen (IN) concentrations. However, IN intensity, a measure of exposure of soil microbes (in both time and magnitude) to IN concentrations was strongly correlated with annual soil N2O fluxes.