Maren Oelbermann

Evaluating carbon dynamics and microbial activity in arctic soils under warmer temperatures

A large portion of carbon (C) is stored in the world’s soils, including those of peatlands, wetlands and permafrost. However, there is disagreement regarding the effects of climate change on the rate of organic matter decomposition in permafrost soils of the arctic. In this study it was hypothesized that soil exposed to a higher ambient temperature would have a greater flux of CO2 as well as a change in the metabolic diversity of culturable soil microorganisms. To evaluate this hypothesis we determined soil C dynamics, soil microbial respiration and activity, and 13C and 15N fractionation in laboratory incubations (at 14 and 21°C) for an organic-rich soil (Mesic Organic Cryosol) and a mineral soil (Turbic Cryosol) collected at the Daring Lake Research Station in Canada’s Northwest Territories. Soil organic C (SOC) and nitrogen (N) stocks (g m-2) and concentration (%) were significantly different (P < 0.05) between soil horizons for both soil types. Stable isotope analysis showed a significant enrichment i...

Crop Residue Input and Decomposition in a Temperate Maize-soybean Intercrop System

Producers in the Argentine Pampa are implementing legume-based intercropping to maintain crop productivity. The objectives of this study were to quantify carbon (C) and N inputs from crop residues and their rate of decomposition in maize (Zea mays L.) and soybean (Glycine max L. Merr.) sole crops and two intercropping systems [1:2 intercrop (one row of maize and two rows of soybeans) and 2:3 intercrop (two rows of maize and three rows of soybeans)]. Carbon input from crop residues was significantly greater (P < 0.05) in the maize sole crop and 2:3 intercrop, but N input from crop residues was not significantly different between treatments. The amount of C and N remaining after 9 months of crop residue decomposition was significantly different between treatments, with the significantly lowest amount of residue C and N remaining in the soybean sole crop. The decay rate constant (k) and half-lives (t1/2) for crop residues C and N were significantly different between treatments. The highest k value was observed in the soybean sole crop and the lowest in the maize sole crop, whereas values for the intercrops were between those of the sole crops. Based on the values of crop residue input, the contribution of this organic material, the more difficult to decompose portion of soil organic matter was greatest in the maize sole crop followed by the 2:3 and 1:2 intercrops and the soybean sole crop. The amount of N mineralized was greatest in the soybean sole crop, followed by the maize sole crop, and the 2:3 and 1:2 intercrops. Results from this study contributed further information on the most optimal non-legume-legume configuration to maximize the long-term sequestration of C in the soil.

Quantifying carbon dioxide and methane emissions and carbon dynamics from flooded boreal forest soil.

The boreal forest is subject to natural and anthropogenic disturbances, but the production of greenhouse gases as a result of flooding for hydroelectric power generation has received little attention. It was hypothesized that flooded soil would result in greater CO(2) and CH(4) emissions and carbon (C) fractionation compared with non-flooded soil. To evaluate this hypothesis, soil C and nitrogen (N) dynamics, CO(2) and CH(4) mean production rates, and (13)C fractionation in laboratory incubations at 14 and 21 degrees C under non-flooded and flooded conditions and its effect on labile and recalcitrant C sources were determined. A ferro-humic Podzol was collected at three different sites at the Experimental Lakes Area, Canada, with a high (19,834 g C m(-2)), medium (18,066 g C m(-2)), and low (11,060 g C m(-2)) soil organic C (SOC) stock. Soil organic C and total N stocks (g m(-2)) and concentrations (g kg(-1)) were significantly different (p < 0.05) among soil horizons within each of the three sites. Stable isotope analysis showed a significant enrichment in delta(13)C and delta(15)N with depth and an enrichment in delta(13)C and delta(15)N with decreasing SOC and N concentration. The mean CO(2) and CH(4) production rates were greatest in soil horizons with the highest SOC stock and were significantly higher at 21 degrees C and in flooded treatments. The delta(13)C of the evolved CO(2) (delta(13)C-CO(2)) became significantly enriched with time during decomposition, and the greatest degree of fractionation occurred in the organic Litter, Fungal, and Humic forest soil horizons and in soil with a high SOC stock compared with the mineral horizon and soil with a lower SOC stock. The delta(13)C-CO(2) was significantly depleted in flooded treatments compared with non-flooded treatments.

Decomposition of Erythrina poeppigiana leaves in 3-, 9-, and 18-year-old alleycropping systems in Costa Rica

Timing the application of organic residues and therefore the release of nutrients during decomposition may be critical to the growing crop in tropical alleycropping agroforestry systems. Field experiments were carried out in Turrialba, Costa Rica, to determine differences in Erythrina poeppigiana (Walp.) O.F. Cook leaf decomposition in 3, 9 and 18-year alleycropped agroforestry systems. Treatments consisted of mulch-only, and mulch plus Arachis pintoi Krapov. and W. Gregory var. CIAT 18347 in 3 and 9-year old alleycrops under no-till cultivation. The 18-year old site consisted of treatments with mulch-only and mulch plus chicken manure under disk plow cultivation. Litterbags, filled with E. poeppigiana leaves from 3, 9 and 18-year old trees, were placed on the soil surface and collected over a period of 84 days. Results showed no significant differences in the amount of plant residues remaining after 84 days in the 3-, 9-, and 18-year-old systems, or between the manure and mulch-only treatments. Comparing mulch-only treatments, leaves in the 18-year old system decomposed most rapidly which may be due to disk-plow cultivation practices where litterbags were in direct contact with the soil as opposed to the no-till system in the younger alleycrops.

An evaluation of biochar pre-conditioned with urea ammonium nitrate on maize (Zea mays L.) production and soil biochemical characteristics

Dil, M., Oelbermann, M. and Xue, W. 2014. An evaluation of biochar pre-conditioned with urea ammonium nitrate on maize (Zea mays L.) production and soil biochemical characteristics. Can. J. Soil Sci. 94: 551-562. Biochar can enhance soil fertility, plant nutrient uptake and crop production. Using a potted study, we quantified the effects of adding biochar at 1 t ha-1 (Char), biochar pre-conditioned with urea ammonium nitrate [UAN (Char+)], or UAN only to a control (Contr) with no amendments on maize (Zea mays L.) biomass production, tissue carbon (C) and nitrogen (N) concentrations, N uptake (NU), N utilization efficiency (NUtE), and soil chemistry and biology in coarse-, medium- and fine-textured soils over 6 wk. Soil pH decreased (P<0.05) in Char+ and UAN treatments for all soil textures. Soil organic carbon (SOC) increased (P<0.05) in the coarse and medium textured soil in Char and Char+ treatments. Soil ammonium and soil nitrate were different (P<0.05) among treatments; increasing or decreasing depending upon soil texture. Soil microbial biomass C was lowest (P<0.05) in the UAN treatment for all soil textures. Soil potential microbial activity was significantly greater in the coarse-textured soil in only the Char and Char+ treatments. Maize biomass, tissue N concentration, and NU increased (P<0.05) in soils amended with Char+ or UAN only. NUtE was lower (P<0.05) in Char+ and UAN treatments in the coarse- and medium-textured soils, but this was reversed for the fine-textured soil.

Gliricidia sepium Carbon Inputs and Soil Carbon Pools in a Costa Rican Alley Cropping System

Alternative land management practices, including agroforestry, help to maintain levels of soil organic matter (SOM) and can facilitate soil carbon (C) sequestration for mitigating atmospheric CO2 emissions. This study quantified C inputs and determined the changes of the soil C pool in a 19-year-old Gliricidia sepium alley cropping system, studied at two fertiliser levels (tree prunings only [− N], and tree prunings plus chicken manure [+ N]), and was compared to a sole crop system. Carbon input from tree prunings ranged from 455 to 457 g C m− 2 y− 1, whereas C inputs from crop residues were similar between alley- and sole crops ranging from 121 to 159 g C m− 2y− 1. The soil organic C (SOC) pool in the alley crop was 16–23% higher than the sole crop. In the 19th year of alley farming, SOC was significantly higher (p < 0.05) in the alley crop (3.2%) compared to the sole crop (2.4%), and was also greater compared to that at the time of establishment of the agroforestry system (2.8%). Gross SOC turnover to a 20-cm depth ranged from 12 to 14 years in the + N and −N alley crops compared to 49 and 50 years in the + N and −N treatments for the sole crops. Residue stabilisation efficiency in the alley crops was 39% and 55% in + N and −N treatments respectively.

Depth-dependent influence of different land-use systems on bacterial biogeography

&NA; Despite progress in understanding microbial biogeography of surface soils, few studies have investigated depth‐dependent distributions of terrestrial microorganisms in subsoils. We leveraged high‐throughput sequencing of 16S rRNA genes obtained from soils collected from the rare Charitable Research Reserve (Cambridge, ON, Canada) to assess the influence of depth on bacterial communities across various land‐use types. Although bacterial communities were strongly influenced by depth across all sites, the magnitude of this influence was variable and demonstrated that land‐use attributes also played a significant role in shaping soil bacterial communities. Soil pH exhibited a large gradient across samples and strongly influenced shifts in bacterial communities with depth and across different land‐use systems, especially considering that physicochemical conditions showed generally consistent trends with depth. We observed significant (p ≤ 0.001) and strongly correlated taxa with depth and pH, with a strong predominance of positively depth‐correlated OTUs without cultured representatives. These findings highlight the importance of depth in soil biogeographical surveys and that subsurface soils harbour understudied bacterial members with potentially unique and important functions in deeper soil horizons that remain to be characterized.

Sequestration of native soil organic carbon and residue carbon in complex agroecosystems

ABSTRACT Knowing short-term gains and losses of soil organic carbon (SOC) is crucial for understanding the role of different land management practices in climate change mitigation. This study evaluated the flow of carbon (C) in soil from two differently configured intercrops [1:2 (one row of maize and two rows soybean); 2:3 (two rows of maize and three rows of soybean)] compared to a maize and soybean sole crop as a result of residue addition. Addition of soybean or maize residues significantly increased (p < 0.05) SOC, light fraction (LF-C), and soil microbial biomass (SMB). Soil organic C from native sources was significantly greater (p < 0.05) than C from new (residue) sources. The LF had a significantly greater (p < 0.05) C content from new sources. Treatments amended with soybean residue had a significantly greater (p < 0.05) contribution from new C sources for SOC and LF than treatments amended with maize residue. The SMB-C was significantly greater (p < 0.05) in the 2:3 intercrop. Cumulative soil CO2 emission was significantly lower (p < 0.05) in intercrops than in sole crops. CO2 emissions derived from new C sources was significantly greater (p < 0.05) than that derived from native sources in maize amended treatments; and not significantly different (p < 0.05) for treatments amended with soybean residues.

Inundating contrasting boreal forest soils: CO2 and CH4 production rates.

Abstract: Flooding boreal forest ecosystems for hydroelectric power generation may release substantial amounts of carbon (C) to the atmosphere, contributing to global warming. The objectives of this study were to evaluate CO2 and CH4 production rates using spring/fall (14 °C) and summer (21 °C) temperatures under non-flooded and flooded conditions. Incubation temperatures represented the mean annual air temperature in May and September (14 °C), and in July (21 °C). Greenhouse gas production rates were quantified using laboratory incubations of 2 contrasting soil types (Humo-Ferric Podzol [very dry, mineral] and a Histic Folisol [moist, organic]) collected at the Experimental Lakes Area in northwestern Ontario, Canada. The mean production rate of CO2 and CH4 in the headspace of the incubation jars was significantly influenced by temperature, flooding and soil type. Results showed that the mean CO2 (65 [Podzol]; 43 [Folisol]) and CH4 (0.06 [Podzol]; 0.06 [Folisol]) production rates (µg·g-1·d-1) were significantly higher (P < 0.05) at 21 °C and in flooded treatments from both soil types. The greatest CO2 and CH4 production rates (µg·-1·d-1) occurred from the Folisol (110 [CO2]; 0.03 [CH4]) and the L and FH horizons of the Podzol (250 [CO2]; 0.05 [CH4]). Q10 values showed that decomposition of soil organic matter was more temperature dependent in non-flooded treatments, with values ranging from 1.57 to 5.03, than in flooded treatments (1.31 to 3.58). The greatest loss of soil organic carbon relative to the original C content (g·m-2) occurred in the Ah horizon of the Podzol in non-flooded (0.01% [14 °C]; 0.02% [21°C]) and flooded (0.02% [14 °C]; 0.03% [21 °C]) treatments and at both temperatures. Information presented in this paper helps to evaluate how 2 contrasting soil types (Podzol and Folisol) responded to flooding and provided further insight into the dynamics of greenhouse gas (GHG) production rates as a result of hydroelectric reservoir creation. This will aid in future planning, construction, and management of hydroelectric reservoirs to help minimize GHG emissions and boreal forest disturbance.

Local food production in a subarctic Indigenous community: the use of willow (Salix spp.) windbreaks to increase the yield of intercropped potatoes (Solanum tuberosum) and bush beans (Phaseolus vulgaris)

ABSTRACT Addressing food security with local and sustainable food production is a key requirement for supporting a globally sustainable agricultural system. Food insecurity is prevalent in Indigenous communities in Canada, especially in rural and remote regions of northern (subarctic and arctic) Canada. Further, climate change has disproportionately impacted subarctic and arctic regions worldwide − surface air temperatures are now more favourable for agricultural activities − offering the potential for local food production under ambient conditions. The objectives of the present study were to evaluate bush bean (Phaseolus vulgaris L.) and potato (Solanum tuberosum L.) intercrops grown over a two-year period in two sites (treed, windbreak-lined with native willow, Salix. spp.; and non-treed, or open) in the subarctic Indigenous community of Fort Albany First Nation, Ontario, Canada. Intercrops grown in the windbreak-lined site produced significantly greater (p < 0.05) yields and biomass than the open site. An analysis of soil chemistry (pH, P, K, Mg, NO3, NH4 and total N) showed that with some local amendments such as offal and bone meal, both the windbreak-lined and open sites can support continued agricultural use. This study informs Indigenous communities across subarctic regions of the world that climate change not only brings challenges, but also opportunities, such as potentially sustainable local food production.