Paul Voroney

Distribution of organic carbon in the stable soil humic fractions as affected by tillage management

Soil humus comprises a large and stable pool of soil organic matter (SOM); hence a better understanding of the fate of C in soil humic fractions can provide valuable information for the development of alternative tillage practices that will lead to long-term soil C sequestration. We used δ13C techniques to investigate the effects of tillage on the dynamics of native (C3–C) and corn derived C (C4–C) in fulvic acid (FA), humic acid (HA) and humin fractions. Humic substances were extracted from soils cropped to corn for 11 yr and managed under either conventional (CT) or no-tillage (NT), and from a conventionally tilled soil under > 55 yr of tobacco/rye rotation. No-tillage resulted in higher proportions of C4–C in the upper 5 cm and generally lower C4–C proportions below 5 cm than CT. Up to 31, 27 and 34% of C4–C were assimilated into FA, HA and humin fractions, respectively, indicating that even the humin fraction, often described as passive, old or resistant, acted as a sink of recently added C, and that ...

Carbon dioxide exchange dynamics over a mature switchgrass stand.

Switchgrass (Panicum virgatum L.) has gained importance as feedstock for bioenergy over the last decades due to its high productivity for up to 20 years, low input requirements, and potential for carbon sequestration. However, data on the dynamics of CO2 exchange of mature switchgrass stands (>5 years) are limited. The objective of this study was to determine net ecosystem exchange (NEE), ecosystem respiration (Re), and gross primary production (GPP) for a commercially managed switchgrass field in its sixth (2012) and seventh (2013) year in southern Ontario, Canada, using the eddy covariance method. Average NEE flux over two growing seasons (emergence to harvest) was −10.4 μmol m−2 s−1 and reached a maximum uptake of −42.4 μmol m−2 s−1. Total annual NEE was −380 ± 25 and −430 ± 30 g C m−2 in 2012 and 2013, respectively. GPP reached −1354 ± 23 g C m−2 in 2012 and −1430 ± 50g C m−2 in 2013. Annual Re in 2012 was 974 ± 20 g C m−2 and 1000 ± 35 g C m−2 in 2013. GPP during the dry year of 2012 was significantly lower than that during the normal year of 2013, but yield was significantly higher in 2012 with 1090 g m−2, compared to 790 g m−2 in 2013. If considering the carbon removed at harvest, the net ecosystem carbon balance came to 106 ± 45 g C m−2 in 2012, indicating a source of carbon, and to −59 ± 45 g C m−2 in 2013, indicating a sink of carbon. Our results confirm that switchgrass can switch between being a sink and a source of carbon on an annual basis. More studies are needed which investigate this interannual variability of the carbon budget of mature switchgrass stands.

Significance of physical weathering of two-texturally different soils for the saturated transport of Escherichia coli and bromide

This study was carried out to investigate the transport of Escherichia coli NAR and bromide (Br) through repacked (R) and weathered (W) soil columns. A suspension containing E. coli NAR and Br were leached and the effluent from the weathered soil columns had greater contaminant concentrations than that from the repacked soil columns. The time to the concentration peak of (C(max)) E. coli NAR and Br increased in the order CL-W < SL-W < SL-R < CL-R. The breakthrough sequence suggests the formation of a heterogeneous soil pore network induced by weathering and the importance of accelerated flow in the weathered columns. The dual-permeability model in HYDRUS-1D software was used to simulate the E. coli NAR and Br transport parameters by inverse modeling. Parameters of the attachment-detachment model were calculated using the dual-permeability model parameters fitted to the BTCs of E. coli NAR. A greater attachment coefficient associated with soil repacking and the finer textured clayey soil demonstrated the importance of adsorbent site and smaller pore spacing in these treatments. Smaller attachment and adsorption isotherm coefficients in weathered soil columns suggest the need for further research to validate this as a predictive model for the risks for vadose zone contaminant transport.

Assessment of carbon storage under rainforests in Humic Hapludox along a climosequence extending from the Atlantic coast to the highlands of northeastern Brazil

An understanding of the stock of soil organic carbon (SOC) in the umbric epipedon of Oxisols located in the tropical forests surrounded by a semi-arid region is limited but essential because of their importance in the global cycle of carbon (C). The purpose of this study was to assess the effects of climatic (temperature and rainfall), soil organic matter (SOM) composition and litter on the stability of C in surfaces and subsurfaces in five Humic Oxisols along a 475-km climosequence from 143 to 963ma.s.l. in a tropical environment in northeastern Brazil. We assessed vertical changes in SOC; soil total nitrogen (N); C from the microbial biomass; δ(13)C, δ(15)N and the humified composition of SOM; the composition of the humin (HUM) fraction by Fourier Transform Infrared (FTIR); and Thermogravimetry (TG) and Differential Scanning Calorimetry (DSC) at depth. The elemental and isotopic composition of the litter samples were analyzed in all areas studied. The results indicated that the current climate and recalcitrant organic compounds are not preponderant factors in the formation of the umbric epipedon, as suggested by the partial influence of temperature and rainfall on SOM. In addition, SOM was dominated by easily decomposable compounds, as indicated by the predominance of aliphatic C-H groups in the HUM fraction in the FTIR spectra; by the thermal oxidation through DSC-TG, which revealed that approximately 50% of the HUM was composed easily decomposable compounds; and by the high proportion of organic C present in the microbial biomass. Values of δ(13)C showed a predominance of C3 plant-C in SOM whereas δ(15)N patterns indicated that N dynamics differ among the profiles and drive the accumulation of C. These findings can help to characterize the susceptibility of these soils to changes in climate and land use and the implications for the sequestration of soil C.

Long-term Cultivation and Landscape Position Effects on Aggregate Size and Organic Carbon Fractionation on Surface Soil Properties in Semi-arid Region of Iran

ABSTRACT This study was carried out to investigate the effects of long-term cultivation and landscape position on organic carbon content and soil aggregation. Sampling sites were determined based upon land use at the end of 50 years soil use and management, cultivated/annual wheat cropping and grazed pasture, and landscape position in Chaharmahal-va-Bakhtiary province, southwest Iran. Soil samples were collected from the 0–5 cm and 5–15 cm depths in two adjacent fields that have the same slope and aspect. The soil was silty clay at the summit and footslope positions, and was a silty clay loam at the backslope. Wet-sieving analysis and aggregate-size fractionation methods were used to separate the samples into three aggregate fractions (i.e., 2–4.75, 0.25–2, and 0.053–0.25 mm). The treatments were arranged in a factorial design. Land use significantly affected the water-stable aggregate fractions, so that the wet soil stability of the macroaggregates (i.e., 2–4.75 mm) was higher in the pasture, whereas it was greater for the meso-aggregates (i.e., 0.25–2 mm) in the cultivated soils. Cultivation decreased both the wet-aggregate stability and percent of macroaggregates whereas long-term pasture enhanced aggregation. Soil organic carbon (SOC) content within aggregates and primary particles was also significantly influenced by landscape position, land use, and the depth of sampling. The SOC content was higher in clay than those in silt and sand contents. The SOC content decreased as depth increased in all fractions. In general, the highest and lowest wet-stable aggregates were observed on the footslope and backslope positions, respectively.

Sodium Persulfate and Potassium Permanganate Inhibit Methanogens and Methanogenesis in Stored Liquid Dairy Manure

Stored liquid dairy manure is a hotspot for methane (CH) emission, thus effective mitigation strategies are required. We assessed sodium persulfate (NaSO), potassium permanganate (KMnO), and sodium hypochlorite (NaOCl) for impacts on the abundance of microbial communities and CH production in liquid dairy manure. Liquid dairy manure treated with different rates (1, 3, 6, and 9 g or mL L slurry) of these chemicals or their combinations were incubated under anoxic conditions at 22.5 ± 1.3°C for 120 d. Untreated and sodium 2-bromoethanesulfonate (BES)-treated manures were included as negative and positive controls, respectively, whereas sulfuric acid (HSO)-treated manure was used as a reference. Quantitative real-time polymerase chain reaction was used to quantify the abundances of bacteria and methanogens on Days 0, 60, and 120. Headspace CH/CO ratios were used as a proxy to determine CH production. Unlike bacterial abundance, methanogen abundance and CH/CO ratios varied with treatments. Addition of 1 to 9 g L slurry of NaSO and KMnO reduced methanogen abundance (up to ∼28%) and peak CH/CO ratios (up to 92-fold). Except at the lowest rate, chemical combinations also reduced the abundance of methanogens (up to ∼17%) and CH/CO ratios (up to ninefold), although no impacts were observed when 3% NaOCl was used alone. With slurry acidification, the ratios reduced up to twofold, whereas methanogen abundance was unaffected. Results suggest that NaSO and KMnO may offer alternative options to reduce CH emission from stored liquid dairy manure, but this warrants further assessment at larger scales for environmental impacts and characteristics of the treated manure.