Comparison of three carbon determination methods on naturally occurring substrates and the implication for the quantification of 'soil carbon'

Soil Research ◽  
2011 ◽  
Vol 49 (1) ◽  
pp. 27 ◽  
Author(s):  
M. K. Conyers ◽  
G. J. Poile ◽  
A. A. Oates ◽  
D. Waters ◽  
K. Y. Chan
Keyword(s):  
Soil Carbon ◽  
Annual Variation ◽  
Organic Substrates ◽  
Test Procedures ◽  
Organic C ◽  
Soil C ◽  
Long Term Trends ◽  
Carbon Determination ◽  
Almost All

Accounting for carbon (C) in soil will require a degree of precision sufficient to permit an assessment of any trend through time. Soil can contain many chemically and physically diverse forms of organic and inorganic carbon, some of which might not meet certain definitions of ‘soil carbon’. In an attempt to assess how measurements of these diverse forms of C might vary with analytical method, we measured the C concentration of 26 substrates by three methods commonly used for soil C (Walkley–Black, Heanes, and Leco). The Heanes and Leco methods were essentially equivalent in their capture of organic C, but the Leco method captured almost all of the inorganic C (carbonates, graphite). The Heanes and Walkley–Black methods did not measure carbonates but did measure 92% and 9%, respectively, of the C in graphite. All three of the common soil test procedures measured some proportion of the charcoal and of the other burnt materials. The proportion of common organic substrates (not the carbonates, graphite, or soil) that was C by weight ranged from ~10% to 90% based on the Heanes and Leco data. The proportion of the organic fraction of those same substrates, as measured by loss-on-ignition, that was C by weight ranged from 42% to 100%. The relationship between Walkley–Black C and total C (by Heanes and Leco) showed that Walkley–Black C was a variable proportion of total C for the 26 substrates. Finally, the well-known, apparent artefact in the Cr-acid methods was investigated: dichromate digestion should contain at least 7–10 mg C in the sample or over-recovery of C might be reported. Our observation that common soil C procedures readily measure C in plant roots and shoots, and in burnt stubble, means that there will likely be intra-annual variation in soil C, because avoidance of these fresh residues is difficult. Such apparent intra-annual variation in soil C will make the detection of long-term trends problematic.

Changes in soil carbon under long-term maize in monoculture and legume-based rotation

2001 ◽  
Vol 81 (1) ◽  
pp. 21-31 ◽  
Author(s):  
E G Gregorich ◽  
C F Drury ◽  
J A Baldock
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Organic Matter ◽  
Soil Organic Matter ◽  
Magnetic Resonance ◽  
Soil Carbon ◽  
Crop Residues ◽  
Cropping Systems ◽  
Natural Abundance ◽  
Organic C ◽  
Soil C

Legume-based cropping systems could help to increase crop productivity and soil organic matter levels, thereby enhancing soil quality, as well as having the additional benefit of sequestering atmospheric C. To evaluate the effects of 35 yr of maize monoculture and legume-based cropping on soil C levels and residue retention, we measured organic C and 13C natural abundance in soils under: fertilized and unfertilized maize (Zea mays L.), both in monoculture and legume-based [maize-oat (Avena sativa L.)-alfalfa (Medicago sativa L.)-alfalfa] rotations; fertilized and unfertilized systems of continuous grass (Poa pratensis L.); and under forest. Solid state 13C nuclear magnetic resonance (NMR) was used to chemically characterize the organic matter in plant residues and soils. Soils (70-cm depth) under maize cropping had about 30-40% less C, and those under continuous grass had about 16% less C, than those under adjacent forest. Qualitative differences in crop residues were important in these systems, because quantitative differences in net primary productivity and C inputs in the different agroecosystems did not account for observed differences in total soil C. Cropping sequence (i.e., rotation or monoculture) had a greater effect on soil C levels than application of fertilizer. The difference in soil C levels between rotation and monoculture maize systems was about 20 Mg C ha-1. The effects of fertilization on soil C were small (~6 Mg C ha-1), and differences were observed only in the monoculture system. The NMR results suggest that the chemical composition of organic matter was little affected by the nature of crop residues returned to the soil. The total quantity of maize-derived soil C was different in each system, because the quantity of maize residue returned to the soil was different; hence the maize-derived soil C ranged from 23 Mg ha-1 in the fertilized and 14 Mg ha-1 in the unfertilized monoculture soils (i.e., after 35 maize crops) to 6-7 Mg ha-1 in both the fertilized and unfertilized legume-based rotation soils (i.e., after eight maize crops). The proportion of maize residue C returned to the soil and retained as soil organic C (i.e., Mg maize-derived soil C/Mg maize residue) was about 14% for all maize cropping systems. The quantity of C3-C below the plow layer in legume-based rotation was 40% greater than that in monoculture and about the same as that under either continuous grass or forest. The soil organic matter below the plow layer in soil under the legume-based rotation appeared to be in a more biologically resistant form (i.e., higher aromatic C content) compared with that under monoculture. The retention of maize residue C as soil organic matter was four to five times greater below the plow layer than that within the plow layer. We conclude that residue quality plays a key role in increasing the retention of soil C in agroecosystems and that soils under legume-based rotation tend to be more “preservative” of residue C inputs, particularly from root inputs, than soils under monoculture. Key words: Soil carbon, 13C natural abundance, 13C nuclear magnetic resonance, maize cropping, legumes, root carbon

Herbage biomass and its relationship to soil carbon under long-term grazing in northern temperate grasslands

2019 ◽  
Vol 99 (6) ◽  
pp. 905-916
Author(s):  
E.W. Bork ◽  
M.P. Lyseng ◽  
D.B. Hewins ◽  
C.N. Carlyle ◽  
S.X. Chang ◽  
...  
Keyword(s):  
Soil Carbon ◽  
Root Biomass ◽  
Mineral Soil ◽  
Belowground Biomass ◽  
Cattle Grazing ◽  
Shoot Biomass ◽  
Positive Contribution ◽  
Temperate Grasslands ◽  
Soil C

While northern temperate grasslands are important for supporting beef production, it remains unclear how grassland above- and belowground biomass responds to long-term cattle grazing. Here, we use a comprehensive dataset from 73 grasslands distributed across a broad agro-climatic gradient to quantify grassland shoot, litter, and shallow (top 30 cm) root biomass in areas with and without grazing. Additionally, we relate biomass to soil carbon (C) concentrations. Forb biomass was greater (p < 0.05) in grazed areas, particularly those receiving more rainfall. In contrast, grass and total aboveground herbage biomass did not differ with grazing (total: 2320 kg ha−1 for grazed vs. 2210 kg ha−1 for non-grazed; p > 0.05). Forb crude protein concentrations were lower (p < 0.05) in grazed communities compared with those that were non-grazed. Grasslands subjected to grazing had 56% less litter mass. Root biomass down to 30 cm remained similar between areas with (9090 kg ha−1) and without (7130 kg ha−1) grazing (p > 0.05). Surface mineral soil C concentrations were positively related to peak grassland biomass, particularly total (above + belowground) biomass, and with increasing forb biomass in grazed areas. Finally, total aboveground shoot biomass and soil C concentrations in the top 15 cm of soil were both positively related to the proportion of introduced plant diversity in grazed and non-grazed grasslands. Overall, cattle grazing at moderate stocking rates had minimal impact on peak grassland biomass, including above- and belowground, and a positive contribution exists from introduced plant species to maintaining herbage productivity and soil C.

The effects of cultivation method, fertilizer input and previous sward type on organic C and N storage and gaseous losses under spring and winter barley following long-term leys

2002 ◽  
Vol 139 (3) ◽  
pp. 231-243 ◽  
Author(s):  
A. J. A. VINTEN ◽  
B. C. BALL ◽  
M. F. O'SULLIVAN ◽  
J. K. HENSHALL
Keyword(s):  
Spring Barley ◽  
Balance Sheet ◽  
N Fertilizer ◽  
Net N Mineralization ◽  
No Tillage ◽  
Confidence Limits ◽  
Organic C ◽  
Soil C ◽  
C And N

The effects of ploughing or no-tillage of long-term grass and grass-clover swards on changes in organic C and N pools and on CO2 and denitrified gas emissions were investigated in a 3-year field experiment in 1996–99 near Penicuik, Scotland. The decrease in soil C content between 1996 and 1999 was 15·3 t/ha (95% confidence limits were 1·7–28·9 t/ha). Field estimates of CO2 losses from deep-ploughed, normal-ploughed and no-tillage plots were 3·1, 4·5 and 4·6 t/ha over the sampling periods (a total of 257 days) in 1996–98. The highest N2O fluxes were from the fertilized spring barley under no-tillage. Thus no-tillage did not reduce C emissions, caused higher N2O emissions, and required larger inputs of N fertilizer than ploughing. By contrast, deep ploughing led to smaller C and N2O emissions but had no effect on yields, suggesting that deep ploughing might be an appropriate means of conserving C and N when leys are ploughed in. Subsoil denitrification losses were estimated to be 10–16 kg N/ha per year by measurement of 15N emissions from incubated intact cores. A balance sheet of N inputs and outputs showed that net N mineralization over 3 years was lower from plots receiving N fertilizer than from plots receiving no fertilizer.

Soil organic matter in rainfed cropping systems of the Australian cereal belt

Soil Research ◽  
2001 ◽  
Vol 39 (3) ◽  
pp. 435 ◽  
Author(s):  
R. C. Dalal ◽  
K. Y. Chan
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
Management Practices ◽  
Performance Indicator ◽  
Annual Rainfall ◽  
Soil Productivity ◽  
Organic C ◽  
Soil C ◽  
Eastern Australia

The Australian cereal belt stretches as an arc from north-eastern Australia to south-western Australia (24˚S–40˚S and 125˚E–147˚E), with mean annual temperatures from 14˚C (temperate) to 26˚C (subtropical), and with annual rainfall ranging from 250 mm to 1500 mm. The predominant soil types of the cereal belt include Chromosols, Kandosols, Sodosols, and Vertosols, with significant areas of Ferrosols, Kurosols, Podosols, and Dermosols, covering approximately 20 Mha of arable cropping and 21 Mha of ley pastures. Cultivation and cropping has led to a substantial loss of soil organic matter (SOM) from the Australian cereal belt; the long-term SOM loss often exceeds 60% from the top 0–0.1 m depth after 50 years of cereal cropping. Loss of labile components of SOM such as sand-size or particulate SOM, microbial biomass, and mineralisable nitrogen has been even higher, thus resulting in greater loss in soil productivity than that assessed from the loss of total SOM alone. Since SOM is heterogeneous in nature, the significance and functions of its various components are ambiguous. It is essential that the relationship between levels of total SOM or its identif iable components and the most affected soil properties be established and then quantif ied before the concentrations or amounts of SOM and/or its components can be used as a performance indicator. There is also a need for experimentally verifiable soil organic C pools in modelling the dynamics and management of SOM. Furthermore, the interaction of environmental pollutants added to soil, soil microbial biodiversity, and SOM is poorly understood and therefore requires further study. Biophysically appropriate and cost-effective management practices for cereal cropping lands are required for restoring and maintaining organic matter for sustainable agriculture and restoration of degraded lands. The additional benefit of SOM restoration will be an increase in the long-term greenhouse C sink, which has the potentialto reduce greenhouse emissions by about 50 Mt CO2 equivalents/year over a 20-year period, although current improved agricultural practices can only sequester an estimated 23% of the potential soil C sink.

Assessment of Nonresearch Industry Payments to Otolaryngologists in 2014 and 2015

2018 ◽  
Vol 158 (6) ◽  
pp. 1028-1034 ◽  
Author(s):  
Neil Pathak ◽  
Rance J. T. Fujiwara ◽  
Saral Mehra
Keyword(s):  
Annual Variation ◽  
Public Awareness ◽  
Large Change ◽  
Cross Sectional ◽  
Food And Beverage ◽  
Long Term Trends ◽  
The Mean ◽  
Open Payments ◽  
Made In

Objective To characterize, describe, and compare nonresearch industry payments made to otolaryngologists in 2014 and 2015. Additionally, to describe industry payment variation within otolaryngology and among other surgical specialties. Study Design Retrospective cross-sectional database analysis. Setting Open Payments Database. Subjects and Methods Nonresearch payments made to US otolaryngologists were characterized and compared by payment amount, nature of payment, sponsor, and census region between 2014 and 2015. Payments in otolaryngology were compared with those in other surgical specialties. Results From 2014 to 2015, there was an increase in the number of compensated otolaryngologists (7903 vs 7946) and in the mean payment per compensated otolaryngologist ($1096 vs $1242), as well as a decrease in the median payment per compensated otolaryngologist ($169 vs $165, P = .274). Approximately 90% of total payments made in both years were attributed to food and beverage. Northeast census region otolaryngologists received the highest median payment in 2014 and 2015. Compared with other surgical specialists, otolaryngologists received the lowest mean payment in 2014 and 2015 and the second-lowest and lowest median payment in 2014 and 2015, respectively. Conclusion The increase in the mean payment and number of compensated otolaryngologists can be explained by normal annual variation, stronger industry-otolaryngologist relationships, or improved reporting; additional years of data and improved public awareness of the Sunshine Act will facilitate determining long-term trends. The large change in disparity between the mean and median from 2014 to 2015 suggests greater payment variation. Otolaryngologists continue to demonstrate limited industry ties when compared with other surgical specialists.

Soil acidification and the carbon cycle in a cropping soil of north-eastern Victoria

Soil Research ◽  
1998 ◽  
Vol 36 (2) ◽  
pp. 273 ◽  
Author(s):  
W. J. Slattery ◽  
D. G. Edwards ◽  
L. C. Bell ◽  
D. R. Coventry ◽  
K. R. Helyar
Keyword(s):  
Soil Depth ◽  
Organic C ◽  
Soil Layers ◽  
Soil C ◽  
Soil Zone ◽  
North Eastern ◽  
Soil Buffering ◽  
The Impact ◽  
Total Organic C

Changes in soil organic matter were determined for a long-term (1975–95) experiment at the Rutherglen Research Institute in north-eastern Victoria. The crop rotations in this experiment were continuous lupins (LL) and continuous wheat (WW). The soil at this site was a solodic or Yellow Dermosol with a soil pH of 6·08 (pH in 0·01 М CaCl2 1 : 5) in 1975 in the surface 10 cm, which had declined by 0·8 and 1·5 pH units for WW and LL, respectively, in the 0–20 cm soil zone by 1992. Acidification rates decreased with increasing soil depth. The acidification rate in the 0–60 cm soil zone was 12·5 kmol(H+)/ha·year for the LL rotation and 4·6 kmol(H+)/ha·year for the WW rotation. The amount of CaCO3 required to neutralise the acidification of wheat-lupin rotations as calculated in this paper was up to 3·8 t/ha ·10 years for a WLWL rotation or 3 ·3 t/ha ·10 years for a WWL rotation; these amounts are significantly higher than previously reported rates. In this paper, we calculate the impact of changes in soil carbon (C) status over time, and therefore soil buffering, on the rates of acidification in incremental soil layers to a depth of 60 cm. Total organic C for these rotations in 1992 was 1·12% for WW and 1·17% for LL in the 0–10 cm soil zone. An investigation of the humic and fulvic acid fractions of these 2 rotations to a depth of 60 cm showed that the LL rotation had significantly higher (P < 0·05) C at depth than the WW rotation. Acidification due to the net decrease in soil C over the 15-year study period plus acidification due to the alkali removed in the seed was calculated to be –4·88 kmol(H+)/ha·year for the LL rotation and –6·52 kmol(H+)/ha·year for the WW rotation.

scholarly journals Population structure and spatial distribution of porbeagles (Lamna nasus) in Irish waters

2019 ◽  
Vol 76 (6) ◽  
pp. 1581-1590 ◽  
Author(s):  
Luke W J Cameron ◽  
William K Roche ◽  
Jonathan D R Houghton ◽  
Paul J Mensink
Keyword(s):  
Population Structure ◽  
Spatial Distribution ◽  
North Atlantic ◽  
Population Decline ◽  
The North ◽  
Aggregation Site ◽  
Show Evidence ◽  
Long Term Trends ◽  
Almost All

Abstract Porbeagles throughout the North Atlantic have experienced severe population decline through overfishing, with the northeastern population listed as critically endangered. Management of this population is constrained by the paucity of data on porbeagle population structure, distribution and behaviour in this region. Here we use a long-term (47 year) Irish capture-mark-recapture dataset to investigate the population structure, spatial distribution and seasonal movements of this species. From 1970–2017, a total of 268 sharks (9 recaptures) were ID tagged, with most individuals likely being juvenile based on length at maturity estimates (mean total length = 143.9 cm, SD = 35.4). Almost all captures were recorded at three distinct locations near angling hubs along the south, west and north coasts with catches peaking in August. Long-term trends in capture date indicated a shift towards earlier capture dates in the northern site (n = 153). Our findings suggest Irish waters may act as a persistent summer aggregation site for juveniles, which show evidence for seasonal site fidelity, returning to nearby locations between years. These findings demonstrate the utility of such programmes, which can be implemented, with minimal expense by engaging with the angling sector, to elucidate the population structure and distribution of wide-ranging fish species.

Management effects on the dynamics and storage rates of organic matter in long-term crop rotations

2004 ◽  
Vol 84 (1) ◽  
pp. 49-61 ◽  
Author(s):  
E. A. Paul ◽  
H. P. Collins ◽  
K. Paustian ◽  
E. T. Elliott ◽  
S. Frey ◽  
...  
Keyword(s):  
Organic Matter ◽  
C Sequestration ◽  
Organic C ◽  
Soil C ◽  
Site Analysis ◽  
Laboratory Incubation ◽  
C And N ◽  
A Site ◽  
Management Effects

Factors controlling soil organic matter (SOM) dynamics in soil C sequestration and N fertility were determined from multi-site analysis of long-term, crop rotation experiments in Western Canada. Analyses included bulk density, organic and inorganic C and N, particulate organic C (POM-C) and N (POM -N), and CO2-C evolved during laboratory incubation. The POM-C and POM-N contents varied with soil type. Differences in POM-C contents between treatments at a site (δPOM-C) were related (r2= 0.68) to treatment differences in soil C (δSOC). The CO2-C, evolved during laboratory incubation, was the most sensitive indicator of management effects. The Gray Luvisol (Breton, AB) cultivated plots had a fivefold difference in CO2-C release relative to a twofold difference in soil organic carbon (SOC). Soils from cropped, Black Chernozems (Melfort and Indian Head, SK) and Dark Brown Chernozems (Lethbridge, AB) released 50 to 60% as much CO2-C as grassland soils. Differences in CO2 evolution from the treatment with the lowest SOM on a site and that of other treatments (δCO2-C) in the early stages of the incubation were correlated to δPOM-C and this pool reflects short-term SOC storage. Management for soil fertility, such as N release, may differ from management for C sequestration. Key words: Multi-site analysis, soil management, soil C and N, POM-C and N, CO2 evolution

scholarly journals Geomorphic influences on the contribution of vegetation to soil C accumulation and accretion in <i>Spartina alterniflora</i> marshes

2018 ◽  
Vol 15 (1) ◽  
pp. 379-397 ◽  
Author(s):  
Tracy Elsey-Quirk ◽  
Viktoria Unger
Keyword(s):  
Plant Biomass ◽  
Accumulation Rate ◽  
Belowground Biomass ◽  
Sediment Supply ◽  
Organic C ◽  
Soil C ◽  
Coastal Plain Estuary ◽  
Labile C ◽  
Accretion Rates

Abstract. Salt marshes are important hotspots of long-term belowground carbon (C) storage, where plant biomass and allochthonous C can be preserved in the soil for thousands of years. However, C accumulation rates, as well as the sources of C, may differ depending on environmental conditions influencing plant productivity, allochthonous C deposition, and C preservation. For this study, we examined the relationship between belowground root growth, turnover, decay, above- and belowground biomass, and previously reported longer-term rates of total, labile, and refractory organic C accumulation and accretion in Spartina alterniflora-dominated marshes across two mid-Atlantic, US estuaries. Tidal range, long-term rates of mineral sedimentation, C accumulation, and accretion were higher and salinities were lower in marshes of the coastal plain estuary (Delaware Bay) than in the coastal lagoon (Barnegat Bay). We expected that the conditions promoting high rates of C accumulation would also promote high plant productivity and greater biomass. We further tested the influence of environmental conditions on belowground growth (roots + rhizomes), decomposition, and biomass of S. alterniflora. The relationship between plant biomass and C accumulation rate differed between estuaries. In the sediment-limited coastal lagoon, rates of total, labile, and refractory organic C accumulation were directly and positively related to above- and belowground biomass. Here, less flooding and a higher mineral sedimentation rate promoted greater above- and belowground biomass and, in turn, higher soil C accumulation and accretion rates. In the coastal plain estuary, the C accumulation rate was related only to aboveground biomass, which was positively related to the rate of labile C accumulation. Soil profiles indicated that live root and rhizome biomass was positively associated with labile C density for most marshes, yet high labile C densities below the live root zone and in marshes with high mineral sedimentation rates and low biomass signify the potential contribution of allochthonous C and the preservation of labile C. Overall, our findings illustrate the importance of sediment supply to marshes both for promoting positive plant-C accumulation-accretion feedbacks in geomorphic settings where mineral sediment is limiting and for promoting allochthonous inputs and preservation of labile C leading to high C accumulation and accretion rates in geomorphic settings where sediment supply is abundant.

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