Soil organic matter management: the roles of residue quality in C sequestration and N supply.

2009 ◽  
pp. 97-219 ◽  
Author(s):  
G. Cadisch ◽  
K. Giller
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
C Sequestration ◽  
Residue Quality ◽  
N Supply ◽  
Organic Matter Management

Spatial organization of soil microaggregates

2020 ◽  
Author(s):  
Eva Lehndorff ◽  
Nele Meyer ◽  
Andrey Radionov ◽  
Lutz Plümmer ◽  
Peter Rottmann ◽  
...  
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
Spatial Organization ◽  
Inorganic Compounds ◽  
Spatial Relationship ◽  
Clay Content ◽  
Spatial Arrangement ◽  
C Sequestration ◽  
Spatial Correlations ◽  
Soil Minerals

<p>The physical arrangement of soil compounds in microaggregates is important in many ways, e.g. by controlling soil stability and C sequestration. However, little is known about the spatial arrangement of organic and inorganic compounds in soil microaggregates, due to the lack of in-situ analyses in undisturbed material. Here we hypothesize that microaggregates are spatially organized, resulting in deterministic, predictable spatial patterns of different organic matter and mineral phases and that this organization depends on the abundance of specific phases such as on clay mineral content. We separated the water stable, occluded large and small microaggregate fractions from Ap horizons of a sequence of sandy to loamy Luvisols (19 to 35% clay, Scheyern, Germany) and subjected in total 60 individual aggregates to elemental mapping by electron probe micro analysis (EPMA), which recorded C, N, P, Al, Fe, Ca, K, Cl, and Si contents at µm scale resolution. Spatial arrangements of soil organic matter and soil minerals were extracted using cluster analyses. We found a pronounced heterogeneity in aggregate structure and composition, which was not reproducible and largely independent from clay content in soil. However, neighborhood analyses revealed close spatial correlations between organic matter debris (C:N app. 100:10) and microbial organic matter (C:N app. 10:1) indicating a spatial relationship between source and consumer. There was no systematic relationship between soil minerals and organic matter, suggesting that well-established macroscale correlations between contents of pedogenic oxides and clay minerals with soil organic matter storage do not apply to soil microaggregates.</p>

Three long-term trials end with a quasi-equilibrium between soil C, N, and pH: an implication for C sequestration

Soil Research ◽  
2012 ◽  
Vol 50 (7) ◽  
pp. 527 ◽  
Author(s):  
Mark Conyers ◽  
Philip Newton ◽  
Jason Condon ◽  
Graeme Poile ◽  
Pauline Mele ◽  
...  
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
Chemical Properties ◽  
C Sequestration ◽  
Soil Chemical Properties ◽  
Quasi Equilibrium ◽  
Soil C ◽  
Eastern Australia ◽  
N Fertility

The aim of this study was to assess the long-term changes in some key soil chemical properties at the completion of three long-term trials in south-eastern Australia and the relationship between those soil properties. From a soil organic matter perspective, the build-up of carbon (%C) requires an accumulation of nitrogen (%N), and the build-up of %C and %N fertility comes at the cost of soil acidity. Rotation, tillage, and stubble practices combine to alter the quantity, quality (C : N), and the depth distribution of organic matter in a soil, but the three soil chemical properties reported here seem to also be in quasi-equilibrium at the three long-term sites. The consequence is that if the build-up of soil organic matter leads to soil acidification, then the maintenance of agricultural production will require liming. The emission of CO2 when limestone reacts with soil acids, plus the C cost of limestone application, will negate a proportion of the gains from C sequestration as organic matter in soil. Such cautionary information was doubtless unforeseen when these three long-term trials were initiated.

Allocation into soil organic matter fractions of 14C captured via photosynthesis by two perennial grass pastures

Soil Research ◽  
2013 ◽  
Vol 51 (8) ◽  
pp. 748 ◽  
Author(s):  
M. M. Roper ◽  
I. R. P. Fillery ◽  
R. Jongepier ◽  
P. Sanford ◽  
L. M. Macdonald ◽  
...  
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
Perennial Grass ◽  
Extended Period ◽  
C Sequestration ◽  
Carbon Accounting ◽  
Pulse Labelling ◽  
Rhodes Grass ◽  
Plant Soil ◽  
The Stability

Perennial grass pastures are being increasingly adopted, but little is known about the flows of carbon (C) from photosynthesis into soil organic matter (SOM) that could be used for calculations in carbon accounting. Repeat-pulse labelling of perennial grass pastures (kikuyu and Rhodes grass) with 14C in the field in Western Australia was used to trace the allocation of C to SOM fractions and to determine the stability of each fraction over an extended period. For kikuyu, >40% of the 14C fed to the plants was allocated belowground within 10 days of labelling, and after 1 year half of this remained. Allocation of 14C belowground under Rhodes grass ranged between 20 and 24% of 14C applied and remained constant for up to 6 months. At least 90% of the 14C belowground was found in the surface 300 mm of soil. The allocation of 14C to the coarse (50 µm–2 mm) and fine (<50 µm) SOM fractions was similar in magnitude for the two grasses and remained stable through time. It was estimated that in 1 year ~1 t C ha–1 was assimilated into the coarse + fine SOM fractions under kikuyu. However, Rhodes grass was not uniformly distributed across the paddock, thereby reducing the estimates of assimilation of C belowground in these systems to one-tenth of that under kikuyu. Data obtained will help validate plant–soil models for assessing rates of C sequestration under perennial pastures.

Soil texture mediated microbial activity affects the transfer of litter-derived carbon to soil organic matter

2020 ◽  
Author(s):  
Gerrit Angst ◽  
Jan Pokorný ◽  
Travis Meador ◽  
Tomáš Hajek ◽  
Jan Frouz ◽  
...  
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
Microbial Activity ◽  
Litter Decomposition ◽  
Soil Texture ◽  
Mineral Soil ◽  
C Sequestration ◽  
Soil Microbial Activity ◽  
Soil C ◽  
Soil Organic Matter Formation

&lt;p&gt;Knowledge about the nexus between litter decomposition and soil organic matter formation is still scarce, likely because litter decomposition studies are often conducted in the absence of mineral soil. Even if mineral soil is considered, variations in soil texture, which should substantially influence decomposition and soil C sequestration via, e.g., different capacities to store C or host microbial communities, have been neglected. Here, we examined the effect of soil texture on litter decomposition and soil organic matter formation by incubating sand- and clay-rich soils. These soils, taken under C3 vegetation, were amended with C4 litter to trace the fate of organic matter newly entering the soil. While we found only small amounts of litter-derived carbon (C) in the mineral soils after our six-month experiment, the microbial activity and amount of remaining litter between the sand- and clay-rich soils substantially differed. A high microbial activity combined with higher amounts of litter-derived C and a higher remaining litter mass in the clay-rich soil indicate a more effective transformation of litter to soil organic matter as compared to the sand-rich soil. In the sand-rich soil, microbial activity was lower, less soil C was litter-derived, and the litter lost more of its mass. We explain the apparently contradictory results of higher microbial activity and concurrently higher C contents with a more effective microbial pathway of SOM formation in the clay-rich soil. Our results indicate that soil texture does not only play a role in the provision of reactive surfaces for the stabilization of C but will also affect the decomposition of litter via effects on microbial activity, ultimately determining if litter C is transferred to the soil or respired to the atmosphere.&lt;/p&gt;

Modelling the influence of soil carbon on net greenhouse gas emissions from grazed pastures

2016 ◽  
Vol 56 (3) ◽  
pp. 585 ◽  
Author(s):  
Rachelle Meyer ◽  
Brendan R. Cullen ◽  
Richard J. Eckard
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
Annual Variation ◽  
Ghg Emissions ◽  
C Sequestration ◽  
N2o Emissions ◽  
Soil C ◽  
High Rainfall ◽  
Sequestration Potential ◽  
Ch4 And N2o

Sequestering carbon (C) in soil organic matter in grassland systems is often cited as a major opportunity to offset greenhouse gas (GHG) emissions. However, these systems are typically grazed by ruminants, leading to uncertainties in the net GHG balance that may be achieved. We used a pasture model to investigate the net balance between methane (CH4), nitrous oxide (N2O) and soil C in sheep-grazed pasture systems with two starting amounts of soil C. The net emissions were calculated for four soil types in two rainfall zones over three periods of 19 years. Because of greater pasture productivity, and consequent higher sheep stocking rates, high-rainfall sites were associated with greater GHG emissions that could not be offset by C sequestration. On these high-rainfall sites, the higher rate of soil organic carbon (SOC) increase on low-SOC soils offset an average of 45% of the livestock GHG emissions on the modelled chromosol and 32% on the modelled vertosol. The slow rate of SOC increase on the high-SOC soils only offset 2–4% of CH4 and N2O emissions on these high-rainfall sites. On low-rainfall sites, C sequestration in low-SOC soils more than offset livestock GHG emissions, whereas the modelled high-C soils offset 75–86% of CH4 and N2O emissions. Greater net emissions on high-C soils were due primarily to reduced sequestration potential and greater N2O emissions from nitrogen mineralisation and livestock urine. Annual variation in CH4 and N2O emissions was low, whereas annual SOC change showed high annual variation, which was more strongly correlated with weather variables on the low-rainfall sites compared with the high-rainfall sites. At low-soil C concentrations, with high sequestration potential, there is an initial mitigation benefit that can in some instances offset enteric CH4 and direct and indirect N2O emissions. However, as soil organic matter increases there is a trade-off between diminishing GHG offsets and increasing ecosystem services, including mineralisation and productivity benefits.

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