Chemical composition of cover crops and soil organic matter pools in no‐tillage systems in the Cerrado

Cover plants are essential for the sustainability of no-tillage systems in tropical regions. However, information on the effects of these plants and N fertilization on soil organic matter fractions is still scarce. This study evaluated the effect of cover crops with different chemical composition and of N topdressing on the labile and humified organic matter fractions of an Oxisol of the Cerrado (savanna-like vegetation). The study in a randomized complete block design was arranged in split-plots with three replications. Four cover species were tested in the plots and the presence or absence of N topdressing in the subplot. The following cover species were planted in succession to corn for eight years: Urochloa ruziziensis; Canavalia brasiliensis M. ex Benth; Cajanus cajan (L.) Millsp; and Sorghum bicolor (L.) Moench. In general, the cultivation of U. ruziziensis increased soil C levels, particularly of C in the humic acid and particulate organic C fractions, which are quality indicators of soil organic matter. The C in humic substances and mineral organic C accounted for the highest proportions of total organic C, demonstrating the strong interaction between organic matter, Fe and Al oxides and kaolinite, which are predominant in these weathered soils of the Cerrado.

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Soil physical attributes and organic matter accumulation under no-tillage systems in the Cerrado

Soil Research ◽

10.1071/sr19047 ◽

2019 ◽

Vol 57 (7) ◽

pp. 712

Author(s):

J. L. R. Torres ◽

J. C. Mazetto Júnior ◽

J. Silva Júnior ◽

D. M. S. Vieira ◽

Z. M. Souza ◽

...

Keyword(s):

Organic Matter ◽

Soil Organic Matter ◽

Crop Production ◽

Conventional Tillage ◽

Native Forest ◽

Organic Carbon Content ◽

No Tillage ◽

Deep Soil ◽

Tillage Systems ◽

Physical Attributes

Soil management has a major effect on soil physical characteristics, and consequently on soil organic matter (SOM) content, which are important for the success of crop production. The aim of this study was to evaluate the soil physical attributes and the accumulation of SOM in no-tillage systems (NTS) with different periods of implantation in a conventional tillage area and to compare them with native forest (NF) in the Cerrado biome. The experiment was planned in a 3 × 4 factorial scheme, consisting of three soil treatments (NTS for 17 years (NTS17), NTS for 5 years (NTS5) and NF) and four soil depths (0–0.1, 0.1–0.2, 0.2–0.3 and 0.3–0.4 m), with a completely randomised design and four replicates. At deep soil layers (0.2–0.4 m) the NTS17 area had a greater soil density than the NTS5 and NF areas, and greater SOM compared with the NTS5 area. Soil macroporosity in the NTS5 area was below 10% at all soil depths evaluated. The NF area had the greatest total organic carbon content (1.39 dag kg–1), stock of carbon (16.63 Mg ha--1), amount of soil organic matter (28.66 Mg ha--1) and equivalent carbon credits (60.96 Mg ha–1). Carbon stocks were similar in the NTS areas in all soil depths evaluated. The results indicate that conventional tillage areas can be successfully recovered under the Cerrado edaphoclimatic conditions with the implantation of an NTS.

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Soil organic matter of aggregates physicogenic and biogenic in areas under no-tillage system in the Cerrado, Brazil

Research Society and Development ◽

10.33448/rsd-v10i5.15012 ◽

2021 ◽

Vol 10 (5) ◽

pp. e39910515012

Author(s):

Luiz Alberto da Silva Rodrigues Pinto ◽

Melania Merlo Ziviani ◽

Igor de Sousa Morais ◽

Robert Ferreira ◽

Wanderson Farias da Silva Junior ◽

...

Keyword(s):

Organic Matter ◽

Soil Organic Matter ◽

Organic Carbon ◽

Cover Crops ◽

No Tillage ◽

Aggregate Formation ◽

Density Fractionation ◽

Sampling Area ◽

Sunn Hemp ◽

Tillage System

The aim of this study was to evaluate i) the different cover crops contribution used in no-tillage system (NT) to biogenic aggregation; and ii) the influence of aggregate formation pathways on the compartmentalization and the soil organic carbon origin. Two areas managed under NT with different implementation times (6 and 18 years, NT06 and NT18, respectively) and cover crops were evaluated, totaling six sampling areas: NT06, millet (NT06MI); NT06, brachiaria (NT06BR); NT06, sunn hemp (NT06SH); NT18, millet (NT18MI); NT18, brachiaria (NT18BR); NT18, and sunn hemp (NT18SH). In each sampling area, five pseudo-replicates were collected in the 0.00-0.05 and 0.05-0.10 m layers. The samples were air-dried and sieved using sieves with 9.7 and 8.0 mm mesh, and the aggregates retained within this interval were selected. The percentage of each type of aggregate (physicogenic and biogenic) was quantified. Total organic carbon (TOC) and the natural abundance of δ13C (‰) were analyzed and the physical fractionations of SOM were performed: particulate organic carbon (POC) and mineral-associated organic carbon (MAOC) and density fractionation (free light fraction carbon, FLFC). Physicogenic aggregates were quantified in greater proportion, except for the areas of NT06BR and NT18BR in the 0.00-0.05 m layer. The biogenic aggregates showed the highest contents of TOC, POC, MAOC, FLFC and more negative values of δ13C. The use of grasses, especially Brachiaria spp., as cover plants in NT after 6 and 18 years of adoption favors the formation of aggregates through the biogenic pathway and they influence the compartmentalization and origin of stored organic carbon.

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Urease activity and its relation to soil organic matter, microbial biomass nitrogen and urea-nitrogen assimilation by maize in a Brazilian Oxisol under no-tillage and tillage systems

Biology and Fertility of Soils ◽

10.1007/s003740000213 ◽

2000 ◽

Vol 32 (1) ◽

pp. 52-59 ◽

Cited By ~ 26

Author(s):

R. Roscoe ◽

C. A. Vasconcellos ◽

A. E. Furtini-Neto ◽

G. A. A. Guedes ◽

L. A. Fernandes

Keyword(s):

Organic Matter ◽

Soil Organic Matter ◽

Microbial Biomass ◽

Urease Activity ◽

Nitrogen Assimilation ◽

No Tillage ◽

Tillage Systems ◽

Microbial Biomass Nitrogen ◽

Urea Nitrogen

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Effects of climate change on soil organic matter chemical composition and carbon content in different physical fractions

10.5194/egusphere-egu21-9216 ◽

2021 ◽

Author(s):

Moritz Mohrlok ◽

Victoria Martin ◽

Alberto Canarini ◽

Wolfgang Wanek ◽

Michael Bahn ◽

...

Keyword(s):

Climate Change ◽

Organic Matter ◽

Chemical Composition ◽

Soil Organic Matter ◽

Soil C ◽

Size Classes ◽

Soil Fractions ◽

Total Soil ◽

C And N ◽

Amp Clay

Soil organic matter (SOM) is composed of many pools with different properties (e.g. turnover times) which are generally used in biogeochemical models to predict carbon (C) dynamics. Physical fractionation methods are applied to isolate soil fractions that correspond to these pools. This allows the characterisation of chemical composition and C content of these fractions. There is still a lack of knowledge on how these individual fractions are affected by different climate change drivers, and therefore the fate of SOM remains elusive. We sampled soils from a multifactorial climate change experiment in a managed grassland in Austria four years after starting the experiment to investigate the response of SOM in physical soil fractions to temperature (eT: ambient and elevated by +3&#176;C), atmospheric CO2-concentration (eCO2: ambient and elevated by +300 ppm) and to a future climate treatment (eT x eCO2: +3&#176;C and + 300 ppm). A combination of slaking and wet sieving was used to obtain three size classes: macro-aggregates (maA, > 250 &#181;m), micro-aggregates (miA, 63 &#181;m &#8211; 250 &#181;m) and free silt & clay (sc, < 63 &#181;m). In both maA and miA, four different physical OM fractions were then isolated by density fractionation (using sodium polytungstate of &#961; = 1.6 g*cm-3, ultrasonication and sieving): Free POM (fPOM), intra-aggregate POM (iPOM), silt & clay associated OM (SCaOM) and sand-associated OM (SaOM). We measured C and N contents and isotopic composition by EA-IRMS in all fractions and size classes and used a Pyrolysis-GC/MS approach to assess their chemical composition. For eCO2 and eT x eCO2 plots, an isotope mixing-model was used to calculate the proportion of recent C derived from the elevated CO2 treatment. Total soil C and N did not significantly change with treatments.&#160; eCO2 decreased the relative proportion of maA-mineral-associated C and increased C in fPOM and iPOM. About 20% of bulk soil C was represented by the recent C derived from the CO2 fumigation treatment. This significantly differed between size classes and density fractions (p < 0.001), which indicates inherent differences in OM age and turnover. Warming reduced the amount of new C incorporated into size classes. We found that each size class and fraction possessed a unique chemical fingerprint, but this was not significantly changed by the treatments. Overall, our results show that while climate change effects on total soil C were not significant after 4 years, soil fractions showed specific effects. Chemical composition differed significantly between size classes and fractions but was unaffected by simulated climate change. This highlights the importance to separate SOM into differing pools, while including changes to the molecular composition might not be necessary for improving model predictions.&#160;&#160;&#160;&#160;

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Composition changes of eroded carbon at different spatial scales in a tropical watershed suggest enrichment of degraded material during transport

Biogeosciences ◽

10.5194/bg-11-3299-2014 ◽

2014 ◽

Vol 11 (12) ◽

pp. 3299-3305 ◽

Cited By ~ 3

Author(s):

C. Rumpel ◽

V. Chaplot ◽

P. Ciais ◽

A. Chabbi ◽

B. Bouahom ◽

...

Keyword(s):

Organic Matter ◽

Chemical Composition ◽

Soil Organic Matter ◽

Isotope Composition ◽

Spatial Scales ◽

Suspended Sediments ◽

Resonance Spectroscopy ◽

Vertical Decomposition ◽

Degraded Material ◽

Soil Units

Abstract. In order to assess whether eroded carbon is a net source or sink of atmospheric CO2, characterisation of the chemical composition and residence time of eroded organic matter (EOM) at the landscape level is needed. This information is crucial to evaluate (1) how fast EOM can be decomposed by soil microbes during its lateral transport and (2) its impact at deposition sites. This study considers a continuum of scales to measure the composition of EOM across a steep hillslope landscape of the Mekong basin with intense erosion. We sampled suspended sediments eroded during rainfall events from runoff plots (1 and 2.5 m2) and the outlets of four nested watersheds (0.6 × 104 to 1 × 107 m2). Here we show that changes in the chemical composition of EOM (measured by nuclear magnetic resonance spectroscopy) and in its 13C and 15N isotope composition from plot scale through to landscape scale provide consistent evidence for enrichment of more decomposed EOM across distances of 10 km. Between individual soil units (1 m2) to a small watershed (107 m2), the observed 28% decrease of the C/N ratio, the enrichment of 13C and 15N isotopes as well as O-alkyl C in EOM is of similar magnitude as changes recorded with depth in soil profiles due to soil organic matter "vertical" decomposition. Radiocarbon measurements indicated ageing of EOM from the plot to the watershed scale. Therefore transport of EOM may lead to enrichment of stabilised soil organic matter compounds, eventually being subject to export from the watershed.

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