Oxidizable Carbon Fractions Research Articles

Cow dung compost and vermicompost amendments promote soil carbon stock by enhancing labile organic carbon and residual oxidizable carbon fractions in maize field soil

AbstractEnhancing soil quality and promoting the accumulation of soil organic carbon through economically and environmentally sustainable practices are essential for modern agriculture. This study aimed to investigate the effects of various organic amendments and rotation systems on soil properties and sweet corn growth in sandy loam soil. A split‐plot field experiment was conducted over 2 years, including rotations with or without Sesbania sesban as the main plot and six fertilizer treatments: a no fertilizer control, chemical fertilizer and four organic amendments as subplots. The cropping system did not significantly influence soil properties and sweet corn growth. However, the application of soybean meal, castor meal, cow dung compost and vermicompost resulted in sweet corn yields comparable to those achieved with the chemical fertilizer treatment. Notably, the soil organic matter (SOM) content was significantly higher in the cow dung compost and vermicompost treatments compared with both the no fertilizer and chemical fertilizer treatments. Moreover, these two amendments significantly increased soil carbon stock because of significant increases in labile organic carbon (TOC400) and residual oxidizable carbon (ROC) fractions in the maize field soil. A significant positive correlation was observed between fresh ear weight with husks and several soil parameters, including electrical conductivity, available P, exchangeable K and Zn, NO3–N, NH4–N, inorganic C and N, TOC400, ROC and SOM. In conclusion, cow dung compost and vermicompost not only result in sweet corn yields comparable to those from chemical fertilizer but also significantly enhance soil carbon stock by increasing TOC400 and ROC. Therefore, they can partially substitute for chemical fertilizers in promoting sustainable agricultural production of sweet corn.

Organic fertilizer substitution promotes soil organic carbon sequestration by regulating permanganate oxidizable carbon fractions transformation in oasis wheat fields

Organic fertilizer substitution (OFS) technology effectively mitigates the adverse effects of excessive synthetic fertilizer application while promoting soil organic carbon (SOC) sequestration in farmlands. However, how the permanganate oxidizable carbon fractions (KOCs) transformation affects SOC under OFS remains unknown. In this study, two typical farmland soils (grey desert soil, GS; meadow soil, MS) were selected for a 3-year field fertilization experiment (no fertilization, NF; synthetic fertilizer alone, SCF; and organic fertilizer substituted 20% synthetic N fertilizer, OFS). Field experiments conducted from 2018 to 2020 showed that SOC could be used to evaluate wheat yield and soil quality, so further study the effects of OFS on SOC and KOCs and their corresponding C pool management index (CPMIs). The results showed that OFS in GS and MS increased SOC (by 3.37%–15.62%, 4.92%–20.28%) and its fractions content (except low-activity KOC, LKOC) and CPMIs (except CPMI-L) year by year compared to SCF and NF. The recalcitrant organic C (ROC), KOC, high-activity KOC (HKOC), and medium-activity KOC (MKOC) were the key fractions affecting SOC. Moreover, HKOC and MKOC and their corresponding CPMIs (CPMI-H and CPMI-M) showed higher sensitivity. Structural equation modeling revealed that OFS in GS and MS increased SOC by increasing ROC and KOC (by regulating KOCs transformation) content, and increased CPMI-H and CPMI-M by increasing HKOC and MKOC content. Overall, the process of OFS promoted SOC sequestration and improved soil C pool in two soils were revealed from the perspective of KOCs transformation. Also, we proposed corresponding fertilization recommendations and showed that HKOC and MKOC could be used to evaluate and monitor soil quality and SOC. This study provides guidance for SOC sequestration, crop yield, and soil quality improvement in oasis wheat fields, contributing to the sustainable development of farmland.

Spatial distribution of acidity components and oxidizable carbon fractions in a silvopastoral system

The silvopastoral system (SPS) stands out as an agroecological production system that has improved the soil's chemical quality. However, these chemical properties may have distinct changes with greater or lesser distances from the tree row tracks of the silvopastoral system. The objective of this study was to investigate the effects of the distance of the soil sampling points from the eucalyptus tree rows in a 2-year silvopastoral system on acidity components and oxidizable organic carbon fractions of the soil, as well as to compare these chemical properties with the conventional pasture system and native Cerrado vegetation. In the silvopastoral system (SPS), the soil samples were collected at 2.5, 5.0, 7.5, and 10 m of transverse distance from the eucalyptus tree row tracks. Soil samples collected in a conventional pasture area (CP) and a native Cerrado vegetation area (NV) were used as reference treatments. Soil samples were collected at depths from 0.0–0.10, 0.10–0.20, and 0.20–0.30 m. The acidity components (pH, Al3+ and H + Al) and oxidizable organic C fractions (F1: labile fraction; F2: moderately labile fraction; and F3: poorly labile fraction) were determined. The results showed that the lowest soil acidity level was observed at 2.5 and 10.0 m distances from the eucalyptus tree rows. However, the spatial distribution of soil sampling points to the eucalyptus tree rows in a 2-year silvopastoral system did not change the oxidizable fractions of the soil organic carbon. The 2-year silvopastoral system and native Cerrado vegetation area had the highest concentrations of organic carbon in the labile (F1) and poorly labile (F3) fractions in the soil profile compared to the conventional pasture system. A 2-year silvopastoral system in a low fertility tropical soil from the Brazilian Cerrado has not yet been able to improve the soil's chemical quality; therefore, further research should be carried out to investigate the medium and long-term effects of the silvopastoral system on the acidity components and oxidizable organic carbon fractions of the soil.

Soil organic carbon fractions and humic substances are affected by land uses of Caatinga forest in Brazil

Caatinga is a Brazilian dry ecosystem that occupies around 1 million km2 and is one of the largest tropical dry forests of the world. About 46% of the area that was originally covered has been deforested. Land use can cause pronounced reduction in soil carbon stocks that play a major role in the global carbon cycle. The objective of this study was to improve our understanding of the effect of land use on oxidizable carbon fractions, total carbon stocks and humic substances in different layers of soil in a Brazilian semi-arid region. We analyzed soils from tropical dry forest (TDF), forest succession with Anadenanthera falcata (ANA), with Tabebuia alba (TAB), secondary scrubby regeneration (SCR), and non-irrigated maize (MS). Forests showed larger fractions of more labile carbon, except for TDF. The most recalcitrant fraction of carbon stock, humin fraction stock, with the different land use decreased by 38–53% compared to TDF. Oxidizable carbon fractions, carbon stocks, and humic fraction stocks were able to differentiate the successional land uses and agricultural cover from TDF, mainly in the 0–5 cm layer. Our results show that changes in land use, especially with ANA forest succession, showed a larger labile carbon fraction, indicating easy decomposition and loss. Our results provide an alternative tool for the management of deforested areas in tropical dry caatinga ecosystems. This would contribute to the conservation of dry forest systems and could serve as guideline for sustainable management of agriculturally impacted caatinga areas.

Granulometric and oxidizable carbon fractions of soil organic matter in crop-livestock integration systems

The identification of the labile and recalcitrant forms of soil organic matter (SOM) allows to rapidly define, or even predict if the management used favors increments or losses of carbon in the soil. Thus, the objective of this work was to assess the effects of different grazing intensities and soybean crops on the oxidizable and granulometric fractions of the SOM in a crop-livestock integration combined with no-tillage system (CLI-NTS), established in 2009 in the Goiás Federal University. The treatments consisted of three different pasture heights (0.25 m P25; 0.35 m P35; 0.45 m P45), and areas without grazing (AWG), and a native vegetation area of the Cerrado biome (NCA), adjacent to the experimental area, was evaluated as references and compared with the cultivated areas. Soil samples (Oxisol - USDA; typic distroferric Red Latosol - SiBCS) were collected in the layers 0.00-0.05; 0.05-0.10 0.10-0.20 and 0.20-0.40 m of each area, and arranged in a completely randomized experimental design with six replications. The soil total carbon was quantified (TC) by dry combustion. The SOM granulometry and oxidizable SOM were fractionated into particulate carbon (OCp), carbon bond with minerals (OCm) and four oxidizable fractions with increasing degrees of recalcitrance (F1 < F2 < F3 < F4). These soil attributes were evaluated at two different times, representing the post-pasture cycle (PP) and post-soybean crop (PC) periods. The lower contents of total soil carbon (TC) were found in the F1 and F3 fractions of the area without grazing, suggesting that the crop-livestock integration increases the organic matter content in the soil surface layer regardless of the pasture height. The areas without grazing and with different pasture heights in CLI had similar contents of OCp and OCm due to the experiment short time of implementation (3 years). The fractionation of the oxidizable SOM was more sensitive in differentiating the treatments, showing that the higher intensity of grazing used (P25) provided a better balance of carbon accumulation between the SOM labile and recalcitrant fractions.

Oxidizable carbon fractions in Red Latosol under different management systems

The aim of this study was to evaluate the oxidizable fractions of organic C in a Red Latosol in an area of cerrado under a no-tillage system (NT) with different years of implantation, and to compare them to areas of native cerrado and pasture. The experimental design used was completely randomized with five replications. Treatments consisted of five areas: native cerrado (NC) stricto sensu; pasture (PA) planted with Brachiaria decumbens; NT with 3 (NT3); NT with 15 (NT15) and NT with 20 (NT20) years of implantation. There was an increase in the ground-surface mass of vegetable residue as a function of the time of implantation of the NT. An increase in C content and the carbon-management index (CMI) can be seen as a function of the time of implantation of the NT. In the area of NT20 the greatest values of C were quantified, compared to the area of cerrado. In general, there are increased labile and stable MOS fractions as a function of the implantation time of the NT, while the areas SPD15 and SPD20 present a C content among fractions, respectively similar and/or superior to the area of NC. Regardless of the area evaluated, a predominance of the more stable MOS fractions (F3+F4) can be seen. The area of PA, due to inadequate management, shows a more advanced stage of degradation when compared to the other areas, as there is a large reduction in the levels of total C, of C in the more labile and stable MOS fractions, as well as lower CMI values.

Oxidizable carbon and humic substances in rotation systems with brachiaria/livestock and pearl millet/no livestock in the Brazilian Cerrado

The crop-livestock integration system significantly increases the carbon content in chemical fractions of soil organic matter (SOM). This study aimed to evaluate chemical indicators of SOM attributes for sites under brachiaria/livestock and pearl millet/no livestock in Goias, Brazil. A third area covered with natural Cerrado vegetation (Cerradão) served as reference. Soil was randomly sampled at 0-5, 5-10, 10-20 and 20-40 cm. Total organic carbon stocks (TOC), oxidizable carbon fractions (OCF) (F1>F2>F3>F4), carbon content in the humin (C-HUM), humic acid (C-HAF) and fulvic acid (C-FAF) fractions were evaluated. F1/F4, F1+F2/F3+F4, C-HAF/C-FAF and (C-HAF+C-FAF)/C-HUM indices were calculated, as well as stocks chemical SOM fractions. Brachiaria/livestock produced greater TOC stocks than pearl millet/no livestock (0-5, 5-10 and 10-20 cm). In terms of OCF, brachiaria/livestock generally exhibited higher levels in F1, F2, F4 and F1/F4 than pearl millet/no livestock. C-HUM (0-10 cm) and C-HAF (0-20 cm) stocks were larger in brachiaria/livestock than pearl millet/no livestock. Compared to the Cerradão, brachiaria/livestock locations displayed higher values for TOC (5-10 and 10-20 cm), C-HAF and C-HAF/C-FAF (5-10 cm) stocks. TOC, C-HAF stock and OCF show that land management with brachiaria/livestock was more efficient in increasing SOM than pearl millet/no livestock. Moreover, when compared with pearl millet/no livestock, brachiaria/livestock provided a more balanced distribution of very labile (F1) and recalcitrant (F4) carbon throughout soil layers, greater SOM humification. Brachiaria/livestock leads to higher values of F1 and F4 in depth when compared to pearl millet/livestock and provides a more homogeneous distribution of C-FAF and C-HAF in depth compared to Cerradão.

CO2-C losses and carbon quality of selected Maritime Antarctic soils

AbstractPolar Regions are the most important soil carbon reservoirs on Earth. Monitoring soil carbon storage in a changing global climate context may indicate possible effects of climate change on terrestrial environments. In this regard, we need to understand the dynamics of soil organic matter in relation to its chemical characteristics. We evaluated the influence of chemical characteristics of humic substances on the process of soil organic matter mineralization in selected Maritime Antarctic soils. A laboratory assay was carried out with soils from five locations from King George Island. We determined the contents of total organic carbon, oxidizable carbon fractions of soil organic matter, and humic substances. Two in situ field experiments were carried out during two summers, in order to evaluate the CO2-C emissions in relation to soil temperature variations. The overall low amounts of soil organic matter in Maritime Antarctic soils have a low humification degree and reduced microbial activity. CO2-C emissions showed significant exponential relationship with temperature, suggesting a sharp increase in CO2-C emissions with a warming scenario, and Q10 values (the percentage increase in emission for a 10°C increase in soil temperature) were higher than values reported from elsewhere. The sensitivity of the CO2-C emission in relation to temperature was significantly correlated with the humification degree of soil organic matter and microbial activity for Antarctic soils.