Carbon In Particle-size Fractions Research Articles

Soil organic carbon in particle-size fractions under three grassland types in Inner Mongolia, China

Transferring CO2 to soil organic carbon (SOC) is an important carbon sequestration mechanism that may mitigate global climate change. Grasslands can preserve 10–30% of total SOC stock. This study investigated the contribution of different soil particle-size fractions to SOC sequestration in grasslands, which play an important role for stabilization of SOC. Soil layers at 0–10, 10–20, 20–40, and 40–60 cm were sampled from meadow steppe, typical steppe and desert steppe in Inner Mongolia, northern China in July and August, 2016. Bulk soils were fractionated by wet-sieving method to investigate SOC stock in different particle-size fractions. SOC was determined with ElementarVario MAX CNS analyzer after removing soil inorganic C. The SOC stock in 0–60 cm depth was 163.0 Mg C ha−1 in typical steppe soils, 127.3 Mg C ha−1 in meadow steppe and 44.4 Mg C ha−1 in desert steppe. The silt (2–53 μm) and clay (< 2 μm) fractions accounted for 62.2 and 19.2% in meadow steppe, 35.3 and 12.7% in typical steppe, 12.2 and 6.6% in desert steppe of total soil mass. The SOC stock in silt and clay fractions accounted for 59.8 and 32.0% of total SOC stock in meadow steppe, 58.9 and 19.8% in typical steppe, and 43.9 and 28.2% in desert steppe, respectively. The SOC concentration and stock were positively correlated with mean annual precipitation (MAP) and negatively correlated with mean annual temperature (MAT). Our study demonstrated that climatic factors and soil texture are main reasons for the difference of SOC stocks among three grassland types. The distribution of soil particle-size fraction and its associated organic C showed distinct variations under three grassland types in Inner Mongolia. Management practices, such as changing grazing intensity in three grassland types, are important for the sustainable use of grasslands.

Distribution of organic carbon in particle size fractions of a red soil under long-term fertilization

Soil samples were collected from two depths i.e. , 0-15 and 15-30 from the long term experiment field at Zonal Agricultural Research Station, GKVK Bengaluru after harvest of maize in the year 2008 to study the soil organic carbon (SOC) distribution in particle size fractions. The soil was sandy loam of texture with acidic pH and low organic carbon status. The results of the study revealed that the soil pH was decreased due to the imbalanced fertilizer treatments and was maintained near initial level due to treatments involving both balanced fertilizers and FYM addition. The use of organics alone or organics along with fertilizers resulted in build up of SOC compared to use of only inorganic fertilizers. Soil organic carbon estimation in each size fraction indicated that the clay fraction had the highest OC concentration followed by silt and sand in the both depths of the soil. Soil organic carbon in sand declined rapidly upon cultivation, mostly due to oxidation and disintegration of unstable aggregates to enter siltsize or clay-size fraction because of intensive cultivation of the soil for 25 years. The study revealed that C was very slowly sequestered in the clay and silt fractions of the soil.

Distribution of Plant Nutrient Elements and Carbon in Particle Size Fractions of Broiler Litter Ash

An estimated 10.8 million tons of broiler litter and 3.0 million tons of turkey litter were produced in the United States in 2009. Poultry litter is a mixture of manure, bedding material (e.g. wood chips, sawdust, or straw), feathers, and spilled feed. Poultry litter contains high levels of Ca, N, P, and K, and is often applied as a fertilizer on fields in close proximity to poultry houses. Repeated poultry litter application to these fields can increase soil P to levels in excess of plant requirements, resulting in potential environmental risk. An alternative to land application of poultry litter is its use as a fuel in electricity generation. Ash from this process has been used as a fertilizer after sieving to 0.5 mm) fractions. Nevertheless, the amount of P in the coarsest frac- tion ranged from 15 to 25 percent of the total extractable phosphorus in the ash. With such high P content in the coarse fraction, there is a potential of P leaching when this fraction is disposed of in landfills. We recommend that the coarse fraction should be crushed and mixed with the fine fractions before the ash is used as a fertilizer and soil amendment.

Mineralization of active soil organic carbon in particle size fractions of a Brookston clay soil under no-tillage and mouldboard plough tillage

Soil organic matter is a heterogeneous mixture of organic substances with different compositions and stabilities. To enhance soil organic carbon (SOC) sequestration, it is helpful to understand the distribution of SOC among the soil particle size fractions, the stabilities of the SOC within each fraction, and the influence of management practices, such as tillage, on SOC mineralization. Hence, the objectives of this study were to determine the distribution and mineralization rate of active SOC in the sand (53-2000 µm), silt (2-53 µm) and clay (&lt;2 µm) size fractions of a Brookston clay soil under a corn-soybean rotation and three tillage scenarios. The tillages included long-term (24 yr) mouldboard plough (MP83), long-term (24 yr) no-till (NT83) and short-term (10 yr) no-till (NT97). Bulk soil from the top 10 cm was dispersed into sand, silt and clay size fractions by applying ultrasound energy (750 J mL-1) to a 1:4 soil:water suspension. The sand, silt and clay fractions of the three tillages were aerobically incubated at 20°C and 30% moisture (wt/wt), and the CO2-C emissions were measured over 103 d. The SOC contents followed the order clay &gt; silt &gt; sand for all three tillages. On a whole-soil basis and averaged over the tillage treatments, 55.8% of the SOC was in the clay size fraction, 37.2% was in the silt fraction and 7.0% was in the sand fraction. Carbon mineralization rate in the incubated samples decreased over time, and was related to both particle size fraction and tillage practice. There was very good agreement between a first-order decay model (Ct= C1 + C0 (1-e-kt)) and measured SOC mineralization rates for all size fractions and tillages. The C mineralization data indicated that: (1) the SOC in the clay and sand fractions was more decomposable than the SOC in the silt fraction; and (2) the SOC associated with the clay and silt fractions was more readily decomposable under no-till than under mouldboard plough.

Refractory organic carbon in particle-size fractions of arable soils I: distribution of refractory carbon between the size fractions

Refractory compounds are responsible for the long-term sequestration of organic matter in soil. The aim of this study is to assess the storage of refractory compounds, i.e. compounds with long turnover times, across size separates in arable soils. The contents and distribution of organic carbon (OC) and nitrogen (N) in size fractions were examined for two contrasting treatment types from long-term agroecosystem experiments, i.e. C-depleted and fertilized plots. The soil organic carbon (SOC) pool of the C-depleted plots is considered to be relatively enriched in refractory compounds compared with the SOC in the fertilized counterparts. In two of the three long-term experiments, the relative retention of OC in separates <20 μm was considerably higher than in separates 2000–20 μm (OC contents in depleted plots compared with fertilized plots). Highest residual contents of OC were found in fractions <6 μm. In the third experiment, additionally to the very fine fractions, separates 250–20 μm retained a high proportion of OC. The behavior of N was analogous to that of OC: the highest relative residues in the depleted plots were found in fine separates. These results indicate that in the investigated arable soils, C and N compounds associated with fine separates are most stable. Refractory OC in arable soils may be largely stored in fine particle-size fractions.

Refractory organic carbon in particle-size fractions of arable soils II: organic carbon in relation to mineral surface area and iron oxides in fractions

The interaction of organic compounds with the mineral phase is considered as one stabilization mechanism for organic carbon (OC) in soils. The objective of this study is to assess the role of mineral surfaces for the long-term stabilization of OC in arable soils, with special emphasis on iron oxides. Soil samples were taken from two contrasting treatment types, i.e. fertilized plots and C-depleted plots, in long-term agroecosystem experiments. The soil organic carbon pool of the C-depleted plots is considered to show a lower contribution of labile compounds and consequently to be relatively enriched in refractory compounds compared with the fertilized counterparts. In fractions <6 μm, OC was studied in relation to total mineral surface area, surface area contributed by oxides and silicates, and the content and type of iron oxides (dithionite and oxalate extractable iron, Fed and Feo). In two sandy soils, OC contents were linearly related to total mineral surface area and the content of the two iron oxide fractions (Fed and Feo). The surface area developed by the silicates was low and thus the surface area contribution from oxides was dominant in fractions <6 μm. In contrast to the sandy soils, in a loamy soil OC was not correlated with surface area or the iron oxide content. However, the different soils agreed with respect to the behavior of C in density fractions: losses of OC occurred mainly from the light fraction (⩽2 g cm−3), whereas C in the heavy fraction (>2 g cm−3) proved to be stable. For the sandy soils, mineral surface area appears to control the storage of OC in fine fractions. Given the dominant surface area contribution from oxides, OC storage here primarily depends on the oxides. The C-depleted plots in particular show that surface area controls the accumulation of refractory C. The interaction of organic compounds with the mineral phase, mainly with the surface of oxides, seems to be a major mechanism for the long-term stabilization of OC in these sandy soils. An interaction with minerals seems to be important for stabilizing OC also in the loamy soil, although this is not reflected by a proportional relation between OC and surface area across the fractions.

The dynamics of carbon in particle-size fractions of soil in a forest-cultivation sequence

Cultivation of forest and grassland soils induces heavy changes in soil organic matter (SOM) dynamics. To better predict the effect of cultivation, there is a need to describe which organic pools are affected and to which extent. We used a chronosequence of thick humic forest soils converted to maize cultivation for 40 yr in southwest France. The dynamics of soil carbon was investigated through particle-size fractionation and the use of 13C allowed to distinguish forest-derived organic matter and new crop-derived organic matter. This partitioning of soil carbon by size on one hand and by age on the other provided a precise description of carbon turnover. The level towards which tend the organic pools under cultivation showed that the decay rates of soil carbon were one order of magnitude higher under cultivation than under forest. SOM can thus be considered as deprotected under cultivation. All size fractions appeared to be deprotected to the same extent. A progressive transfer of silt-sized C to clay-sized C was nevertheless suspected and attributed to the decreasing stability of fine silt-sized microaggregates with cultivation. SOM furthermore contained some very stable C present as silt-sized and possibly clay-sized particles. The turnover times of maize-derived organic matter was the same as that observed in similar soils cultivated for centuries. This indicated that the new conditions induced by cultivation were reached in the very first years after forest clearing and that the high initial SOM content and high mineralization rate of initial organic matter did not affect the dynamics of newly incorporated carbon.

Long term trends in fertility of soils under continuous cultivation and cereal cropping in southern Queensland. III. Distribution and kinetics of soil organic carbon in particle size fractions

Distribution of soil organic carbon in sand-, silt- and clay-size fractions during cultivation for periods ranging from 20 to 70 years was studied in six major soils used for cereal cropping in southern Queensland. Particle-size fractions were obtained by dispersion in water using cation exchange resin, sieving and sedimentation. In the soils' virgin state no single particle-size fraction was found to be consistently enriched as compared to the whole soil in organic C in all six soils, although the largest proportion (48%) of organic C was in the clay-size fraction; silt and sand-size fractions contained remaining organic C in equal amounts. Upon cultivation, the amounts of organic C declined from all particle-size fractions in most soils, although the loss rates differed considerably among different fractions and from the whole soil. The proportion of the sand-size fraction declined rapidly (from 26% to 12% overall), whereas that of the clay-size fraction increased from 48% to 61% overall. The proportion of silt-size organic C was least affected by cultivation in most soils. It was inferred, therefore, that the sand-size organic matter is rapidly lost from soil, through mineralization as well as disintegration into silt-size and clay-size fractions, and that the clay fraction provides protection for the soil organic matter against microbial and enzymic degradation.