Distribution In Particle Size Fractions Research Articles

Boron characterization and distribution in particle-size fractions and humic substances in forest and agricultural Tunisian soils

Boron characterization and distribution in particle-size fractions and humic substances in forest and agricultural Tunisian soils

Evaluation of the Effect of Changes in the Distribution of Particle Size Fractions on the Mechanical Properties of the Lateritic Gravelly-limestone (0/31.5) Mixture

Evaluation of the Effect of Changes in the Distribution of Particle Size Fractions on the Mechanical Properties of the Lateritic Gravelly-limestone (0/31.5) Mixture

Comparison of near and mid-infrared reflectance spectroscopy for the estimation of soil organic carbon fractions in Madagascar agricultural soils

Assessing the different pools of soil organic carbon (SOC) improves our understanding of how and at what rate the different forms of carbon (C) are being formed or lost in soils. Physical fractionation of soil organic matter (SOM) has often been used to separate and quantify SOC pools, but this approach is very tedious and can rarely be performed on large sample sets. Infrared spectroscopy has proven useful for time- and cost-effective quantification of total SOC, which prompted us to study its ability to characterise the distribution of SOC in physical fractions. This study aimed to compare the potential of near- and mid-infrared reflectance spectroscopy (NIRS and MIRS, respectively) to predict the distribution of SOC in particle-size and particle-density fractions, using spectra of unfractionated soils. A set of 134 sieved (< 2 mm) soil samples originating from seven sites in contrasting pedoclimatic regions of Madagascar was studied. For each sample, five SOM fractions were separated: the particulate organic matter fraction (POM) and the particle-size fractions >200 μm, 50–200-μm, 20–50-μm and < 20 μm. The mass (g fraction 100 g−1 soil), SOC concentration (gC kg−1 fraction) and SOC amount (gC fraction kg−1 soil) were determined for each fraction in the laboratory. The NIR and MIR spectra were acquired on finely ground (< 0.2 mm) aliquots of unfractionated soil. Then, spectra were used for the prediction of each variable (i.e., the mass, SOC concentration and amount of each fraction, and SOC content of unfractionated soil), which was achieved with locally weighted partial least squares regression (LW-PLSR) on NIRS and MIRS data separately. For both spectral ranges, the same samples were used for calibration (n = 109, selected for spectral representativeness) and validation (n = 25).Models based on NIRS and MIRS yielded excellent predictions for SOC content in unfractionated soil (R2 = 0.98 and ratio of performance to interquartile range RPIQ ≥13) and accurate predictions (R2 ≥ 0.75 and RPIQ ≥2) for the mass, SOC concentration and SOC amount in most fractions. The predictions of SOC concentrations and SOC amounts were better in the fractions <200 μm (R2 ≥ 0.85 and RPIQ >3), especially in the fraction <20 μm (R2 > 0.9 and RPIQ >4.5). In most cases, NIRS slightly outperformed MIRS. This result contradicts most previous studies performed on soils from temperate regions but confirms those performed on soils from tropical regions.Infrared spectroscopy allowed accurate prediction of SOC distribution in particle-size fractions, which paves the way to high-throughput characterization of SOM.

Heavy metal distribution in particle size fractions of floodplain soils from Dongchuan, Yunnan Province, Southwest China.

The heavy metal pollution level in soils is heavily affected by the soil particle size distribution. However, the heavy metal loss during particle size extraction and the effect of calcite on the heavy metals removal in terms of the particle size are unclear. In this study, the distribution of heavy metals (Cu, Cd, Cr, Co, Ni, Zn, Pb, U, and V) was determined in five particle fractions (> 2, 2-0.25, 0.25-0.02, 0.02-0.002, and < 0.002 mm) of two soil and one sediment samples collected from the floodplain of Dongchuan, Yunnan Province, Southwest China. The sampled floodplain soils were mainly composed of gravel and sand fractions (> 97%). The concentrations of all nine heavy metals in the sampled soils and sediment increase significantly with decreasing particle sizes. The maximal loss rate of Cd and Cu reaches 54% and 8.6%, respectively, which should be considered in the process of particle size fraction extraction in soils. The removal amount and removal rate of heavy metals in solution by pure calcite ranks in the order of Pb2+ > Cu2+ > Cr6+, while the removal rate of Pb (93.13%) is much higher than that of Cu (24.56%) and Cr (10.71%), which increase with the calcite particle size decreasing. The stabilization of carbonate minerals in soils is crucial for heavy metal pollution control in floodplain soils with high carbonate concentrations in Dongchuan, China.

Land use, spatial heterogeneity of organic matter, granulometric fractions and metal complexation in reservoir sediments

Abstract Aim This study aimed to evaluate land use, distribution of particle size fractions, organic matter (OM) and perform a metal quantification liable to complexation in the Itupararanga Reservoir (São Paulo, Brazil). This aquatic ecosystem is used for water supply and energy generation and is constantly subjected to anthropogenic impacts that alter its physical and chemical characteristics. Methods In a single campaign, samples of surface sediment (10 cm) were collected from nine sampling stations, in triplicate, along the reservoir. The collection was carried out with a “Lenz” type bottom sampler. The physicochemical variables, including the quantification of the metals copper, chromium, manganese, nickel, lead and zinc, were evaluated by basic descriptive statistics techniques combined with geostatistics and the use of remote sensing. Results All along the reservoir the sediment is predominantly organic and water depth interfered directly in the OM concentration and particle size distribution. Therefore, heterogeneity was observed regarding OM contents, particle size fractions and metals, with the exception of chromium, and the three zones of the reservoir proved to be distinct from each other. The land use classification showed the real situation of the Environmental Protection Area (EPA) and the results indicate that the central portion is more subject to anthropic impacts, while the dam region has high levels of metals, probably originated from the activities in the reservoir’s surroundings. Conclusions The soil erosion in the reservoir’s region shows the lack of efficiency in the Itupararanga EPA’s management, being needed a strategic coordination among the municipalities to enhance its conservation.

Boron Characterization, Distribution in Particle-Size Fractions, and Its Adsorption-Desorption Process in a Semiarid Tunisian Soil

Boron is essential for crop growth but needed in very small amounts. The range between boron deficiency and toxicity for plants is quite narrow. These stress conditions gravely reduce yield and quality of many crop species. Therefore, understanding the factors and the reactions affecting boron availability in soil is necessary. Against this framework, our research aims to determine the available boron status in a semiarid soil of Dour Ismail irrigated perimeter (North Tunisia). The objectives are also to investigate boron distribution in different particle-size fractions throughout the soil profile and to understand boron adsorption-desorption mechanisms according to some soil properties. For this purpose, one soil profile was dug in the field plot that had not received any previous boron fertilization. Soil samples were gathered from the different horizons of the profile and analyzed for the main physicochemical properties. Our results showed that the studied soil is Stagnic Fluvisol (clayic). The highest boron amounts were recorded in deep horizons and were greatly affected by soil salinity, organic matter, and clay contents. However, the increase in the pH level and the high percentage of total lime significantly diminished the available boron amounts in surface layers. The investigation of depth boron distribution in the different particle-size fractions indicated a considerable contribution of the silt (2–50 µm) fraction (52% of the soil total available boron), while the coarse (&gt;50 µm) and clay (&lt;2 µm) fractions seem to play a less important role. The adsorption data were fitted to Freundlich adsorption isotherm. It revealed that adsorption of boron increased with the increase of boron concentrations in soil solution. Desorption isotherm denotes that the accumulated boron in soil was not easily released. Adsorption and desorption of boron in soil were greatly affected by soil properties, such as pH, salinity, sand content, clay content, total organic carbon, total nitrogen, and cation exchange capacity.

Arsenic and Trace Metals in Three West African rivers: Concentrations, Partitioning, and Distribution in Particle-Size Fractions.

Despite increasing mining activities, and fertilizer and pesticide use in agriculture, little information is available on the status of metal(loid) contamination in rivers in West Africa. Sixty water samples were collected from three significant rivers (the Bandama, Comoé, and Bia Rivers) in Côte d'Ivoire, the world's top cocoa producer, to examine As, Pb, Cu, Fe, Cd, and Zn concentrations, partitioning, and distribution in suspended particle-size fractions. The results showed higher total metal(loid) concentrations during the dry and flood seasons than during the rainy season. Significant As and Pb concentrations, moderate Cu and Fe concentrations, and low Zn concentrations were observed during the flood season. The metal(loid) concentrations decreased upstream to downstream primarily due to increased deposition through flocculation. Inverse or no obvious spatial trends often were observed, indicative of local contamination from anthropogenic activities. The suspended solid phase and the strength of metal affinity to the particles controlled the metal(loid) concentrations. Furthermore, total metal(loid) concentrations increased significantly with decreasing suspended particle-size fractions. The results underline that As and Pb contents in the Comoé and Bia Rivers threaten the health of at least 3million people in southeastern Côte d'Ivoire. Filtering river waters before use will significantly reduce human health risks.

Data synthesis of carbon distribution in particle size fractions of tropical soils: Implications for soil carbon storage potential in croplands

Organic carbon saturation in soils refers to the theoretical maximum soil organic carbon (SOC) that can be associated with and stabilized on fine silt plus clay particles (F<20μm). We reviewed the literature dealing with SOC distribution between soil fractions to evaluate carbon saturation for tropical soils and estimate the C storage potential of cropland.We collected 258 data points on SOC distribution between soil fractions in tropical soils from 84 sites in 27 countries. We used boundary line analysis to estimate the maximum stabilized SOC depending on soil group, clay type and land use. SOC storage potential was calculated as the SOC saturation deficit, the difference between the actual SOC content and the maximum stabilized SOC content.We found that the maximum SOC in the fine fraction of tropical soils (53gCkg−1 fine fraction) was lower than previous assessments of global SOC storage scale based mainly on temperate soils. The F<20μm fractions were closer to SOC saturation in forest soils than in croplands. The cropland had a higher soil C storage potential, but changing agricultural management practices did not fill the deficit that is calculated using the whole dataset. The deficit was much lower when it was estimated with grassland or cropland data only: this provides a more realistic estimate for SOC storage potential for croplands.The SOC content in the coarser fraction (F>50μm) did not depend on soil texture and significantly contributed to the total SOC, especially in sandy soils (41.3%). This is affected by changes in agricultural management practices. We concluded that, although the aim of increasing SOC stabilization originally arose from climate change mitigation strategies, it must now be more viewed as being more relevant to food security and local adaptation to climate change.

Predicting and mapping of soil particle‐size fractions with adaptive neuro‐fuzzy inference and ant colony optimization in central Iran

In arid regions, knowledge of the variation in soil texture is crucial for land management because it affects soil physical, chemical, biological and most importantly hydrological properties. The availability of information on soil texture is scarce even though it is required to support land‐use management and sustainable development. Because it is costly to obtain information about the individual particle‐size fractions (PSFs), we used digital soil mapping methods (DSM) with environmental covariates that are less costly to obtain. Specifically, we explored the use of a digital elevation model and remote sensing data as environmental covariates to predict the vertical (i.e. 0–0.15, 0.15–0.3, 0.3–0.6 and 0.6–1 m) and lateral variation in PSFs over a 150‐km2 area in central Iran. We used a combination of equal‐area spline depth functions and three data‐mining techniques: multiple linear regression (MLR), artificial neural networks (ANN) and the neuro‐fuzzy inference system (ANFIS). In addition, we explored the effect of the reduction in dimension of feature space with ant colony optimization (ACO) and correlation‐based feature selection (CFS) on the accuracy of prediction of spatial models for each PSF. The results showed that the prediction of clay at 0–0.15‐m depth with ACO indicated the importance of including Landsat ETM+, the digital numbers of band 7 of Landsat images (B7) and clay index, whereas at 0.60–1‐m depth the wetness index and multi‐resolution valley bottom flatness index (MRVBF) were important. Model evaluation by leave‐one‐out cross‐validation with 191 soil observations indicated that the predictions by the ACO‐based ANFIS model (RMSE = 4.51% and R2 = 0.74 for clay at 0–0.15‐m) were more accurate than those by MLR and ANN. Spatial prediction was also better for the topsoil (0–0.15‐m) than at depth (RMSE = 7.1% for clay at 0.6–1 m); therefore, we conclude that the environmental covariates tested cannot resolve subsurface variation as accurately. Nevertheless, we recommend prediction by the ACO‐based ANFIS model and splines of lateral and vertical distribution of PSFs in other arid regions of Iran with the same agro‐ecological conditions.HighlightsDigital soil mapping of particle size‐fractions (PSF) by adaptive neuro‐fuzzy inference and ant colony optimization. Use of ant colony optimization (ACO) to assist in feature selection of environmental covariates. Neuro‐fuzzy inference system (ANFIS) superior to multiple linear regression (MLR) and artificial neural networks (ANN). PSF prediction by ACO‐based ANFIS model and splines is optimal.

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.

Organic Carbon and Nitrogen Distribution in Particle-size Fractions of Soils Under Cassava, Plantain and Rubber Based Land Use

Organic Carbon and Nitrogen Distribution in Particle-size Fractions of Soils Under Cassava, Plantain and Rubber Based Land Use

Spatial and vertical analysis of soil properties in a Mediterranean vineyard soil

AbstractSoil physical properties influence vineyard behaviour; therefore, the knowledge of their spatial variability is essential for making vineyard management decisions. Little work has been conducted at high spatial resolution on soil properties at depths lower than 0.30 m which is of special relevance to perennial crops. The objectives of this work were to (i) analyse the spatial and vertical variability of soil depth, particle size fractions and water‐holding capacity (WHC) by geostatistical techniques; (ii) study the causes of the variability, with additional information from classical soil sampling; and (iii) assess the significance of WHC through its relationship with vine vigour. The work was carried out in a vineyard of eight hectares within the D.O.Ca. Rioja (northern Spain). Soil variability was determined via grid sampling at three depth ranges (0–0.30, 0.30–0.60 and 0.60–0.90 m). A conventional soil survey provided additional information on soil variability. Clay, sand and silt fractions, soil organic matter content, WHC and pruning weight were determined. Most soil properties had strong or moderate spatial dependence, with the exceptions of sand at 0.30–0.60 m and silt in the topsoil. Topography and soil erosion caused the spatial variability of soil depth and contributed to the spatial distribution of particle size fractions in the topsoil, while the heterogeneity of parent material influenced the spatial pattern of soil properties at 0.60–0.90 m. The WHC and soil depth spatial distributions related well to that of vine vigour, demonstrating the importance of knowing the spatial variability of these soil properties.

Spatial variability of particle size fractions of an Oxisol cultivated with conilon coffee

Information on the spatial distribution of particle size fractions is essential for use planning and management of soils. The aim of this work to was to study the spatial variability of particle size fractions of a Typic Hapludox cultivated with conilon coffee. The soil samples were collected at depths of 0-0.20 and 0.20-0.40 m in the coffee canopy projection, totaling 109 georeferentiated points. At the depth of 0.2-0.4 m the clay fraction showed average value significantly higher, while the sand fraction showed was higher in the depth of 0-0.20 m. The silt showed no significant difference between the two depths. The particle size fractions showed medium and high spatial variability. The levels of total sand and clay have positive and negative correlation, respectively, with the altitude of the sampling points, indicating the influence of landscape configuration.

Soil carbon dynamics as influenced by tillage and crop residue management in loamy sand and sandy loam soils under smallholder farmers’ conditions in Malawi

Conservation agriculture (CA) characterised by minimal soil disturbance, permanent soil surface cover by dead or living plants and crop rotations is one way of achieving higher soil organic carbon (C) in agricultural fields. Sandy loam and loamy soil samples from zero tillage (ZT) and conventional tillage (CT) plots were taken from farmers’ fields during the dry season in August 2006. Soil organic carbon (SOC) and soil organic nitrogen (SON), microbial biomass carbon (MB-C) and microbial biomass nitrogen (MB-N), C mineralization and SOC distribution in particle size fractions in 0–20 cm layer were evaluated. Forty eight farmers’ fields were randomly sampled at four different locations in Central and Northern Malawi, representing ZT plots maintained for a different number of years, and ten fields under CT with similar soil type and crop grown were selected. SOC and SON in ZT fields were 44 and 41 % (4 years ZT) and 75 and 77 % (5 years ZT) higher, respectively, than CT plots. MB-C and MB-N in ZT fields were 16 and 44 % (4 years ZT) and 20 and 38 % (5 years ZT) higher, respectively, than CT plots. However, MB-C and MB-N in ZT fields were 27 and 25 % (2 years ZT) and 17 and 9 % (3 years ZT) lower than in CT plots. The proportion of the total organic C as microbial biomass C was relatively higher under CT than ZT treatments. The higher SOC and MB-C content in the ZT fields resulted in 10, 62, 57 % higher C mineralization rate in ZT plots of 3, 4 and 5 years of loamy sand soils and 35 % higher C mineralization rate in ZT plot of 2 years than CT of sandy loam soils in undisturbed soils in the laboratory. Simulating plough from the undisturbed soils that were used for C mineralization experiment resulted in linear curves indicating that all organic C was already depleted during the first incubation period. The relative distribution of soil organic matter (SOM) in silt and clay size fractions was strongly correlated (r = 0.907 and P ≤ 0.01) with silt percentages. Easily degradable carbon pool (CA,f) was correlated (r = 0.867 and P ≤ 0.05) with organic carbon in sand size fraction. In developing viable conservation agriculture practices to optimize SOC content and long-term sustainability of maize production systems, priority should be given to the maintenance of C inputs, crop rotations and associations and also to reduced soil disturbance by tillage.

Long-term fertilization effects on carbon and nitrogen in particle-size fractions of a Chinese Mollisol

Yan, Y., He, H., Zhang, X., Chen, Y., Xie, H., Bai, Z., Zhu, P., Ren, J. and Wang, L. 2012. Long-term fertilization effects on carbon and nitrogen in particle-size fractions of a Chinese Mollisol. Can. J. Soil Sci. 92: 509� 519. The response of soil organic matter (SOM) dynamics to long-term fertilization may be deduced from changes in the accumulation and distribution of different soil organic carbon (SOC) and nitrogen (N) pools. The SOC and N in particle-size fractions were therefore measured to assess the influences of pig manure and synthetic fertilizer application on the characteristics of these pools. A long-term fertilization experiment, established in 1979 in the Mollisol area (Gongzhuling, China) was used for this study. Composite soil samples (0� 20 cm) were collected in 2005 from 12 treatment plots that had received annual applications of pig manure, synthetic fertilizers or combinations of both. Soils were fractionated into fine clay (B0.2 mm), coarse clay (0.2� 2 mm), silt (2� 50 mm), fine sand (50� 250 mm) and coarse sand (250� 2000 mm) and then SOC and N contents in each particle-size fraction were measured. Although most of the SOC and N were associated with clay and silt fractions, the large proportion of silt in the soil mass played a key role in the retention of SOC and N. The application of pig manure alone increased accumulation of SOC and N in each particle-size fraction, but preferential enrichment was found in the coarse sand fraction. This indicates that pig manure is efficient in restoring SOM in the temperate Chinese Mollisol under a tilled maize (Zea mays L.) monocropping system and having a long frozen period in winter. The application of synthetic fertilizers had no clear effect on SOC and N accumulation or their distribution in particle-size fractions. However, the combined application of pig manure and synthetic fertilizers enhanced the accumulation of SOC and N in all particle-size fractions, and led to a shift of SOC and N from fine to coarse particles. We extended the hierarchy model for SOC protection to consider a shift in SOC accumulation from fine to coarse particles, depending on the initial SOC content of the specific soil. The findings reveal a clear positive interaction between pig manure and synthetic fertilizers that may improve the quantity of SOM in the temperate Chinese Mollisol.

Long-term fertilization effects on carbon and nitrogen in particle-size fractions of a Chinese Mollisol

Yan, Y., He, H., Zhang, X., Chen, Y., Xie, H., Bai, Z., Zhu, P., Ren, J. and Wang, L. 2012. Long-term fertilization effects on carbon and nitrogen in particle-size fractions of a Chinese Mollisol. Can. J. Soil Sci. 92: 509–519. The response of soil organic matter (SOM) dynamics to long-term fertilization may be deduced from changes in the accumulation and distribution of different soil organic carbon (SOC) and nitrogen (N) pools. The SOC and N in particle-size fractions were therefore measured to assess the influences of pig manure and synthetic fertilizer application on the characteristics of these pools. A long-term fertilization experiment, established in 1979 in the Mollisol area (Gongzhuling, China) was used for this study. Composite soil samples (0–20cm) were collected in 2005 from 12 treatment plots that had received annual applications of pig manure, synthetic fertilizers or combinations of both. Soils were fractionated into fine clay (&lt;0.2 µm), coarse clay (0.2–2 µm), silt (2–50 µm), fine sand (50–250 µm) and coarse sand (250–2000 µm) and then SOC and N contents in each particle-size fraction were measured. Although most of the SOC and N were associated with clay and silt fractions, the large proportion of silt in the soil mass played a key role in the retention of SOC and N. The application of pig manure alone increased accumulation of SOC and N in each particle-size fraction, but preferential enrichment was found in the coarse sand fraction. This indicates that pig manure is efficient in restoring SOM in the temperate Chinese Mollisol under a tilled maize (Zea mays L.) monocropping system and having a long frozen period in winter. The application of synthetic fertilizers had no clear effect on SOC and N accumulation or their distribution in particle-size fractions. However, the combined application of pig manure and synthetic fertilizers enhanced the accumulation of SOC and N in all particle-size fractions, and led to a shift of SOC and N from fine to coarse particles. We extended the hierarchy model for SOC protection to consider a shift in SOC accumulation from fine to coarse particles, depending on the initial SOC content of the specific soil. The findings reveal a clear positive interaction between pig manure and synthetic fertilizers that may improve the quantity of SOM in the temperate Chinese Mollisol.

Spatial variability in the distribution of particle-size fractions in agrogray soils and agrogray soils with the second humus horizon

The degree of spatial variability in the distribution of particle-size fractions has been determined for agrogray soils of an experimental field of Bryansk Agricultural Academy. The degree of spatial variability is close to the analytical error; for comparing different plots, particle-size distribution analysis has to be performed in two-three replicates. If the particular sets of data (e.g., data sets on the content of clay in the upper and lower parts of the plow horizon) are used, the statistical probability of differences increases. Cluster analysis can be used for the initial grouping of particle-size distribution data.

Pairwise comparison of soil organic particle-size distributions in native savannas and Eucalyptus plantations in Congo

Conversion of native vegetation into fast-growing tree plantations is known to affect soil organic matter (SOM): soil carbon (C) and nitrogen (N) content and their distribution in particle-size fractions can be modified in various ways depending on numerous factors, such as soil properties, SOM levels prior to conversion, climatic conditions, silvicultural practices and fire occurrence. Since 1978, 43,000 ha of clonal eucalyptus plantations have been established on sandy coastal plains under savannas near Pointe-Noire, Congo. We investigated the effects of afforestation on topsoil (0–10 cm) C and N through the analysis of their distribution in particle-size fractions using a pairwise experimental design that compared adjacent savannas and plantations. The studied plantations were of different ages (2–30-year-old stands) and differently affected by accidental fires. No significant difference in total topsoil C, N or C/N was observed between young plantations and savanna. In old plantations that had not been affected by fire, total topsoil C content was twice as high as in savanna ( p = 0.0016 ), on average, mostly involving fractions > 50 μ m. By contrast, total topsoil N did not differ significantly at these sites. In old plantations affected by fire, total topsoil C content did not differ significantly from that in savanna, but total topsoil N was 26 % lower in plantations than in savanna ( p = 0.0063 ), on average, and the decrease affected fractions < 200 μ m especially. Whatever the fire occurrence, total topsoil C/N was higher in old plantations than in savanna, in fractions > 20 μ m especially.

Long‐term effects of fallow, tillage and manure application on soil organic matter and nitrogen fractions and on sorghum yield under Sudano‐Sahelian conditions

Abstract. Soil organic matter (SOM) controls the physical, chemical and biological properties of soil and is a key factor in soil productivity. Data on SOM quantity and quality are therefore important for agricultural sustainability. In 1990, an experiment was set up at Saria, Burkina Faso on a sandy loam Lixisol to evaluate long‐term effects of tillage (hand hoeing or oxen ploughing) with or without 10 t ha−1 yr−1 of manure and fallowing on SOM and N concentrations and their distribution in particle size fractions. The field was sown annually to sorghum (Sorghum bicolor [L.] Moench). Ten years later, total organic C and total N, SOM fractions and their N concentrations, and sorghum yield were determined. Continuous sorghum cultivation without organic inputs caused significant losses of C and N in the hoed and ploughed plots. However, addition of manure to hoed plots was effective in maintaining similar levels of C and N to fallow plots. Without manure, SOM was mainly stored in the size‐fraction &lt;0.053 mm (fine organic matter, FOM). SOM was mainly stored in the size‐fraction between 0.053 and 2 mm (particulate organic matter, POM). In plots with manure and in fallow plots, the addition of manure more than doubled POM concentrations, with levels in tilled plots exceeding those of the fallow plots, and the highest levels in manually hoed plots. Nitrogen associated with POM (POM‐N) followed a similar trend to POM. Hoeing and ploughing led to a decline in sorghum grain yield. Manure application increased yields by 56% in the hoed plots and 70% in the ploughed plots. Grain yield was not correlated with total SOM but was positively correlated with total POM. This study indicated that POM was greatly affected by long‐term soil management options.

Carbon and monosaccharide distribution in particle-size fractions from a clayey ferrallitic soil (Congo)

A study was undertaken on a clayey ferrallitic soil from Congo, exploring techniques of particle-size fractionation and gas chromatography for characterizing the carbon distribution and carbohydrate (sugar) composition of soil organic matter-mineral associations. The whole soil under savannah vegetation contained 43 g C kg−1 soil, considerably more than under long-term cultivation, the clay-sized fraction accounting for most of the total soil carbon in both sites. Amongst the sugar monomers in the savannah site, glucose was the most abundant, followed by mannose with surprisingly high concentrations of ribose. The same observation held for the particle-size fractions of the soil with the exception of the coarse sand-sized fraction (>200 μm), where xylose (a sugar essentially of plant origin) was the next most abundant sugar after glucose; this was in accordance with the particulate plant character of this fraction. The ratio galactose + mannose/arabinose + xylose, an indicator of the decomposition of plant residues and the accumulation of microbial metabolites, increased 4- to 6-fold from coarse to finer fractions. The same trends persisted after a 17-year cultivation of cassava. Results were evaluated in comparison with data provided in the literature for temperate and tropical soils.