Showing 8 results for Aggregate Stability
F. Tajik,
Volume 8, Issue 1 (4-2004)
Abstract
Aggregation is an important temporal property of soil structure that is affected by intrinsic soil properties and also soil use and management. Aggregate stability has a strong influence on many processes in soil such as infiltration, aeration, strength, erosion, and soil’s ability to transmit liquids, solutes, gases, and heat. In this study, undisturbed soil specimens from 0-10 and 10-20 cm depths were sampled during summer 1999 from some regions in Iran including Golestan, Kermanshah, West Azerbaijan, and Mazendaran. After drying the samples in lab, the different sizes of aggregates were separated and the wet aggregate stability (WAS) and dispersible clay (DC) were determined on 2-2.8 mm aggregates according to Pojasok & Kay procedure (1990). The variance analysis of data showed significant differences among soils in all regions. The averages were compared by Duncan test to find the following order: Mazendaran > Golestan > Kermanshah > West Azerbaijan. Regression analysis of data of whole regions showed that the variability of aggregate stability was mainly explained by organic carbon content (R2=0.723 in P > 0.0001). The clay content had the greatest effect on aggregate stability in samples from Golestan while sand content had the greatest effect in samples from West Azerbaijan. The resulting equations from stepwise regression can be used to estimate aggregate stability from other soil variables in the study regions.
M. Yoosefi, H. Shariatmadari, M.a. Hajabbasi,
Volume 11, Issue 42 (1-2008)
Abstract
Adopting proper agricultural management and conserving soil organic matter are important components of sustainable agriculture. Soil organic matter content is a key attribute in soil quality. Labile organic matter pools can be considered as suitable indicators of soil quality that are very sensitive to changes in soil management practices. This research was carried out to investigate some organic carbon labile pools as an indicator evaluating the effects of different managements on some quality parameters of two calcareous soils. The study was conducted in 2 locations: 1- plots that receiving 0 (C1), 25 (C2), 50 (C3) and 100 (C4) Mg/ha of manure for five years successively with a cropping rotation of wheat –corn every year and plots under three cropping rotations (C5, C6 and C7) at Lavark experimental farm and 2- inquiry research station of Fozveh at different plots with three different cropping rotations (C8, C9 and C10) with a given cropping history recorded for the last 5 years. Soil samples were taken from the center of each plot and the depths of 0-5 cm and 5-15 cm. Their organic carbon, hot water soluble carbohydrate, particulate organic matter (POM), organic carbon and hot water soluble carbohydrate of POM, mean weight diameter of water stable aggregates were determined. Different managements consisting of different levels of manure and types of cropping rotation had significant effects on the soil characteristics measured. The greateast amount of carbohydrate and aggregate stability was obtained in the plots of 100 Mg/ha of manure in Lavak and in alfalfa plots in Fozveh station. Also, the results showed that aggregate stability has a better correlation with hot water soluble carbohydrate in comparison with other soil organic pools. Therefore, the carbohydrate extracted by hot water may be used as an index to assess the impacts of different agricultural management systems on soil quality.
F. S. Moosavi , F. Raiesi ,
Volume 14, Issue 54 (1-2011)
Abstract
Although the crucial function of earthworms in improvement of soil physical properties is well -know, but very little is known of the interactive influence of earthworms and organic materials on soil properties such as soil aggregate stability, particularly in arid and semi-arid soils. The low organic matter content and the significant role of earthworms in improving physical properties of arid and semi-arid soils necessitate studying the interactive effects of organic materials and earthworms. Thus, the main objective of this study was to identify the interactive effects of anecic earthworm (Lumbricus terrestris L.) and various organic residues (including alfalfa, compost, mixture of alfalfa and compost and cow dung) on soil aggregate stability expressed as the Mean Weight Diameter (MWD), Geometric Mean Diameter (GMD) and Aggregation Ratio (AR), and furthermore soil Ca and Mg contents. The experiment consisted of a 2×5 factorial treatment organized in a completely randomized design with four replications under controlled greenhouse conditions, lasted for 150 days. Results showed that earthworm inoculation and organic materials addition alone increased significantly all the indices of soil aggregation and aggregate stability, and Ca and Mg contents. However, the combined use of earthworms and organic residues resulted in more stable aggregates. Results indicated that earthworm inoculation in the presence of organic materials resulted in 39, 58, 2, 67, 43 and 74% increases, respectively in MWD, AR, GMD, Ca, Mg and macroaggregates whereas microaggregates were reduced by 13.5% in earthworm-worked soils. We observed a significant relationship (R2=0.945) between soil Ca content and MWD, demonstrating that earthworms apparently excrete calcite that helps bonding clay particles and soil organic matter via cationic (Ca+2) bridging. In summary, results of this study show that the simultaneous applications of anecic earthworms and organic materials may considerably help in improving the structure of arid and semi-arid soils with low carbon level.
M. Ajami, F. Khormali,
Volume 15, Issue 57 (10-2011)
Abstract
Biological soil covers such as lichens have critical roles in soil stability and prevention of erosion. In order to study the effect of lichen biological covers on aggregate stability and soil conservation, loess hills covered with lichen and uncovered ones were selected in Northern Golestan Province. Five samples were taken from the depth 0 to 5 cm of both two areas for physico-chemical analyses. The undisturbed soil samples were taken for micromorphological studies, too. Analyses of soils revealed that soil organic carbon content increased markedly, compared to uncovered soils. Mean weight diameter also increased about three folds in soils covered with lichen. Fungal hyphae and polysaccharides excretions bind soil particles together and increase size of aggregates. Micromorphological study of thin sections showed that uncovered soils had a weak and massive structure, but soils covered with lichen had a crumb granular and also well -separated angular block and higher proportion of voids. Due to the effect of lichen on upward movement of calcium carbonate, crystallitic b-fabric appeared in the surface layer of covered soils and speckled b-fabric underneath. Excremental pedofeatures are the most common pedofeatures in the covered soils.
N. Ghorbani Ghahfarokhi, Z. Kiani Salmi, F. Raiesi, Sh. Ghorbani Dashtaki,
Volume 17, Issue 63 (6-2013)
Abstract
Free and uncontrolled pasture grazing by animals may decrease soil aggregate stability through reductions in plant cover and subsequent soil organic C, and trampling. This could expose the soil surface layer to degradation and erosion. The objective of this study was to determine the influence of pasture management (free grazing, controlled grazing and long-term non-grazing regimes) on aggregate-size distribution and aggregation parameters by wet and dry sieving methods in two native pastures, protected areas in Chaharmahal va Bakhtiari province. The studied pastures were 1) SabzKouh pastures protected from grazing for 20 years, and 2) Boroujen pastures protected from grazing for 25 years. Soil samples were collected from 0-15 cm depth during the grazing season in summer 2008. Samples (finer than 2 mm) were analyzed for aggregate-size distribution and aggregation parameters by wet and dry sieving methods. Results showed that pasture management had a significant influence on aggregate-size distribution and aggregation parameters in the two areas. The two methods indicated that macro-aggregates in non-grazing and controlled grazing regimes were higher than those in free grazing regime, whereas in free grazing management micro-aggregates showed an opposite trend, and were greater compared with the other grazing regimes. Similarly, soil aggregate stability indices (i.e. mean weight diameter, aggregate geometric and ratio mean diameter) were all improved by non-grazing regimes, suggesting that animal grazing and trampling break down large soil aggregates due largely to compaction and reduced plant coverage. However, the extent to which grazing affects soil aggregation depends in large part on grazing intensity and duration, and the area involved.
S. Rahmati, A. R. Vaezi, H. Bayat,
Volume 23, Issue 1 (6-2019)
Abstract
Saturated hydraulic conductivity (Ks) is one of the most important soil physical characteristics that plays a major role in the soil hydrological behaviour. It is mainly affected by the soil structure characteristics. Aggregate size distribution is a measure of soil structure formation that can affect Ks. In this study, variations of Ks were investigated in various aggregate size distributions in an agricultural soil sample. Toward this aim, eight different aggregate size distributions with the same mean weight diameter (MWD= 4.9 mm) were provided using different percentages of aggregate fractions consisting of (< 2, 2-4, 4-8 and 8-11mm). The Ks values along with other physicochemical properties were determined in different aggregate size distributions. Based on the results, significant differences were found among the aggregate size distributions in Ks, particle size distribution, porosity, aggregate stability, electrical conductivity (EC), organic matter and calcium carbonate. The aggregate size distributions with a higher percentage of coarse aggregates (4-8 and 8-11 mm) also showed higher Ks as well as clay percentage. A positive correlation was also observed between Ks and clay, aggregate stability and EC, whereas sand showed a negative correlation with Ks. No significant correlations were found between Ks and silt, porosity and organic matter. Further, multiple linear regression analysis showed that clay and aggregate stability were the two soil properties controlling Ks in the aggregate size distributions (R2=0.80, p<0.01). Aggregate stability was recognized as the most important indicator for evaluating the Ks variations in various aggregate size distributions.
A. Karami, K. Khavazi,
Volume 23, Issue 2 (9-2019)
Abstract
Due to unsuitable soil physical conditions, calcareous soils, and the existence of a huge amount of sulfur in the country, the study of sulfur effects on the soil structure and other soil properties is necessary. Therefore, the effects of different rates of sulfur including: 0, 750, 1500 and 3000 kg/ha, when accompanied by Halothiobacillus neapolitanus bacteria, on the soil properties in the corn-wheat rotation in two years were investigated. Parameters of soil pH, EC, sulphate, organic carbon, soil structure and wheat yield were measured. For the quantification of soil structure and quantity evaluation of sulfur effect on the soil structure, with measuring the aggregate size distribution, the mean weight diameter (MWD) and geometric mean diameter (GMD) of the aggregate indices, and the amounts of fractal dimension were determined. The r results indicated that with the progress of the experiment and further application of sulfur along with thiobacillus bacteria, aggregation and aggregate stability were increased. The effect of sulfur treatments on MWD and GMD was significant; based on quantification indices, it had 28 percent positive effect on the soil structure. Sulfur with 3 percent reduction of fractal dimension had a significantly positive effect on the soil structure. Application of sulfur decreased a small amount of soil pH and increased 12 percent of the soil EC and 40 percent of the soil sulphate. So soil structure improvement and reclamation of soil physical condition can be very effective on the soil conservation and sustainability of the production resources and the conservation of environment.
N. Moradian Paik, S. Jafari,
Volume 26, Issue 4 (3-2023)
Abstract
Changes in land quality factors were investigated according to the change in land use of two conventional cropping systems in Khuzestan (Dimcheh region, periodic cultivation system, sugarcane, forest, and deforesting in Zaras region). The results showed that by the change of forest land use, organic carbon from 0.93 to 0.55%, cation exchange capacity (CEC) from 19.6 to 13.3 cmol/kg, C/N from 7.4 to 3.8%, the mean weight diameter of aggregate (MWD) from 1.7 to 1.3%, and microbial respiration from 0.11 to 0.06 mg of CO2 /gr of soil per day decreased and in contrast, the dispersible clay from 4.6 to 19.3% increased. PCA analysis for the parameters showed that five factors justified more than 90% of the variance in the values of FC, PWP, AW, and AF. In the Dimcheh region, the average volumetric moisture content of FC from 31.3% to 27.3%, available water from 12.9% to 9.8%, dispersible clay from 56.1% to 12.3%, and bulk density reduced from 1.6 to 1.4%, organic carbon from 0.45 to 0.78%, C/N from 6.3 to 10.0%, microbial respiration from 0.01 to 0.04 mg of CO2 /gr soil per day and MWD of aggregates increased from 0.77 to 1.3 mm. Five factors including FC, AW, BD, DC, and OM explained more than 90% of the variance.
