Showing 4 results for Dispersible Clay
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.
R. Karimi, M. Hassan Salehi, F. Raiesi,
Volume 18, Issue 69 (12-2014)
Abstract
Improper use of rangelands may lead to their destruction. Therefore, the conversion of these degraded rangelands to agricultural lands and other land uses may improve their soil quality. The purpose of the present study was to evaluate the impact of cultivation in the degraded rangelands on some soil characteristics in Safashahr region of Fars province. Four land uses including the rangeland with sparse vegetation (degraded rangeland), the rangeland converted to agricultural land over 17 years, the agricultural land converted to apple orchard for 4 years and also to an apple orchard for 40 years were selected. Samples were randomly taken from each land use at two depths (0-20 and 20-50 cm) with five replications. The results revealed that land use change significantly increased organic matter and MWD in both soil depths. Bulk density and water dispersible clay increased in agricultural land and new orchard while a decrease was observed for old apple orchard. It is suggested the traditional farming to be replaced with new cultivation methods like minimum tillage and no tillage. Overgrazing of the rangelands must also be avoided.
F. Hosseini, M. R. Mosaddeghi, M. A. Hajabbasi, M. R. Sabzalian, M. Soleimani, M. Sepehri,
Volume 21, Issue 2 (8-2017)
Abstract
Soil water repellency can affect several soil properties such as aggregate stability. Soil texture and organic matter are two main internal factors responsible for the variability of soil water repellency. Major sources of organic matter in soil include plant residues, and exudates of plant roots and soil microorganisms. Tall fescue (Festuca arundinacea Schreb.) as an important cool-season perennial forage grass is usually infected by a fungal endophyte (Epichloë coenophiala) which often enhances resistance to biotic and abiotic stresses as well as altering the litter decomposition rate and soil properties. In this study, the effects of endophyte-infected (E+) and endophyte-free (E−) tall fescue residues (in three different levels of 0, 1 and 2%) on soil organic carbon, basal microbial respiration, water-dispersible clay and water repellency index (determined by intrinsic sorptivity method) were investigated in four texturally-different soils in the laboratory. E+ and E− tall fescue residues were completely mixed with moist soil samples and then were incubated at 25 °C. During two months of incubation period, the amended soil samples were subjected to 10 wetting and drying cycles and then, the above-mentioned soil properties were measured. The results indicated that soil organic carbon and water-dispersible clay were greater, while basal soil respiration and repellency index were lower in fine-textured soils. Water repellency index was increased by production of hydrophobic substances (for the rate of 1%) and was reduced by induced greater soil porosity (for the rate of 2%). Presence of endophyte in plant residues had no significant effect on water sorptivity, ethanol sorptivity and water repellency index; nevertheless, E+ residues increased soil organic carbon and decreased water-dispersible clay significantly. Overall, it is concluded that tall fescue residues, especially those with E+, can improve soil physical quality due to improving soil organic carbon storage and water repellency index and decreasing water-dispersible clay (as an index for aggregate instability). These E+ species and the residues have great potential to be used in sustainable soil conservational managements.
Dr. Ali Reza Vaezi, Saeideh Akbari, Fereshteh Haghshenas,
Volume 30, Issue 1 (3-2026)
Abstract
Splash erosion is the initial stage of soil erosion by water, which can be significantly influenced by soil properties. The rate of this type of soil erosion in drylands of semi-arid regions is high due to sparse vegetation cover, particularly during the early stages of plant growth. This study was conducted to investigate the soil properties determining splash erosion in semi-arid drylands. Soil aggregates with a diameter of 6 to 8 mm were taken from the soil surface (0-30 cm depth) in thirty dryland farms at three replications. Soil aggregates were purred into splash bowls and exposed to simulated rainfalls with an intensity of 60 mm h-1 for 30 minutes. Different soil properties were determined in ninety soil samples. Based on the results, the highest splash erosion occurred in clay loam (0.0021 gm⁻²s⁻¹), while the lowest value was in loamy sand texture (0.0008 gm⁻²s⁻¹). Splash erosion was significantly affected by grain size distribution; so that positive correlations were found with silt (r= 0.43), clay (r= 0.44), and dispersible clay (r= 0.47), whereas negative correlations existed with sand (r= -0.46) and gravel (r= -0.53). Furthermore, splash erosion was considerably influenced by organic matter (r= -0.23), calcium carbonate (r= -0.22), bulk density (r= -0.60), aggregate stability (r= -0.44), and hydraulic conductivity (r= -0.44). This study revealed that the drylands with fine-textured soils and having a lower amount of organic matter as well as calcium carbonate, have a higher susceptibility to splash erosion in semi-arid regions.
