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Showing 3 results for Sorptivity
Effects of Endophyte-infected (Epichloë coenophaila) Tall Fescue Residues on Water Repellency and Structural Stability of Texturally-Different Soils
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.
 


Estimation of Soil Hydraulic Properties Curve through Beerkan Infiltration Experiment Algorithms
T. Ahmady, M. Delbari, P. Afrasiab,
Volume 23, Issue 2 (9-2019)
Abstract
Nowadays, the Beerkan computational algorithms (BESTslope and BESTsteday) are known as the suitable indirect methods for estimating soil saturated hydraulic conductivity (Ks) and sorptivity (S), as well as the scale parameter (hg) in van Genuchten soil water retention equation through the data collected in the Beerkan infiltration experiment and other required data. The purpose of this study was to compare these algorithms in estimating Ks and S, as well as the soil water content corresponding to the suctions of 33 kPa, 100 kPa, 200 kPa, 300 kPa and 1500 kPa. For this purpose, a total of 40 Beerkan infiltration experiments were carried out in Sistan dam research field. From all Beerkan experiments, 30 tests in loam and sandy loam textures having a relative error less than 5.5% (Er <5.5%) were selected for further analysis. The statistical criteria RMSE, ME and ωr2 were used to compare the measured and estimated water content values at each suction. The results showed that the BESTsteday algorithm, which had a more simple calculating process than the main algorithm (i.e. BESTslope), could provide the Ks and S values and the soil water content of the near field capacity with an acceptable accuracy. The model performance in estimating water content corresponding to the 1500 kpa suction head (i.e. θfc) was not acceptable for both algorithms. Moreover, the relative error of estimating soil water content (Er(h,θ)) was decreased gradually by an increase in clay %.

Comparison Methods of Determining the Degree of Hydrophobicity Based on the Measurement of Soil-Water Contact Angle
R Mousavi Zadeh Mojarad, S. H. Tabatabaei, N. Nourmahnad,
Volume 25, Issue 2 (9-2021)
Abstract
The contact angle is a numerical index of differentiation between hydrophilic and hydrophobic soils. The objectives of this research are: 1) assessing different methods such as capillary rise, the molarity of ethanol droplet, repellency index, and sessile drop, and 2) Determining the most efficient method in a typical soil with sandy loam texture. In this study, hydrophobic soil was hydrophobized artificially using stearic acid and according to the water drop penetration time classification method. Calculated contact angles of hydrophilic soil with capillary rise method, the molarity of ethanol droplet method, repellency index (two methods of calculation), and sessile drop method were 89.9, 75.41, (57.81), 56.28, and 58.91, respectively. Using the contact angle measuring device, the contact angle of five hydrophobic levels were 58.91, 104.92, 120.48, 129.96, and 173.07, respectively. According to the precession of the device where the operator is capable to control data and processes and there is no limitation in usage, therefore, the sessile drop method is the most suitable method to measure contact angle. The contact angle of the late method and water drop penetration data are positively correlated (R2 = 0.975).

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