Showing 5 results for Soil Structure
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.
S Zandsalimi, M Mosadeghi, A Mahbobi,
Volume 12, Issue 46 (1-2009)
Abstract
Organic fertilizers are the sources of many human-pathogenic microorganisms which potentially threaten the human health. This study was carried out to explore the possible effects of soil and manure types on filtration, transport and fate of manure-borne bacteria through undisturbed soil columns. The manure treatments consisted of cow manure, poultry manure and sewage sludge which were distributed at the rate of 10 Mg ha-1 on the surfaces of intact columns of two sandy clay loam and loamy sand soils. The manure-treated soil columns were leached by tap water with similar unsaturated flux of 4.8 cm h-1 up to four pore volumes (PV). The influent and leachate were sampled at different PVs. Gram-negative bacteria concentrations were determined for the influent and the columns’ leachate. Average influent concentration, average effluent concentration, relative filtration, and transported bacteria fraction during the leaching events were determined. Significant differences (P<0.05) were observed between the poultry manure and the other two manures in terms of average influent (i.e. manure-released) bacteria concentration. Stable structure and preferential pathways facilitated the bacteria movement in the sandy clay loam soil columns. The loamy sand soil strained 1.45 times more bacteria than the sandy clay loam soil due to its weak structure and blocked-dead pores. Relative contamination of the effluent was higher for poultry manure when compared with the other fertilizers. The low ionic strength of sewage sludge suspension caused the lower filtration of bacteria through the soil columns. The high concentration of soluble organics in cow manure resulted in a relative transport of the bacteria 1.12 times greater than the poultry manure. In general, management of organic fertilizers especially household poultry manure, as a considerable source of pathogenic bacteria, is important to control the environmental risks of pathogenic pollutions. Moreover, the soil texture and structure significantly affected the fate of manure-borne bacteria.
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.
N. Shahabinejad, M. Mahmoodabadi, A. Jalalian, E. Chavoshi,
Volume 24, Issue 3 (11-2020)
Abstract
Wind erosion is known as one of the most important land degradation aspects, particularly in arid and semi-arid regions. Soil properties, by affecting soil erodibility, can control the wind erosion rate. The aim of this study was to attribute the soil physical and chemical properties to the wind erosion rate for the purpose of determining the most important property. To this aim, wind erosion rates were measured in-situ at 60 points of Kerman province using a portable wind tunnel facility. The results indicated that wind erosion rates varied from 0.03 g m-2 min-1 to 3.41 g m-2 min-1. Threshold wind velocity decreased wind erosion rate following a power function (R2=0.81, P<0.001). Clay and silt particles, shear strength, mean weight diameter (MWD), surface gravel, dry stable aggregates (DSA<0.25mm), soil organic carbon (SOC), calcium carbonate equivalent (CCE) and the concentrations of the soluble Ca2+, K+ and Mg2+ were inversely proportional to the wind erosion rates following nonlinear functions. On the other hand, Wind erosion was significantly enhanced with increasing the sand fraction, soluble Na+, electrical conductivity (EC) and sodium adsorption ratio (SAR). According to the final results, among the studied soil properties, SAR and MWD were s the most effective properties controlling wind erosion in the soils of Kerman province. Therefore, it is recommended to consider suitable conservation practices in order to prevent the sodification and degradation of arid soils.
A.r Vaezi, Kh. Sahandi, F. Haghshenas,
Volume 28, Issue 3 (10-2024)
Abstract
Water erosion can be affected by land use change and soil degradation by agricultural activities. This study was conducted to investigate the effects of land use change in poor pastures on soil physical degradation and water erosion in semi-arid regions. Experiments were performed in 42 soil samples taken from seven areas covering the two land uses: poor pasture and rainfed agriculture, which have different soil textures (clay loam, silty clay loam, sandy clay loam, silt loam, loam, sandy loam, and sandy loam). The physical characteristics of soils were measured in the samples of both types of land use and its changes were expressed as physical degradation of the soil. The soil's susceptibility to water erosion was measured under simulated rainfall with 50 mm h-1 intensity for 60 min. The results showed that the land use change in pastures leads to the physical deterioration of soils; so bulk density, porosity, macropore, field capacity, saturated point, aggregate size, and aggregate stability were degraded with a rate of 28, 22, 41, 11, 5, 62, and 63 percentages. The structural characteristics of soil (aggregate size and stability) had the highest physical deterioration due to the land use change in the pastures. The change in land use change greatly increased the sensitivity of soils to water erosion. A significant relationship was found between the susceptibility of water erosion and the soil's physical degradation. The soils with coarser and more stable aggregates have higher physical degradation by the land use change and in consequence show more susceptibility to water erosion.
