JWSS - Journal of Water and Soil Science

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The increased potential for soil erosion and compaction due to continuous row crop production and intensive tillage is causing some concern and has led to the consideration of reduced tillage techniques as part of the solution. The objective of this study was to investigate the short-term (one-year) influences of different management practices on the physical properties of a sandy loam soil under corn crop. Treatments were the combinations of three tillage systems (no-till, NT chisel plow, CP and moldboard plow, MP) and three composted cattle manure rates [0, 30 and 60 ton (dry weight) ha^-1]. The experiment was carried out in a split-plot design. Three replicates of the treatments were applied in a randomized block design. Saturated hydraulic conductivity (K_s), total porosity (TP), macro-porosity (Macro-P), micro-porosity (Micro-P) of soil and mean weight diameter (MWD) of aggregates, were measured to a depth of 22.5 cm when 100 percent of the tassels appeared. Tillage and manure combination had significant effects on Log[ K_s], TP, Macro-P and Micro-P. The MP system increased pore space and continuity due to complete inversion and loosening, and as a result K_s, TP, Macro-P and Micro-P were higher than NT system. Higher Macro-P observed for CP might have caused higher K_s versus MP. Reduced tillage systems increased MWD and the increment of manure caused an increase in MWD over all tillage treatments. The results indicate short-term positive effects of manure application on soil pore size characteristics and aggregate stability under moldboard and chisel plowings in the region.

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Transport and filtering of pathogenic bacteria through porous media and groundwater resources are important and، therefore the effect of various factors on bacteria transport and filtering has been given a great attention nowadays. In this study، effects of calcium sulfate and carbonate on Psedomonas fluorescens filtration and filtering parameters were investigated in saturated sand columns under steady-state flow. The calcium carbonate levels included 0، 5، 10 and 20 %w/w and calcium sulfate levels consisted of 0، 5 and 10 % w/w which were thoroughly mixed with sand (0.15-0.25 mm). The experiment was considered factorial in completely randomized design with three replicates. The treated sands were poured into pyrex cylinders with length of 20 cm and diameter of 7 cm. Then، steady-state saturated flow with constant flux was applied to the columns. When the steady-state flow was established، the bacteria suspension with concentration of 10⁶ CFU cm^-3 (C0) was injected as step input into the columns. The leaching then was continued up to 5 times of pore volume (PV). The effluent concentration of the bacteria (C) was measured at 0.25 PV intervals. Then، the sand columns were divided into 0-5، 5-10، 10-15 and 15-20 cm layers in order to measure the filtered bacteria in each layer. The results showed that the effects of calcium carbonate on retaining of the bacteria in the 5-10 and 10-15 cm layers were significant at 1% level. It was significant at 5% for the 15-20 cm layer. The effect of calcium sulfate was also significant at 5% for the 10-15 cm and 15-20 cm layers. The interactive effects of treatments on bacteria adsorption was significant for the 5-10، 10-15 and 15-20 cm layers. The retained concentration profile and the filtration coefficient were significantly affected by the treatments، showing higher bacteria adsorption at lower depths and predominance of physical filtering. The results showed the high filtering capacity of carbonate and sulfate minerals which could ultimately reduce bacteria transport in saturated porous media towards groundwater resources.

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Soil physical and chemical properties, and test conditions might affect soil structural stability. In this study, the effects of test conditions as well as intrinsic soil properties on structural stability were investigated for selected soils from Hamedan Province. Mean weight diameter (MWD) and tensile strength (Y) of aggregates were determined by wet sieving method and indirect Brazilian test, respectively. The soil samples were pre-wetted slowly to matric suction of 200 kPa before the wet sieving. The pre-wetted samples were wet-sieved for 5, 10 and 15 min in order to simulate different hydro-mechanical stresses imposed on soil structure. Tensile strength of soil aggregates were also measured at air-dry and 500 kPa matric suction conditions. Short duration shaking (i.e. 5 min) could effectively discriminate the Hamedan soils in terms of structural stability due to their fairly low aggregate stabilities. The soil organic matter content had the highest impact on MWD followed by both clay and CaCO₃ content. The same was true for the Y values i.e. OM played the highest role in mechanical strength of soil aggregates. The highest coefficient of determination (R²) was obtained between Y and the intrinsic soil properties for matric suction of 500 kPa. The organic matter content had an important role in water and mechanically stable soil aggregates. The results indicated that short-duration wet sieving (i.e. 5 min) and measurements of tensile strength at matric suction of 500 kPa could be recommended for aggregate stability assessment in Hamedan soils

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In this study, the transport of nalidixic acid-resistant Escherichia coli (E. coli NAR) through two soils of sandy loam and clay loam was investigated. Saturated and unsaturated flow conditions were applied at two temperatures of 5 and 20ºC. Leaching was done using large repaired soil columns which had been subjected to physical weathering. A 20-cm diameter disk infiltrometer was set up to establish the steady-state flow conditions. Effluent was sampled at three depths of 15, 30 and 45 cm of soil columns. Saturated flow condition, temperature of 20 ºC and clay loam soil resulted in increasing the bacteria concentration in the leachate. Filtration coefficient and relative adsorption indices in sandy loam soil (average flow conditions, temperature and depth) were greater than those of clay loam soil with the respective values of 33% and 23%. These results may be related to the instability of soil structure and abundance of micropores in the sandy loam columns. In other words, the bacteria were physically blocked and entrapped in the fine pores of sandy loam soil. Effluent bacteria concentration decreased by depth of soil column, indicating the effect of soil on bacterial filtration as a natural filter. Leaching with cold water led to decrement of flow rate and consequently increment of bacterial filtration in the two soils of clay loam and sandy loam (average flow conditions, temperature and depth) with the respective values of 100% and 68%.

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The effects of soil intrinsic properties on soil structural stability were evaluated. Soil samples (33 series) with wide ranges of properties and structural stability were collected from Hamadan province. Two structural stability indices were used: mean weight diameter (MWD) using Yoder method and De Leenheer-De Boodt index (DDI). Wetting pre-treatments (fast wetting to saturation and slow wetting to a matric suction of 30 kPa) were applied before wetting. Linear and multiple regression relations of MWD and DDI with the soil intrinsic properties (organic matter, clay, fine clay, silt, sand, calcium carbonate, EC and pH) were assessed. Results showed that organic matter had the highest impact on the two mentioned indices. Following organic matter, clay, fine clay and calcium carbonate were ranked respectively one after another. Fast wetting caused a higher aggregate break-down, due to its destructive energy, air entrapment, and non-uniform swelling of the soil whereas slow wetting exhibited better differentiation of soils with low structural stability. The findings of this research demonstrated high agreement (R2>75%) between the MWD and DDI, recommended both to be used for evaluating of the aggregate stability in Hamedan province

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In agriculture, cow manures are used to enhance soil fertility and productivity. Escherichia coli is the most common fecal coliform in cow manure and considered as an index for microbial contamination of groundwater resources. The objective of this study was to investigate the transport of Escherichia coli (released from cow manure) through the field soil. Lysimeters (with internal diameter of 20.5 and height of 50 cm) were inserted into an in situ clay loam soil. Unsaturated soil water flow was controlled at an inlet matric potential of –5 cm using a tension infiltrometer. When the steady-state flow was established, air-dried fresh cow manure was applied on the lysimeters at a rate of 10 Mg ha-1 (dry basis) and the soil-manure leaching started. Soil solution was sampled at 1, 2, 4, 6, 12 and 24 h after leaching initiation using plastic samplers installed at depths of 20 and 40 cm. Concentrations of Escherichia coli in the soil solution (C) and the influent (C0) were measured using the plate count method. Impacts of soil depth, sampling time, and their interaction on C and C/C0 were significant (P<0.01). In all leaching times, relative adsorption index (SR) was lower when both soil layers were considered and the filtration increased with soil depth. When the concentration was corrected for the second layer (i.e. 20–40 cm), the SR values in this layer were considerable and greater than those in the first layer at 4 and 6 h. The influence of surface layer was substantial in bacterial filtration however, the preferential flows especially in the initial leaching times resulted in bacterial movement towards the second layer. Temperature drop reduced bacteria release from the manure, increased viscosity of the flowing water, and consequently diminished significantly the bacteria concentration in the soil solution at 24 h. Overall, it was found that similar to surface layer, subsurface layer might have great role in bacterial filtration due to its higher clay and carbonate contents

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This study was conducted to investigate the effect of water salinity and sodicity on pore size distribution and plant-available water of two clay and sandy clay loam calcareous soils. All combinations of water EC values of 0.5, 2, 4 and 8 dS m-1 and SAR values of 1, 5, 13 and 18 (in total 16 solutions) were used to wet and dry the soil samples for five cycles. Then, water retention of the soil cores was measured at matric suctions of 0 (θs), 10 (θ10) 100 or 300 cm (θFC) and 15000 cm (θPWP). The following quantities were calculated: the difference between θ100 or θ300 and θ15000 considered as available water contrent, the θs and θ10 as macrorosity, the θ10 and θ100 as mesoporosity, and the θ100 as microrosity. The initial porosity of both soils was similar, but the greater values of pore indices and θFC, θPWP and AWC were measured in the clay soil due to clay swelling. As water EC increased, mesopores were destructed and altered to macropores and micropores. Salinity altered the mesopores into macropores due to contraction of diffuse double layer and particle’s flocculation and consequently decreased the θFC, and created new micropores which were responsible for the higher value of θPWP. These trends ultimately diminished the AWC. As water SAR increased, mesopores were destructed and altered to micropores but it did not significantly affect the macropores. With increment of SAR, both θFC and θPWP increased due to structural distruption clay swelling and dispersion resulting in increased adsorptive and interlayer surfaces. The increasing effect of SAR on θPWP was greater and more distinct so that AWC was reduced. As a result, high values of SAR of irrigation water decreased the soil available water to plants besides its toxicity and hazardous effect on plants. With increment of irrigation water salinity, the destructive impacts of SAR diminished. The influence of water quality on water retention was pronounced for the clay soil.‎

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Hardsetting phenomenon is an indicator of poor soil physical quality. Hardsetting soils are soils with high rate of mechanical strength increase upon drying and are hardened and/or compacted when dry out. It is difficult to till such soils. Hardsetting soils have additional limitations such as poor aeration at wet conditions, low infiltrability and high runoff and erosion. Most of Iran soils have low organic matter content and it is expected that hardsetting phenomenon occurs in some of these soils. This study was conducted to investigate the hardsetting phenomenon on 9 soil series collected from Hamadan province. Three types of mechanical strength consisting tensile strength (ITS), unconfined compressive strength (UCS), and penetration resistance (PR) were measured on the repacked soil samples prepared in the lab. The ITS, UCS and PR tests were done on the soil cores which had been prepared at bulk density (BD) equal to 90% of critical BD for root growth (0.9BDcritical). The effects of intrinsic properties on the hardsetting phenomenon were studied, too. Based on the suggested definition in “International Symposium on Sealing, Crusting and Hardsetting Soils” to International :::union::: of Soil Science, in which a hardsetting soil has air-dry tensile strength ≥ 90 kPa, one soil (medium-textured) out of the studied soils showed the hardsetting phenomenon at 0.9BDcritical. It might be concluded that medium-textured soils are more susceptible to hardsetting. For all of the studied soils, the ITS increased with the increase in clay content. The increasing impacts of clay and carbonate contents were also observed for the UCS and PR, respectively. Calcium carbonate could act as a cementing agent in between the soil particles and brings about the soil susceptibility to hardsetting. Moreover, the decreasing trend of all soil mechanical strengths was observed with water content increase. Slope (b) of the exponential model (fitted to the soil mechanical strength characteristic curve), as an index of hardsetting, had positive correlation with the sand content and negative correlation with the silt content. Overall, texture and calcium carbonate content are major and effective properties in terms of hardsetting phenomenon in Hamadan soils.

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This study was conducted to assess the long-term effects of soil texture and crop management on transport of lithium (Li+) and bromide (Br-) under unsaturated flow conditions. Treatments were two different soil textures of clay loam and sandy loam to be cropped with either wheat or alfalfa for 4 years. Undisturbed soil columns were taken for the steady-state flow condition using tap water prior to applying a pulse of 0.005 M (C0) LiBr solution as the influent. Four pore volumes (4PV) leaching for each column was obtained. Bromide and lithium concentrations of the effluent (C) were measured in 0.2PV intervals using bromide selective electrode and flame photometer, respectively. Relative concentrations (C/C0) of Br- and Li+ in the effluent were drawn vs. pore volumes. The results showed that the effluent concentrations were significantly affected by crop type and soil texture (in combination by soil structure). The breakthrough curves illustrated the early appearance of Br- in the effluent due to anion repulsion and retarded movement of Li+ because of surface adsorption through the soil columns. Both Br- and Li+ concentrations decreased with time and converged at low levels justifying the minor effect of macropores on continuation of leaching and final transport via soil matrix. The Br- and Li+ concentrations were higher in the effluent of clay loam soil under alfalfa due to higher structural stability compared with sandy loam soil under the same crop. It was also shown that in both soil textures the concentrations of Br- and Li+ appeared to be higher under alfalfa than under wheat, indicating the importance of crop management in contaminant transport compared with soil texture. The trends of breakthrough curves of Li+ were similar to Br- with lower concentration in effluent as a result of its adsorbtion on active surfaces.

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Organic carbon pools and carbon lability directly affect soil biological, physical and chemical characteristics. Besides, capacity of self-organization of soil is related to the organic carbon pools. Sand size fraction (> 50 µm) organic matter is more labile than silt+clay size fraction organic matter. Assessment of this organic carbon variation can be a suitable index to determine soil quality. The aim of present study was to evaluate the impact of land use change on particle size fractions of organic carbon and carbon pool index. In September 2010, soil samples were collected from the three major land use types including wetlands around the lake, wetlands converted to wheat, and alfalfa cultivations. Soil samples were collected from the 0-30, 30-60 and 60-90-cm depths in each of land use. According to the results of particle size fractionation of organic carbon in 0-30-cm layer, the highest and lowest amounts of sand size fraction organic carbon were obtained in wetland (67.01 g.C.kg-1soil) and wheat land use (24.57 g.C.kg-1soil), respectively. Land use change from wetland to alfalfa and wheat caused a decrease of silt+clay size fraction organic carbon in 0-30-cm by 48.39 and 45.14 t.C.h^-1, respectively. In the 30-60-cm layer of cultivated land, soil organic carbon storage in silt+clay size particle was more than sand size fraction organic carbon. Results showed that carbon pool index in alfalfa, and wheat land was decreased by 50 and 60% compared to wetland, respectively. And carbon management index in alfalfa and wheat was declined by 44.90% and 66.70%, respectively.

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In this study, the effect of soil structure under saturated and unsaturated flow conditions on nonreactive bromide (BR) transport was investigated. The soil structure treatments consisted of undisturbed columns (prismatic and granular structures), and disturbed columns (single- grain structure). A constant concentration (C0= 0.005 M) of bromide was supplied on the surface of the columns in a steady-state flow condition. For the saturated flow condition, a flux equal to the highest saturated hydraulic conductivity (Ks) of the columns was applied on all of the columns. To create the unsaturated flow condition, a flux equal to the half of the lowest Ks of the columns was imposed on all of the columns. The leaching of the columns was followed for five pore volumes (5PV) and the bromide concentration of the effluent was measured at 0.2PV intervals using bromide selective electrode. The breakthrough curve (BTC) of single- grain structure was sigmoidal (S-shaped) and similar to piston-capillry flow form. In contrast, BTCs of the granular and prismatic structures had a steep initial part and later gradual tailed part. The preferential pathways caused the early appearance of bromide in the leachate of columns of these two structures. Tailing of the BTCs might be due to dispersion and diffusion between mobile and immobile water fractions. In saturated condition, the bromide plume appeared earlier than that in the unsaturated condition because of domination of mass flow and rapid macroporous stream. The results demonstrated the importance of soil structure, preferential pathways, and flow conditions in solute and pollutant transport.