JWSS - Journal of Water and Soil Science

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Saturated hydraulic conductivity (Kfs) and macroscopic capillary length of soil pores are important hydraulic properties for water flow and solute transport modeling. Measuring these parameters is tedious, time consuming and expensive. One way is using indirect methods such as Pedotransfer functions (PTFs). The objective of this research was to develop some PTFs for estimating saturated hydraulic conductivity and inverse of macroscopic capillary length parameters (*). Therefore, the coefficients, Kfs and * from 60 points of Azadegan plain in Shahrekord were measured using single ring and multiple constant head method. Also, some of the readily available soil parameters from the two first pedogenic layers of the soils were obtained. Then, the desired PTFs were developed using stepwise multiple linear regression. The accuracy and reliability of the derived PTFs were evaluated using root mean square error (RMSE), mean error (ME), relative error (RE) and Pearson correlation coefficient (r). The highest correlation coefficients of 0.92 and 0.72 were found between Kfs-bulk density and *-bulk density, respectively. There was no significant correlation between soil particle size distribution and Kfs and *. This can be related to the fact that most of the soil samples were similar in texture and macro pores. The most efficient PTFs in predicting Kfs and * could explain 85 and 66 percent of the variability of these parameters, respectively. All the derived PTFs underestimated the Kfs and * parameters.

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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.

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Usually, dry soil readily absorbs water .However, not all soils display such characteristics. Some soils (hydrophobic soils) show resistance to wetting. Because of the importance of this subject and lack of research, we evaluated the effect of heating on water repellency and some of soil physical and chemical characteristics. So soil was combined with compost and heated at deferent temperatures, 100, 200, 300, 400 and 500 °C for 30 minutes in an oven or muffle furnace. The results showed that control treatment and heated soil at 300 °C had WDPT and MED 45 (s), 17% and 80 (s), 23% respectively. So, little water repellency was present prior to heating the soil. When soil was heated up to 300°C, intense water repellency resulted, but it was abruptly eliminated by increasing the heating. The soil texture was changed from loam to sandy loam at high temperatures (400 & 500 °C) and the sand percentage was increased. Organic matter decreased by increasing the temperature. Amount of pH decreased up to 200 °C and then increased at 500°C because of increasing ash in soils. Diminution of mineral and organic matter caused EC to decline in all the heated soils.

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Soft computing techniques have been extensively studied and applied in the last three decades for scientific research and engineering computing. The purpose of this study was to investigate the abilities of multilayer perceptron neural network (MLP) and neuro-fuzzy (NF) techniques to estimate the soil-water retention curve (SWRC) from Khozestan sugarcane Agro-Industries data. Sensitivity analysis was used for determining the model inputs and appropriate data subset. Also, in this paper, the van Genuchten and Fredlund and xing models were used to predict SWRC. Measured soil variables included particle size distribution, organic matter, bulk density, calcium carbonate, sodium adsorption ratio, electrical conductivity, acidity, mean weight diameter, plastic and liquid limit, resistance of soil penetration, water saturation percentage and water content for matric potentials -33, -100, -500 and -1500 kPa. The results of this study in terms of various statistical indices indicated that both MLP and NF provide good predictions but the neural network provides better predictions than neuro-fuzzy model. For example, using MLP and NF models values of NMSE at prediction θs, θr, α, n and m in Fredlund and Xing equation corresponded to (0.059, 0.065), (0.154, 0.162), (0.109, 0.117), (0.129, 0.135) and (0.129, 0.145), respectively. Furthermore, α and n parameters at the first depth, and θr and α parameters at the second depth in Fredlund and Xing equation were estimated with higher accuracy compared with equivalent parameters in van Genuchten equation

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The use of organic matter such as urban sewage sludge may help sustainable soil fertility via improving the physical, chemical and biological soil characteristics. The main purpose of this study was to determine the effect of urban sewage sludge on chemical properties, soil basal respiration and microbial biomass carbon in a calcareous soil with silty clay loam texture. Therefore, three levels of water repellency (zero, weak and strong) were artificially created in a silty clay loam soil by adding urban sewage sludge (S0=0:100; S50=50:50 and S80=80:20 sludge weight: soil ratio). Water repellency was determined by water drop penetration time (WDPT) method. Also some chemical properties such as soil acidity (pH) and Electrical Conductivity (EC), Soil Organic Carbon (OC), soluble sodium (Na⁺) and soluble potassium (K⁺) were measured. The samples were incubated at 23-25 ºC for 30 days and their moisture was maintained at 70-80 % under field capacity and soil basal respiration and microbial biomass carbon of incubation period were evaluated. The results showed that the effect of urban sewage sludge on chemical properties was significant (P ≤0.0001). The application of urban sewage sludge led to significant increase in basal respiration (16 and 27 times) and microbial biomass carbon (15.2 and 26.5 times) in the water repellency soils (S50 and S80) compared to control soil. The observed positive effect of sewage sludge might be due to a high content of organic carbon and nutrients in urban sewage sludge and decrease in the labile organic matter and nutrients during incubation period.
 
 

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