JWSS - Journal of Water and Soil Science

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Tillage system effect, Conventional (CT) vs. No-Till (NT), on soil physical properties and Br transport was studied at two locations in North Carolina. The soil types were a Typic Paleudults at Coastal Plain (site 1) and a Typic Kanhapludults at Piedmont (site 2). Bulk density (BD), total porosity (TP), macroporosity (MP), and saturated hydraulic conductivity (K_s) .were measured in plant row (R), and trafficked (T) and untrafficked (N) interrows. A rainfall simulator was used to apply two early season rainfalls to 1 m² plots where KBr suspension was surface applied for Br leaching study. The first simulated rainfall event (30 min) consisted of a low (1.27 cm h^-1) or a high (5.08 cm h^-1) rate applied, 24 h after Br application. One week later, the high rainfall rate was repeated on all plots.

 Soil samples were taken two days after applying first and second simulated rainfall (a week between them) and the end of season from different depths for measuring Br concentrations. Soil physical properties were affected by both tillage system and position.

Bulk density was higher in NT versus CT and in T position versus Rand N positions. Total porosity was lower in NT versus CT but MP was significantly higher in NT. Saturated hydraulic conductivity was about 90% lower at T position versus N and R positions. Coefficient of variation was quite large, making it difficult to obtain statistical differences between tillage systems. The surface l0-cm of soil contained the highest Br concentration for depth treatments with treatment differences occurring primarily in 0 to 25 cm depth. In first and second sampling dates, more Br leached under NT versus CT system. However, there was no significant difference between the two tillage systems in Br leaching at the end of the growing Season. In site 1, Br leached more due to the coarse texture and high Ks of the soil.

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The objective of this research was to evaluate bromide leaching in a field under corn, wheat and alfalfa. Potassium bromide (300 kg/ha) was uniformly applied and 15 mm of water was sprinkled over the plots in the first and second years. Plots were leached 8 times during the first year and 9 times in the second year (each time with 100 mm of water). Soil samples were collected at 0-30, 30-60, 60-90 and 90-120 cm depths two days after each leaching practice. Bromide concentration in soil samples was measured using an ion selective electrode. Moisture content in each plot was measured using a neutron meter to a depth of 120 cm and after calculation of evaporation from soil surface, the net water applied was determined. CXTFIT software and Regional Stochastic Model (RSM) were used to simulate leaching under field conditions. The results showed that flow velocity and dispersivity of treatmens were not significantly different from the control in the first year, indicating that treatments had no effect on preferential flow. Control treatments were not significantly different in the first and second years. In the second year, flow velocity in wheat, corn and alfalfa treatments were 1.54, 1.86 and 2.21 times higher than flow velocity in the control, respectively. Dispersivity in alfalfa and corn treatments were 4.30 and 5.30 times higher as compared to the control. The increase in flow velocity and dispersivity is caused by an increase of preferential flow in the second year. The root channels remaining in soil at the end of the first year may also have increased preferential flow. After adding 25 cm of water, 30% of bromide leached from the top 50 cm soil in all plots in the first year and control plots in the second year but the values in the second year were 47, 67 and 70% of bromide leaching from the top 50 cm soil in wheat, corn and alfalfa plots, respectively.

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The objective of this study was to evaluate effects of cow manure on soil hydraulic properties and bromide leaching in a sandy loam soil (coarse loamy mixed, Typic Torrifluvents). Manure was applied at 0, 30, and 60 tha^-1 at three replications in a completely random design. Three months after manure application potassium bromide (KBr) at rate of 300 Kg ha^-1 Br was uniformly applied on the surface. Soil bulk density, porosity, organic matter, and soil moisture at18 levels of matric potentials were determined. Soil samples to the depth of 105 cm at 15-cm increments were collected after 100, 200 and 400 mm of irrigation. Soil bulk density, porosity, organic matter content, and soil moisture at different levels of matric potential increased significantly with manure application. Manure application also significantly affected the hydraulic parameters. Bromide leaching was significantly lower in plots with manure application and the greatest leaching occurred at the zero manure application treatment. The center of mass evaluation indicated a relatively similar result with measured values.

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Since performing field experiments for determining the optimum amount of water for soil desalinization is costly and time consuming, use of computer models in leaching studies has received more attention. However, the accuracy of the results of these models should be evaluated by comparison with the results of the field experiments. In this study SWAP and LEACHC models were used for the simulation of soil moisture profile and salinity, and the results were compared with those of a field leaching experiment. The SWAP model gave better results in simulating soil moisture movement and profile, compared to LEACHC model, but statistical indexes showed that both models produced satisfactory results in predicting soil moisture profile. LEACHC model gave better results in comparison to SWAP model for the prediction of soil salinity profile at different time, possibly because it takes into account different solute transport mechanisms such as advection, diffusion, dispersion and also chemical interactions such as adsorption, precipitation and dissolution. In spite of the differences between predicted and measured values of salinity in the initial stages of leaching process, both models were able to predict the trend of leaching process with an acceptable accuracy.

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Nitrate leaching from agricultural lands can pollute groundwater, and the degree of pollution caused significantly depends on agricultural practices implemented on farms. Field studies required to evaluate the effects of various agricultural management strategies on nitrate leaching are expensive and time consuming. As a result, it is suggested to use crop models to simulate the effects of management practices on nitrate leaching. Plant growth models such as DSSAT software package can simulate daily plant growth and development, and also are capable of simulating daily nitrate leaching and nitrogen uptake by plants. However, it is required to evaluate the performance of any model before using it for any specific region. In this study, the performance of nitrogen balance model of DSSAT software package was evaluated to simulate nitrate leaching from the root zone of silage maize at different levels of applied water and nitrogen fertilizer. The experiment consisted of three levels of nitrogen fertilizers, including zero, 150 and 200 kg N ha-1 and four levels of applied water 0.7SMD (soil moisture depletion), 0.85SMD, 1.0SMD and 1.13SMD. Nitrate-nitrogen leaching from 36 plots at the 60 cm depth during the growing period was measured by soil moisture suction equipment (ceramic suction cups, CSC). After calibrating the model by using field data, its performance was evaluated to simulate nitrate leaching. Maximum amount of N leaching 8.4 kg N ha-1 was obtained from over irrigation treatment with the application of 150 kg nitrogen per hectare. The model simulated nitrate leaching for this treatment as 7.8 kg N ha-1. The model consistently underestimated the nitrate leaching however, it followed the behavior of nitrate leaching during the growing season. In deficit irrigation treatments, the nitrate leaching was very low and close to zero and the model simulated the same result accordingly. The results showed that the model, in addition to phenological stages and performance indicators, can simulate nitrate leaching from the root zone and could be used to evaluate the effects of various irrigation and fertilizer management strategies on nitrate leaching.

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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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The reclamation of salt-affected soils which occur on 831×106 ha can be effective in increasing agricultural production. Cultivation of plant species which are resistant to salinity can improve the soil by increasing the solubility of calcite and releasing the calcium in soil solution. This study was conducted as a column experiment with a saline-sodic soil (SAR = 23.8, EC= 12.88 dS m-1, pH= 7.7, CaCO3= 15.15 %). Three plant treatments including Sesbania acuelata, Cyanodon dactylon and Rubia tinctorum, and three chemical treatments including gypsum in two levels (50% and 100% gypsum requirement) and sulfuric acid with a control were arranged. All treatments were replicated 3 times. The soil columns were similarly leached by 41 liters of tap water during 30 days in 8 stages. After leaching, SAR and EC in soil, the amounts of sodium in leachate and total amount of sodium in plants shoot were determined. Results showed that the SAR was decreased compared to control by the plant treatments and the chemical amendments by about 59% and 65%, respectively. Moreover, two plants of Cyanodon dactylon and Rubia tinctorum had maximum amount of leachate sodium, which shows an impressive role of these plants in dissolution and leaching of exchangeable or sediment sodium in comparison with the other treatments. According to salient performance of phytoremediation in improvement of physicochemical properties of soil compared to chemical amendments, phytoremediation can be recommended as a profitable low-cost and effective method for remediation of saline-sodic soils.

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In this study, the effect of clinoptilolite zeolite, as a soil amendment, on the parameters related to water and nitrogen movement in soil was investigated. Parameter and uncertainty estimation in the unamended (control) and amended soil (Z), was performed using the sequential uncertainty fitting algorithm (SUFI-2) which is linked to LEACHN (in the LEACHN-CUP software). The goodness of prediction uncertainty was judged on the basis of P-factor and R-factor. P factor, R-factor, and Nash-Sutcliffe coefficient (NS) was obtained 0.71, 0.76, and 0.92, respectively, in the prediction of the accumulated drainage from control. The results in prediction of the accumulated drainage from Z treatment using hydraulic parameters obtained in control were satisfactory (P-factor = 0.87, R-factor = 0.78, and NS = 0.87). P-factor, R factor, and NS were 0.87, 1.36, and 0.91, respectively, in the prediction of NO3-N leaching at control. According to the P-factor and R-factor values (P-factor = 1, R-factor = 2.46), application of the control parameter ranges in the prediction of NO3-N leaching at Z treatment produced a large uncertainty. By adjusting the parameters in control for zeolite amended soil, the estimated values for denitrification rate, distribution coefficient, and soil/solution NO3-N nitrification rate were greater in zeolite-amended soil compared to control.

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The conventional application of nitrogen fertilizers via irrigation is likely to be responsible for the increased nitrate concentration in groundwater of areas dominated by irrigated agriculture. This requires appropriate water and nutrient management to minimize groundwater pollution and to maximize nutrient use efficiency and production. To fulfill these requirements, drip fertigation is an important alternative. Design and operation of drip fertigation system requires understanding of nutrient leaching behavior in cases of shallow rooted crops such as potatoes, which cannot extract nutrient from lower soil depth. This study deals with neuro-fuzzy modeling of nitrate leaching from a potato field under a drip fertigation system. In the first part of the study, a two-dimensional solute transport model (HYDRUS-2D) was used to simulate nitrate leaching from a sandy soil with varying emitter discharge rates and various amounts of fertilizer. The results from the modeling were used to train and validate an adaptive network-based fuzzy inference system (ANFIS) in order to estimate nitrate leaching. Radii of clusters in ANFIS were tuned and optimized by genetic algorithm. Relative mean absolute error percentage (RMAEP) and correlation coefficient (R) between measured and obtained data from HYDRUS were 0.64 and 0.99, respectively. Results showed that ANFIS can accurately predict nitrate leaching in soil. The proposed methodology can be used to reduce the effect of uncertainties in relation to field data.

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The present study was conducted to increase phytoextraction efficiency of Festuca ovina L. in lead contaminated soil in the EDTA-assisted (0, 1.5, 3, 1.5+1.5, 3+3, 6 mmol kg&minus;1), assess the best time of plant harvesting to increase Pb uptake and method of EDTA application to reduce Pb leaching risk. The results revealed that the greatest Pb uptake was observed in 3EDTA treatment. Therefore, 3mmolkg-1 was used in the second step for assessing harvest time for 15, 30 and 45 days. Results showed that the concentration of Pb in plant tissues was increased with the passage of time and the best harvest time to achieve maximum removal of Pb was 60 days of the first harvest. In the third step to reduce leaching of Pb-chelate, 3mmolkg-1 EDTA in five ways of single, double, triple, quadruplet, quintuplet were added to the soil. The results indicated that under quintuplet application, Pb content reached its minimum concentration in the soil and in the plant organs, the Pb concentration was maximum and metal concentration in the plant organs did not vary significantly when triple, quadruplet and quintuplet dosages were added (p<5%). Overall, optimum phytoextraction of F. ovina L. and Pb leaching reduction were achieved when 3mmol kg&minus;1 EDTA was added in quintuplet dosage and the plant was harvested at the end of growth stage.

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Consequences of heavy metal accumulation in soils are of great concern. One way of decontaminating heavy metals from soils is using chelating agents, particularly EDTA. In this research, three contaminated soils (with total concentration of these metals of 10.5, 55.8 and 80.6 mmol kg-1) were collected from the surface layer of the lands surrounding a zinc-lead smelting plant in Zanjan province. The extent of Zn, Pb and Cd release by Na2H2EDTA (100 mmol kg-1 of dry soil) from these soils in column leaching experiments (both continuous and pulse addition methods) assembled into half of saturated hydraulic conductivity was assessed. In preliminary experiments, the leaching was stopped due to a drop in hydraulic conductivity. Therefore, the continuous addition method was performed with calcium nitrate as the background solution and the pulse addition method was conducted using this background solution coupled with pH adjustment to 8. Based on the results, the percentage removal of Cd as well as Pb was relatively the same for the two addition methods while the removal of Zn was 13% on average higher in the continuous addition method than in the pulse addition method. For both methods, the removal efficiencies followed the order of complex stability constants (as Pb>Zn>Cd) in a limited concentration range of EDTA to complex heavy metals. Furthermore, in contrast to Cd and Pb, a direct linear relationship was found between the percentage removal of Pb and its total amount in the soils. Surprisingly, the Pb concentration was on average only about one-twentieth of the Zn concentration. The breakthrough curves of both methods showed the mobility order of Cd>Zn>Pb. In general, it seems that the removal pattern of soil heavy metals is dependent not only on the soil type but also on the removal method.

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Chemical fertilizers have important role in modern agriculture, and in the other hand led to rigid environmental pollution. Urea fertilizer is one of the most widely used and least expensive nitrogen fertilizers in Iran. Since it is high solubility in water a significant of it, if irrigation or precipitation is heavy, easily washed and led to change to change the quality of groundwater, rivers or seas. Hence, in this study the effects of deficit irrigation and fertilization on pollution using SWAT for Tashk-Bakhtegan basin (land area between Dorudzan dam and Khan Bridge) were simulated. This model by comparing model outputs with actual observations of hydrological, crop yield (wheat, barely, corn and rice) and nitrate by using SUFI2 algorithm in SWAT_CUP software were calibrated and validated. Then the calibrated model used to evaluate different management strategies (e.g. irrigation and fertilizer amount). When the impacts of different levels of urea (0 to 70 percent reduction in urea application) were modeled, yield of these crops reduced between 1 to 27, 0.8 to 24, 0.42 to 21 and 0.47 to 9 percent for wheat, barely, corn and rice, respectively. However, these tends to decline nitrate leaching 16-81, 18-80, 15-85 and 12.5 to 83.6 percent, respectively for these crops.  Therefore, by comparing yield and nitrogen loss changes, this result can conclude that a significant reduction in nitrogen loss by minimum cost on yield can achieved by optimize fertilizer application. 

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