JWSS - Journal of Water and Soil Science

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Increasing application of herbicides such as atrazine raises concerns about soil and groundwater pollution. This study investigated spatial and temporal variation of atrazine concentration and its transportation in the Daneshkadeh soil series (Fine, mixed, mesic, Calcixerollic Xerochrepts) at the experimental field of Agricultural College, Shiraz University. The risk of soil and water contamination due to applying atrazine was also assessed. The PRZM-2 model was evaluated for the simulation of the atrazine concentration. The experiment had 3 plots, 209 m² each (19 by 11 m). Atrazine was applied on corn at a rate of 3.5 kg a.i./ha per plot. During the growing season, soil samples were collected from each plot 7 times through 1 m soil depth with 0.10-m increments. The observed data showed temporal reduction of atrazine concentrations in the soil profile. The maximum depth of atrazine traced was about 50 cm below the soil surface. Statistical parameters ME, RMSE, EF, and CRM were obtained to compare PRZM-2 predicted and observed soil residue concentrations. For all data, the mentioned parameters were calculated and found to be 2.78 mg/kg-soil, 12.73 mg/kg-soil, 0.49, and 0.25, respectively. The simulation results were in close agreement with the observed data. Therefore, PRZM-2 could be used for simulation of atrazine transport and groundwater pollution.

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In this research the effect of Super Absorbent Polymer (SAP) on the crop growth, wilting point, sunflower survival, water holding capacity, and irrigation interval was investigated. The experiment was conducted with different concentrations of absorbent hydrogel (Igeta): 0% (control treatment), 0.05%, 0.1%, 0.2%, and 0.3% (w/w). The soil textures were sand, loam, and clay. The experiment was a completely randomized design with three replications. The results of this research are: 1- Adding of Igeta to the soil changed solid, liquid, and gas phases. Application of 0.05%, 0.1%, 0.2%, and 0.3% (w/w) of Igeta increased the volume of clay, loam and sand soils between 10-40% , 5-32% and 9-37%, respectively. 2- With application of Igeta, absorption of nutrients (N, P, and K) was increased. Maximum absorption nutrients occurred at the level of 0.05%, 0.1%, and 0.3% with confidence level of 90% for clay, loam, and sandy soils, respectively. 3- Igeta increased water holding capacity and irrigation intervals. Increasing in irrigation interval was between 30-130% in clay, 60-120% in loam, and 150-300% in sandy soils. Water saving in clay, loam, and sandy soils was 30%, 40%, and 70%, respectively. 4- at the level of 0.3% Igeta, starting time of temporary wilting point was delayed from 4 to 10 days (150%) in clay and loam soils, and from 4 to 12 days (200%) in sandy soil. The starting time of permanent wilting point was delayed from 8 to 12 days (50%) in clay, 7 to 12 days (71.4%) in loam, and 9 to 14 (55.5%) days in sandy soils. Therefore, application of Igeta delayed starting time of permanent wilting point between 50-71% and temporary wilting point between 150-200%.

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In this research, the hydraulic behavior of two kinds of envelopes including synthetic envelope, PP450 and gravel envelope with USBR standard in two soil tank models with silty loam texture was investigated. Three water heads including 55, 75 and 105 cm (water logging) from drain level were used. The discharge of pipe drain in the steady state condition for gravel envelope and at 55, 75 and 105 cm water heads was 188.9, 172.0 and 897.0% more than those in PP450, respectively. Envelope hydraulic conductivity rates at gravel envelope for 55, 75 and 105 cm water heads were 24.6, 14.0 and 21.2 times higher than those in PP450, respectively, and gradient ratios in these water heads for gravel envelope were 14.5%, 2.8% and 14.2% lower than those for synthetic envelope. There were also different behaviors in the two kinds of envelopes for hydraulic conductivity and entrance resistance of pipe and envelope in 55 and 75 cm water heads relative to 105 cm. In general, according to the measured parameters in this research, gravel envelope showed a better performance.

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Evaluation of pollutant transportation in soil is important from different environmental aspects such as soil and groundwater contamination. The purpose of this study is to measure 2, 4-D concentrations in a silty loam soil under two different treatments (normal and deficit irrigation) in a corn field and simulate the results using the PRZM-3 and LEACHP models. Total concentrations of 2, 4-D in the soil profile in 8, 13, 23, 30, 37, and 57 days after application for normal irrigation were 18.5, 16.36, 11.67, 10.47, 8.47 and 3.2 mg kg^-1, respectively. For these dates, PRZM-3 model simulated 18.5, 16.36, 11.67, 10.47, 8.47 and 3.2 mg kg^-1 of 2,4-D, respectively and LEACHP model simulated 23.34, 20.93, 16.7, 16.3, 12.9 and 11.41 mg kg^-1 of 2, 4-D, respectively. Total concentrations of 2, 4-D in the mentioned dates for deficit irrigation were 20.2, 16.7, 11.22, 10.05, 8.8 and 7.3 mgkg^-1, respectively. For these dates, PRZM-3 model simulation results were 21.9, 19.89, 14.2, 10.62, 9.6 and 8.22 mg kg^-1, respectively and LEACHP model simulation results were 25.22, 21.3, 19.43, 18.58, 18 and 16.27 mg kg^-1, respectively. The simulation results showed that performance of PRZM-3 model was better than LECHM model in both treatments. In this research, the half-lives of 2, 4-D for 0-10 cm and 10-20 cm of soil depth were 7 and 33 days in a normal irrigation, and 9 and 34.65 days in a deficit irrigation, respectively.

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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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The uniformity parameters in drip irrigation system are influenced by the slope of manifold and therefore, the evaluation of drip irrigation systems is important in slopping lands. In this research, different slopes of 0.2, 6, 11, 16, 20 and 25% were applied on the ground surface and manifold of drip irrigation system with diameters of 50, 63 and 75 mm and length of 70 m were installed on these uniform slopes. The lateral pipes with 16 mm diameter and 40 m length were placed on the contour lines and connected to manifold bilaterally. The results showed that in the normal emitters in above slopes, the qv(avg) values were 289, 6740, 46, 135, 38 and 27 percent, respectively, qv(max) values were 222, 48, 53, 90, 27 and 9 percent, respectively, and the CV values were 300, 114, 33, 140, 63 and 25 percent, respectively, higher than compensating emitters. However, in the normal emitters in above slopes, the EU values were 33, 34, 12, 25, 17 and 9 percent, respectively, EUa values were 26, 23, 6, 21, 15 and 13%, respectively, UC values were 17, 16, 4, 13, 14 and 9%, respectively, and US values were 10, 8, 2, 8, 5 and 4 percent, respectively, less than compensating emitters. Therefore, even in high slopes (20 and 25%), the irrigation efficiency in compensating emitters were better than normal emitters. The relationship between slope and discharge of emitters represented small changes in discharge of compensating emitters in sloping lands.
 

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