A. Zarei; T. Sohrabi; H. Ojaghlou; Z. Bigdeli
Abstract
Introduction: In recent years, to increase the efficiency of surface irrigation methods, new techniques such as surge irrigation have been developed. Numerous studies have shown that the surge flow can reduce water consumption in the advance phase and subsequently improve irrigation efficiency and ...
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Introduction: In recent years, to increase the efficiency of surface irrigation methods, new techniques such as surge irrigation have been developed. Numerous studies have shown that the surge flow can reduce water consumption in the advance phase and subsequently improve irrigation efficiency and water distribution uniformity. One of the factors affecting the performance of surface irrigation systems is the accurate estimation of infiltration. Due to continuous changes in the infiltration process during on-off cycles in surge irrigation, determining the empirical equation of infiltration in surge irrigation method is complex and requires time-consuming and costly field data. As a result, proper selection and parameterization of empirical equations with a simplified procedure are needed. The goal of this research was the field evaluation of the point method (surge infiltrometer) to simulate the infiltration process in advance phase surges. Materials and Methods: A field experiment was conducted at the experimental station of the College of Agriculture and Natural Resources, University of Tehran, Karaj, Iran. A ring infiltrometer was modified by connecting a pipe arm for inward and outward water flow to the ring and from the ring to the pipe to create on-off surge cycles, respectively. Water entered the ring through the inlet hole at the top of the pipe arm and water depth was recorded at different time intervals during the on-time of each cycle. Four treatments were performed for infiltration tests under surge flow, including different cycle time and ratio. Also, infiltration tests were performed under continuous flow conditions. To simulate the first (dry soil) and second irrigation conditions, infiltration experiments were conducted twice on an 8-day interval. The Kostiakov infiltration equation was corrected by applying surge factors to predict infiltration water depth for subsequent surges, using first surge data. The empirical coefficients of the Kostiakov equation were calculated by applying the two-point technique. Results and Discussion: Results of the study revealed that the infiltration data simulated by the developed Kostiakov equation matched closely with those collected from the surge-ring infiltrometer. The coefficient of determination and the root mean square error were calculated to be 0.92 to 0.97 and 0.03 to 0.16 cm, respectively. In general, the amount of cumulative infiltration in the second and subsequent surges decreased. The ratio of the infiltration depth at the end of the second to the first surge was less than 0.5. In all experiments, the depth of water infiltrated in the third surge was significantly reduced and almost reached to the final infiltration rate. As the cycle ratio increased, the cumulative infiltration also increased. However, the effect of on-off time on the infiltrated water depth in the first experiment was greater than that in the second experiment. It was concluded that in the first experiments, the surging phenomena substantially reduced water movement and the reduction in cumulative infiltration ranged from 50 to 70% during the second surge and from 59 to 85% during the third surge. The above values were determined 52 to 76% and 61 to 88% for the second experiment, respectively. A significant difference was observed between surge and continuous flow tests. The surge flow led to a 46 to 76% reduction in the cumulative infiltration depth compared to the continuous flow. The effect of surge flow was greater in the first experiments. Conclusion: One of the most important points in designing surface irrigation systems is to determine the infiltration equation parameters. In particular, the difficulty involved in the planning and design of surge irrigation systems is the prior knowledge and understanding of how infiltration changes occur during surging. The main objective of the present study was to evaluate the surge ring infiltrometer test to predict the infiltration in the second and third surges using the first surge data. The results obtained from the surge infiltrometer experiments showed that the use of surge irrigation has the potential to reduce infiltration. The observed and predicted cumulative infiltration for the second and third surges showed a good agreement. The surge-ring infiltrometer has the potential for creating an on-off mechanism and is best suited to determine the cumulative infiltration from surges for constant on-off time surge intervals.
zeinab bigdeli; ahmad golchin; saeid shafiei
Abstract
Introduction: Dynamics of organic carbon and nitrogen are controlled by several factors, including physical, chemical and biological properties of soil. Heavy metals contaminate soils and change soil properties and affect organic carbon and nitrogen dynamics. Since toxicities of heavy metals are different ...
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Introduction: Dynamics of organic carbon and nitrogen are controlled by several factors, including physical, chemical and biological properties of soil. Heavy metals contaminate soils and change soil properties and affect organic carbon and nitrogen dynamics. Since toxicities of heavy metals are different and organic carbon and nitrogen dynamics are affected by available concentrations of these metals, the aims of this experiment were to assess the effects of different levels of soil cadmium on mineralization of organic carbon and nitrogen.
Materials and Methods: To assess the effects of different levels of soil cadmium on mineralization of organic carbon and nitrogen, a factorial pot experiment was conducted using litter bag method. The factors examined were different levels of soil cadmium (0, 10, 20, 40, and 80 mg kg -1soil) and incubation periods (1, 2, 3 and 4 months) that were applied in three replications. Soil samples were artificially contaminated with cadmium to desirable levels using cadmium sulfate and the samples were placed in plastic pots and the pots incubated at constant moisture and temperature for one month. Then litter bags containing 15 g wheat residues were buried in pots and incubated for different periods of time. At the end of incubation periods, the remaining amounts of plant residues were measured and analyzed for organic carbon and nitrogen concentrations using Walkley and Black and Kjeldahl methods respectively. The decomposition rate constants of organic carbon and nitrogen were calculated using Mt = M0 e –kt equation. Organic carbon and nitrogen losses were calculated by subtracting the remaining amounts of organic carbon and nitrogen in one incubation time interval from those of former one.
Results and Discussion: The results showed that the effects of soil cadmium levels and incubation periods were significant on organic carbon and nitrogen mineralization. The losses of organic carbon and nitrogen from wheat residues decreased as the levels of soil cadmium increased. The highest and the lowest organic carbon and nitrogen losses were measured in control and treatments with 80 mg Cd kg -1 soil respectively. Increase in soil cadmium levels decreased the losses of organic carbon and nitrogen from wheat residue. The losses of organic carbon for a period of four months were 37.54, 37.21, 36.11, 35.12 and 33.69 (%) in treatments with soil cadmium levels of 0, 10, 20, 40 and 80 mg kg -1 respectively. The loss of organic carbon in the first month of incubation was (30.78%) and in the other three months of incubation was (9.74%) with a sum of (40.52%) for a period of 4 months. Similarly, the loss of organic nitrogen in the first month of incubation was 23.69% and in the other three months of incubation was 8.56% with a sum of 32.25 (%) for a period of 4 months. The highest losses of organic nitrogen from wheat straw residue were measured in treatment of control cadmium (31.64 percent) and lowest losses of organic nitrogen (23.86percent) related to treatment with 80 mg of cadmium / kg of soil. The losses of organic nitrogen, after 4 months were 31.64, 30.69, 28.68, 26.25, and 23.86 (%) when treatment of cadmium contamination of soil was 0, 10, 20, 40 and 80, respectively. The decomposition rate constants for organic carbon were 0.0076, 0.0075, 0.0073, 0.0070 and 0.0066 day -1 when soil cadmium levels were 0, 10, 20, 40, and 80 mg kg -1 respectively. The rate constants for organic nitrogen at the mentioned soil cadmium levels were also 0.0061, 0.0059, 0.0054, 0.0048 and 0.0044 day -1 respectively.
Conclusions: The results of this research indicate that contamination of soils by heavy metals increases the residence time of organic carbon and nitrogen in soils and slows down the cycling of these elements. The mineralization rate of organic nitrogen was affected by soil cadmium levels more than that of organic carbon. The amounts of organic carbon and nitrogen losses are higher in the first month of incubation than those of other months and decomposition of wheat residue had a fast and a slow stage. The results of this study indicate that due to the adverse effects of heavy metals on soil organisms, mineralization rate of plant residue carbon is slower in polluted soils compared with non polluted soils.
