جستجوی مقالات مرتبط با کلیدواژه "شمال غرب ایران" در نشریات گروه "آب و خاک"

Accurate determination of the amount of incoming solar radiation at Earth’s surface is important for both climate studies and solar power applications. Satellite-based datasets of solar radiation offer wide spatial and temporal coverage, but careful validation of their quality is a necessary prerequisite for reliable utilization. In this study, daily SARAH satellite data was used to estimate daily solar radiation at weather stations in northwest Iran in 2009 and 2010. According to the results, SARAH radiation data had a high accuracy in estimating solar radiation at all five stations. At the Tabriz station, the error of estimation of radiation was less than that of other stations. According to GSD evaluation criteria, in each station, the estimation error in summer and winter was the lowest (GSD = 6.2 - 12.5) and the highest (GSD = 18.2-25.2) respectively. The results showed that factors such as topography and snow cover affect the accuracy of SARAH radiation data estimation.

Dryland farming is a major agricultural practice in northwest of Iran. Accurate understanding of soil fertility status is one of the basic needs of dryland agricultural system. Soil chemical properties play an important role in soil fertility. Assessing soil fertility is an essential need to identify environmental-friendly strategies leading to more sustainability in agricultural systems. Unfortunately, plant nutrients are insufficient in many dry farming areas of Iran, or soil conditions do not allow plant to uptake certain nutrients. Therefore, soil scientists focus on using commercial fertilizers and manures (rotation system and conservation tillage) to add nutrients and organic matter to soil. The fertility of soils can be further improved by cultivation of cover crops through adding organic matter to the soil which leads to a healthy soil with more macro-nutrients and micro-nutrients content and better structure. Therefore, evaluation of soil fertility is a basic tool for decision management in drylands and estimation of capacity of soil to maintain a continuous supply of plant nutrients for a crop production. Evaluation of soil fertility in drylands of the northwest Iran have two objectives 1) Assess nutrient status of soil-crop system 2) Diagnose suspected nutrient imbalances.

This study was carried out in northwest of Iran drylands including: west Azarbayjan, east Azarbayjan, Kurdistan and Kermanshah provinces. A total of 674 soil samples were collected from farmer’s fields in east Azarbayjan, west Azarbayjan, Kurdistan and Kermanshah 414, 97, 90 and 73 samples, respectively. The surface soil samples were taken from 0-25 cm depth in each field before the sowing of the rainfed plants in autumn by composite sampling method. After collection, soil samples were immediately dried, grounded, screened through 2 mm sieve, labelled and stored in plastic container. The samples were analyzed for 12 chemical and physical parameters include: soil texture (hydrometer method), pH (saturation paste) and EC (saturated extract), organic carbon, Total N (Kejeltak), calcium carbonate equivalence (acid-neutralizing value), phosphorus (Olsen), potassium (sodium bicarbonate extracted) and iron, zinc, Mn and copper (DTPA extracted). Soil samples were categorized as low, medium and high on the basis of their availability in soils by two Gomes (1985) (equation 1) and common (nutrient classification by critical level method for dryland wheat) methods. Low Medium Equation (1) High Where, , and SD are soil property, average of soil property in all area and standard deviation of soil property, respectively. In order to compare the levels of soil fertility of one province with those of another it is necessary to obtain a single value for each nutrient. Nutrient index value (NIV) was calculated by Parker et al., (1951) method (equation 2) for soil samples of each province or district from the proportion of soils under low, medium and high categories using following equation: Equation (2) Where, , and are number of samples testing low, medium and high category in each province, respectively. If the NIV is less than 1.67, the soil fertility status is low, the value of 1.67-2.33 reveals optimum fertility (sufficient nutrients). The values greater than 2.33 denote high fertility status.

The results showed that, the Gomes (1985) method could not classify the soil properties in all studied regions (population) correctly, due to the tends towards central limit theorem (optimal condition). Calculation of NIV showed that using conventional method (critical levels) for classification of soil properties was better than Gomes (1985) method because it was more compatible with the field conditions. The results revealed that soil salinity and calcium carbonate did not seriously make problems in dryland areas. However, increasing the amount of calcium carbonate decreased soil phosphorus, potassium, Fe, Mn, Zn and Cu, significantly. Soil phosphorus and Zn were more influenced by increasing calcium carbonate. Assessment of soil fertility status by NIV showed that, soil organic matter was low (deficient) in west and east Azerbaijan with 92 and 69 percent of those areas. But total nitrogen was optimum (sufficient) in all areas with 98 percent averagely (except east Azarbayjan). This is mainly due to the application of nitrogen fertilizers in wheat drylands and conservation tillage system in some areas. Soil phosphorus was evaluated low in two west Azerbaijan (81%) and Kermanshah (67%) provinces, but in east Azerbaijan (68 %) and Kurdistan (85%) were sufficiency or high for wheat production. Potassium was more than sufficiency (high) in 90 percent of all areas averagely. Micronutrients deficiency were observed in some provinces. The results showed the deficiency of Fe with 100 and 69 percent in west Azarbayjan and Kurdistan, respectively. Deficiency of Mn with 89 percent of west Azarbayjan, Zn with 84 percent in east Azarbayjan and Cu with 100 and 87 percent in west and east Azarbayjan were also the other obtained results of this study, respectively. The results of present study suggested that nitrogen and phosphorus fertilizer applications can also be important in micronutrient management in dryland areas.

It can be concluded that the capability of critical level method is better than Gomes (1985) method in classification of soil properties. Nutrient index value (NIV) method can efficiently evaluate soil fertility status in Iran drylands. According to this research, Fe, Zn and Cu nutrient deficiencies are just as important as P and N deficiencies in Iran dryland areas.

Evapotranspiration is one of the key elements of hydrological cycle. This parameter plays a crucial role in different water related studies such as agricultural water management, environmental energy budget, water balance of watersheds, water reservoirs and water conveyance structures (such as channels, dams, barriers and so on). Increasing greenhouse gases has led to increased atmosphere temperature. Such changes in air temperature and other atmospheric parameters caused some natural hazards in many regions. One of the important parameter impacted by climate change is potential evapotranspiration. Different studies conducted in the recent decade to detect the monotonic trends and abrupt changes in meteorological parameters. Most of them are on trend analysis of meteorological and hydrological parameters. In the recent years, monotonic trend analysis of reference crop evapotranspiration (ET0) has interested many investigators around the globe. Many investigators attempted to find the possible reasons of trends in ET0. In many cases, this is accomplished by sensitivity analysis of ET0 to different meteorological parameters. Other investigators attempted to model ET0 using the hydrologic time series modeling. Detection of sudden change point in different time series including ET0 is very important in changing climate. However, in spite of tremendous studies on monotonic trend analysis, it seems that no serious work has been conducted to detect abrupt changes in ET0 in Iran, especially in west and northwest of Iran. This region has fertile soils and produce an important portion of cereal yields of Iran, thus providing water to agricultural section is crucial under climate change. Therefore, the main objectives of this study were i) estimation of ET0 values in the selected stations in west and northwest of Iran using the FAO-Penman Monteith method, and ii) detection of significant change points in ET0 time series using the nonparametric Pettit test.
The 32 synoptic stations were selected in this area for analysis. Data needed for this study were gathered from IRIMO. Meteorological parameters were daily records of maximum air temperature, minimum air temperature, sunshine hour duration, wind speed, and relative humidity. The ET0 values were estimated using FAO-56 Penman-Monteith model. In order to detect the significant change point the non-parametric, Pettitt test was used. Both monthly and annual time scales were used in analysis. The null hypothesis of test is there is no sudden change point in the time series. We calculated the p-values for time series under test and compared it with significance level (5%). If the calculated p-value was less than the significance level (0.05), then the null hypothesis is rejected, and the alternate hypothesis (i.e. there is a significant sudden change point in the time series) will be accepted.
The results showed that around 60% of the monthly time series had significant sudden change points. For instance, Urmia showed significant abrupt changes in ET0 for all months. Specifically, more than 86 and 78 % of the stations experienced sudden change in ET0 in March and August, respectively. The strongest abrupt change observed at Maragheh, in which the difference in monthly ET0 before and after the change point date reached to about 45 mm. It is worth to mention that all detected sudden changes had upward direction. In annual time scale, more than 80 % of the stations showed significant abrupt changes in ET0. Among all stations, Sararoud- Kermanshah showed a large difference in mean annual ET0 for the subseries of before and after the change point date which was approximately 235 mm. In annual scale, all sites (except Sahand and Parsabad) experienced upward ET0 abrupt changes. In order to inspect the reason this change, we plotted different meteorological parameters time series. The results indicated that the wind speed showed negative trends (except for two stations) leading to ET0 increase. Furthermore, it was found that almost all stations exhibited increasing trends in air temperature. These changes caused an increase in ET0. The most prominent abrupt change date in ET0 time series was found for the years from 1995 to 1998. For example, in February, April, May, and June, monthly ET0 time series suddenly increased in 1998, which were statistically significant (p The sudden change in ET0 was confirmed in west and northwest of Iran. According to the results, ET0 time series (in monthly or annual time scales) exhibited upward sudden changes. Such changes in ET0 time series ring the alarms and decision makers should be, therefore, cautious in management of water resources.

Nowadays, with a growing population and the increasing trend of recent droughts, scientific attention to the mentioned drought phenomenon is inevitable. In this study the Stream flow Drought Index (SDI) was used for analyzing the hydrological droughts over the last three decades in the northwest of Iran (Ardebil province). The periods of 3, 6, 9, and 12 months and also 5 and 10 years were selected for the spatiotemporal monitoring of the hydrological droughts. The temporal drought analysis showed that the most of drought events over the reference periods have occurred in the last 15 years. In other words, there was an approximately normal status in the most of stations in the first study period of 15 years. The most severe hydrological droughts occurred in the Poleh Almas and Poleh Soltani on the Balokhlo-Chai and Khiav-Chai gauging stations, respectively, at the 3- and 6-month scales in 2010. The results revealed that the most severe hydrological drought periods occurred in 2010.

Fractal dimension (Dm) of particle size distribution (PSD) has been introduced as a predictor of soil texture-related properties. This study investigates relationships between Dm and some of the physical properties of soils. Samples from 36 soil series with varying properties were collected from northwest of Iran. Sand fraction was determined by sieving, and silt and clay fractions by the hydrometer methods. Fractal dimension of PSD was computed by Bird et al. model. Organic matter content and total porosity of the samples were measured by wet oxidation and gravimetric methods, respectively. A rainfall simulator with drainable tilting flume (1×0.5 m) at 9% slope was employed and the effective hydraulic conductivity (Ke) was calculated at 20, 37, and 47 mm h-1 rainfall intensities. Statistical analysis showed that in contrast to significant and positive correlations occurred between Dm and each of clay (0.963**), silt (0.371**) and total porosity (0.642**), the correlations between Dm and either of sand (0.748**) or geometric mean diameter of particles (dg) were negative (0.748**). Therefore, Dm had significant relations with soil textural fractions and textural classes, and might be used as an integrating index in modeling studies. Results also showed that greater Dm was associated with greater self-similarity in pore size distribution.