Desert
Volume:14 Issue: 2, Summer - Autumn 2009

Determination of the relationships between soil and plant cover indispensible in the in planning and management of the arid regions, the aim being to revitalize plant cover, conserve soil and to combat desertification. Among factors affecting plant cover, particularly in arid and semiarid areas are soil traits. During the present study, the effect of Haloxylon aphyllum Cultivation on soil physiochemical properties (at different depths) was investigated. A split plot design was employedin the study, in which cultivated and non-cultivated areas were considered as inter-related factors, whereas soil depths of(0-10), (10-30) and (30-60) cm as intra- related factors. Soil texture, EC, pH, nitrogen, phosphorous and organic matter was assessed. Soluble salts of Na, Ca, Mg, Cl, K, carbonate and bicarbonate were measured. Haloxylon aphyllum has led to a significant difference between Ca, Mg and bicarbonate in the first layer as compared with the third. A significant difference has been observed between nitrogen in the first soil layer in comparison with that in the second layer. Significant differences were also observed among all Haloxylon aphyllum cultivated soil layers as to the contents of Soluble K, absorbable K as well as phosphorous.

To identify critical sediment sources in large catchments, using easily available terrain information at a regional scale, a methodology was developed to obtain a qualitative assessment necessary for environmental management. Fargas et al method was employed in the research. The study was carried out in one of the sub-basins of Hableh Rood basin called Dehnamak in the arid and semiarid climate of Iran. The main objective of the model is to use basic terrain data related to the erosive processes that contribute to the production, transportation and accumulation of sediments throughout the main water paths in the watershed. This model is based on a selection of homogeneous zones regarding drainage density and lithology, achieved through interrelating the basic units based on a rating system. The values of drainage density are rated according to an erosion class. The lithology is rated by erosion indexes, adapted from FAO (1977). The combination and reclassification of the results brings about five qualitative classes of sediment risk according to Fargas et al (1997). The advantage of this method is that only two main factors of erosion, namely lithology and drainage density are employed in it, and these factors are available in our geological and topographic maps in Iran. This methodology has been employed for studying the watershed Dehnamak in NE Iran with an area of 248 km2. The mapping scale was 1:50000 and the model implemented through a vector GIS (Arc View). The validation was carried out through interpretation of aerial photos and fieldwork which revealed a viability of 75.15%. The tested methodology has been proven useful as an initial approach for erosion assessment and soil conservation planning at regional level, as well as for a selection of priority areas where further analyses can be made to finally manage the environment.

The most usual type of petroleum mulch, which has been successfully used to combat desertification in large area in Iran for more than thirty years, is produced by heavy residue petroleum cuts. The petroleum mulch consists of a wide range of different heavy hydrocarbons such as Polycyclic Aromatic Hydrocarbons (PAHs). PAHs are present at low level in petroleum mulch, where there is contact with water and soil and the potential for transferring of compounds into environment. Some of PAHS especially benzo (a) pyrene (BaP) have been recommended for determining and comparing with standard criteria on causing cancer .Although Iran has a long domestic experience in sand dune fixation by using petroleum products but so far there is no proper research in probable effects of using petroleum mulch on environment either in Iran or any other involved countries. In this study it was assumed that rainfall and temperature would affect mulch disintegration process, then considering these parameters, different climatic zones in three provinces -Khuzestan, Kerman and Sistan - were selected and samples were prepared from several sites of any provinces, both in mulch-sprayed sites and non-sprayed sites (observation). In order to estimate the content of PAHs, several soil samples were taken in different depths from the above-mentioned sites. Quartering Procedure selected the soil samples beneath mulch layer and the PAHS analysis was performed by solvent extraction and HPLC method with UV fluorescence detection and results were compared to standard criteria. The results indicated that the content of PAHs and mostly BaP in petroleum mulch and soil samples beneath mulch layer are less than the permitted limit in national standards. This component, in the depth of 5 cm, decreased to 1/40 of the initial even after years. Then, it shows very low penetration. Therefore, the petroleum mulch and contaminated soils can be considered as safe materials.

This study was conducted to identify drought event and its emerging regions in Markazi desert, Iran with focus on Semnan province in a 30 years statistical period. In this research, 61 stations having adequate data selected and used after extracting annual statistic from monthly and daily data. Standardized precipitation index values for each station were calculated and classified. The Results have shown that there was drought condition in 17 studied stations. Also among 44 stations with no drought condition, there was one humid year in 20 cases. Khareh sarlazor station has the first position of drought and humid condition among other stations, with 10 drought years and 5 humid years. The number of common years with normal condition is 3 years and the most extensive drought in 1999 has occurred in 10 dry stations and 1 very dry station. The existence of common trend of variation using study of correlation among stations has resulted in determination of 7 groups which these results can be useful according to temporal distance of one or two years in appearing drought in the same group of stations.

Precipitation and air temperature data, only, are often recorded at meteorological stations, with radiation being measured at very few weather stations, especially in developing countries. Therefore there arises a need for suitable models to estimate solar radiation for a completion of data sets. This paper is about an evaluation of eight models for an estimation of daily solar radiation (Q) from commonly measured variables in six synoptic stations of Iran, namely: Mashhad, Kerman, Tabriz, Esfehan, Hamedan and Zanjan using daily rainfall and temperature data for a duration of three years of 2000, 2001 and 2002. These stations represent several arid and semiarid sub-climates of Iran as based on extended-De Martonne climatic classification (semiarid-cold: Mashhad and Tabriz, arid-cold: Esfehan, Kerman, semiarid-extracold: Hamedan and Zanjan). The STATISTICA (ver. 6.0) software was employed for non-linear multivariate regression. The results indicated that most of the models overestimated in lower values of solar radiation while underestimating in the higher ranges, indicating a systematic error. Performance of the models was evaluated based on the Root Mean Square Errors (RMSE) as well as R2. RMSE ranged from 1.14 to 7.76 Cal cm-2min-1 for the whole data range and in all the six stations. Among the eight models, the Richardson model rendered the best agreement with the measured data in Kerman and Zanjan stations. In case of Hamedan station, Bristow and Campbell model was the most suitable. As for Tabriz station, De Jong and Stewart model using rainfall and range of daily temperature data led to the best performance. In Mashhad station, McCaskill equation can be recommended. Analysis of the data in Esfehan station showed no significant difference among the models. Due to variation in equations'' performances, to come to valid conclusions and to choose the most suitable radiation models, further study would be required from other climatic regions the country.

A greenhouse experiment was conducted to evaluate the competitive effects of different densities of wild mustard as against rapeseed. The experiment was performed in a randomized complete block design with four replications using replacement series in which wild mustard and rapeseed were respectively planted in different ratios of 4:0, 3:1, 2:2, 1:3 and 0:4 plants per pot. Results indicated that the maximum height, number of siliques per plant, silique length and number of seeds per silique in rapeseed vs. the maximum height, silique length and number of seeds per silique in wild mustard were obtained in their monoculture states. Overall evaluation of relative yield showed that both species were exploiting the resources in different ways or even somehow benefiting each other. Relative crowding coefficient of rapeseed as against wild mustard in the 3:1 treatment was greater than that in the other plant ratio treatments. Competition indices revealed that rapeseed benefited from a more competitive ability than wild mustard.

Land surface temperature (LST) is a significant parameter for many applications. Many studies have proposed various algorithms, such as the split-window method, for retrieving surface temperatures from two spectrally adjacent thermal infrared bands of satellite data. Each algorithm is developed for a limited study area and application. In this paper, as part of developing an optimal split-window method in the southeast of Tehran province, Iran, four commonly applied algorithms to retrieve the LST from AVHRR were compared. This study was carried out in a wheat farm site located in the Pakdasht Agricultural Region. Measurements of LST over the farm were made with a manual infrared radiometer at the time of NOAA overpass for 18 days of May to June 2004. These days were cloud free over the study area. A total of 18 NOAA images were acquired for the days that LST measurements were made. The temperatures derived by the different split-window algorithms were compared to ground truth measurements. The performance of the split window algorithms was checked with three statistical indices: root mean square error (RMSE), mean bias error (MBE) and coefficient of determination (R2). The results showed that the Ulivieri split-window algorithm produced the lowest value of RMSE and MBE (2.71 and 0.26 K, respectively) and its highest value of R2 (0.92) gave more accurate results than the other algorithms.

Salt stress is one of the most chalanging abiotic stresses affecting natural productivity and causing significant crop losses worldwide. A greenhouse experiment was conducted to evaluate the response of two alfalfa cultivars (Bami and Hamedani) to 6 levels of salinity (0 as control, 25, 50, 75, 100, 125 mM NaCl) at the College of Agriculture, Shiraz University, Shiraz, Iran in 2008. Plant dry weight per pot in both cultivars decreased with increasing salinity levels. However, Bami as compared to Hamedani, with the lowest Na sequestration, produced the greater dry matter weight. Leaf area per pot was significantly affected by salt stress with Bami cultivar showing a higher leaf area than Hamedani. Na accumulation also increased by increase in the salinity level in either one of the cultivars; however, Na sequestration of Bami as compared to Hamedani, was lower due to Na exclusion mechanisms occurring in this cultivar. Although Cl- accumulation increased with increasing salinity level in either one of the cultivars, Cl- accumulation was higher in Hamedani than in the other cultivar. Similar to Kﳖ ratio, Ca2ﳖ ratio also decreased by an increase in salt stress levels and there were highly significant differences observed between 25 and 125 mM of NaCl in either one of the cultivars. There was a strong positive relationship observed between plant dry matter weight and leaf relative water content for both Bami (R2=0.94) and Hamedani (R2=0.96) cultivars under salt stress conditions. All in all, it appears that less adverse effect of salinity on Bami cultivar has made it suitable for growth in saline soils as compared to Hamedani in saline areas prevailent in south Iran.

Emissivity mapping of the Earth’s surface is the prerequisite to thermal remote sensing. A precise determination of a surface''s temperature is dependent upon the availability of precise emissivity data for that surface. The present study area is a part of sugarcane plantation fields in the west part of Khuzestan province. In this work, Temperature Emissivity Separation algorithm (TES) was applied to five different ASTER L1B images. It was found out that TES method overestimates temperature in all the five thermal bands, and underestimates the emissivities as compared to the laboratory values. The differences in the emissivity values (as compared to laboratory values) varied from 10% in band 10 to 3% in band 14. The main reasons for these discrepancies were a lack of proper calibration of the thermal bands, the possible presence of radiometric noises in the calculation of the emissivity Maximum Minimum Differences (MMD) as well as mixed pixels. To overcome these uncertainties in the TES algorithm, an Improved TES method (ITES) was introduced. In the ITES method, the surface exiting thermal fluxes were simulated. The emissivities of four different reference surfaces, along with air temperature measured at nearby weather stations (believed to represent LST of full vegetated pixels) and the band 14 temperature, were employed as inputs. The results show noticeable improvements in the predicted emissivity to around 1% for band 10 and less than 1% for bands 13 and 14 as compared to the corresponding laboratory values. The root mean square error (RMSE) of emissivities for full vegetation cover was less than 0.015 and less than 0.01 for partial vegetated cover, bare soil, and sea water surface. Finally, emissivity maps for one sample image, employing the five thermal bands, were produced. It is believed that these maps can be used in other satellite images as layers of emissivity values for the purpose of a proper estimation of surface temperatures.

Flood is one of the most calamitous natural disasters that causes extensive property and life damages across the world. It however, could be a blessing due to its special natural water resources recharging value. By simulating the magnitude of probable floods considering the anthropogenic and natural effects and implementing contingency plans, their damages could be reduced. In this paper, the General Circulation Model (GCM) climate change scenarios are employed to simulate future floods. The GCM scenarios include simulation of climatic signals of the future considering green house gas emission forces. In this study a statistical downscaling model (SDSM) has been applied for rainfall downscaling to provide regional results from GCM outputs. Then, a rainfall-runoff model called HECHMS has been employed to estimate runoff in the region. The maximum simulated rainfall for each year that is of high enough potential to cause flood, is introduced into the rainfall-runoff model to simulate the plausible hydrograph of the flood. The proposed procedure is applied to the Kajoo River basin in South Baloochestan region, south-east of Iran.

Wind, in the duration of its erosional process, affects considerable changes in a grain''s morphology from its removal (detachment) step to sedimentation. In other word, a grain undergoes its gradual evolution during the transit process. In this project, the maturation of Aeolian sand grains had been studied upon as based on texture maturity indicator which includes: sorting, mean size grain, roundness as well as abrasion coefficient parameters. The study area is the transport region of Khartouran Erg sediments, which founded on the basis of ground index of wind erosion. According to these indicators, the direction of prevailing or strong winds is notably mentioned. In a later step, four transects are selected in different area in alignment with wind direction. Samples of sediment grains are taken at varied distances in any one of the transects. The samples were taken from the windward slope of Rebdou landform. The samples were evaluated to using granulometry and morphoscopy techniques. Grain size analysis of was done using dry sieve analysis while morphoscopy of grains carried out by studying the quartz grains of 150 to 300 μm diameter by using binocular microscope. Results indicate a gradual maturity (evolution) in sediment texture in all transects starting from the upper parts (near sand source) toward the lower parts (in transportation area). Also, results indicate that from among the four indicators of grain maturity namely: sorting, grain size, roundness and abrasion coefficient the respective factors of either «abrasion coefficient index» or «roundness index» in the first value and then «sorting» and finally «grain’s mean size index» are the ones accounted for validation for determination of maturity.

Shortage of water resources and increasing demand to consumption of this scarce resource, leads to some noticeable limitations. On the other hand, population growth and consequently, increasing demand for water in arid and semi arid regions , needs production in exchange of little amount of water consumption. To approach this objective, an experiment in the complete randomized blocks carried out in four replications for cumin plant growing in Zabol, southeastern Iran. Experimental treatments included irrigation periods at three levels. Then using CROPWAT model, the water requirement of the plant is met. Analyzing the data resulted from production gathered in different times of irrigation and consumption of water in the three times irrigation case with sound efficiency (1750 m3/ha), is more little than the water amount which is simulated by the CROPWAT model in 2003 (6070 m3/ha) and (5363 m3/ha) in 2004. It then showed that this model is not effective in determining the water requirement of cumin at this region.