Desert
Year:2001 | Volume:6 | Issue:2|Papers Count:12

Desertification is a phenomenon that is affected by many factors such as natural, social, economical and reciprocally affects these factors. The first step in performing dedesertification projects and preventing desertification must be based on the recognition of phenomena that cause desertification. In this research, at first by combining information from topographic and geologic maps, air photos and field survey, the area was divided into 15 geomorphological facies or subfacies, each of which was considered as the main unit for evaluation of desertification. For an investigation of desertification factors and evaluation of the intensity of desertification, based on presented regional characteristics, rating of seven factors affecting desertification was done in each geomorphological unit. The factors were climate, geomorphology, lithology, hydrology, pedology, land management, land use and the present situation of desertification. The class of desertification was determined for each geomorphological unit. By adding up all the ratings obtained from desertification factors, the intensity of desertification of land unit in five classes of insignificant, low, medium, intense and very intense was estimated. At the end, the result of evaluation was presented as a desertification intensity map of the area. The results of this research were as follows: Desertification was active in the area was on a rise. Among the main desertification phenomena, salinization and alkalinization were active in %51 of the area. In these areas, in addition to climatic and pedologic conditions, the main factors of desertification were geomorphology, lithology and hydrology (the depth of saline underground water and saline incoming runoff) and in %49 of lands, wind and water erosions and degradation of vegetation and water resources under natural and human effects such as lithology, geomorphology, climatology, pedology, overgrazing and unwise exploitation of underground water resources were active. About 68.8 Km (%8.6) of the area was under medium, 400.8 km2 (%50.1) under intense and 330.4 km2 (%41.3) under very intense desertification status.

Surface and subsurface waters from the regions surrounding Khorian, Melhe, Kabodeh, Arche, Chah Hoseini and Chah Shirin are being drained into a playa located 45 Km south of Semnan. In order to study water table fluctuations in the playa margin, ten pits were dug in different facies of both sides of the salt mine road that goes into the playa. Every month (20th-day) water table was measured from a constant point above each pit and hydrograph of each pit was plotted and amount of monthly water table fluctuations was measured and compared with its level in September. It was concluded that water table fluctuation in different facies depends not only on evaporation, but also related to other factors such as soil texture, porosity, permeability, topography, hydrulic gradient, amount of salt, and other hydrology and hydrogeology factors. The results showed that average rise in water table in 10 pits were 6.2 Cm in the month of May. Therefore, May was the best time for cultivation of hydrophyte and halophyte plants that collect their needed water from storage. The average maximum decrease in water table was -8 Cm in November. If this situation continues for several years, November month will be a critical time for hydrophyte and halophyte plants, because of maximum decline in the water table. The average annual amount of water table decline in 10 pits was 6.5 Cm and the volume of water decline in 14 hectare was 455 m3. This may indicate that the area was in a dry period.

South Bafgh lands are among the central Iran arid areas which have low rainfall and poor vegetation. Deflation of these bare lands has caused soil erosion and in addition to degradation of soil texture, damages to roads especially Tehran-Bandar Abbas and Tehran-Kerman railroads in South Bafgh and also agricultural lands and adjacent villages. Due to accumulation of transported sediments in southeast Bafgh, an Arg with 37Km2 area has been made. In order to control wind erosion in the region, first of all, the main source regions needed to be identified. Therefore, for determination of source area, the method of phase by phase source-identification was used in the region. The results showed that the erosive winds blow from south-west and transport sediments towards sand dunes. Geomorphologic and sedimentological studies showed that the source of sand dunes has been close and local and it is located on epandage plain of south west part of Arg, beds of Zarand Shoor-River and the other eolion erosive facies of this plain. In general, the main source is adjacent regolite plain.

Although, the term desert is often less pleasant and unattractive in public minds; however, paying a slight attention and thinking about the life, development and activities of inhabitants of desert cities in Iran would show that there is a lack of in-depth understanding about history and life style of desert dwellers. Because of the lack of understanding about past lessons and experiences, and emphasis on façade and physical being instead' of thoughtful mind in principles and fundamentals, enormous sources of knowledge, experience, art and technology belonging to society have been ignored and foreign, non-native models have become commonplace. The latter are alien to native culture and nature and many social and economical conditions in our society. This study is aimed at identifying architectural characteristics of Iranian desert cities that show peculiarities regarding the past Iranian culture that can be a source of principles for design and human environmental management.

Multiculture cropping plants instead of continues monoculture of one or several crops and pest management, are the two very important aspects of sustainable agriculture today. One of the most effective methods of weed control is the use of rapidly growing plants accompanied by row crops that is valued in protecting the nature from destructive effects of herbicides. Therefore, this study was conducted in Farm Research, Faculty of Agriculture, University of Tehran in 1998. To determine the role of bean (Phaseolus vulgaris L.) in controlling weeds of maize (Zea mays L.). Experimental design was randomized complete block with four replications and nine treatments including unweeded sole crop of maize (MC), sole crop of maize with one time weeding (MW1), sole crop of maize with two times weeding (MW2), intercropping of 100% maize + 50% bean (MB50), 100% maize + 30% bean (MB30), 100% maize + 10 % bean (MB10), 75% maize + 25% bean (M75B25), 50% maize + 50% bean (M50B50) and sole crop of bean (B). During the growing season in two week intervals and at harvest time, dry matter and leaf area of two crops and dry matter of each weed species were measured. Results indicated that weeding increased the biological yield of maize, but intercropping had no effect on this character. Intercropping of 100% maize + 50% bean (MB50) among often intercropping treatments had a maximum effect on weed dry matter. This treatment (MB50) reduced to the dry matter of Amaranthus sp. and Solanum nigrum L. as compared with the unweeded sole crop of maize (MC). Weeding increased the Leaf Area Index (LAI) of maize but there were no differences among the intercropping treatments, and as the density of bean was increased in intercropping, the Leaf Area Index of bean increased overall, the rate of bean leaf area expanding was determinant success in intercropping under weed conditions.

In this work, the gypsy flora in the west of Semnan province was studied in 32 stations using transects and unique plots. The major factors studied were the presence and relative coverage of the plants, characteristics of gypsifrous soils, the rate of gypsophily potentials of plants and percentage of gypsum contents in their soil samples. Based on these results, the plants were classified into three groups: obligatory gypsy flora (eight species), preferential gypsy flora (28 species) and nondifferential kinds (70 species). In this area, of 106 species determined, two species were gymnosperms, 11 monocotyledons and the rest belonged to the dicotyledons. All obligatory species were native to Iran, and six species were endemic to the Semnan province.

Growth, development and yield of five wheat cultivars were predicated by a general wheat simulation model for arid and semi-arid environments (SIMTAG), after validation with experimental results. Weather inputs of the model including global radiation, temperature and precipitation under Mashhad conditions were generated by running a general circulation model (UKMO). With doubled CO2 concentration. The SIMTAG model was adapted to increased CO2 level through its effect on radiation use efficiency. Simulation results under doubled CO2 level were compared with those under current climatic conditions. Overall response to increased CO2 level and the resulting climatic changes were the same among the wheat genotypes. Temperature rise due to doubling CO2 leveled to a reduction in average duration from sowing to maturity by 27 days. However, leaf area index, leaf number per plant, and total above-ground dry matter increased by 6, 12, and 6.4%, respectively. Pattern of dry matter partitioning was also affected by climatic conditions. Under doubled CO2 level contribution of spikes in total dry matter was 8% higher than current conditions which resulted in a 30% increase in grain yield when averaged over all wheat cultivars. It was concluded that wheat will take advantages from doubling CO2 level under Mashhad climatic conditions by developing a higher green area index, allocation of more dry matter to reproductive organs and consequently higher harvest index and grain yield.

The effect of planting pattern and plant density on yield and yield component of two maize hybrid including, single cross 704 and three way cross 647 were studied in a factorial experiment in a randomized complete block design with three replications in year 1999 in the experimental farm of the Faculty of Agriculture, University of Tehran. Planting pattern treatment included normal planting and two rows of planting in the wide ridge (every other furrows) and plant density treatment included 70000, 80000 and 90000 plants per hectare. The results of this study showed that grain yield and biological yield (total dry matter) increased with increasing plant density and most of yield components decreased. The greatest number of ear row, kernel number per ear row were obtained from 70000 plants/hectare densities and maximum grain and biological yields were obtained from 90000 plants/hectare. Planting pattern had a significant effect on yield and yield component and the greatest amount of grain yield and biological yield were obtained from normal planting pattern. Most of the yield components were higher in normal planting pattern. Among the two studied cultivars, single cross 704 had a greater grain yield and biological yield than three-ways cross 647 and the two cultivars showed no differences in yield components except the thousand-grain weight.

This paper investigates the nitrogen compounds in Zahedan aquifer that are important groundwater pollutants in urban and agricultural regions. The groundwater is the only source of water supply for various uses in Zahedan city. This work is based on the field study, laboratory analysis and collection of the available data. The results revealed that in a large portion of the aquifer, over which the Zahedan city has expanded, the concentration level of nitrogen compounds has increased much above the admissible limit. For example, the nitrate concentration has increased to more than 5 times of the standard level. The high concentrations of ammonium and nitrite in some places indicate the discharge of fresh domestic wastes into the aquifer. This situation is alarming to the authorities to take a serious action in order to protect the groundwater resources.