Desert
Year:2002 | Volume:7 | Issue:1|Papers Count:11

Wheat as a principal crop in Iran and mostly grown under arid and semi - arid conditions, hence irhas low productivity. To evaluate drought tolerance and productivity of 12 improved wheat cultivars under rainfed conditions, a field experiment was conducted at research farm of College of Agriculture, University of Tehran, Karaj, Iran, in 1999-2000, in a randomized complete block design with three replications. Each plot contained nine rows with 25 cm apart and seven m length. The final harvest area was 10.5 m2 (7 rows, 6 m long each). As moisture conservation practices were not performed in fallow year (before sowing), the crop was irrigated only once before seed germination. Total precipitation during the growing season was 200 mm. The improved wheat cultivars comprised of six dryland varieties and six irrigated ones. The attributes recorded were- grain yield, grain weight, spike length, plant height, tiller number, and dates of stem elongation, heading and maturity. The coefficient of correlation between grain yield and plant height spike length and grain weight showed the important effects of these characters on yield under rainfed conditions. Similarly, the negative correlation of grain yield with date of heading (r=-0.38*) and maturity (r=-0.29*) indicated that earliness enables the cultivars to escape drought towards the end of growing season. The cultivars Ghods, Rashid and Cross - Omid produced the highest yields, but Rashid was the earliest in maturity. Sardari, a well - known dryland cultivar, also produced high yield and had the highest total number of tillers and grain weight, under rainfed conditions.

Salsola sp. known as shoor or shooreh in most parts of the country, are annual or perennial plants from Chenopodiaceae family. In desert regions, especially in northern margins of Iranian central desert Salsola sp. is available and extended from 1000 m above sea level altitudes. These plants are resistant to drought conditions and tolerate relative salinity of soils. In Semnan province, 13 species of this genus were collected and determined among which six were annual and seven perennial. The most important genera of Sal sola in this region based on their role in supplying forage and in green cover composition of ranges, were S. arbuscoliformis, S. rigida cf Orientalis and S. arbuscula. Although some annual species like S. kali have shown special abilities in forage production under harsh conditions in many parts of the world, this study was carried out to determine Salsola characteristics in Iran. In ranges of arid regions, especially in winter grazing ranges of Semnan province, Salsola sp. is an important component of green cover. Animal husbanderers, especially nomads believe that Sa/sola plays a role by providing salt for domestic animals in addition to its essential role as a forage in grazing cycle from ranges. Usually in ranges with Salsola, a part of grazing time that ordinarily is at the end of the day will be devoted to these ranges. Domestic animals would graze and take needed salts from these plants so that there is no need for putting salt stones in the area. This part of grazing is effective in health of livestock nutrition and helps the shepherd to lead the herds toward watering places. Protein and dry matter production of some Salsola sp. is considerable and can be compared with Medicago sativa.

Flood mitigation and utilization are vital to arid areas, because of destructive flooding and water shortages in these areas. Flood spreading on the permeable terrain is one of the flood control and utilization methods. Determination of appropriate site for water spreading is one of the most important stages of this project. In this research, applicability of different models was evaluated for flood water spreading site selection in the study area. Three information layers (slope classes, geomorphology and soil hydrology groups) were combined in three different models of Boolean, Index overlay and Fuzzy logic. Based on comparison between output maps from models and control areas, it was recognized that the gamma operator (0.1-0.3) in fuzzy logic model is the best one among the models for the study area.

Drought is a major environmental factor reducing grain production of rainfed wheat (Triticum aestivum L.) in semiarid regions. In an experiment aimed at evaluating effects of drought on some morphological traits of wheat and assessing relationships between these traits and stress susceptibility index, eight wheat genotypes, including four landraces from Iran and four commercial cultivars, were grown under wel-watered and rainfed environments, at the University of Tehrans' Research Farm in Karaj. Stress susceptibility of each genotype was estimated using a calculated index based on grain yield. Significant differences were found between all genotypes for all studied traits. Landrace genotypes and improved cultivars .that were evaluated, exhibited a wide range of stress susceptibility. Stress susceptibility and yield potential were not associated, to indicating that they might be independent components both contributing in adaptation to stress environments. Stress susceptibility index was negatively correlated with grain yield and biomass under stress conditions, indicating that selection for these characters under stress conditions might result in decreased susceptibility to drought. Analysis of variance showed that days to heading, harvest index, 1000 grain weight, number of grains per spike, grain yield, biomass, number of tillers, length of peduncle, plant height, length of spike, number of leaves per plant, and area of flag leaf decreased under drought conditions; however, stomatal frequency of flag leaf increased under such conditions. Among yield components, number of heads per plant was affected the least and number of grains per head was affected the most under stress conditions. Results showed that drought tolerant genotypes might be found in Iranian wheat collections.

In the present study, yearly climation drought in Atrak watershed was investigated using yearly data of precipitation in 21 stations during twenty nine years period. Amounts of drought severity were estimated using percent normal index and extraction of return periods of 2, 5, 10, 20, 25, 50 and 100 years for all networks. At first, regional analysis was used through correlation with altitude. This method was eliminated due to a negligible correlation between altitude and drought severity. Kriging method was considered in next step. Regionalization of drought severity for different return periods was carried out by using this method. Finally, severity of drought for each return period was extracted for all stations. Analysis of drought isoseverity showed that greater return period was due to high drought severity. In addition, consideration of severity, duration and return period curves revealed that increment of drought duration, severity of drought for different periods tend to be constant.

One of the common methods in rangeland reclaimation is seeding with adaptable plant species. Medicago sativa cultivars such as Kerisari, Simerjanskaya, Ranger and Cody were imported into Iran about 25 years ago. Cultivation of exotic species, will probably make some changes under normal conditions in the region. Thus, this study was carried out to investigate the effects of cultivation of different cultivars of Medicago sativa on soil fertility characteristics in Tabarian and Tavacolbagh in Khorasan province. Using randomized - systematic method, eight plots were selected (four plots in control and four plots in cultivated areas), per region per cultivar. Soil sampling was done with digging profiles inside plots at 0-30, 30-60 and 60-90 cm layers. T -test was carried for comparing soil characteristics between the two regions (cultivated areas and control region). Results showed that in cultivated lands with Medicago saliva, organic matter and nitrogen content increased, whereas, potassium and phosphorus decreased.

Various indices have been suggested to forecast drought worldwide. Regional analysis of low flows in areas with short term or lacking available data is one of the best indices for hydrologic drought prediction. Hence, determining the most appropriate distribution function is of importance to regional hydrologic analysis. In this study, 16 hydro metric stations with available data based on statistical period were selected among all hydrometric stations of the basin. Low flows of 7 and IS-days were fitted to the data of each station on the basis of residual sum of squares (SR.S.S.) using eight probability distribution function during two different Statistical periods. The results showed that log Pearson type III distribution had the best fitness for 7 and 15days of low flows.

In spite of the fact that Lut desert is one of the most important phenomenons because of its rare harsh climatic conditions in the world, it has drawn a very little attention in the country. To characterize some thermal condition and limitations of surface temperature of Lut Desert, Landsat TM data, aerial photos, topographic maps and some other additional maps were used. To extract some information from TM Thermal band, the TM Thermal DN values were converted to the radiance and brightness temperature. In this study, the temperature maps were obtained using TM thermal data and taking into account six emissivities (1, 0.99, 0.98, 0.96, 0.94 and 0.92). The temperature maps and their minimum and maximum temperatures of 46.8°C and 53.54°C and the minimum temperature of 35.6°C and 42.1°C for emissivities of 1.00 and 0.92 were obtained at the time of Landsat overpass, respectively. The range brightness temperature of 39.33°C - 41.2°C were obtained for Yardang zone for the emissivity of 1.0. In order to determine Lut thermal regiment and study sunface temperature in other dates and seasons, study of regional thermal variation in proposed.

Salinity is second to aridity in terms of occurrence, and a significant portion of natural and agricultural ecosystems of the world is affected by salinity with different degrees. This problem is rather widespread in Iran and it is estimated that 15% of total land area of the country is salt affected. An attempt was made to study certain physiological characteristics of a well known salt tolerant species of the desert environment, Aeluropus littoralis, with a wide range of salinity namely 0, 20, 25, 30 dsm-1 under glasshouse conditions. The present work was conducted with a completely randomized design and four replications. Salinity levels were imposed by applying solutions of NaCI and CaCl2 in Hoagland's medium circulated in a sand culture closed system. Parameters namely SPAD readings (chlorophyll content), N content, stomatal resistance, specific leaf weight (SL W=Lwaf weight/leaf area), leaf area, stem length/root length ratio were determined. Results showed that increasing salinity level upto 25 dSm-1 increased SPAD readings and N content, whereas these same parameters were decreased by further increasing the salinity level. As it was expected, salinity increased stomatal resistance. With increasing salinity level, SL W was increased but leaf area per a fully expanded leaf was decreased and this was also true for stem length/root ratio.

This study was conducted in order to survey factors affecting distribution of vegetation types and the relationship between vegetation and soil characteristics in Sirjan playa, Southwestern Kerman province. The study area was one of the most ancient catchments in central Iranian plateau including formations from Precambrian to Holocene, an area of about 274194 ha. After identifying playa area by aerial photographs and topography maps, vegetation was studied using plotting method along transect. In addition, for pedological study, profiles were dug in each vegetation type. Soil characteristics such as texture, acidity, electrical conductivity, organic matter, lime, gypsum, sodium, potassium, calcium, sulfate and bicarbonate were measured. Results showed that from center of playa toward heights, in all aspects of playa, water table depth increased and electrical conductivity decreased. The amount of anions and cations of soil varied, and ratio of anion/cation was obtained. In addition, soil texture became lighter and stability of soil structure improved. This variation caused different vegetation types from margins of playa to heights of 1650-1710m. Vegetation types established from center to outer of playa were as follows: Halocnemum, strobilaceum-Halostachys, belangriana, Tamarix passerinoides, Seidlitzia rosmarinus-Salsola sp., Seidlitzia rosmarinusArtemisia sieberi. After humid margins, vegetation types such as Artemisia sieberi-Zygophyllum eurypterum and Artemisia sp.-Astragalus sp. were established respectively. Therefore, in this region, two factors such as salinity and water ground table were the most important factors affecting on establishment of vegetation types.