Desert
Volume:13 Issue: 1, Winter - Spring 2008

Wheat (Triticum aestivum) growth and yield are depressed by physical and chemical interference of weeds. Recently, wild barley (Hordeum spontaneum) population has increased in wheat fields of many provinces of Iran. Since, little is known about the allelopathic effects of wild barley residues in soil, greenhouse studies were conducted to examine the effects of soil amended residues of wild barley at 0, 0.2, 0.4, 0.8, and 1.6 kg m-3, and its root exudates on growth and yield of wheat. There were no significant differences in wheat seedling height and FW when exposed to 0.2 and 0.4 kg m-3, whereas, the two high residue levels, i. e., 0.8 and 1.6 kg m-3 significantly reduced these parameters. Two high residue levels also significantly reduced seedling and mature plant height fresh and dry weights, and yield of wheat. Root exudates that released from wild barley seedlings into the soil, did not affect wheat seedling height, whereas, those released from tillers significantly decreased seedlings and mature plants heights, FW and DW and yield of wheat. Key words: Allelopathy; Soil amended residues; Wild barley; Hordeum spontaneum; Wheat growth; yield

Climate is the most important factor which control desertification. In order to detect climate changes in desert zones, time trend analysis is applied to extreme indices in Kashan station using extreme climate index software (ECIS). Results show significant trends in extreme indices during the past decade 1995-2004 and the pronounced warming is associated with a negative trend in cold extremes. The finding revealed that the frequency of warm (cold) extreme indices is increased (decreased) and probability, the problem of desertification in Kashan region will be extended.

Two laboratory and greenhouse experiments were carried out to compare and evaluate the nutrition of Phaseolus vulgaris L. plant with foliar spray and root media. In laboratory, effect of four treatments; N- nutrition solution; Urban solid waste leachate (USWL); vermi-compost extract and control (distilled water) on germination and seeding growth of Phaseolus vulgaris L. was examined for 10 days in incubation at 20?C. In greenhouse, in addition to four treatments mentioned earlier, vermi-compost paste (after extraction) + sand (1:1 ratio) was included as fifth treatment. Foliar spray of all treatments except the fifth treatment was performed at plant two leaf stage daily for one month. The results showed that foliar spray with organic compounds of low concentrations had a positive effect on vegetative growth and plant weight. In these treatments leaves were thicker, more succulent and dark green in color, probably due to higher photosynthetic activity of plant. Foliar spray with organic compounds increases the droplet persistence on leaf surface and hence more absorption of plant nutrient element

To assess the effects of livestock grazing on soil compaction (density changes), the trampling action of livestock was simulated. The research field was located to the south west of Nazarabad in Savojbolagh district, south west of Tehran Province. Samples were annually collected based on a completely randomized design. From the triple regions (reference, key and critical) 36 cylindrical cores were taken they were 8 and 15 cm in diameter and depth respectively. Sampling was done at the end of each grazing season (early fall) in 2004-2005, pot experiments being composed of 9 treatments in 4 replicates. Collected data were analyzed in a completely randomized block design using ANOVA. The means were compared using Duncan Test. The results show that during conversion from critical to key and reference situations, germination rate and the height in critical condition, critical to key and critical to reference conditions have increased. The organic matter for these conversions were 0.033, 0.07 and 0.23 respectively, among which significant statistical differences are observed (P?0.05). In conversion of key to critical and reference conditions, germination rates (in pot environments) for key, key to critical and key to reference conditions were reduced respectively. The organic matter contents were 0.052, 0.026 and 0.107 gr. While the heights being 51.19, 27.69 and70.62 cm respectively. Stipa barbata shows significant differences in germination rate as well as height. With decrease of bulk density and compaction in the first treatment, and with reverse conditions for the second one, in both treatments, germination rates were decreased. In converting reference to key and critical conditions, germination rates for pots of reference, reference to key and reference to critical conditions were 50, 56.25 and 29.69% respectively. The heights and organic matter were reduced and while in all treatments significant differences being observed (P?0.05).

Gully erosion is widespread process of land degradation in dryland regions and has attracted the interest of a large number of researches. Although much research has carried out on soil erosion in arid and semi arid regions of Iran, few studies have been conducted to understand the threshold conditions of gully incipient. This study was conducted on gullying mechanism and topographic threshold conditions of gullies in an arid region of Iran. Since the dynamics of gully development channel initiation and extension are controlled by a variety of processes and factors, the data collection and analysis consist of field studies to the determine predominance process responsible for incipient gullying and Digital Model Elevation (DEM) analysis to examine slope-area relationship. Soil attributes (EC and SAR) and landuse practices were known as major factors to initiate piping and the potential of this process to initiate gully is very significant for bank gullies. It seems that topography and soil attributes are the major factors determining the effective process for incipient gullying in our study area. In the other hand all of gullies occurred in the main drainage streams and consequently are the main processes for landscape evolution. Correlation analysis showed an inverse linear relationship in log-log plot of upslope area and local slope dataset related to permanent gully heads. However for dataset associated with landsliding the S-A relation was not significant. Results of S-A relation can be used to determine vulnerable areas to gullying.

Dormancy breaking and germination requirements were investigated in seeds of Ferula ovina and Ferula gummosa. Seeds of rather species were collected from north and eastern-north rangelands of Iran. Seeds of each of the species were subjected to different treatments including various levels of GA3, chilling and combination of GA3 and chilling (GA-chilling). In contrast to treated seeds, non-treated seeds did not germinate. Germination of both species increased at higher concentration of GA3. In the case of Ferula ovina the highest germination percentage was obtained when the seeds were treated with 1000 ppm GA-chilling with 76% of germination. For Ferula gummosa seeds, the highest germination percentage was found when exposed to 1500 ppm GA-chilling with 53% germination. Both species well responded to different periods of cold stratification (30/60 days), especially F. ovina with 36% and 55% germination, respectively. The results suggest that F. gummosa has deeper dormancy. For both species, germination rate was positively correlated with germination percentage.

Interest in arid ecosystems as a source of food supply for rapidly increasing population of the world, on the one hand, and the problems pertaining to the climatic characteristics, water shortages and soil sensitivity for the inhabitants in such areas, on the other have prompted efforts at both national and international levels to develop a better understanding of these problems as well as to find proper ways for the optimized utilization of the available natural resources. Iran is characterized by arid and semi–arid ecosystems for most parts (around 90%). Despite climatic problems in arid areas; there is also a great potential whose optimal management could decrease the problems. This article is an attempt to provide a model for sustainable development in arid areas and ecosystems of Iran. The focus of research and analysis has been as follows: The factors affecting dry weather in arid ecosystems, The problems and limitations in arid ecosystems, The potentials in arid ecosystems, Approaches to the environmental management and sustainable development in arid ecosystems.

Mungbean (Vigna radiata (L.) Wilczek) or green gram as a dryland grain legume is exposed to varied timings and severity of drought stress, resulting in variability in photoassimilate production. In order to evaluate some physiological responses in one mungbean cultivar to timing and severity of drought stress, a 3-replicate RCBD (randomized complete block design) field experiment was carried out during year 2004 year at the experimental farm of University College of Agriculture and Natural Resources, University of Tehran. Plants were exposed to either moderate or severe water deficit at either vegetative (VS) or reproductive growth stages (RS). Parameters were recorded at the middle stages of vegetative growth. In general, water stress reduced net photosynthesis rate (Pn), stomatal conductance (gs), transpiration rate (Tr) and leaf relative water content (RWC) while increasing leaf temperature (T). The greatest effects of drought on these parameters occurred at reproductive stage. Photosynthetic water use efficiency increased and decreased during VS and RS respectively. The results showed a clearly close correlation between RWC and gs in VS (r=0.912**) and RS (r=0.976**) treatments. Although water stress at vegetative growth stage significantly decreased Pn, gs, Tr, and RWC, these parameters were recovered upon rewatering at reproductive stage. It is concluded that to maximize mungbean Pn in dry zones, irrigation should be extended across all growth stages, especially during the reproductive stage.

Undoubtly, land degradation causes apparent decrease of natural resources potential which are highly linked to desertification. Different countries and also international organization have realized a great number of projects to combat desertification. Unfortunately these projects have not reach to their goals. The experiences shows that the reason of these unsuccessful works is lack of consideration on human factors as well as socio-economics issues. To find out the criteria, indicator and indices in desertification, the mentioned factors should be noticed. The importance of socio-economics issues, and establishing a realistic framework based on qualitative indicators and indices, are the main objectives of current research, which are adapted to situation of Iran, They are summarized in four groups and classified items as; population, poverty and economics, rights and institution and socio-cultural criteria.

The result of wind dynamic (capacity and potential) is transport of soil or sediment particles and subsequent formative desert landforms based on the severity of erosion or sedimentation. The Khartouran region, because of its geology, geomorphology and climatology conditions is a special place in the arid region on the closed basin of Dasht-e-kavir. It is evident that the ecosystem balance of the region is affected by anthropogenic exploitation and wind activity, so this area has a geoecological structure with special features. The wind erosion process in the Khartouran area can be categorized as origin, transport and sedimentation sites. In this research, the studied area was about 200000 ha, southwest of the town of Sabzevar covering sand origin and transport areas. The studies were carried out based on topographic, geologic maps, landsat images, aerial photographs and field observation. Based on these documents, the area was divided into a 9 km2 (3?3 km) grid and identity points of each grid were determined (214 points). On each identity point, indices of wind erosion (deflation, abrasion and accumulation), were collected. The results have shown two geomorphologic units (pediment playa) in project area and the geomorphologic facies (landforms) such as desert pavement, small yardang (kalotak), rebdou, nebka and sand ripple have been found by aeolian transport of sand. Based on ground indicators, determined removal and transit zones. Based on studies and results can conclude that these regions were affected by wind erosion in the past more than of current time and khartouran Erg is a result of wind activity in the past. Currently, the rate of sand flux and the balance between erosion and sedimentation are dominant factors in shaping geomorphologic facies (Aeolian landforms).