Desert
Year:2004 | Volume:9 | Issue:1|Papers Count:13

There are a lot of problems due to salt in arid and semiarid regions. These areas cover 25% of the earth surface. More than 75% of area in Iran is salt affected. Agriculture is a major problem in these areas. Salinization is partly related to initial causes such as geologic formation and salty dunes. Prevention of salinization should be considered through preventive measures. Unsuitable irrigation systems and incorrect management of agricultural lands must be avoided. Correct management is one of the most important ways to prevent salt expansion. In this way, ecosystem balance will also be protected. In order to follow these aims, a region in Khodabandeh, Zanjan province, was distinctly chosen for an experiment with a completely randomized block scheme. Different agricultural land as well as rangelands were considered as treatments. Values of EC (Electrical Conductivity) and SAR (Sodium Adsorption Ratio) were obtioned from surface and subsurface layers. Results indicated that there are significant differences between these layers for factors under study. Duncan comparison means indicated that irrigation lands with monoculture plants exhibit the most values of EC and SAR in surface layers. In subsurface layer, EC is the highest in irrigated lands with monoculture crops as well as in rangelands, Irrigated lands show to be the highest in values of SAR.

The relationship between wind erosion (an index of desert areas), and the status of animal habitats located in these areas has received little attention and has not been academically attended to so far. The importance of unique and worthwhile animal species in desert areas as well as a description of the scientific relationship between the rate of wind erosion and the circumstances of habitats in desert areas within Khorasan province account for the undertaking of this research work. The region under consideration is situated within Sarakhs city suburbs at the farthest end of northeastern Iran. The research is conducted in two executive parts: The first consist of an estimation of wind erosion based on IRIFR.E.A model, obtained~ through surveying the region, preparing, geomorphologic, pedagogical and vegetation maps, studying meteorological statistics and developing an isoerodent map. The second part consists of an approximate demarcation of the habitat scope for each animal species in the area conducted on the basis of field observations, authentic reports and data gathered from local inhabitants through filling in questionnaires. The next part of the research is determining the approximate value of each habitat in the region based on three variables of: food, water and safety (human influences). The correlation between the value of each animal habitat and the average rate of wind erosion in that habitat forms the last part of this research work. The results obtained are expressive of the fact that there is a significant -and reverse correlation (r=-0.93,R2=0.87)between the sediment content due to wind erosion in the desert area in question and the value status of the habitats situated there; to the effect that factors affecting an increased rate of wind erosion affected animal habitats quality in the area, as well as reduce the value of each habitat in proportion to their dimension.

Monthly, seasonal, and annual total precipitation records of five oldest meteorological stations in Iran over the climatic period 1877-2001 are analyzed to assess the existence of a trend. These stations consisted of Bushehr, Esfahan, Tehran, Mashhad and Jask. During the First and Second World Wars, no observations in any of the above mentioned stations have beenrecorded. To reconstruct the lacuna in annual total precipitation series, the method of autocorrelation was used. The homogeneity tests for series showed that the records of the Jask station are heterogeneous and hence its data were eliminated from the trend analysis. On the other hand, the data of the other stations could be analyzed for-trend.In the next stage, some methods of trend analysis were applied to the annual, seasonal and monthly series. These methods included the Mann-Kendall test and Linear Regression Model. The obtained results indicated very limited support for the existence of trend or precipitation climate change.

This research was carried out to determine the loss of main soil nutrients as well as organic matter in lands with different crop covers under the effect of runoff and erosion. The experiment was carried out in the agricultural research center of Bakhtajerd, Darab. Three main crops: wheat, cotton residues, residues of corn as well as bare land constituted the four treatments that were selected for a complete randomized block design with three replications at the end of May, 2002. Plots of 2x1.8m size were designed for the artificial rainfall. They were isolated with sheets of metal to enable the collection of the respective runoff and sediments. Artificial rainfall with 75 mm hr-1 intensity of ten year return period was generated with a rainfall simulator. Nutrient losses of potassium, nitrogen, phosphorous as well as organic matter loss were determined in the laboratory. The loss of potassium, phosphorous, nitrogen and organic matter for a rainfall of 30 minutes, was recorded as 0.67, 0.63, 1.37,0.41 g/m2 for wheat cover; 0.002, 0.006, 0.007, 0.005 for corn residues; 0.15, 0.54, 0.84, 0.66 for cotton residue cover, and 1.88, 5.77, 8.68, 7.08 g/m2 for bare land plots respectively. The loss of phosphorous, nitrogen and organic matter was the highest in cotton residue plots while the lowest was from wheat plots. The loss of potassium from plots with cotton residue was the highest while from the bare land plots it was the lowest.

Tendency towards monoculture has caused a pronounced decline in genetic range in agro ecosystems. On the other hand, the number of improved cultivars with a narrow tolerance level and a so called limited date of performance has been on the increase. In spite of the availability of a tremendous number of commercial varieties, crop production is restricted to a limited number of these varieties. Iran is rich in terms of genetic resources, and diversity of genotypes. Races and populations have been high in number in the past, but this has been reduced to only a few numbers of varieties that presently constitute the main sources of crop production. In this study biodiversity of field crops was investigated at variety level by collecting data from 183 counties in 27 provinces. Based on these data, variety richness, Sorenson similarity index, and Margalef richness index were calculated. Results indicated that despite variance among provinces, wheat and rice exhibited to be the highest in number of variety richness, while oil crops the lowest. From among 34 wheat varieties grown in the country, 10 varieties cover 84% while two varieties 29% of acreage of wheat indicating a low spatial diversity for varieties as based on Shannon index. Even for rice with a high level of variety richness, indices did not exceed 1.5-1.7.

Different regression models are used to determine weed economic damage threshold. An experiment was conducted in 2002 in Shirvan area to determine the threshols of economic damage of effective weeds to wheat yield using Swinton method. Using a quadrate (50cm x 50cm), data were collected from destroyed and non-destroyed samples. To define inter and intraspecific competition in wheat-weeds competition, 1/W and l/LnW regression models showed to better fit the data. According to these models, from among Avena ludoviciana, Erysimum sp., Polygonum aviculare, Rapistrum rugosum, Chenopodium album, Salsola kali, and Sonchus sp., reduction effect of only Avena ludoviciana, Salsola kali, and Rapistrum rugosum on wheat yield was significant. Therefore, the threshold of economic damage was determined for these weeds, being about 6.16 TCL (Total Competitive Load); equivalent to 6.16 Avena ludoviciana, 13.02 Salsola kali, and 27.80 Rapistrum rugosum plants per unit area.

Sarein, as an important tourism sight of a semi-arid area in Ardebil Province of Iran is facing the problem of solid waste disposal. So, considering this problem, this research has been carried out to find managerial methods for the disposal of solid waste materials in Sarein. Data were gathered by collection and production of information through sampling, preparation and distribution of questionnaires, interviews, and observations. Physical analysis was carried out of the Municiral solid waste materials during four seasons in a year including Noruz holidays. Four samples. were collected at a time. Questionnaire contained multiple-choice as well as descriptive items in three different forms. According to the results the rate of solid waste disposal in Sarein on average was 16.8 tons per day, the density being 444.78 kg/m3.The rates varied during different seasons of the year because of the area being a tourist arrtaction sight. The results of physical analyises have shown that the components comprising the solid wastes consist of: 8.7% plastic, 7.65% paper, cardboard, and carton,2.78% metals, 48.90% foods" refuse, 3.77% textiles, 1.76% pane, 3.1% wood and garden refuse, and 22.87% other materials (rubbish, sweepings, ...). Finally, through analysis of the data and the results obtained from the study suitable, places for present and future landfills were determined. Collection system of solid waste in efficient and productive ways in Sarein has been recommended using applicable methods.

Two experiments were conducted in 2001 2002 and 2002 2003 growing seasons in a field, 17 kilometers west of Isfahan. The Experimental design was split factorial in randomized complete block with three replications. Four drought stress (S1= full irrigation, S2= withholding irrigation in vegetative growth stage, S3= withholding irrigation in flowering stage, .andS4= withholding irrigation in seed filling stage) were randomized to the main plot units while 12 treatments from combination levels of three cultivars (C1= Zarghan 279, C2= Varamin 295 and C3= LRV 5151) and four foliar applications (F1= no foliar application, F2=foliar application of water, F3 = foliar application of Zinc Sulfate (3000 ppm) and F4=foliar application of manganese sulfate (3000 ppm» were randomized to the subplot units. Free praline, total soluble sugars (TSS), SPAD and chlorophyll fluorescence were measured in S2 drought stress. Results indicated that drought stress increased praline, TSS and SPAD, but has no effect on chlorophyll flourescence (fv/fin). In case of praline and TSS significant interactions were found among between foliar application, drought stress and cultivars. At full irrigation, foilar application of manganese and zinc could not change praline and TSS in either cultivar. However praline and TSS in Cl increased with zinc and manganese foliar application. Drought stress also increased SPAD and so did zinc and manganese foliar application. Generally Cl had maximum praline, TSS concentration, and SPAD in drought stress condition as well as with zinc and manganese foliar application. It was concluded that foliar application of micronutrients, such as Zn or Mn, under drought stress conditions, could increase drought tolerance in safflower.

Analysis of low flow frequency indices is an applied method in studying hydrological drought. Annual low flows were defined as the lowest mean daily flow with in continuous period of7, 15,30 and 60 days in a year. Estimation of low flow is often needed at catchments that are not equipped with gauging stations, therefore regional analysis methods are often used. In this study, suitable gauging stations in Atrak river basin were selected. After determining the annual low flow series with a duration of 7, 15,30 and 60 days, 8 probability distributions were fitted to the data set. Log-Pearson was selected as a suitable regional distribution for low flow frequency analysis in the study area. Regional homogeneity of the study area was assessed through cluster analysis was two homogeny areas being regionalized. Regional analysis was performed for two methods of multivariate regression and low flow index method. Results showed that multivariate regression method is a better measure than low flow index method. Finally, using the regional models, low flows with return periods in the homogenous regions were estimated. Forecasting maps of drought with return periods of 2 and 10 years were drawn. Results showed that the more the number of return periods of drought, the more the drought severity. In total, observed return periods indicated that the eastern and central parts of the watershed experienced a more severe drought than the other locations. These regions require more attention in the future water resources studies.

Crop growth simulation models simulate crop growth and development basis of underlying processes such as photosynthesis, respiration with due consideration of the environmental effects on these processes. The objective of this research was the evaluation of CERES-Wheat model simulation of different growth parameters as well as wheat phasic development prediction as compared with field experiment observations. To facilitate determination of the genotype coefficients, CENCALC software is used to the realization of cultivar differences. To evaluate the phenological results Root Mean Square Error (RMSE) was calculated which was zero for flowering in both experiments with RMSE for physiological maturity being 6.5 and 7.49 days for Mashhad and Birjand trials respectively. This was less than 10% of observation mean as a model accuracy. Biomass production time course was simulated accurately, however it overestimated the total biomass. It seems that the main cause in biomass overestimation is the constant parameter in the model equations not being changeable by the user as well as these values differing from our observations.

Land cover changes due to human activities are of the main subjects in regional planning. Change detection is a major application of remotely sensed data. In this study which was carried out based visual - digital procedure, the various changes during the last 23 years and in three time series were detected. Digital images of MSS (20 July 1977), TM (7 Sep. 1988) and ETM+ (20 July 2000) were used. The three multi source images were geometrically as well as radio metrically calibrated against each other and used as input change detection methods such as image overlaying, image differencing and post classification comparisons. The obtained results indicated that during the 23 years, 74% of changes were related to desertification, 68% of which occurred between years 1985-2000.