THE SCIENTIFIC JOURNAL OF AGRICULTURE (SJA)
Year:2007 | Volume:29 | Issue:4|Papers Count:15

In most hydrological and water resources studies, rainfall estimation is an important parameter. Different interpolation methods such as nearest neighbors, inverse distance, minimum curvature etc. can be used to show the distribution of rainfall over the watershed. Since the number of rain gauges is usually insufficient and there are high uncertainties in measurements, the estimated rainfall is not accurate. In the last few decades, geostatistics have been developed and applied in many engineering fields successfully. In this research, spatial distribution of rainfall over the Maroon Watershed has been estimated using statistical and geostatistical methods in GIS environment. On the other hand, artificial neural networks (ANN) have been applied as an interpolation tool and in combination with geostatistical methods. Results proved that geostatistical methods especially Kriging and Co-Kriging have better ability for estimation.

To study the effects of different concentrations of gensteine on growth and morphology of annual medics under 5°C root- zone, an experiment was carried out under controlled conditions of growth chamber with 25/20°C day/night air temperature. Three annual medic species (Medicago polymorpha cv. Santiago, Medicago radiata cv. Radiata, and Medicago rigidula cv. Rigidula), which are adapted from cold and temperate conditions were used. Gensteine concentations with 5 levels: 0, 10, 20, 30 and 40 micromol per litre were used. Experimental design was based on factorial in randomized complete blocks design with three replications. Result showed that there was a significant difference between species in respect to dry matter and yield components, M rigidula had the highest leaf, stem and root dry matter, plant hight, root length, leaf and stem to root ratio, leaf to stem ratio, leaf surface and yield compared with other species. The result showed that in 5°C gensteine had a significant effect on yield and yield components of annual medic species. Increasing in gensteine concentration led to increasing in plant height, root length, dry matter of root, leaf and stem, allocation of higher dry matter to aerial parts of plant, number of brunch, stem and leaf node and leaf surface area of annual medic species. Interaction effect of species and gensteine showed that M rigidula cultivar in 20 micro mol gensteine per litre in respect to root length, dry matter of root, stem and leaf, rate of leaf and stem to root, rate of leaf to stem, leaf number, leaf surface and node number was better than other species. M rigidula in low root-zone temperature had better growth and development in 20 micro mol gensteine per litre, so this treatment is more suitable for ley-farming system in cold and temperate regions. Also cereal- pasture rotation system in the regions with low soil temperature about 5°C will be successful if gesteine is applied. In these regions, cereal- legume ley farming system can be a suitable alternative for cereal- fallow systems.

Large hydraulic structures and the consequent dangers originated from the break of such structures make the designers apply extreme conditions in their designs. Probable maximum flood (PMF) is one of the design criterions that are widely used in this regard. To calculate PMF, huge data and information such as probable maximum precipitation (PMP), storm duration, rainfall temporal pattern and antecedent soil moisture condition are required. This study aims at calculating PMF, considering the conditions governing ungauged catchments. For this purpose a combination of effective factors affecting PMF, especifically rainfall temporal pattern accompanied with different rainfall systems direction and antecedent soil conditions have been evaluated for the rivers located in the east of Hormozgan Province. The results show that combining the observed average of temporal patterns and random block procedure is a relevant approach for the study area.Also the results show sensitivity of PMF to antecedent soil moisture and not significant response of PMF to the rainfall systems direction.

Resistance to erosion in cohesionless sediment is a result of gravity only, but erosion of cohesive sediment is quite different with cohesionless sediment. Before cohesive sediment can be eroded, the interparticle bond must be broken. Thus, a critical shear stress has to be exceeded before erosion of cohesive sediment can occur.The objectives of this study are. to study erosion process and determinaing the critical shear stress of erosion of cohesive sediment collected from bed material of six Khozestan irrigation channels, including Dasht-Evan, Hendijan, Veis, Shadegan, Khalaf-Abad and Voseyleh. For each sample two different experiment series were performed. At first, the samples were analyzed to determine the physical and chemical properties of each sample, and then the hydraulic experiments were run to determine the critical shear stress of erosion for each sample. Experimental results are shown that shear stress of erosion for this channel varied from 0.96 N/M2 in Shadegan channel, to 2.3 NIM2 in Hendijan channel. The main point of this study is that in the areas that the sediments are cohesive, it is very important to find the critical shear stress of erosion and use it as a correct criterion for designing channels and hydraulic structures.

Iron (Fe) is one of the essential elements for plant growth. Plant analysis for total Fe concentration is frequently used for chlorosis diagnosis because of Fe deficiency. But between total Fe concentration in the plant and chlorosis occurrence there good relation, because chlorotic plants usually contain similar or higher amount of total Fe than the healthy green plants. The objectives of this study were to (1) present a suitable method to determine Fe2+,the fraction of iron involved in the synthesis of chlorophyll processes: and (2) correlation between chlorophyll and Fe2+ in citrus leave. The choice of 1-10 0-phenanthroline (o-ph) as an extractor for Fe2+ was based on its remarkably higher stability constant for Fe2+ than Fe3+. In this study, after sampling and preparing, four concentrations of Phenanthroline solution (1,1.5,2 and 2.5 percentage) on different pH (2,3,4 and 5) with different ratios of plant samples to extractent solution (1:5,1:10,1:15 and 1:20) were tested in the completely randomized design (with threereplicaFion). On the basis of the acquired results Phenanthroline solution (2%), with pH=3, ratio of plant sample to extractor 1:10, time of reading 12hours and reading with Spectrophotometer at 510nm wave length were suggested to determine Fe2+.Chlorophyll and Fe2+ content of both chlorotic and green leaves showed straight and significant correlation.

The goal of this study is the investigation of relationship between rainfall parameters and USLE R factor. In this method, at first, rainfall kinetic energy must be calculated and then its erosivity computed by using maximum 30 minutes rainfall intensity. 3 meteorological stations in Khuzestan province and one station in Kohgiloyeh & Boyer Ahmad and Boushehr provinces were selected and their recorded hyetographs of 13 years were analyzed. For all hyetographs, rainfall erosivity was computed monthly, seasonally and yearly and also corresponding rainfall parameters were extracted.Temporal and spatial variations of rainfall erosivity were studied and relationships between R factor and rainfall characteristics were investigated using regression analysis.Results showed that February, December, March and January and winter has the most erosivity risk. Spatial analysis of rainfall erosivity in the study area showed that Dezful has the maximum erosivity factor. Mean annual erosivity factor of Khuzestan province was computed 36.80 ton.m/ha.h. Regression analysis results showed strong relationship between rainfall amount (mm) and maximum 30 minutes rainfall intensity (cm/h) with R factor.

During two years (2000-2001) by using different methods of sampling such as leaf samples, cylindrical and corrugated yellow sticky traps, seasonal population changes of eggs, nymphs, pupae and adults of the whitefly, Bemisia tabaci (Genn.) (Horn., Aleyrodidae) were studied on cucumber in Ahwaz. The rate of seasonal parasitism of pupae by parasitiod wasp Eretmocerus mundus Mercet (Hym., Aphelinidae) was also recorded. Results showed that total mean of seasonal parasitism rate on upper, middle and lower leaves were 0, 21.39 and 49.83%, respectively for year 2000. But in 2001, on upper, middle and lower leaves it was 0, 13.15 and 27.84%, respectively. Population of whitefly increased gradually in mid May and peaked in July and August, then declined at the end of September and early October and it was rare in November. Study on vertical distribution of this pest showed that eggs and adults settled on the upper and middle third of plant but nymphs and pupae were on the middle and lower.

The biology and life tables of Aphidius rhopalosiphi De S.P. and Praon volucre (Hal.) (Hym: Aphidiidae) were studied at temperatures of 16, 20, 24 and 28°C on Metopolophium dirhodum (Wlk.) (Horn: Aphididae). At the above temperatures developmental periods from egg-to-adult were 22.86, 16.93, 14.25 and 10.39 days for A. rhopalosiphi; 21.62, 17.44, 14.19 and 10.39 days for P. volucre respectively. Temperature thresholds (t) and thermal constants (DD) of A. rhopalosiphi were 6.03°C and 237.03 DD, and those of P. volucre were 5.43°C and 245.16 degree-days. Mean adult longevities of A. rhopalosiphi lasted 11.15, 8.52, 7.20 and 6.50 days, while the adults of P. volucre lived for 13.18, 12.32, 8.80 and 7.05 days at the experimental temperatures. Mean number of eggs at the same conditions were 296.15, 270.22, 168.52 and 69.09 for A. rhopalosiphi; 334.67, 389.82, 263.26 and 123.19 for P. volucre. The intrinsic rates of increase were also 0.200, 0.249, 0.252 and 0.249 for A. rhopalosiphi; 0.183, 0.245, 0.268 and 0.276 for P. volucre respectively.

This study was conducted in order to evaluate and compare specific fuel consumption and specific drawbar energy for two similar powers rating tractors but having different structural features (MF285 and ITM750). Measurements were carried out at actual field condition using standard Nebraska and DECD test cods. A split plot design was used based on complete randomized block.Tests were performed on three different working surfaces (concrete, unplowed and plowed surface). Significant difference was found regarding the effect of different surface on both specific fuel consumption and specific drawbar energy .on each and between two tractors. Results also showed that two tractors had less specific fuel consumption and higher specific drawbar energy on concrete surface and unplowed soil as compared to plowed soil. Results obtained for slip test showed that slip rate in ITM750 were less than MF285 tractor. In overall MF285 had less specific fuel consumption and higher specific drawbar energy than those rating to ITM750 tractor.

Khuzestan province is one of the agricultural poles in Iran. It could be a main center of production and export of agricultural crops, if a suitable planned investment used in the agricultural sector. A delicate attention to the comparative advantage of crops is an important aspect of economic planning. In this research comparative advantage of the main crops such as wheat and barley (irrigated and rainfed), rice, corn, sugar beet, watermelon, tomato, onion, potato and cucumber were studied in 1998-1999. Two groups of indices were used. The first one includes Net Social Profitability (NSP), Domestic Resource Cost (DRC) and Social Cost-Benefit (SCB) ratio. Absolute and relative purchasing power parity (ppp) price used to determine the mentioned indices. The second one includes Efficiency Advantage Index (EFI), Scale Advantage Index (SCI) and Aggregate Advantage Index (AAI). Based on the first group of indices and absolute ppp wheat and barley (irrigated), corn, rice, sugar beet, watermelon, cucumber and tomato had comparative advantage in production and trade. The others had no comparative advantage. In addition to the above crops, potato had a comparative advantage, using relative ppp. Based on the EAI index sugar beet, watermelon, cucumber, potato, onion, tomato and rainfed wheat had comparative advantage in yield. The others had no comparative advantage in yield. SAI was more than one in wheat (irrigated and rainfed). It showed the extent of concentration of wheat in the region relative to that at national average was more. The other crops showed vice versa. AAI was also more than one in the wheat only (irrigated and rainfed). It means that the wheat in the region had a comparative advantage over the national average and vice versa for the others.

Radiation use efficiency (RUE) is a parameter that represents the ability of crop canopy to convert intercepted solar energy to dry matter and can vary with crop type and environment. The rate of radiation use efficiency depends on intercepted photosynthetically active radiation, which is in turn affected by planting pattern or rows cultivation. In order to evaluate the effect of planting pattern on radiation use efficiency and accumulation of dry matter on spring canola, an experiment was conducted in 2003- 2004 at the College of Agriculture, Shahid Chamran University of Ahvaz. A split-plot design, with row spacing as main plots in four levels (15cm, 30cm, 50cm row spacing and 60 cm width ridges with 2 cultivated rows) and 3 cultivars as sub-plots were used with three replications. Seventy plants per m2 were planted constantly in all plots. Results indicated that the effect of planting pattern and cultivar were significant on the radiation use efficiency and intercepted PAR, which are two important parameters in accumulation of dry matter. LAI and PIPARs were also affected by planting pattern and cultivar.Higher rate of accumulation of dry matter and RUE was obtained in 15cm row spacing. Also, between the cultivars, Hyola 401 had a higher rate of accumulation of dry matter and radiation use efficiency.

Aphids of potato plants in Yassuj (cold Region) and Behbahan (hot region) were collected weekly and the seasonal fluctuation of Myzus persicae and its natural enemy, Aphidius matricariae (Hymenoptera: Braconidae) were studied during 2001 and 2002.Migration of this aphid was also studied by using yellow traps in cities of Dogonbedan, Deal and Dehdashat at the locations between Behbahan and Yassuj. In Behbahan region the peak of the population was observed from the end of March to the end of April for wiche then decreased shrply. In Yassuj, two peaks of the population were observed in June and September. Population of M persicae and its parasitoid A. matricariae were almost synchronously increased. This pest does not lay eggs in Behbahan region and it was not observed on their shelters and yellow traps of this region during July and September (hot season). However, it was observed at the locations between Behbahan and Yassuj in November. From these data and observations, the possibility of the annual aphid migration from Yassuj to Behbahan has been discussed.