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Search Results: 1 - 10 of 601552 matches for " A.R. Sepaskhah "
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Rice Optimal Water Use in Different Air Temperatures at Flowering, Nitrogen Rates and Plant Populations
N. Pirmoradian,A.R. Sepaskhah
Pakistan Journal of Biological Sciences , 2007,
Abstract: Present study was conducted to determine optimal amounts of irrigation water for rice in different nitrogen application rates, flowering stage air temperatures, Tf and plant populations. The results indicated that in water limiting conditions in the study area, the optimum irrigation water was affected by crop management (N application rate and plant population) and climatological factors such as Tf. The optimum amounts of water, ww decreased at a higher rate (from 1988 to 1226 mm) by increase in nitrogen application rate (from 0 to 150 kg N ha-1) at higher Tf and plant population. These values were 2692 to 2191 mm of water for 0 to 150 kg N ha-1 for low value of Tf and plant population. Under unfavorable air temperature condition and low plant population, the ww decreased by 19% at 150 kg N ha-1, compared with 0 kg N ha-1. However, under favorable air temperature condition and high plant population, this value was 38%. Therefore, under water limiting conditions in the study area, the higher plant population and favorable climatological factor can highly reduce the optimum irrigation water at higher N application rate. Also, N application rate, plant population, P, air temperature at the flowering stage and applied irrigation water affected the net income. The maximum net income was obtained in Tf = 28.2°C (near optimum air temperature during the flowering stage, 30-33°C), P = 25 hills m-2, 120 kg ha-1 N application and 2138 mm applied irrigation water. The field management factors such as applied irrigation water, nitrogen application rate and plant population can be controlled by field manager and the optimum amounts may be applied. However, the climatological factors are unpredictable, therefore, these factors should be considered in economic analysis of crop yield production and field management.
Estimating and Mapping 24-h Probable Maximum Precipitation by Statistical Methods as Compared to Synoptic Method for Iran
M. Khalaji Pirbalouty,A.R. Sepaskhah
Journal of Science and Technology of Agriculture and Natural Resources , 2002,
Abstract: Probable Maximum Precipitation (PMP) is the maximum possible amount of precipitation which could occur in a gauging station, a region, or in a watershed. Probable maximum precipitation is usually estimated by two general methods: the first is synoptic method in which short period (hourly) meteorological parameters such as dew point, wind speed and air pressure are used. The second is statistical method which is based on the statistical analysis of the 24-h maximum precipitations. In this study, the amount of 24-h PMP was estimated by Hershfield, Bethlahmy and modified Bethlahmy methods using date obtained from meteorological and Ministry of Energy over 15 or more years. The results showed that there exist large differences between statistical and synoptic methods; however, there are rather smaller differences between Bethlahmy and synoptic methods. For modified Bethlahmy method, the results were multiplied by a coefficient of relative humidity. Then the calibrated 24-h PMP values were estimated for all meteorological stations of Iran and a contour map of 24-h PMP for the country was developed. Results showed that a minimum value of 24-h PMP (110 mm) occurred in the central part of country and a maximum amount (260 mm) was found in both south and north parts of Iran.
Rice Yield Modeling under Salinity and Water Stress Conditions using an Appropriate Macroscopic Root Water Uptake Equation
A.R. Sepaskhah,A. Yousofi-Falakdehi
Pakistan Journal of Biological Sciences , 2010,
Abstract: The objectives of this study were to evaluate the application of different macroscopic root water extraction models for prediction of rice grain yield based on data obtained in a greenhouse experiment. In this experiment, the irrigation treatments were continuous flooding (control), intermittent flooding (1- and 2-day intervals) and the salinity levels of irrigation water were 0.6 (control), 1.5, 3, 4.5 and 6 dS m-1 in the year of 2005 and 0.6 (control), 1.5, 2.5, 3.5 and 4.5 dS m-1 in the year of 2006. A local cultivar (Ghasrodashty/Komphiroozy) was planted in pots under greenhouse condition during years 2005 and 2006. Grain yield and evapotranspiration at different treatments were determined. The effect of salinity and water stress on root-water uptake coefficient was determined by FAO and Homaee and Feddes methods and grain yield was predicted by production functions. The FAO method did not predict the interaction effects of salinity and water stress on reduction of water uptake coefficient especially at high salinity levels, while the Homaee and Feddes method predicted properly the effects of salinity and water stress on root-water uptake coefficient. Further, yield was predicted by using the root-water uptake coefficient suggested by FAO and Homaee and Feddes methods. The results indicated that the FAO method did not predict the yield properly especially in continuous flooding and salinity level of more than threshold values, but the Homaee and Feddes method predicted the grain yield with minimum error.
Application of Maize Simulation Model) MSM( for Management of Applied Water and Nitrogen
A Nehzati Pghaleh,SH Zandparsa,A.R Sepaskhah
Journal of Science and Technology of Agriculture and Natural Resources , 2009,
Abstract: Water and fertilizer applications management should be improved due to scarce resources and environmental protection aspects. An analysis of crop yield production and profit maximization was conducted to determine the optimal water and nitrogen allocation. In this study, maize grain yields were predicted for 25 different amounts of irrigation water (350-1700 mm) and 46 different rates of nitrogen application (0-450 kg N/ha) were predicted using MSM (Maize Simulation Model) model. Irrigation water was distributed in growth period based on maize evapotranspiration. 30% and 70% nitrogen fertilization was used 19 and 50 days after planting date, respectively. Based on field operational costs and present market value in Fars province, optimal amounts of applied water and nitrogen were determined in different conditions of maximum yield (Wm and Nm, respectively), maximum profit under limited land (WL and NL, respectively) and maximum profit under limited water (Ww and Nw, respectively). At present market value ( 88 Rls m-3 for water, 1946 Rls kg-1 for nitrogen and 1570 Rls kg-1 for maize grain), the amounts of Wm, WL and Ww were 1336, 1008, 844 mm, respectively, and the amounts of Nm, NL and Nw were 450 kg N ha-1. Because of the low price of nitrogen, the optimum amounts of nitrogen in the analyzed conditions were similar. If the price of nitrogen and water are increased (i.e. 30000 Rls kg-1 N and 1000 Rls m-3 water), the optimum amounts of applied nitrogen and water in the analyzed conditions are changed to 450, 120 and 210 kg N ha-1, and 1336, 899 and 874 mm, respectively.
Every-Other-Furrow Irrigation with Different Irrigation Intervals for Grain Sorghum
A.R. Sepaskhah,M.M. Ghasemi
Pakistan Journal of Biological Sciences , 2008,
Abstract: The water stress effects caused by every-other-furrow irrigation on yield may be alleviated by more frequent irrigation intervals. This research was conducted to determine yield and water use efficiency of grain sorghum under fixed and variable every-other-furrow and every furrow irrigations at different irrigation intervals and shallow and deep water table conditions. Water needs of grain sorghum grown on a fine-texture soil may not be met by using Every-Other Furrow Irrigation (EOFI) especially under 15 and 20 day irrigation intervals. The water stress decreased the grain yield mainly through decreasing the number of grains per cluster and in a lesser degree by decrease in 1000-seed weight. The clay soil with a layer of high clay content at depth of 70-100 cm and shallow water table may restrict the root growth and consequently the longer irrigation intervals with greater soil water stress can cause lower grain yield in these conditions. However, more frequent EOFI using 10 day intervals has produced very similar results with only a marginal reduction in crop yield. Furthermore, there was no statistically significant difference in grain yield between fixed and variable every-other -furrow irrigations. In general, at given applied water, the relative grain yield with respect to the maximum grain yield of sorghum at EOFI was higher than those at EFI. At relative applied water of 85% (mild deficit irrigation), EOFI may be recommended to obtain the same grain yield as that of EFI with full irrigation. Furthermore, it may result in 23% more grain yield than that obtained by EFI with the same amount of applied water as deficit irrigation.
Application of Dew Point in the Prediction of Chilling Stress (Case Study in Jahrom, Fars Province)
M.J. Nazemosadat,A.R. Sepaskhah,S. Mohammady
Journal of Science and Technology of Agriculture and Natural Resources , 2001,
Abstract: In the Islamic Republic of Iran, the occurrence of chilling and freezing stresses have frequently caused great damages to crops and horticultural products. In southern Fars Province (south Iran) the cultivation of citrus orchards is popular and the economic losses due to injury from chilling and freezing stresses may exceed billions of Rials annually. The drop of ambient air temperature (above zero) reduces the ordinary metabolism activity of plants and causes chilling stress. If the temperature drops below zero and remains there for a considerable time, intercellular freezing may occur. This process always kills the cells and provokes tissue injury. In the present study, the possibility of predicting daily minimum temperature using the dew point of a previous day measured at 18:30 was examined. It was found that the prediction of minimum temperature is possible if the dew points are modified on the basis of the air relative humidity. For the episodes that relative humidity varies from 45% to 55%, minimum temperature at day i+1 was found to be almost equal to the dew point on the previous day (day i). For the periods that relative humidity is above (below) this range, the minimum temperature on day i+1 was observed to be greater (lower) than the estimated dew point on day i.
Economic Optimization of Irrigation Water and Nitrogen Fertilizer for Wheat under Variable Seasonal Rainfall (in Maraghe Region)
A. Azizian,A. R. Sepaskhah,A.R. Tavakoli,M. Zibaee
Journal of Science and Technology of Agriculture and Natural Resources , 2007,
Abstract: Irrigation water Scarcity is the major limiting factor for crop production in irrigated farming. Therefore, optimal use of water is influenced by seasonal rainfall especially where the water price is high. Nitrogen also plays a key role in plant nutrition. In this study, wheat grain yield production as a function of applied water (irrigation plus seasonal rainfall) and nitrogen fertilizer (applied plus soil residual nitrogen) using existing data of a field experiment, were used. This function was obtained based on the data from the Maraghah Agricultural Experiment station. Based on this production function, maximum attainable yield can be 8.12 t/ha obtained by the consumption of 1.56 m of water (irrigation plus rainfall) and 193 kg/ha of nitrogen. An economic analysis based on the Iso-Quant curve was conducted to optimize the application rates of production inputs (water and nitrogen). When land is limited, the optimum water and nitrogen use will be based on maximizing net returns from land unit area. The optimal levels of these inputs were determined on the basis of farmer ability for paying the costs of water and nitrogen. Furthermore, optimum amounts of water and nitrogen were determined for different levels of wheat yield. The results indicated that despite low price of irrigation water and nitrogen fertilizer, at present market value, optimum values of water were more variable than those of nitrogen, for its high effective role in wheat production. The results also indicated that when there is no limitation of the source and use of water and nitrogen, and farmers are also able to pay their costs, application of 1.47 m of water (irrigation plus rainfall) and 190 kg/ha of nitrogen (applied plus soil residual) will produce maximum profit per hectare, reaching Rls 12,207,506. When water is limited, optimum levels of water and nitrogen will be based on the maximizing profit per unit of water. In this analysis, the use of 0.556 m of water (irrigation plus rainfall) and 190 kg/ha of nitrogen (applied plus soil residual) resulted in maximum net income per unit of applied water (irrigation plus rainfall) amounting to Rls/m3 1203. This amount of water use, which is 64.4 % lower than its amount under maximum yield condition, resulted in 181 % increase of cultivated area. Graphic expansion path on the isolines of yield showed more dependence of wheat production on water than nitrogen. Therefore, the optimum amounts of nitrogen in the three mentioned conditions are close to each other due to its subsidized price and lower effect on wheat production relative to
An Evaluation of Meteorological Drought in Fars Province
V. Karimi,A.A. Kamkar-Haghighi,A.R. Sepaskhah,D. khalili
Journal of Science and Technology of Agriculture and Natural Resources , 2002,
Abstract: Drought can occur at such times when variables such as rainfall depth, run-off, soil moisture, etc. show a deficiency, or variables such as temperature show an increase, or when ground water level shows a decrease in comparison with the average level. Therefore, drought can be evaluated with respect to agricultural, meteorological, or hydrological variability. In this research, considering the meteorological aspects, the method by Herbst et al., later modified by Mohan and Rangacharia, was applied in drought evaluation in Fars Province, Iran. Monthly rainfall measurements over a period of 21 years for 51 stations obtained from Fars Regional Water Board, were used in the analysis. Maps showing lines of iso-duration and iso-intensity lines were developed for the province. Based on the results, northeast, southeast, south, and southwestern parts of the province have the highest potential for being affected by drought events.
Determination of Optimum Irrigation Depth of Corn in Sprinkler Irrigation
S.H. Zand-Parsa,GH.R. Soltani,A.R. Sepaskhah
Journal of Science and Technology of Agriculture and Natural Resources , 2001,
Abstract: In this study, the optimum irrigation depths for corn grain production under different conditions, i.e. maximum grain yield production and maximum benefit under limited land and water conditions, were determined under sprinkler irrigation in Bajgah (15 km. north of Shiraz). The results showed that, the optimum depth of irrigation for maximum grain yield production was 77.0 cm. Because of low price of irrigation water and sensitivity of corn crop to water deficit, the optimum depths of water were 76.8 and 73.4 cm under land and water limitations, respectively. Therefore, under limited water conditions, only 4.7 percent of the full irrigation water (maximum corn grain production) can be saved for maximum profits.
Post-Aneurysmal Subarachnoid Hemorrhage Vasospasm, Clinical Correlation between the Aneurysm Site and Clinical Vasospasm  [PDF]
Ahmed Ali, Mohamed A.R. Soliman
Open Journal of Modern Neurosurgery (OJMN) , 2018, DOI: 10.4236/ojmn.2018.83025
Abstract: Background: Intracranial vasospasm is a common complication following subarachnoid hemorrhage (SAH). The radiographic vasospasm can reach up to 90% of aneurysmal SAH. Materials and Methods: 139 consecutive patients admitted to Cairo University Hospitals from June 2013 to September 2014 with SAH who had been enrolled in a retrospective controlled study were analyzed retrospectively for the occurrence of vasospasm. The data collected from the charts of Cairo University Hospitals were the patient’s demographics, clinical presentation, aneurysm location, treatment modality, and Glasgow Outcome Scale (GOS) scores. We excluded 24 patients with nonaneurysmal SAH, 3 internal carotid artery (ICA) aneurysms, 7 with multiple aneurysms and 4 patients died before treatment. Results: 72 males and 29 females were included in the study, mean age 53.5 ± 11.5 years. Twelve patients had aneurysms located in the vertebral artery group, 24 had middle cerebral artery aneurysms, 11 had pericallosal aneurysms, and 54 patients had anterior communicating artery (ACoA) complex aneurysms. Radiographic vasospasm occurred in 62.4% with the highest incidence (75.9%) at the ACoA complex group. Symptomatic vasospasm occurred in 48.5% with the highest incidence (63%) at the anterior communicating artery complex aneurysm location. The mean GOS at 6 months follow-up was 4.2. The worse GOS was found in the vertebral artery (VA) aneurysm group with a mean of 3.75. Conclusion: Aneurysms of the anterior communicating artery complex group have a greater risk of both radiographic and clinical vasospasm. Also, the worse 6 months follow-up GOS when an aneurysm was located in the VA group.
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