مجله تحقیقات آب و خاک ایران
سال چهل و چهارم شماره 1 (پیاپی 12، فروردین و اردیبهشت 1392)

Global warming، as a consequence of greenhouse gases accumulation، has exerted significant impacts on biosphere. Methane، a product of reduction processes of organic carbon in anaerobic conditions، is mainly emitted from paddy fields. The aim followed in this research is to evaluate the impact of midseason drainage on methane emission from paddy fields. The research was conducted with three treatments of traditional، surface، and subsurface drainages in a CBD in Sari region. Gas sampling was done weekly following the first week of transplanting till harvest time. Twenty five days after planting، irrigation was ceased for a week، which caused lowering of water table depth to 0. 03، 0. 1، and 0. 7m for traditional، surface، and subsurface drainages، respectively. Methane emission decreased as subsurface water table dropped. Gas emission reduction and the return period to before drainage practice were significantly higher in subsurface drainage. The lowest methane emission occurred two weeks after midseason drainage، as compared with the other two. where emission was reduced by 25، 45 and 315 percent in traditional، surface، and subsurface drainages، respectively. In conclusion، based on the obtained results، water table drawdown، and thus change in anaerobic conditions of root zone to an aerobic one could reduce methane emissions from paddy fields. Abstract Global warming، as a consequence of greenhouse gases accumulation، has exerted significant impacts on biosphere. Methane، a product of reduction processes of organic carbon in anaerobic conditions، is mainly emitted from paddy fields. The aim followed in this research is to evaluate the impact of midseason drainage on methane emission from paddy fields. The research was conducted with three treatments of traditional، surface، and subsurface drainages in a CBD in Sari region. Gas sampling was done weekly following the first week of transplanting till harvest time. Twenty five days after planting، irrigation was ceased for a week، which caused lowering of water table depth to 0. 03، 0. 1، and 0. 7m for traditional، surface، and subsurface drainages، respectively. Methane emission decreased as subsurface water table dropped. Gas emission reduction and the return period to before drainage practice were significantly higher in subsurface drainage. The lowest methane emission occurred two weeks after midseason drainage، as compared with the other two. where emission was reduced by 25، 45 and 315 percent in traditional، surface، and subsurface drainages، respectively. In conclusion، based on the obtained results، water table drawdown، and thus change in anaerobic conditions of root zone to an aerobic one could reduce methane emissions from paddy fields.

Wind speed is one of the major parameters required for an estimation of evapotranspiration and determination of crop water requirements. Hence، several models and methods have been developed for a prediction of this needed climatic variable. In recent years، by development of soft computing tools، such intelligent systems as Artificial Neural Network (ANN) approach have been widely employed in agrometeorological studies. In this study، three types of four layers ANN models of different number of neurons were generated and utilized for a prediction of wind speed، using hourly data of Jiroft Agrometeorological Station، during a 6 month period، April to September، 2010. During these months winds are of higher speeds than those during the rest of the year. Statistical indices of RMSE، ME and EF (Efficiency Factor) were utilized for comparisons and as well for models'' evaluations. The results revealed that an ANN model with 20 neurons in each layer is of the most suitable performance in prediction of wind speed with the respective corresponding values of these indices as 1. 1827، 0. 6947 and 0. 9246.

Flood frequency analysis method is employed to predict the design floods needed for the implementation of hydraulic structures along a river. In this method، the magnitudes of floods are made related to their frequencies using statistical distribution functions. The accuracy of flood estimation depends on some factors including fitting the best probability distribution function along with an estimation of its parameters، period of available data، commonplace errors in measurement and an existence of outlier data. Calibrated hydrological models can also be applied to simulate large flood events. Uncertainties arising from the hydrological modeling، e. g. the modeling assumptions and the uncertainties in inputs and in parameters which are used in the models، are the factors which affect the simulated peak discharges. In the course of this paper، flood frequency analysis was performed using a hydrological modeling approach with the results compared with traditional flood frequency analysis as based on the observed data. The method was applied to Tangrah Watershed. The average rainfall values were initially calculated for different durations and for different return periods. For each rainfall value، a Monte Carlo scheme was employed to consider the uncertainties in rainfall spatial distribution and Antecedent soil Moisture Condition (AMC). Using different combinations of rainfall depths along with their spatial distributions over watershed and also AMC conditions as the inputs of hydrologic model (HEC-HMS)، peak discharges of different return periods were found out. Besides the modeling approach، the best probability distribution was fitted as based on «Anderson–Darling» goodness-of-fit test with flood peak discharges being calculated while using the observed data. It was deduced that the outlier rainfall exerts a significant effect on rainfall – runoff simulation results and this effect increases with increase in return period. For instance، the simulated peak discharge of 50% probability reduces from 1297 to 338 cm2 following an omission of the outlier for the case of 200 year return period of 6hr duration rainfalls. The spatial rainfall distribution and antecedent soil moisture conditions largely influence the peak discharge of different return periods. Also، an observed peak discharge is seen as greater than the results obtained from rainfall simulation. As an example، for a return period of 200 years، hydrologic modeling results are found out as lower than the frequency analysis results by about 30. 4%. An incorrect selection of statistical distribution plays a major role in increasing the difference between the results obtained from these two methods.

An Application of new irrigation methods to increase water use efficiency is essential، due to global water shortages، and as well a consumption of more than 70% of fresh water in the agricultural sector. In this study، the effect of Full Irrigation (FI)، Partial Root-zone Drying (PRD) treatments at two levels (provision of 75% of ET (PRD75) and 55% of ET (PRD55)) vs. Deficit Irrigation treatments at the same levels (75% (DI75) and 55% (DI55)) on yield and yield components of maize under a complete randomized design and under open filed conditions has been investigated during two growing seasons (2010 and 2011). Results revealed that the differences (for some yield components)، between FI and PRD treatments were lower than those observed between FI and DI treatments. Results also indicated that the level of kernel yield، (in PRD75 treatment)، as the most economical constituent of yield trait، was not significantly different from that of FI treatment (the difference being less than 10% for each year). An assessment of soil water content revealed that in PRD75 treatment plant water uptake was more efficient. Therefore، it can be concluded that PRD75 treatment، which resulted in a non-significant decrease of yield and yield components and while resulting in a 25% decrease in water use during the treatment periods (increase in water use efficiency of 16% and 20% during years 2010 and 2011 respectively)، would be a promising water-saving method as in MazandaranProvince.

An ignoring of the customers'' demands constitutes one of the most important problematic issues to be reconsidered in design and operation of irrigation and drainage projects. This، if not properly heeded would cause many inconveniences، specially farmer''s dissatisfaction and as a consequence inefficiency of the constructed water works. Towards this، employment of the patterns of management in successful cooperation could be an effective approach to successful irrigation network management. Among some several management methods، the quality performance application، QFD (Quality Function Deployment) is a notable implement to translate the voice of customer into service providing. An employment of the quality factors would lead the organization to themes that are notable to the customers. In this paper، the state of affairs of operation is investigated through an application of the data of status quo vs. the previous experiences of one of the major irrigation districts in Iran (Ghazvin Irrigation District) while using QFD management method and creating the HOQ (House of Quality). Also through an analysis of the results، some solutions have been proposed and categorized to increase the service quality for water users. The results indicated that application of QFD in management of irrigation and drainage networks، similar to other themes of management، works so useful in quality improvement and as well in service provisions.

Cadmium effects on soil microbial indices and on the interaction of Arbuscular Mycorrhiza Fungi (AMF) and as well on Plant Growth Promoting Rhizobacteria (PGPR) were investigated. The experiments were performed in the framework of a factorial design with levels of cadmium (0، 10، 30 and 100 mg kg-1 soil)، and microbial inoculations (Control، PGPR and AMF) employing Russian Kanapweed as the experimental plant. The experiments were triplicated. The results indicated that soil Cd pollution caused significant decline in plant growth، microbial respiration، Substrate Induced Respiration (SIR)، Carbon Availability Index (CAI)، Microbial Biomass Carbon (MBC) as well as microbial population. In PGPR and AMF treatments، MBC decreased respectively by 57 and 60% as compared with control (Cd0). Cd addition significantly increased qCO2، this index being 22% higher in Cd100 as compared with Cd0. The results indicated that Cd exerts toxic and inhibitory effects on soil microbial activity even at low concentrations. Nonetheless a presence of growth-promoting microorganisms could decline the inhibitory effects of cadmium against plant growth and as well against soil biological activities.

The species of Pseudomonas genus show different levels of resistance to soil''s heavy metals pollution. Since، there exists is a relationship between heavy metal resistance and plasmid profile of bacteria، in this study، plasmid profile of Plant Growth Promoting Rhizobacteria (PGPR) Pseudomonas fluorescence isolates were studied in the presence of cadmium and zinc. The bacteria were initially isolated from soybean rhizosphere and characterized as based on biochemical and biological properties. Then، different concentrations of Zn and Cd، in the H. E. P. E. S and M. E. S solid mediums، were employed to evaluate the resistance of the isolates to these heavy metals. Based on the growth in the presence of Zn and Cd، the isolates were classified into 4 groups. Two isolates taken from each group were exposed to different concentrations of Zn and Cd for a period of 2 months. Then، the isolates were sub-cultured and their plasmids isolated using alkaline lysis procedure. The plasmid profile of isolates indicated that the toxic effect of the cadmium was higher than that of zinc even when at lower concentrations. At concentrations of cadmium، all the isolates lost their plasmids. Three isolates also showed multiple resistances to heavy metals.

In order to investigate the effect of Mn and salinity on some physiological and echophysiological characteristics of pistachio seedlings (cv. Badami-e-Zarand) in sand culture (perlite medium)، a factorial greenhouse experiment was carried out in the framework of a completely randomized design comprised of two factors namely: salinity (Zero، 75، 150، 225 and 300 mM NaCl) and Mn (Zero، 12، 24 and 36 µM MnSO4) in four replications. Results revealed that with an application of 150 mM of the salt، chlo a، chlo b as well as chlo a+b decreased by 12، 16 and 21% in comparison with control while Mn increased chlo a، chlo b as well as chlo a+b as compared with control. Carotenoids were observed to be significantly decreased through salt application but salinity×Mn interactions (at their different Mn levels، and salt application) did not significantly affect carotenoids. Although Superoxide Dismotaze (SOD) activity decreased in stage one (one week after application)، but it significantly increased (>30%) by application of 12 µM of Mn. SOD activity was assessed at the end of the experiment (8 weeks after salinity application). Results indicated that application of 30 mM of NaCl caused an increase of SOD activity، as a result of which the resistance of pistachio seedlings increased against salinity stress. An addition of Mn did not significantly affect the stress. Salinity treatment in each of the three experimental periods exerted a significant effect on Fv/Fm، and while salinity×Mn interaction did not significantly affect this parameter. Thus، it seemes to be finally concluded that Mn increase resistance against salinity in pistachio seedlings (cv. Badami-e-Zarand).

Phytoremediation is a sustainable and environment friendly remediation technique، the potential of which in removal of soil contaminants has been well documented. On the other hand the activity of earthworms helps improve soil conditions. Hence، it is expected that in soil presence of earthworms can enhance the rate of phytoremediation as regards Anthracene. The aim followed in this work was to investigate the effect of a simultaneous application of Eisenia fetida along with Lolium perenne on the remediation of Anthracene pollutant in the soil. The experiments were carried out in the framework of a completely randomized design of seven triplicated treatments. A dose of 500 mg. kg-1 of Anthracene was introduced into the soil. The experiments were continued for a period of 3 months، following which the residual Anthracene was assessed through HPLC. The results revealed that، Eisenia fetida and Lolium prenne could each independently remove 19. 4% vs. 24. 2% of Anthracene، respectively. However، a simultaneous introduction of the earthworm along with an establishment of the plant in soil increased the rate of Anthracene removal up to a complete disappearance.

Rhizosphere is a small zone with chemical، physical، and biological properties different from those of the bulk soil. Information regarding the kinetics of Cu release in the rhizosphere soil is scant. Throughout this research، kinetics of Cu release was investigated in wheat crop rhizosphere vs. non-rhizosphere in 10 calcareous soils by use of rhizobox and in greenhouse conditions. Extracts from rhizosphere and non-rhizosphere soil samples were obtained through successive extraction with DTPA-TEA for 1 to 504 h at 25±1 oC. The available Cu was assessed using chemical extractants (DTPA-TEA، AB-DTPA and Mehlich 3). The results indicated that the level of Cu extracted by chemical extractions from the rhizosphere was lower than those extracted from the nonrhizosphere soils. Also، the level of cumulative released Cu from the rhizosphere was significantly (P<0. 05) lower than that in the non-rhizosphere soils. In the rhizosphere soil، the released Cu ranged from 4. 88 to 10. 66 mg kg-1 while in the non-rhizosphere soils it ranged from 6. 38 to 12. 08 mg kg-1. The results also indicated that parabolic diffusion; first order and power function equations could be employed to describe the kinetics of Cu release. In addition، the rate of Cu release from the rhizosphere soils was also lower than that from the non-rhizosphere soils. In the rhizosphere and non-rhizosphere soils، the characteristics of Cu release were significantly correlated (P<0. 05) with Cu extracted when using chemical extractants. Moreover rate constant coefficient in parabolic diffusion was significantly correlated (P<0. 05) with concentration of Cu in wheat shoot in the rhizosphere area of soils. The results illustrated that characteristics of Cu release in the rhizosphere are different from those in the non-rhizosphere area in soils.