JWSS - Journal of Water and Soil Science

---

Land application of sewage sludge is potentially beneficial as an inexpensive nutrient source. However, problem with the use of sludge may exist from high soil concentrations and subsequent uptake of heavy metals by plant and entering of the metals into the human and animal food chains. A field study with lettuce (_{Lactuca sativa} L.) and spinach (Spinacia oleracea L.) was conducted to examine uptake of heavy metals from a sludge amended soil as affected by sludge rate and time of sludge application. Sludge rates were 0, 22.5, and 45 ton/ha. To determine the effect of time on heavy metal uptake, a year after the first plants were harvested, one third of each plot was planted without sludge application and to the rest of each plot sludge was added in the same rates as before. Total and EDTA-extractable Cu, Zn, Pb, and Cd concentrations in soil were determined. The metal concentrations in shoots and roots of the plants were determined separately. Total metal concentrations showed an increasing trend with addition of sewage sludge. Copper, Zn, and Pb EDTA-extractable concentrations in soil and concentrations of these metals in the plants increased significantly with sludge rate. Time of sludge application did not have any significant effect on EDTA-extractable and plant uptake of metals. Sewage sludge also increased the crop yields significantly.

---

The reproductive development stage is a crucial stage in plant life to study the potential of plant yield. Salt tolerance in this stage is desirable to obtain a stable and high yield. A Cynodon dactylon population from America (Cyn3, London Univ. Collection), was suitable to study the detached immature inflorescence in booting stage on liquid medium. The detached inflorescenes were cultured on a liquid medium prepared with or without various supplements of NaCl (0 to 2%) and kinetin concentrations. The sequence of morphological events of spike development in vitro, and the effects of NaCl on spikelet opening, embryo sac growth, fertilization and caryopsis development were studied. The liquid medium supplemented with 10^-7 M kinetin resulted in natural caryopsis development. Supplementing NaCl to the liquid medium had deteriorating effects on the embryo sac development and resulted in the production of abnormal caryopses. The abnormal caryopses were smaller in diameter with a more fragile pericarp. However, a small number of spikelets grown in liquid medium, supplemented with low salt concentration up to 5%, produced normal caryopses and germinated well on soaked filter paper in petri dishes at appropriate conditions.

---

Estimation of flood flow rate represents a method of preventing damages associated with this natural phenomenon. This estimation is one basis in the design of various hydraulic structures, dam spillways, watershed management and flood control. The maximum flow rate of floods is determined by methods such as Creager, Jarvis-Meyer, Cypress-Creek, and rational method. Rational-probability method is an alternative to estimate peak flood rates, and is expressed as:

 Q(y) = F. C(y). I(tc.y).A

 where Q is maximum flood flow rate (m³/sec) y is the return period (year) C(y) is runoff coefficient with a return period of y A is watershed area (km²) I is rainfall intensity (mm/hr) for a specified return period equal to time of concentration of the watershed and F is the conversion factor equal to 0.278 when the above units are used. The basic concept of this method is the same as that in the rational method except that the return period is also included in the equation. Usually, runoff coefficient, C(y), is determined empirically from tables cited in the literature (e.g., Chow et al., 1988). In the present research, data from 18 hydrometry and 6 rainfall-recording stations (located in Caspian - Sea watershed) were analysed using TR software. The Caspian - Sea watershed (which covers eastern and centeral parts of Iran's No. 1 main watershed) has the sub-basins of Atrak, Tadjan, Chalus, Sardabrood, Siahrood, Gorganrood, Safarood, Kesilian, Babolrood and Neka. Runoff coefficients with return periods of 2, 5, 10, 25, 50 and 100 years were determined for these sub-basins and iso-coefficient curves were plotted. The results showed that computed runoff coefficients were less than the values given in the literature because they are determined from observed flow rate and rainfall intensity in each catchment. It was also shown that runoff coefficient increased with increasing return periods. Application of the computed runoff coefficients in three sub-basins of the area resulted in more accurate estimations of maximum flood rate than when the values for these coefficients cited in the literature were applied.

---

Nitrogen is usually the most limiting nutrient for crop production. Manganese deficiency in some calcareous soils of Iran has been reported. The objective of this study was to evaluate the effect of N and Mn on the growth and chemical composition of spinach (Spinacia oleracea L.) under greenhouse conditions. The experiment was conducted in a soil from Chitgar series (Fine-loamy, carbonatic, thermic, Calcixerollic Xerochrepts). Treatments consisted of factorial arrangement of five N rates (0, 50, 100, 200 and 400 mg kg^-1 as NH₄NO₃) and three Mn rates (0, 15 and 30 mg kg^-1 as MnSO₄) in a completely randomized design with four replications. Plants were allowed to grow for 60 days and a hand-held SPAD-502 chlorophyll meter was used to evaluate leaf chlorophyll status at harvest.

 Results showed that N and Mn application increased shoot dry weight, N and Mn concentrations and total uptake, Mn:Fe ratios and chlorophyll readings, significantly. Nitrogen increased concentrations and total uptake of Zn, Cu and total uptake of Fe in plants, but decreased Fe concentration. Addition of Mn decreased Fe and Zn concentrations in spinach but increased total uptake of Fe and Cu. When maximum dry matter was obtained, the chlorophyll meter reading was about 40. A similar study should be carried out under field conditions before the N and Mn fertilizer recommendations for spinach can be made.

---

Nitrogen is usually the most limiting nutrient for crop production. Thus, N fertilizer is widely used by farmers. Moreover, Mn deficiency in some calcareous soils of Iran with high pH has been reported. Therefore, the addition of nitrogen and manganese to achieve the optimum yield is necessary. The objective of this study was to evaluate the effect of N and Mn applications on the availability of some soil nutrients under wheat (Triticum aestivum L.), corn (Zea mays L.), and spinach (Spinacia oleracea L.) plants in greenhouse conditions. In a factorial test, five levels of N (0, 50, 100, 200 and 400 mg/kg soil as NH₄NO₃) and three levels of Mn (0, 15 and 30 mg/kg soil as MnSO₄) in a completely randomized design with four replication were applied. Corn, wheat and spinach varieties were sc₇₀₄ Falat and Spinacea spp., respectively. After eight weeks, total N content and DTPA-extractable Mn, Fe, Zn and Cu of soil were measured.

 The results indicated that N and Mn applications increased Mn-extractable of soil in three cultures but didn’t affect the soil total N. Nitrogen application in corn increased available Fe in soil. Mn application decreased extractable Zn and Cu of soil in wheat and soil extractable Cu in corn.

---

Prediction of watershed responses and simulation of runoff rate and volume are required for design purposes in most water resources projects. For this purpose, different hydrologic methods and events based on continuous hydrologic mathematical models are applied. In this research, a continuous hydrologic model, Stanford Watershed Model-IV (SWM-IV) is used for simulation of annual and monthly volumes and mean daily runoff flow produced in Roodzard representative basin with an area of 896 km2 located in southwest of Iran. The accuracy of the simulation outputs were checked using the sensitivity analysis over reasonable ranges of input sata related to Roodzard watershed. Calibration and verification of the Stanford model were performed using the data of 1976-1977 and those of the four consecutive years (1978- 1981). The output of the SWM-IV model showed that the values of annual and monthly runoff, groundwater, and monthly interflow can be simulated in close agreement and acceptable precision corresponding to the observed data. The model is also capable of combining the hydrologic components of the basin to determine the dominant flow of the study watershed. Actual evapotranspiration and annual runoff coefficients, are two other parameters that have been estimated successfully by the model. However, the coefficient of determination (R²) for the observed and predicted daily flow values ranged from 0.44 to 0.81 for the available data. Therefore, application of the model is recommended for predicting the hydrologic responses of various sizes of watershed in Iran.

---

Side channel spillways have a common usage in conveyance and distribution networks, high dams, water and wastewater treatment plants, and surface drainage networks. A side channel carries spatially varied flow with increasing discharge and their water surface profiles is a main feature in the design process. Usually, the bottom width of the channel is flared in the flow direction and an end sill is also installed at the downstream end to provide a control section and to generate an even water surface profile. In this study, the impact of installing an end sill on the flow characteristics in a non-prismatic side channel is presented. Six distinct longitudinal profiles were clearly observed in each run and the difference between the mid points of the maximum and the minimum profiles of each run was used to evaluate the sill effects on the water surface profile and the energy dissipation. The results indicated that the maximum and the minimum differences are, respectively, equal to critical depth and half of it generated at the channel downstream end. Also, based on an envelope of the data, a method was proposed to determine the maximum potential impact of an end sill that might have on the flow depth, which could also be considered as a guideline in the design process.

---

Azospirillum brasilense is one of the N2-fixing microorganisms which, in symbiosis with the roots of cereals and other graminae, enhances growth and development of plants. In this research, wheat seeds (Triticum aestivum) of three cultivars (Ghods, Roshan and Omid) were inoculated with Azospirillum strains (Sp7 and Dol). Inoculation increased growth parameters and yield of wheat cultivars, the effect being directly dependent on the strain-cultivar combination. Strain Sp7 induced the greatest grain yield, 1000-seed weight, number of grains per spike, root and shoot dry weight in Cv. Roshan, whereas strain Dol stimulated the best effect on these growth parameters in Cv. Ghods. The response of Cv. Omid was lower as compared to the other cultivars. Thus, it may be concluded that compatible strains are necessary for increasing yield and enhancing growth and development of wheat cultivars. These experiments also illustrated similar results regarding the effect of strains on N content of seeds. The observation of nitrogenase activity of Azospirillum strains in the In vitro experiments and the significant increases in N content in some inoculated cultivars support the hypothesis that biological nitrogen fixation by Azospirillum could be responsible for the observed beneficial effects on growth parameters. The comparison of nitrogenase activity of two strains showed that acetylene reduction rate for strain Dol was 1.5 times more than that for strain Sp7. Also strain Dol had more pronounced effects on growth parameters, yield and N content of grains than did strain Sp7. Strain Dol is a local strain whereas strain Sp7 is a Brazilian isolate thus, it may be concluded that the local isolates should be preferred to the foreign bacteria, as they are better suited to traditional cultivars, environment and soil conditions of the region.

---

In Iran, about 75% of national rice production is supplied in Gilan and Mazandaran proviences which have the highest amount of precipitation. Seasonal prediction of rainfall induces significant improvement on yield production and on preventing climate hazardz over these feritle areas. Canonical correlation analysis (CCA) model was carried out evaluates the possibility of the prediction of winter rainfall according to the states of ENSO events. The time series of (southern oscilation index (SOI) and SST (sea surface temperature) over Nino's area (Nino's SST) are used as the predictors, and precipitation in Bandar Anzali and Noushahr are used as the predictands. Emperical orthogonal functions (EOF) were applied for reducing the number of original predictors variables to fewer presumably essential orthogonal variables. Four modes of variations (EOF1, EOF2, EOF3, EOF4) which account for about 92% of total variance in predictors field were retained and the others were considered as noise. Based on the retained EOFs and precipitation time series, the canonical correlation analysis (CCA) was carried out to predict winter precipitation in Noushahr and Bandar Anzali. The results indicated that the predictors considered account for about 45% of total variance in the rainfall time series. The correlation coefficents between the simulated and observed time series were significant at 5% significant level. For 70% of events the anomalies of observed and simulated values have the same sign indicating the ability of the model for reasonable prediction of above or below normal values of precipitation. For rainfall prediction, the role of Nino's SST (Nino4 in particular) was found to be around 10% more influential than SOI. .

---

The influence of the Sea Surface Temperatures (SSTs) on the seasonal precipitation over northern and southwestern parts of Iran was investigated. The warm, cold and base phases of the SSTs were defined and the median of precipitation during each of these phases (R_w, R_c and R_b, respectively) was determined. The magnitude of R_w/R_b, R_c/R_b and R_c/R_w were used as criteria for the assessment of the effects of the alternation of SST phases on seasonal precipitation. The results indicate that in association with cold SST phase, winter rainfall is above median over western and central parts of the coastal region, central and southern parts of Fars Province and all the stations studied in Khozestan Province. On the other hand, the prevalence of warm SST phase has caused about 20% decrease in winter precipitation over the Caspian Sea coastal area and northern parts of both Fars and Khozestan provinces. In association with warm SST phase in winter, precipitation during the following spring was found to be above normal for all the stations studied in the coastal region of the Caspian Sea. The highest sensitivity levels were found in Bandar- Anzali and Astara for which spring precipitation has increased by 80% due to the dominance of warm winter phase. However, the occurrence of boreal cold SST events causes shortage of precipitation in the eastern parts of the coastal areas along the Caspian Sea. A Possible Physical mechanisem justifying the influence of the Caspian Sea SST on the Precipitation variability was introduced. According to this mechanisem, temporal and spatial variability of the Siberian High is forced by the fluctuations in these SSTs.

---

In order to achieve a sustainable management of land resources and to improve land quality, quantitative assessment of effective factors and soil quality indicators are required. The aim of this study was to evaluate variability of selected soil quality attributes in central Zagros affected by such factors as region, land use and management practices. Twelve sites were selected in three provinces including Chahar Mahal va Backtiari (Sabzku, Broujen), Isfahan (Semirum), and Kohkeloyeh va Boyerahmad (Yasodje). Different management practices were considered such as: protected pasture, intensive grazing, controlled grazing, dryland farming, irrigated wheat cultivation, legume-farming practice, protected forest, and degraded forest. Systematic sampling with taking 50 samples of surface soil in each site was carried out. The results of univariate and multivariate analysis revealed that all factors significantly influenced the spatial variability of selected soil quality attributes namely phosphatase activity, microbial respiration, soil organic matter, and total nitrogen. The results obtained from discriminant analysis indicated that all selected soil quality parameters could significantly be used as soil quality indicators in order to recognize and discriminate sustainable agricultural and forestry ecosystems and/or optimal management practices.

---

Manganese toxicity occurs in many agricultural and natural ecosystems under the various soil conditions such as the nature of substrate, acidity, flooding or vicinity to the mining areas. The objective of this work was to study the effects of excess Mn in the growth medium on three important crop species, namely rice (Oryza sativa L. cv. T. Hashemi), maize (Zea mays L. cv. SC.704) and sunflower (Helianthus annuus L. Mehr). Plants were cultured in the hydroponic medium under controlled environmental conditions and treated with 0 (control), 25 50, 75 and 100 µM Mn for 12 days. Dry mass production, the effect of supplemental Mg and Ca on the toxicity expression, root respiration and K⁺ leakage from shoot and root tissues were studied under the Mn treatments. In order to study the effect of light intensity on the expression of toxicity symptoms, plants were cultured under the different light conditions, thereafter their growth and metal uptake and transport were studied. Sunflower plants treated with the 50 µM Mn and higher, showed dark-brown spots associated with the trichomes on the leaves and petioles. Maize plants developed interveinal chlorosis and any visual leaf symptoms was observed in rice. In all of the studied species, a great portion of the absorbed Mn was translocated into shoot, the highest transport was observed in sunflower and the lowest in maize. No significant correlation was observed between the expression of Mn toxicity and the accumulation rate of Mn. Growing under the low light intensity, in addition to the lowering biomass production, increased or decreased the toxicity effect depending on species. Mn-toxicity-induced root respiration was not associated with the differential response of species to Mn toxicity. In contrast the change of K⁺ leakage from shoot and root tissues was well correlated with the toxicity response of tested plants.

---

To obtain a suitable explant and efficient culture medium for plant regeneration in spinach, two cultivars of Melody and Karaj local seedlings were chosen. A hypocotyl and cotyledon segments as well as shoot tip explants were dissected from seedlings. The explants were then cultured on MS medium supplemented with IAA, GA₃, NAA, and BAP and their response to this media was studied. A completely randomized design with different replicates was used to conduct the experiments. Callus was formed at the base of the hypocotyl explants on the medium containing 15 mg.l^-1 IAA, and 3.4 mg.l^-1 GA₃. Calli capable of regeneration was obtained after subculturing on the medium containing 2 mg.l^-1 IAA, and 3.4 mg.l^-1 GA₃ at the rate of 38 percent. The vitrified plantlets were abnormally glassy, and translucent which might have high water content. It was a physiological disorder which was overcome when an improved agar medium raising to 9 gl^-1 was used. Callus has been obtained only from the hypocotyl explants, while regeneration has been obtained from shoot tip cultured on the medium containing 0.02 mgl^-1 BAP at the rate of 80 percent.

---

Orumiyeh Lake basin is one of the important regions in Iran from water resources and environment standpoints. In this basin, substantial part of the annual precipitation occurrs in spring, winter, and fall seasons. Due to semi-arid climate of the basin, rainfall forecasting is an important issue for proper water resources planning and management, particularly in drought years. On the other hand, investigations around the world show that there is a good conection between climatic signals and the amount of precipitation. In this paper, the relationship between climatic signals and seasonal rainfall was investigated in Orumiyeh Lake basin. For this purpose, monthly SPI (Standard Precipitation Index) was calculated and used along with six climatic signals including SOI (Southern Oscillation Index), PDO (Pacific Decadal Oscillation), PNA (Pacific North America), NAO (North Atlantic Oscillation), NINO3.4 and, NOI (North Oscillation Index). A new method employing the negative and positive phases of signals was proposed and tested to distinguish the relationship between the climatic signals and the individual stations rainfall in the basin. Furthermore, it was found that using joint signals substantially improves the precision of the forcast rainfalls. The results showed that fall and winter rainfalls had the highest correlatetions with SOI and NAO, respectively. Therefore, it would be possible to forecast the basin rainfall using climatic signals of the previous seasons.

---

Limitation of suitable water resources is the most important problem of agriculture in Iran. Considering the condition of shallow and saline groundwater in many parts of Iran, and relative resistance of safflower to salinity, it is necessary to study the contribution of groundwater to water consumption of safflower. In this research, the effects of different water table depths and salinity of groundwater on contribution of groundwater to evapotranspiration of safflower were studied. The treatments were four levels of water table depth (50, 70, 90, and 120 cm), two levels of groundwater salinity (EC of 0.6, and 10 dSm^-1 ), and two irrigation regimes (irrigation with a depth of water equal to 75 percent of evaporation from water surface and frequency of 5 days, and no irrigation). The experiment was performed in a randomized complete block design with treatment combinations arranged in factorial manner and three replications. For fixing the water table in the pots (PVC pipe 200 mm in diameter and 120 cm high), a special equipment was built on the principle of Marriot bottle that was able to measure the contribution of groundwater to evapotranspiration of the plants. Results showed that salinity of groundwater, irrigation regime, and their interactions have significant effects on evapotranspiration of safflower. In addition, effects of water table depth, salinity of groundwater, irrigation regime, interaction of salinity and water table depth, interaction of water table depth and irrigation regime, and interaction of water table depth, salinity, and irrigation regime on evaporation from soil surface were significant. The ratio of contribution of groundwater to plant water consumption and evapotranspiration was in the range of 52.5 and 54.9% for saline groundwater and 81.7 to 82.7% for fresh groundwater. The ratio of evaporation from soil surface and evapotranspiration was in the range of 4.5 to 53.6% for different treatments. In all treatments of groundwater depths, irrigation treatment significantly decreased evapotranspiration, but no significant change in evapotranspiration was observed in irrigated and no irrigated treatments. Maximum amount of evapotranspiration (251 cm) occurred in the 50 cm depth of groundwater with salinity of 0.6 dS/m under irrigated condition, and minimum amount (43.9 cm) occurred in the 90 cm depth to groundwater with salinity of 10 dS/m under no irrigation condition. Generally, salinity of groundwater caused significant decrease in evapotranspiration, evaporation from soil surface, transpiration, and contribution of groundwater to evapotranspiration.

---

During years 2000 and 2001, biology and population changes of two- spotted spider mite (T. urticae) was studied on five bean cultivars of two species at 25±1ºC temp., 45±4% RH and 15: 9 (L:D) photoperiod, using leaf disks made from 2-, 6- leaf and flowering stages of the plants. The mite mass rearing was carried out on tomato plants under the same environmental conditions and the effects of feeding on 4 cultivars of phaseolus vulgaris namely Chiti Var. Zanjan, Picher, Sunray, Contender and Vigna unguiculata, Var. Kameran as host plants. Biological features as fertility, percentage of egg hatch, duration of embryonic and larval development, percentage were also Studied of lraval mortality, duration of nymphal stages, developmental period from lava to pre- oviposition stages, oviposition period, adult mite longevity, number of progenies, their percentage mortalities, and sex ratios were determined. The results indicated that the two cultivars Chiti Var: Zanjan, Contender, and species Vigna unguiculatat Var. Kameran at 2- leaf stage appeared to be suitable hosts causing higher egg production and hatches, lower embryonic and larval developmental time and lower rate of larval mortality, lower nymphal developmental period, lower duration from larval stage to preoviposition, extended oviposition period and higher adult longevity. In contrast, the cultivars, Sunray and Picker were shown to be unsuitable hosts. Regarding 6- leaf stage, the cultivar Contender and Vigna unguiculatat, were considered as suitable hosts in relation to embryonic developmental time, number of larvae, duration of larval stage, and rate of mortalities, nymphal developmental time and duration from larval stage to pre- oviposition, extended oviposition stage, sex ratio and adult longevity. But the cultivars Chiti, Picker and Sunray appeared to be unsuitable hosts. In relation to the number of eggs and percentage of egg hatch, number of larvae and nymphs, nymphal mortality rates and sex ratio, the cultivars, Picker and Sunray were considered as suitable hosts at their flowering stage but Vigna unguiculatat and Contender were identified as unsuitable ones.

---

  A labyrinth spillway is an overflow spillway to regulate and control flow in canals, rivers and reservoirs. The main hypothesis for the development of such a spillway is to increase the discharge per unit width of structure for a given headwater. This type of structure is often an efficient alternative to a gated-spillway type where either the increase of the flood-passage capacity or the control of the water surface upstream is concerned. This study was aimed to investigate the hydraulic performance of labyrinth spillways of general trapezoidal planform with simple curved apexes. In the experimental work, twelve spillway models with double cycles were considered using three different curved apexes (R/w= 0.15, 0.2, 0.25), each with four different crest heights (w/P= 1.5, 2, 3, 4). Based on the cited recommendations, the length magnification was set to a constant ratio of (l/w= 3) the crest shape was to be of a semi-circular form with simple radius (r= 15 mm) and the spillway walls were vertical with the thickness of T= 2r. An intensive experiment was carried out over a wide range of flows, providing 720 flow data ranging from free flow to submerged flow conditions. 1D flow equation was presented using combined mathematical and dimensional analysis. A coefficient of discharge, C_d, was introduced to represent the influence of the effective geometric and hydraulic parameters on the flow capacity over the spillway. Modular limit was also controlled to see whether the flow over the spillway would be submerged. The results of the study indicate that the modified curved planform of the spillway apexes with consistent divergence in the downstream channel introduces a significant improvement in the flow efficiency over the labyrinth spillways. Spillways with narrower curved apexes (i.e. R/w≤ 0.2), and with the vertical-aspect ratio of (2≤w/P<3) provide more stable and higher hydraulic performance than any other labyrinth planforms over a wide range of flows (i.e. 0.10/P<0.6). In terms of the flow capacity, the proposed spillway model is shown to be more efficient than other zig-zag planforms (i.e. triangular and trapezoidal shapes) with an identical crest length.

---

Optimal crop water requirement is needed for precise irrigation scheduling. Prediction of crop water requirements is a basic factor to achieve this goal. In this study, maize potential evapotranspiration (ET_p) was prediced by maize simulation model (MSM). Then, it was evaluated and validated using experimental field data obtained in Agricultural Research Station of Shiraz University (Bajghah, Fars province) during 2003 and 2004. Comparison of measured volumetric soil water content with predicted values by MSM model in 2003 and 2004 indicated that this subroutine (prediction of maize evapotranspiration) did not need modification. Also, daily potential evapotranspiration of maize was estimated by using Penman-Monteith equation considering single and dual crop coefficients. Comparison between the results of predicted ET_p by MSM model, calculated ET_p by Penman-Monteith, and measured irrigation water and soil water content indicated that the prediction of ET_p by MSM model was satisfactory. Model prediction of seasonal ET_p, potential transpiration (T_p) and soil evaporation (E) were 831, 536 and 329 mm, respectively, in 2003, and 832, 518 and 314 mm, respectively, in 2004. The values of ET_p, T_p and E calculated by Penman-Monteith method using dual crop coefficients were 693, 489 and 205 mm, respectively, in 2003, and 700, 487 and 213, respectively in 2004. Maximum rate of predicted potential ET_p, Tp and E were 11.1, 8.2 and 5.1 mm d^-1, respectively in 2003 and 13.0, 9.0 and 4.0 mm d^-1, respectively in 2004. The values of calculated seasonal ET_p by Penman-Monteith method using single crop coefficient were 615 and 632 mm in 2003, and 2004, respectively. Comparison between the results of predicted ET_p by MSM model, calculated ET_p by Penman-Monteith equation with single and dual crop coefficients (FAO-56) and measured values of irrigation water and soil water contents of root depth indicated that FAO-56 methods underestimated the ET_p.

---

The present research was conducted to find the influence of some topographic factors on distribution of large-leaved lime (Tilia platyphyllos Scop.) and its natural regeneration characteristics in "Vaz" forest (northern Iran). After identification of site and preparation of topography map, selective sampling method was carried out for tree inventory in plots. The sample plots were circular in 1000-m² areas with at least 2-3 dominant lime trees in each. In the plots, altitude, slope gradient, direction, forest storey, tree type and natural regeneration were investigated. Results indicate that in this habitat the average diameter at breast height and height of Tilia platyphyllos is 36.9 cm and 23 m, respectively. Tilia platyphyllos prefers 1200-1400 m altitude, 75-100% slope gradient and northeastern to eastern directions and benefits from denser trees in these environments. It consists of some tree types together with Fagus orientalis, Carpinus betulus and Parrotia persica, whereas the dominant type is Tilia platyphyllos-Fagus orientalis. In most of tree types, lime occurs in the upperstorey. Natural regeneration of lime is often observed as sprout (coppice shoot).

---

  Citrus stubborn disease is caused by the helical mollicute Spiroplasma citri. The pathogen is naturally transmitted by sap feeding leafhopper vectors. In the present study attempts were made to detect S. citri in presumptive vectors. Leafhoppers were collected from various wild and cultivated plants in citrus growing areas in Jirfot. Fifteen leafhopper species were identified and 12 species were analyzed for the possibility of carrying S. citri with an antiserum prepared against a citrus strain of S. citri by indirect ELISA. S. citri was detected in leafhopper species by ELISA in Austroagallia sinuata, Psammotettix alienus, Circulifer haematoceps, Orosius albicinctus and Psamotettix striatus. However, S. citri was isolated only from the last three leafhopper species in LD10 medium. These leafhoppers were primarily captured from sesame fields. Therefore, these potential vectors and sesame farms may play a key role in the epidemiology of S. citri in the surveyed area.