نشریه دانش آب و خاک
سال بیستم شماره 1 (بهار 1389)

In the nature an ecological equilibrium exists between organisms and their environment. Human being for many reasons have disturbed this equilibrium by unwise use of land and, thereby, paving the way for altering its plant coverage. Studying the changing processes of plant coverge during the known periods, their destructive consequences and the ways to improve it, are the main parameters in planning and management of land use. In this research vegetation maps of Bejoshan Chai Basin was prepared in 2 period (1993&2007) by using satellites photos, RS and GIS technique, NDVI index of plant coverage, and detailed field researches. By comparing the two vegetation maps and studying of their changing processes, among the two specified types and 6 classes of vegetation in 1993, it was found that one class has been completely wiped out due to reckless utilization of land, and the other types dispersion area have been drastically decreased due to land use alteration. In all vegetation types, coverage conditions of the range reduced one rank below and the range trend has remained negative due to severe disturbance. Utilization of the range lands by livestock or native animals in both periods was more than 2.5 times of the range capacity and plant coverage density has reduced drastically. It appears that, plant coverage alterations during these periods in the studied areas were faster than other areas with similar climates; and the human intervention was one of the main cause for the native plant coverage destruction in the region.

In order to investigate the effects of deficit irrigation on greenhouse grown cucumber، an experiment was performed in randomized complete design with employing of 4 irrigation treatments and 3 replications at the Agricultural and Natural Resources Research Center of Yazd، Iran. Irrigation with restoring 00% of the soil moisture depletion at each water application as the first treatment (T)، restoring its 80% at the second treatment (T2)، and 60% and 40% at the third (T3) and fourth (T4) treatments، respectively، were considered. The amount of water used in each growth stage was effective on yield. The results showed that there was a direct relation between the amount of irrigation water and yield. Variance analysis of the results showed that the effects of irrigation treatments on growth and yield were significant. The more the volume of irrigation water decreased، the more the yield، water use efficiency، plant height، leaf area and soil water EC decreased، while the chlorophyll amount increased. Maximum water use efficiency، 69. kg m-3، was recorded in T. According to the results، deficit irrigation may not be recommended because of significant reduction in yield due to cucumber sensitivity to water deficit. Saving in water، however، due to efficiency improvement is possible. The results showed that، the amount of water consumption in irrigation system of Yazd greenhouses is about 55- 60% higher than water requirement of the cucumber plants. For sever water shortage in the region، application of deficit irrigation after the crop yield stage to minimize the yield reduction i`s recommended or other deficit irrigation methods may be employed for this purpose.

This research was conducted to study the effects of water deficit stress، nitrogen application rates، and Planting density on economic and biologic water use efficiency and nitrogen use efficiency of oily sunflower at Agricultural Research Center of West-Azerbaijan during 2007-2008. The study consisted of split-split-plot experiments using randomized complete block design with 3 replications. The main factor consisted of irrigation treatment including optimum irrigation، moderate stress and severe stress where irrigation was done after depletion of 50%، 70% and 90% of field capacity، respectively. Three nitrogen levels consisting of 00، 60 and 220 Kg N ha- were considered as sub plots and sub – sub plots consisted of three density of 5. 55، 6. 66 and 8. 33 plant m-2. Severe drought stress reduced the grain yield by 44% compared to the optimum irrigation condition. Grain yield increased with nitrogen application rate. Reducing irrigation intervals improved economical and biological water use efficiencies. Increasing nitrogen application rate improved economical and biological water use efficiencies mainly due to increased grain and biological yields. By increasing nitrogen consumption from 00 to 220 kg/ha، nitrogen use efficiency declined 8/89 kg/ha. Results of this study indicated that nitrogen application rate and density for improving nitrogen and water use efficiency should be adjusted accordingly with the availability of water in the soil.

In this study phosphorous fertilization effect on Zn sorption was investigated. Ten composite samples (each from one soil series) located at Tehran province were collected and mixed with P-fertilizer (KH2PO4) and incubated for two weeks at 25 ºC ±. Added phosphorous levels were 0،00 and 000 mgPkg- and Zn levels ranged from to 60 mgZn L-. Phosphorous did not change the L –type zinc isotherm. Analysis of variance indicated that applying phosphorous to the soils at various levels showed no significant effect (p=0. 56) on zinc sorption. With increasing applied phosphorous، zinc sorption slightly reduced which was not significant. In most of the soil series، phosphorous reduced Freundlich isotherm constants. Phosphorous at low level، namely 00 mg P kg-، increased the two surface Langmuir sorption maxima b + b2. At 000 mg P kg- level، the afore-mentioned constants were reduced.

Many hydrological time series exhibit trending behavior or nonstationarity. An important task of hydrological time series is to determine if there exists any trend in the data، and how to achieve stationarity. Therefore، presenting any method to analyze trend and stationarity will be useful. On the other hand، detecting trend and stationarity in hydrological time series may help us to understand the possible links between hydrological processes and global environmental changes. Data of Shaharchai river in Urmia of West Azarbaijan province of Iran with records from 1973-2008 (31 years) consisting of daily، 10-day، monthly and yearly stramflow rates were employed. Trend analyses with Mann-Kendall and seasonal Kendall test show that there is no trend in annual mean discharge but monthly flow series exhibit significant downward trend in specific months. Stationarity of time series after deseasonalizing were investing at using ADF and KPSS tests. All daily and 10-day steamflow series appear to be significantly stationary and most monthly and annual series are stationary. The results imply that in smaller time scales such as daily and 10-day، trend is more obvious and detrending can help series to be stationary. Nonstationarity may be because of existing seasonality or periodic behavior in streamflow time series. For removing seasonality in order to reach statationarity mathematical models can be used.

In order to evaluate the effects of various crop rotations on soil physical and chemical properties in drylands، three sites with Sahand (Fluventic Haploxerepts)، Rajol Abad (Typic- Calcixerepts)، and Darab (Calcic Haploxerepts) soil series were chosen in Maragheh and Hashtroud، North West of Iran. The treatments including continuous wheat cropping (T1)، wheat–chickpea rotation (T2)، wheat-fallow-wheat-wheat-wheat (T3) and wheat–fallow rotation (T4)، were executed for 5 cropping years from autumn 2003 to summer 2008. Disturbed and undisturbed soil samples from 0-10، 10-20، and 20-40 cm depths were taken at these sites on June 2008. Selected soil physical and chemical properties such as texture، pH، EC، carbonate calcium equivalent (CCE)، wet-aggregate stability (WAS)، bulk density (Db)، organic carbon (OC)، saturation hydraulic conductivity (Ks)، CEC and concentration of available P، K، Mn، Fe، Cu، Zn، and total nitrogen were measured by common laboratory methods. For assessing the moisture content soil samples were taken at four growth stages of wheat. Sampling for assessing the biomass was carried out at harvest (late June 2008). The lowest Ks occurred in T1 and T3 (2. 01 cm. hr-1) and had significant difference with T2 and T4. The highest (4. 79 mg kg-1) and lowest (3. 88 mg kg-1) Fe concentration occurred in T4 and T1، respectively، which significantly (p< 0. 05) differed from those of other treatments. Soil WAS in T4 (71. 54%) became significantly (p<0. 05) greater than those of other treatments. Db in T2 (1. 16 g cm-3) and T4 (1. 15 g cm-3) was significantly (p< 0. 05) lower than T1 (1. 29 g cm-3) and T3 (1. 29 g cm-3). Biological yield in T2 (3. 096 t. ha-1) and T4 (3. 052 t. ha-1) significantly (p< 0. 05) differed from that of T1 (1. 501 t. ha-1) and of T3 (1. 573 t. ha-1). In other measured properties and soil moisture content no significant differences among treatments were appeared. Based on the results، alteration from wheat-fallow or wheat-chickpea rotation to continuous wheat cropping، may gradually degrade soils of the region.

Information is still scarce about exposure to toxic heavy metal in Iran. The attempt was made to study about the prevention effect of humic acid (HA) on Cd absorption by lettuce (Lactusa sativa) A factorial CRD experiment was conducted in hydroponic system with 7 replications. Treatments were: control (no additions)، HA (0، 100 and 1000 mgL-1)، and Cd (0، 2 and 4 mgL-1). Cd uptake along with enzyme activities، superoxide dismutase (SOD)، peroxidase (POD)، proline and biomass of lettuce were measured. A significant increase in SOD and POD activity and proline content were observed with increasing cadmium. Cd content increased together with biomass and organic acid decreased in plants received cadmium. The POD activity increased up to 8 and 53% and SOD to 66 and 106 and proline content to 39 and 119% with 2 and 4 mgL-1 of cadmium respectively. HA did not affect P and proline content. HA decreased the toxic effects of Cd through optimizing SOD، POD activity and fresh weight. Therefore، adding HA to lettuce plants stressed by Cd can alleviate the toxic effect of cadmium.

In this study، simulations of water table fluctuations and nitrate concentration of groundwater were investigated in paddy rice fields which were equipped with controlled drainage system. This research was done in Haraz Technology and Development center in Mazandaran province north of Iran. For simulating the qualitative and quantitative variations of groundwater surface in the drained area، DRAINMOD-N model was applied using calibrated and measured data. It was necessary to calibrate the mineralization، denitrification and dispersivity constants in acceptable range to achieve the best fitness between the measured and simulated data. Therefore، the above constants were obtained 0. 000035، 0. 4 and 5 respectively. The analysis was done in graphical and statistical modes between the measured and simulated data. The statistical comparison was done by the mean bias error (MBE)، model efficiency (EF) and correlation factor (r) indices. indices were achieved 3. 38، 0. 53، and 0. 80 for estimation of the ground water level and 0. 61، 0. 97، and 0. 99 for the estimation of nitrate concentration، respectively. The DRAINMOD-N model maybe used as a powerful model in simulation and management of water pollution in drained area for reducing the environmental risks which may be occurred in paddy rice fields.

This study was carried out to determine water requirement and crop coefficients of garlic (Allium sativum L.) at the climatic station of the Agricultural Faculty of Bu-AliSina University، Hamedan. Daily crop evapotranspiration (ETC) during growing season varied from 0. 1 to 11. 22 mmd-1. Garlic water requirement during growing season under full water availability was 546. 5 mm with a water use efficiency of 2. 85 g/kg of evapotranspiration. Crop coefficients at initial، developing، and final growth stages were 0. 5، 1. 4 and 0. 3، respectively. Based on the models recommended by FAO56، single and dual crop coefficients were also determined. In order to predict garlic evapotranspiration from the climatic data، multiple regression models were applied. Results showed that predicted ETC by employing dual crop coefficients produced smaller difference comparing to the lysimeter measured ETC (RMSE=2. 46 mmd-1). Considering ETC computation procedures and time required، single crop coefficient was much simpler than dual crop coefficient.

Necessity to use envelope (filter) in subsurface drainage systems is one of the important aspect that should be taken into consideration of the beginning of a drainage project. The first indicator of the need for a drain envelope is the percentage of clay in the soil. In this research، permeameter test was used to determine gradient ratio and evaluate the clogging potential and probability of soil particle passage through the drain plate openings in three clay and clay loam soils with 20-40 percent clay SAR 17 – 83، and EC 10 – 100dS/m. Treatments in this experiment were drainage systems with and w/o envelopes. In envelope d system two types of envelopes (granular and fiber) were used. Outflow variation، system permeability، gradient ratio and exit gradient were investigated. The results. showed that the gradient ratio in the system without envelope were greater than one implying a high clogging potential. Nonetheless، soil downfall was occurred when this index was bexceeded. The ratio of outflow from the systems with granular and fiber envelopes to systems w/o envelopes ranged 2. 0-3. 5 and 1. 4-1. 8، respectively. As hydraulic gradient was increased، system hydraulic conductivity decreased with the greater decrease occurring in the system w/o envelope. Resistance against pressure head was also studied with determining hydraulic gradient failure compared to exit gradient value at each gradient head. Results indicated that the without envelope system in soil no 2 and 3 had، receptively the minimum and maximum performance.