مجله تحقیقات آب و خاک ایران
سال چهل و چهارم شماره 2 (پیاپی 13، امرداد و شهریور 1392)

Assessment of agricultural drought risk at critical times before and during the growing season can provide sufficient time to policy makers and farmers to implement appropriate strategies to reduce the potential of risk. The purpose of this study is to develop a statistical model to estimate the quality of agricultural drought risk for rainfed barley crop (before planting and during growing season) in East Azarbaijan province، Iran. Model input variables include the amounts of Weekly Standardized Precipitation Index (SPI) in various time windows and the only output variable is the risk of crop yield (with two groups: high risk and low risk). A multivariate technique was used for modeling the relationship between input and output variables during different growth stages. The results showed that the calibrated model can be used to assess real-time agricultural drought risk for barley crop at pre-planting and during crop growth stages by retaining previous، and adding current WSPI data as the crop pass through the various development stages. The accuracy of risk assessment increases as barley crop develops. Model validation revealed that the most appropriate time to asses drought risk for barley crop in the area of study is the flowering stage، but the results for tillering stage is also suitable.

For performance improvement and higher flexibility in irrigation networks، application of automatic systems are expanding and evaluation of their success for achieving the objectives is necessary. Considering various equipment، algorithms، and their applications in different levels of irrigation networks، performance of automatic systems is a function of the performance of all elements، therefore development of performance evaluation model which takes into account all required aspect is necessary. In this study for performance evaluation automatic systems in irrigation networks، INACSEM model is developed، using classical method in terms of technical and general aspects. Technical aspect includes equipment، software and control structures، and general aspect consists of management، social، economic and environmental aspects. Result of the model for automatic monitoring systems (Arian، 2000) in Aghili canal of Gotvand irrigation network shows that performance of the system is 63% with 80% credibility. The result show that the developed model is a suitable tool for performance evaluation of automatic systems used in irrigation networks، which considers all necessary aspects of performance evaluation of automatic systems، and shows the problems of each element of the system.

In agricultural meteorology، the growing season is the period of each year when crops can be grown with the view of thermal condition. This period is generally between the first and last frost dates in autumn and spring in which temperature is above a specific threshold. There are two other definitions using a 50C threshold. One of the methods to study future climate is using the general circulation models (GCMs)، but these models have low temporal and spatial resolution and they can’t show local changes. In this study، statistical model LARS-WG has been used for downscaling GCMs outputs under A2 and B1 emission scenario conditions in several climatic regions of Iran during period of 1961-2004 for estimation of growing season length (GSL). The results showed that growing season with 00C threshold under the two scenarios will increase during 2020 to 2050 in Mashhad، Tehran and Rash stations and will decrease Kerman and Gorgan and Tabriz in comparison with their past climates. GSL with 50C threshold under two scenarios will increase in all stations except for Shiraz station. In general GSL for all three definitions under both scenarios would increase in Mashhad، Rasht and Tehran. In case of Esfahan، no significant trend was observed using 00C threshold and B1 scenario، and increasing trend for rest of the conditions.

Among the most common types of problematic soils، are probably expansive soils. One of the modern methods of strengthening and improving the soil in place is the use of electro-osmotic improving. This paper presents a design apparatus suitable for electro-osmotic treatment. A soil sample with high expansive potential is compacted and the effect of electro-osmotic treatment under different voltages of 12، 24 and 48 with the direct current (DC) and improvement periods of 1، 2، 7 and 28 days are studied. The results show that electro-osmotic treatment intensively reduced the expansive potential of soil (ie. 51-85%0) around of the anode pole. The chemical results show that PH of soil around the anode is reduced (27-46%). Also، the electrochemical change due to electro-osmotic treatment alters the soil properties and increases compression strength of soil up to eight times of initial strength. The increase of the compressive strength of the bed irrigation channels by electro-osmotic is enhanced the channels additional safety and stability.

In this study، the occurrence and intensity of soil water repellency was studied in three sites under Pinus teada، Petrocarya fraxinifolia and Sombucus ebulus in Talesh township in west part of Guilan. Seventy nine undisturbed soil samples (0–5 cm) were collected to determine water repellency and water-soil contact angle in dry season. Soil water repellency was measured using the water drop penetration time test (WDPT) and molarity of ethanol droplet (MED). The significant and positive relationship (r= 0. 77) was determined between MED and WDPT Test. Water-soil contact angles were calculated greater than 90 using MED test in water repellent samples. The soil contact angles raised with increase water repellency، As in samples with WDPT 5820_6000 s، contact angle were calculated between 108. 8 to 109. The average water repellency was measured using WDPT and MED tests in site 3 were significantly higher than two other sites. In this process، was observed in calculated water-soil contact angles also. In this research the high coefficients determined between Log WDPT، MED and contact angle with organic matter content (with r= 0. 8، 0. 83 and 0. 77 respectively). The correlations of these parameter (Log WDPT، MED and contact angle) with pH were negative and meaningful (with r -0. 78، -0. 69 and -0. 72 respectively). The correlations between hydrophobicity (Log WDPT، MED) and soil contact angle with sand percentage were positive and these correlations with clay percentage were negative. However، the relations between soil texture parameters and hydrophobicity were weaker than the correlations of organic matter content and soil acidity with hydrophobicity. Results show that soil organic matter content، texture، and acidity are important factors affecting the occurrence and persistence of water repellency in soils of the studied region.

In response to the demand for soil spatial information، the acquisition of digital auxiliary data and matching it to field soil observation is increasing. With the harmonization of these data sets، through computer based methods، so-called Digital soil Maps are increasingly being found to be as reliable as traditional soil mapping practices but without the prohibitive costs. Therefore، at present research، we have attempted to develop decision tree (DTA) and artificial neural network (ANN) models for spatial prediction of soil taxonomic classes in an area covering 720 km2 located in arid region of central Iran where traditional soil survey methods are very difficult to undertake. In this area، using the conditioned Latin hypercube sampling method، location of 187 soil profiles were selected، which then described، sampled، analyzed and allocated in taxonomic classes according to soil taxonomy of America. Auxiliary data used in this study to represent predictive soil forming factors were terrain attributes، Landsat 7 ETM+ data and a geomorphologic surfaces map. Results showed that the DTA had the higher accuracy than ANN about 7% for prediction of soil classes. Determination of coefficient (R2)، overall accuracy and kappa coefficient calculated for two models were 0. 34، 0. 46، 48%، 52%، 0. 13 and 0. 25، respectively. Our results showed some auxiliary variables had more influence on predictive soil class model which included: wetness index، geomorphology map and multi-resolution index of valley bottom flatness. In general، results showed that decision tree models had higher accuracy than ANN models and also their results are more convenient for interpretation. Therefore، it is suggested using of decision tree models for spatial prediction of soil properties (category and continuous soil data) in future studies.

Rice (Oryza sativa L.) is one of the strategic crops in Iran and water shortage is the most important abiotic stresses limiting its yield. In this research the effect of variety، water regime، nitrogen (N) and phosphorus (P) levels on N، P and K uptake was studied under greenhouse conditions. The experiment design was factorial based on randomized complete blocks with three replications. The factors included two varieties of rice (Hashemi and Ali Kazemi)، two water regimes (flooded and periodic saturation)، three nitrogen levels as urea (0، 75، 150 mg kg-1) and three P levels as mono calcium phosphate (0، 25، 50 mg kg-1). After 90 day growth period، plants were harvested and total content and concentration of N، P and K in shoot and root were determined. The results showed that K concentrations in shoot and root، K content in shoot and N translocation factor in Ali Kazemi were greater than Hashemi variety. But P concentration in root، P translocation factor and P content of the root in Hashemi became higher in Ali Kazemi variety. P concentration of shoot and root، K concentration of shoot، N content of shoot، P and K contents of the shoot and root under flooded conditions were significantly (P<0. 01) higher under periodic saturation conditions. Interaction between N and P produced significant effect on N and K concentrations of shoot and root، P concentration of root، N and P translocation factors، N، P and K contents of the shoot and root.

This study was conducted to investigate the effects of slope gradient and land use changes on aggregate stability and soil organic carbon (SOC) pools in aggregate size fractions in western Iran. Three land uses in the study area including natural forest (NF)، disturbed forest (DF) and cultivated land (CL) and three slope gradients (0-10 %، S1، 10-30 %، S2، and 30-50%، S3) were selected for soil sampling. A total of 99 soil samples were taken from the 0-10 cm surface layer in the whole studied hilly region. The results showed that forest disturbances and continuous cultivation after deforestation significantly decreased water stable aggregates percentage (WSA)، mean weight diameter (MWD) and geometric mean diameter (GMD) values in three selected slope classes. The highest percent of macro-aggregates (2. 00-4. 75mm) and meso-aggregates (0. 25–2. 00 mm) were found in the lower slope (S1) induced by higher C stocks in this position. The highest percentage of macro-aggregates was observed in the natural forest soil and that of micro-aggregates (0. 053-0. 25 mm) was observed in the cultivated and disturbed forest soils. There were significant differences of SOC among three land uses for macro- aggregates، but no significant differences were identified for meso- and micro-aggregates between disturbed forest and cultivated soils. The result also revealed that those significant differences among gradient slopes according to SOC and TN in aggregates for three land uses and the lowest was observed in the steep slopes (S3) with highest soil erosion rate. The relative distribution of total nitrogen among the aggregate fractions and C/N ratios were similar to the SOC distribution.

This study was evaluated the effect of different preparation methods of vermiwash on certain wheat yield and growth indices and Fe، Zn and P uptake in wheat grain. A greenhouse experiment was conducted in a factorial randomize complete block design (RCBD) with four replicates. The treatments were included 1) vermiwash (15 levels) and 2) consumption methods (two levels، sterile and nonsterile). Vermiwash was prepared using three types of substrate، namely، 1-Mature vermicompost (V) 2- Immature vermicompost (IV) 3- Composter Worm (CW. Aqueous extracts of VC and earthworm were obtained using high-purity water (pH 9، 5. 0 and 7. 0)، DTPA full strength and DTPA 1/3 strength. Vermiwash sprayed on plants. Results illustrated that vermiwash application increased seed yield، hundred seed weights، number seed in panicle، plant height and shoot dry weight in comparison with the control treatment. Vermiwash extracted from mature and immature vermicompost by DTPA had the most effect on shoot dry weight، seed yield and hundred seed weights. Sterilization hadn''t significant effect on yield and growth indices and caused just significant increase seed yield. Application of vermiwash increased Fe and Zn uptake in grain wheat in comparison with control treatment.

A greenhouse experiment performed as completely randomized design in a factorial arrangement to evaluate the effect of Arbuscular Mycorrhizal Fungi (AMF) on growth and root antioxidant enzymes changes of two citrus rootstocks (Sour orange and Rough lemon). The factors were mycorrhizal treatments at two levels (inoculation with Glomus mosseae and control) and irrigation treatments in 4 irrigation intervals 2, 4, 6 and 8 days. As water deficit stress increased, shoot and root dry weights decreased, catalase (CAT), superoxide dismutase (SOD) and ascorbate peroxidase (APX) activities in roots increased. Shoot and root dry weights, APX, CAT and SOD activities in roots of two citrus rootstocks were higher in mycorrhizal than non mycorrhizal of two citrus rootstocks under well-watered and water deficit stress conditions. In mycorrhizal plants, root colonization decreased up to 40%, as water deficit stress levels increased.