The portion of soil water that is easily absorbed by plant and usually leads to maximum yield is defined as "Readily Available Water" and is shown as p. This is an important parameter for irrigation scheduling and is useful for determining the irrigation depth (d) and frequency (i). The value of p depends upon the plant species, growth period, rate of evapotranspiration (ETo), and the type of soil.In the present study the value of p is determined for grain corn variety single cross 704 in 2 stages of growth periods in Karaj. The first stage was from seed establishment till appearance of the sixth leaf and the second stage was after appearance of this leaf till soft grain.'This research was carried out with a split plot design in the research station of Seed and Plant Improvement Institute in Karaj for a period of 3 years. The main plots were allocated to the treatments of the first stage and the levels of p fraction in this stage were 0.30 and 0.60. The subplots for the second stage were irrigated when p values were 0.30, 0.50 and 0.70. The amount of p was kept 0.8 for the last growth stage (from soft grain till harvesting). These 6 treatments were replicated 4 times. In this study production potential parameters as grain yield, ear yield dry mater and weight of 1000 grains were determined. Also by measuring the amount of irrigation water, soil moisture balance and evapotranpiration, the water utilization and application efficiency were obtained.Analysis of the results show that by doing short irrigation intervals (p=0.30) during the first stage could be had a good crop establishment and vegetative growth period, then enable us to reduce the number of irrigation (longer irrigation intervals) (p=0.70) in later growth stages. The amount of consumptive use of water in this treatment was 7898 m3ha-1 and grain yield's was 12 ton ha-1.

Since the measurement of soil moisture retention curve and its index points like field capacity and permanent wilting point are costly and time-consuming using direct methods, one of the quick and low costly estimation methods of these properties is estimating of those properties with respect to soil basic properties including particle size distribution and organic matter content as well as bulk density. In this study, index points of soil moisture retention curve such as field capacity, permanent wilting point and available water were estimated using MLP type neural network with three activate functions and regressions methodology with respect to soil basic properties. In order to conduct the aforementioned issue, 60 soil samples were collected from the case study, the region of Robatkarim of Karaj city, with an area of 24 ha. Then, the moisture content of the index points of soil moisture retention curve was measured by using the pressure plate. Further soil basic properties including the percentages of clay, sand, bulk density and organic matter as well as lime and the moisture content of the index points were measured using the aforementioned methodology. The results of the investigations showed that the artificial neural networks by sigmoid activate function a network with 6 neurons in the input layer and 10 neurons in the hidden layer as well as 3 neurons in the output layer with Performance indicators R2 and RMSE variations of 0.6197–0.8902 and 1.6846–2.0225, respectively was introduced as the efficient network which had the best performance in estimation of wanted outputs in comparison with another activate functions (method of artificial neural network) and regression method. Percentage of lime according to results of sensitivity analysis is considered as an effective factor in the range of soils texture tested.

One of the most common approaches for farm irrigation management is using soil readily available water and allowable depletion coefficient. The objective of this study was to determine wheat crop response coefficients, critical moisture content, and soil allowable depletion coefficient using a physically based method in three dominant soils under wheat cultivation in Khuzestan province. Treatments included full irrigation and water stress at three levels low, moderate, and high. The highest and lowest values of wheat crop response coefficient were related to silty clay loam (Ky=1.26) and clay loam (Ky=0.96), respectively. Critical soil moisture content was observed in loam soil (0.25 cm3cm-3)> silty clay loam (0.23 cm3cm-3)> clay loam (0.22 cm3cm-3), respectively. Despite the higher critical moisture content in loam, the most soil allowable depletion coefficient was also calculated in loam (0.54). Soil allowable depletion coefficient in silty clay loam and clay loam were 0.44 and 0.42, respectively. The results confirmed the simultaneous effects of soil and plant properties on the availability of soil water for the plants.

In this study, the applicability of 16 series of the developed pedotransfer functions for estimating soil water characteristic curve (SWCC) of 57 soil samples from Mazandaran and East Azarbaijan provinces were examined. Clay, sand and silt percentages, bulk density, soil particle density, organic carbon percentage and depth of sampling were used as readily available soil parameters to estimate the water contents at different matric suctions, while parameters of Brooks and Corey and van Genuchten models were considered as difficult to measure soil parameters. The measured and estimated water contents at the different matric suctions were compared with each other and the pedotransfer functions were evaluated by statistical criteria. The results showed that clay and organic carbon percentages and bulk density had significant correlations with the most of the coefficients of the Brooks and Corey and van Genuchten models. The Campbell and Shiosawa parametric pedotransfer functions with the inputs of clay and sand percentages and bulk density had the amounts of IRMSE=0. 0676 cm3cm-3 and AIC=-3600 (the best model) and Mayr and Jarvis parametric pedotransfer functions with the inputs of clay, silt, sand and organic matter percentages and bulk density had the amounts of IRMSE= 0. 2452 cm3cm-3 and AIC=-1900 (worst model), for the 0 to 15000 cm matric suctions. The results showed that some of international pedotransfer functions could be used to estimate the water content of Iranian soils.

Cation exchange capacity (CEC) is one of the most important soil properties. This property can describe many of soil properties such as soil fertility, specific area and soil water content. Whereas measuring this property is expensive, time-consuming and laboratory tools needed, hence, prediction of CEC using pedotransfer function (PTF) and soil easily properties is very important in soil science studies. So, the objective of the present study was to develop regression pedotransfer functions to predict the CEC using fractal dimension of soil particles. Consequently, 106 soil samples of UNSODA dataset were used. Fractal dimension of soil particle size was calculated and then was used to develop a PTF to predict the soil CEC. Performance of suggested fractal regression was compared the existed functions that use other soil properties as input. Results showed that between all soil easily properties only fractal dimension, % clay and organic matter had a significant coefficient. Suggested fractal regression model (R2= 0. 62, RMSE= 5. 3 and ME= 0. 004) and validation (R2= 0. 59, RMSE= 5. 4 and ME= 0. 054) had a better performance that other functions including suggested function, Bell and Vankulen. With considering of good performance of the suggested fractal function, applying fractal dimension that shows effects of soil texture with a number is approved.

Soil moisture is a function of physical and chemical properties of soils.However, cultivation can change soil moisture availability, by affecting soil properties. In order to evaluate these changes, some soil samples with different textures including clay loam, loam and clay sandy loam were taken from cultivated and noncultivated areas. Then, soil moisture characteristic curves, pore size distribution, particle size distribution, bulk density, organic carbon, calcium carbonate, cation exchange capacity and pH of the soil samples were determined.The results showed that cultivation decreased available water in three soils, but the soil moisture decrease in clay sandy soil was lowest. The cultivation had the lowest influence in changing soil properties such as texture and structure in sandy soils in comparison with other soil textures.

In order to investigate the water uptake limit of maize at different growth stages and scheduling the irrigation time, research was conducted in Imam Khomeini International University as a factorial experiment in a randomized complete block design. In the control treatment, the water requirement of the plant was supplied. But stress treatments included applying water stress (up to the temporary wilting point), at growth stages of 6-leaf, 12-leaf, flowering and seeds doughing. In the period of water stress, stomatal resistance, canopy temperature and meteorological parameters were measured. Based on the response of crop parameters to water stress, the readily available water (RAW) and crop water stress index (CWSI) were determined. The amount of RAW and CWSI at the 6-leaf, 12-leaf, flowering and doughing stages, were calculated equal to 45, 66, 61 and 70 percent and 0. 37, 0. 54, 0. 63, and 0. 47, respectively. The results showed that crop sensitivity to water stress, was different at maize growth stages. The flowering stage of maize was the most sensitive stage to water stress. Therefore, based on crop response, the irrigation time was determined at the time of water stress. Also, by calculating the exact volume of water required and applying variable irrigation intervals during growth stages, the crop water requirement to be supplied and irrigation losses were prevented. Under these conditions, due to the different sensitivity of water absorption at growth stages, it was possible to increase the water productivity.

Increasing the concentration of heavy metals in soil has adverse effects on ecosystem and causes serious damage to humans. Quantifying pollution can be helpful for soil management. In this study, the pollution of heavy metals has been studied and quantified in agricultural lands around some industrial units at Ardabil plain. For this, we selected 9 industrial units and prepared 46 soil samples (0 to 30 cm). Clay, sand and silt percentages, soil organic carbon content, pH and EC were measured. The heavy metals were extracted by digestion using HNO3 and HCl and the concentration of Pb, Zn, Cu and Cd were measured by AAS. Pollution index (Pi), comprehensive pollution index (Pj), ecological risk (Er) and potential ecological risk (RI) were calculated. The average concentration of heavy metals varied from 0.724 mgkg-1 of Cd to 120.58 mg/kg-1 of Cu. All regions had Pi greater than 2 and showed mild pollution except region 4 which had slight pollution. The pollution index of Cd had the highest value among all heavy metals. Pj had the lowest (1.268) and highest (3.636) mean values in regions 2 and 5, respectively. Region 2 had slight pollution class, regions 1, 6 and 7 had a mild class and regions 3, 4, 5, 8 and 9 had a moderate class. The ecological risk of Pb, Zn and Cu was lower than 3.0 in all regions and ErCd was between 120 and 240 for regions 3, 5, 8 and 9 increasing a serious pollution class and greater than 240 indicating a severe pollution class for other areas. All regions were in the serious pollution class according to the RI index. There is a significant difference between the concentration of Pb (sig. 5%) and Zn and Cu (sig.1%) in all regions. It shows differences between regions cannot be related to parent material and human activities have resulted in an increase in metal concentration.

For an accurate irrigation schedule, the daily soil water depletion should be estimated during the crop growth period. Soil water depletion is dependent on daily evapotranspiration. In this research, daily evapotranspiration of S.C 704 maize was measured in mini-lysimeters. Estimation of daily evapotranspiration was done by continuous measurement of soil moisture. Leaves stomatal resistance was measured daily, by AP4 Porometer device. Soil water allowable depletion was determined in four growth stages of initial (C1), development (C2), mid (C3), and late (C4), based on the leaves stomatal resistance response. At each growth stage, when leaves stomatal resistance increased relative to the control crops, readily available water was ending and the time was right for new irrigation. The main variables included growth stage effect on crop evapotranspiration and water depletion coefficient, which was investigated in a completely randomized basic design, with three replications. Regression functions (models) were used for simulation of allowable soil water depletion coefficient (P) based on the daily evapotranspiration (ETc). The models were calibrated by daily data at initial and development stages, and were evaluated by daily data in mid and late stages. The FAO-56 linear model was compared with the models introduced in this research. The results showed that maize ETc (S.C 704) in initial, development, mid, and late stages was in the range of 1.5-4.5, 3.9 -7.1, 1.4 -7.5, and 0.2 -2.1 mm.d-1, respectively. The allowable soil water depletion in the mentioned stages was calculated as 0.45, 0.66, 0.61 and 0.7, respectively. Different sensitivity in crop growth stages caused readily available water limit not to be constant during growth period. The ETc increase caused a decrease in P, and decrease in ETc increased P. Linear, exponential, logarithmic, polynomial, power, and FAO-56 linear functions were investigated. Polynomial function with statistical indices of RMSE=0.00035, NRMSE=0.054, ME=0.0008, CRM=-0/000005, R2=0.999 and EF=0.999, was the optimal model in estimation of P coefficient. The reason for weak performance of FAO-56 model was the constant limit for readily available water and mean ETc rate in the growing season. Therefore, the FAO-56 model was modified. The research result was to estimate the soil water allowable depletion coefficient (by using ETc), without daily measurement of soil moisture. This method will be useful in irrigation scheduling, especially those with short intervals.

Background and Objectives: Soil physical quality plays a major role in soil quality studies and it is considered necessary for sustainable economic production, conservation of the environment and prevention of soil degradation. To determine the soil physical quality indicators and their optimal range, the specific conditions of land use and type of cultivated plant should also be considered. Unlike other land uses in rice paddies, many soil physical, chemical and biological behavior and properties are altered by adding water to the soil and puddling. Hence, it is expected that its limitations will vary with other soils. Therefore, this study was conducted with the aim of reviewing the definition of soil available water index in assessing soil physical quality based on specific conditions of rice plant and land preparation operations. Materials and Methods: 40 soil samples were selected from rice paddies of Guilan province, and soil physical and chemical properties were measured. In addition to Dexter's S index, the soil available water index for plant (PAW) was calculated in three different ways including 1) by assumption of filed capacity at soil suction of 100 cm as upper limit of soil water availability (PAW100), 2) by assumption of filed capacity at soil suction of 330 cm (PAW330), and 3) Redefining of PAW using soil saturation moisture and soil moisture at a suction of 2000 cm as the upper and lower limits of soil available water indicator for rice, respectively (PAWrice). Results: The results showed that assuming the moisture content of the field capacity at the soil suctions of 100 and 330 cm, 65 and 55 percent of the soil samples had a good physical quality, respectively. While redefining of the PAW indicator of rice paddies (PAWrice) confirmed a good to great soil physical quality in 57. 5% of the studied samples. In the studied samples, the use of PAW100 overestimated the amount of soil available water in all soil texture classes. While the use of the PAW330 concept has led to an overestimation of the soil available water value in medium soil textural classes (i. e. silty loam and silty clay loam). However, as the soil texture becomes clayey, the estimated soil available water using PAW330 was less than actual value. The variation of the average values of Dexter S and PAWrice indicators in different soil texture classes was observed by the same trend and as silty loam > silty clay > silty clay loam > clay loam > clay. It should be noted that despite the redefining of the soil available water indicator in rice paddies, the value of Dexter's S index in its optimal range for studied soils was more than 0. 035. Conclusion: Difference in the range of soil water availability in rice paddy fields and its effect on rice yields confirmed the need to redefine soil available water indicator paddy fields. In addition, despite the redefining the soil available water indicator, the results indicated that the Threshold value of 0. 035 for S index is probably suitable to evaluate soil good physical quality based on the soil water availability for plant in rice paddies.