مجله تحقیقات آب و خاک ایران
سال چهل و دوم شماره 2 (پیاپی 7، بهمن و اسفند 1390)

The release rate of potassium (K) from micaceous minerals plays a significant role in supplying K to plants. The objective of this study was to determine the most appropriate kinetic equation to describe potassium release from micaceous minerals as influenced by organic acids. Muscovite and phlogopite were made to react with 0, 500, 2000 and 4000 μM solutions of oxalic, citric and malic acids for six different periods of time with the level of released K determined through a flame photometer. Pseudo second order, Elovich, power function and parabolic diffusion models were tested to describe the K release data. The rate of K release varied with the type of organic acids and also with the kind of mica. The kinetics of K release from minerals through an application of oxalic acid was best described by a parabolic diffusion model. On the other hand, Elovich and power function models could describe potassium release from phlogopite when citric and malic acid treatments applied.

In this study, the effect of hole mulching application of Zn and Mn on acacia, elm, and plane nutrition was examined in the green spaces of Isfahan. Three different sites were chosen in a randomized complete block design using six treatments of: 1. cow manure compost, 2. cow manure vermicompost, 3. urban waste compost, 4. urban waste vermicompost, 5. dug hole refilled with the same soil coming out of the hole, and 6. blank with no hole dug. Zn, Mn and P elements contents in young leaves were determined several times after the set out of the experiment. Results showed that hole digging could improve the nutrition condition in elm and in acacia trees. In plane trees, treatments did not show significant effects on concentration of Zn and Mn microelements. Cow manure vermicompost and cow manure compost increased Zn and Mn concentration in tree leaves more than the other treatments did. Also, no mulch treatment (digging and refilling the hole with the same soil) showed some positive effects on the element concentrations in leaves, however, this was not as effective as when organic amendments added to the soil refilling the holes.

Field experiments were conducted at the Rice Research Institute (Mazandaran Province) using randomized complete block designs in two fields of different levels of organic carbon (low and medium) during two cropping years. The treatments were repeated in three replicates and while seven nitrogen levels (Urea-N input) 0, 23, 46, 69, 92, 115 and 138 Kg N per ha employed. Results indicated that optimum grain yield was obtained from N92 (92 Kg N ha-1) in the low organic carbon containing field and from N115 (115 Kg N ha-1) in the medium organic carbon carrying field. Agronomic, recovery and physiological efficiency of the treatments with optimum grain yield in low vs. medium organic carbon fields were determined as 14.5 vs. 19.3 Kg of grain per Kg applied nitrogen, 37.6 vs. 35.9 percentage wise, and 36.8 vs. 50 Kg grain per Kg of absorbed nitrogen, respectively. The results revealed that the use of different levels of soil organic matter couldn’t be used as a suitable index for nitrogen fertilizer recommendation in wetland rice.

Soil organic matter is an indicator of soil, agriculture and environmental quality, playing important roles in soil strength and sound environmental functions. Size and chemical fractionation of soil organic matter are long-standing approaches in clarifying their key role in soil processes. Twenty seven surface samples (0-20 cm) and 6 pedons from different landform units were sampled and described according to USDA, 2002 and by means of illustrating the surface as well as vertical distribution of different size and varied chemical fractions of organic carbon. Physico-chemical, mineralogical, physical and chemical fractionations were carried out following standard methods. The results revealed that organic carbon content increases by decrease in the fraction size, reaching its maximum at <250 μ. Also it was observed that 2:1 expandable clays show relatively higher capability in organic carbon complication in comparison with the other mineralogical suits. The results for chemical fractionation demonstrated that humic to fulvic acid ratio increases by increase in organic matter input, itself being followed by increase in soil biological activity.

In the course of the present study, the results of parametric approach are compared with those obtained through fuzzy approach using AHP as well as multivariate regression methods for comparisons and investigating the efficiency of the fuzzy method as applied in land suitability assessments. The correlation coefficients between land index and observed yield in the study area through fuzzy approach plus AHP (r=0.91*) and multivariate regression methods (r=0.88*) are more than those in the parametric approach (r=0.85*). Although, the fuzzy set approach offers a higher accuracy and better results for land suitability assessment, the most critical issue in its application to land suitability assessment remains as the choice of membership functions, cross-over points and weight values as regards different land characteristics.

Balance among different fractions of a carbon sources is of paramount importance in maintenance of very important in soil quality and environmental health. On the other hand, rapid growth of world population, degradation of agricultural soils, along with release of greenhouse gasses are some of the main challenges of the 21st century. The aim of this study was to investigate the extent of changes in land use that have occurred since 1955, their effect on carbon dynamic's and to study the effects of different land uses on organic carbon content in their different size fractions. Twenty seven surface soil samples (0-20cm) were collected from different land use areas and physico-chemical analyses as well as physical size fractionation done on all. Soil organic carbon content showed a decreasing trend in orchards, farms and rangelands respectively. Urbanization and land use changes have prevented from dynamics and storage of 71273 and 190406 MgC/ha respectively.

Dispersive soils are prevailent in many parts of the world, including in Iran. Construction of hydraulic structures on dispersive soils has created various serious problems. Since it is neither economical nor justified to replace a dispersive soil with a non-dispersive one, there fore stabilization of a dispersive soil in one way or another is indispensable and unavoidable. Throughout this research work stabilization of a dispersive soil through addition of lime and Pozzolan, either alone or in mixing, has been put to investigation. The variables taken into account are the curing time and the mixing percentages. Results indicate that with an addition of either lime or Pozzolan alone, along with application of curing treatment, a dispersive soil would tend to become diminished in its dispersivity potential. On the other hand, the soil in which stabilization is carried out through application of a mixture of lime and Pozzolan, the soil becomes also resistant to being washed away. The soil treated in this manner would gain extra compressive strength and be reduced in its plastic index. Reduction of sodium ions in soil solution and increase in electrical conductivity of the treated soil are two other aspects of this last type of dispersive soil stabilization.

The effect of 0, 2, and 5 mM of citric, malic and oxalic acids on phosphorus (P) sorption was evaluated. In the collected soils, the level of total calcium carbonate stood in the range of 4-28%, clay content at 33-56% and the amount of organic matter recorded within 0.6-2.7%. The results indicated that the addition of organic acids causes reduction in P sorption. Citric acid in most soils, was shown to be more effective in this respect than oxalic and malic acids. The level of P sorption significantly decreased in particular at 5 mM concentration of organic acids. The lowest and the highest P sorption as regards the three organic acids were observed at concentrations of 5 mM in soil No. 5 vs. 0 mM in soil No. 4, and where the soils contained low vs. high clay plus calcium carbonate contents, respectively. Therefore, it is concluded that P adsorption by soils is controlled by the kind and concentration of organic acids content, and as well by soil mineral constituents.

Dispersivity (λ) and effective transport porosity (eff) are input parameters in equilibrium Convection Dispersion Equation (CDE). Normally these parameters are obtained from breakthrough curves by inverse method. However, obtaining breakthrough curves in the field is not often possible in practice. The objective of this study was to estimate λ and feff from soil hydraulic data. For this purpose a conceptual model was developed which describes the transport of a nonreactive solute based on soil hydraulic properties. Both deterministic and stochastic simulation approaches are made use of. The breakthrough data obtained from the simulations were utilized to estimate transport parameters through inverse method. Results revealed that there was no significant difference between predicted and observed λ at P < 0.05 in stochastic approach. However the procedure tends to over-predict small values of λ, while under-predicting large values of λ, especially in the deterministic approach. The estimates of the effective transport porosity being less than those of total porosity (), indicated that only a portion of total porosity takes part in solute transport. This procedure can be utilized to estimate λ and eff from soil hydraulic properties in each and any scale.

Use of electrokinetic technique for remediation of contaminated soils has recently been highly attended to, but there are still concerns regarding the effect of this process on soil microbial activity. In this study, changes in concentration of heavy metals extractable through 4N nitric acid, microbial biomass-C, and microbial coefficient, following electrokinetic remediation of a native soil contaminated with heavy metals (zinc, lead, nickel and cadmium) in and at a pilot-scale were evaluated. After 20 days of soil being imposed to a constant voltage gradient of 0.83 Vcm-1 of soil column, the results revealed that over 30 percent of heavy metals close to the anode were removed. However, removal of metals from a distance of 24 cm from cathode about some of the metals (cadmium and lead) is negative. The effect of electrokinetic remediation on biological parameters showed that the level of microbial biomass-C as well as microbial coefficient (following the electrokinetic process) decreased significantly (p< 0.01) with the highest reduction being observed near the cathode where heavy metals had been accumulated. A lack of pH control and its rising trend from anode towards the cathode has most negatively affected the process.

Effects of different soil moisture regimes and P application on available and inorganic P forms were studied in four paddy soils, north of Iran. A factorial experiment in a completely randomized design with two replications was performed in a laboratory study. Factors of soil at four levels (two acid and two alkaline-calcareous soils), soil moisture contents at three different levels (air-dry, 40% Saturation Percentage (SP), and submerged) as well as P fertilizer at two levels (with and without P fertilizer application). Phosphorus fertilizer was added at a rate of 40 mg P per kg of soil as monocalcium phosphate. The treatments were incubated for one month at 25˚C and then analyzed for P fractions employing the method of Jiang and Gu (1989) for calcareous soils and of Kuo (1996) for non-calcareous soils. Available P, was determined through Olsen method. The results indicated that the level of available P, in all soils, increased on the average more than two times following submergence. In acidic soils, the level of available P increased more than that in alkaline-calcareous soils following submergence. After one month of incubation at 40% SP and with no P application, in three out of four soils, the available-P increased, while in one soil it did not change significantly. The average recovery of added P under submerged conditions was lower than that under unsubmerged conditions. The average recovery of added P in alkaline-calcareous soils was higher than that in acidic soils. Effects of soil moisture regimes and P fertilizer on all inorganic P fractions were significant in all soils studied. Higher levels of added P were converted to Fe-P under unsubmerged conditions. Higher amounts of added P were transformed to Al-P in alkaline-calcareous soils relative to acidic soils under both nonsubmerged and submerged conditions. Higher levels of added P were converted to Fe-P in acidic soils relative to alkaline-calcareous ones under at both nonsubmerged vs. submerged conditions. In air dried alkaline-calcareous soils, the following order was observed for inorganic phosphorus fractions: Fe-P< Ca2-P < Ca8-P < Al-P < Ca10-P; and in acidic soils, under the same conditions, the order observed was as follows: NH4Cl-P < Al-P < Fe-P < Ca10-P.

For a determination of optimum levels of water and Nitrogen fertilizer, as regards corn yield and nitrate movement in soil, a split-plot experiment, using a randomized complete block design of three replications was conducted in Safiabad Agricultural Research Center, on a silty clay loam soil. Three irrigation levels (50, 75, and 100% of water requirement) and three Nitrogen fertilizer levels (150, 225, and 300 kg N ha-1) were applied through fertigation in three equal splits of first irrigation, 6 to 8 leaf and flowering stages. The results revealed that the treatment of 100% water requirement with 932 mm of water consumption and 0.75 kg m-3 of water productivity displays a significant difference as compared to the other treatments. In addition, nitrate concentration in the 0-30 cm of soil layers was significantly higher than those in the other layers. The NO3-N leaching in soil layer deeper than 60 cm was not observed in any of the fertilizer level and fertigated stages for the schedueled irrigation in heavy textured soil, and in the climatic conditions of the North of Khouzestan Province.

Carbonates are among the most common soil constituents in arid and semiarid zones. They exhibit many significant differences in their chemical and mineralogical, suite, origin, physical and micromorphological properties and consequently in their activities in soil. The differences cause different properties of calcareous soils. Six profiles of Aridisols and Inceptisols with carbonate accumulations were selected and analyzed as according to standard methods. Following an analysis of the physical and chemical properties, thin sections were prepared and scrutinized for a distinction of the origin of carbonates, using staining with Figel and red Alizarin red solutions. Powder X ray diffractometry was carried out for carbonate detection, while clay mineralogy study being done on the oriented pure clay samples. Micromorphology and mineralogy of carbonates (nodules, sparite, micrite, needle-shape calcite and laminarcap) showed calcium carbonate as the dominant carbonatic mineral. However calcium/magnesium carbonates were also recognized as present in some cases. The dominant clay minerals were spotted as smectites.

Seed inoculation by means of mycorrhizal fungi can alleviate the side-effects of fungicides on production of crops and their yields. An experiment was conducted in 2009 at the Research Field of Islamic Azad University, Faculty of Agriculture, Mahdasht, Karaj. In order to investigate the influence of different kinds of fungicides on colonization of mycorrhizal species and on grain yield in soybean, a factorial experiment on the basis of a completely randomized block design of two factors and four replications was carried out. The first factor was VAM fungi species at four levels of: control, Glomus mosseae, G.etunicatum, G.intraradices. The four fungicide treatments consisted of: control, benomyl, nanosilver as well as biologic (Bacillus subtilis). The results indicated that the most suitable species to increase root colonization (35.33%) in soybean symbiosis was G.intraradices. Grain yield also increased (35.5%) with this species and with nanofungicide application. Biomass recorded the highest (5688 Kg/ha) in a combination of G.intraradices and nanofungicide. Through inoculation of any species of AM with Benomyl, the number of pods, grain and biomass decreased in comparison with control. None of the fungicides exerted any negative effect on grain yield when in combination with any of the species of mycorrhiza.