Iranian Journal of Soil Research
Year:2012 | Volume:26 | Issue:3|Papers Count:11

Fertilizer is known as an important factor in agricultural production since many years ago. Use of chemical fertilizers in Iran started more than 50 years ago and has grown during recent years. Nowadays, issues such as fertilizer quality, distribution, scientific recommendation, methods of application, environmental effects, and chemical residues in crops are very important concerns. Fortunately, attention to “fertilizer” as a subject in national laws and legislations has grown during recent years and, in contrast to earlier years when the focus was just on supply and distribution, nowadays, issues like quality controls and environmental effects are receiving attention as well. However, lack of a comprehensive national law and management system as a regulator of different fertilizer system parts is clear now. Assessment of fertilizer system including production, distribution, application, import and export, and related standards shows that “Comprehensive National Law”, “Institution Responsible for Fertilizer Management” and “National Quality Standards for Different Kinds of Fertilizers” are three important missing components in fertilizer management system.

Reduction of soil physical stability and increasing soil susceptibility to erosion are among the most important consequences of soil quality degradation. In this study, in order to determine soil quality impact on soil physical stability, the relationships between soil quality models and two soil sustainability indices including sustainability index (SI) and cumulative rating (CR) in south Mashhad were evaluated. The SI and CR values had significant correlation with soil erodibility factor of the universal soil loss equation (K factor). Therefore, they were considered as indicators of erosion in the studied region. The results showed that four soil quality models including IQITDS, IQIMDS, NQITDS and NQIMDS had a significant correlation with soil sustainability indices, and the correlation coefficient of SI was higher than that of CR. Therefore, it seems that changes of soil quality could have a significant impact on soil sustainability situation. Since the SI index had high correlation with soil quality and it required less parameters than those required for determianation of CR, it was concluded that SI index can describe the soil quality changes better than CR.

Because of population growth and, consequently, increasing demand for food and agricultural products, the usage of phosphorus fertilizers has recently increased. This has resulted in an increase in phosphorus content of surface and ground waters, nutrients imbalance in soils and plants, and also environment pollution. Therefore, due to the importance and positive and negative effects of phosphorus in plant and human nutrition and health, this research was done to study the quantity of available and soluble phosphorus in soils. It was also performed for improvement and amendment of nutritional management and proper fertilizer recommendation and reduction of environmental hazards that are caused by use of excessive phosphate fertilizers in agricultural lands. For this purpose, soil samples were collected from 30 fields cultivated to potato around Mojen region, located 35 km from Shahrood city. Sampling was carried out in two stages: before planting and during the crop harvest. From each site, soil samples were collected from two depths: 0-25 and 25-50 cm and GPS was used to determine the location of samples. The soil samples were analyzed to measure for soluble and available phosphorus and the pH, EC, OM, and CaCO3. The amount of P in potatoes harvested in the fields was also measured.The results showed that the soil samples had slightly high alkalinity, high calcium carbonate, low organic carbon, and high soluble P (0.04-11.4 ppm).The amount of available P (15.8-48.4 ppm) was much higher than that recommended by Soil and Water Research Institute. Therefore, based on this study, it is suggested to avoid application of phosphate fertilizers in potato fields around this city for at least 2-3 Years.

Physical, chemical, and biological characteristics of soils are considered for studying soil quality, which has high importance for evaluating the degradation or improvement of lands. The soil quality of 140 samples in Karaj plain (Iran) was evaluated by using cumulative rating (CR) and Sustainability Index (SI) approaches. Some soil attributes such as, organic carbon percent (OC), mean weight diameter of aggregates (MWD), the slope of retention curve at inflection point (Sgi index), plant available water content (AWC), aeration porosity (Fa), acidity (pH), electrical conductivity (ECe), and sodium absorption ratio (SAR) of saturated paste extraction, soil texture, relatively field capacity (RFC), and bulk density (Bd) were measured for all 140 soil samples. SI for each sample was determined according to Sgi index, Fa, Bd, MWD, AWC, and OC. Relative weighing factor (RFC) was calculated for all attributes to determine CR.Then, sustainability situation of each sample was determined based on summation of RFC values. The results of SI approach showed that 62.14 % of the studied soils had unsustainable quality for use as agricultural land. In the studied soils, only 2.14 % had sustainable situation based on CR approach, 37.86 % will be sustained if more inputs or proper management are applied (such as returning the plant residues, reducing the tillage operatons, and modern irrigation methods) and 60 % were unsustainable for agricultural purposes. Thus, it seems that special management practices are necessary for the studied regions, which are located in arid and semi- arid area.

Due to the high levels of Ca++in soil solutions and high pH values in calcareous and alkali soils that exist in large areas of Iran, the soil nutrients, whose absorptions depend on pH, will become less available. It has been a common practice in many regions of the world to use elemental sulfur as an acidifying source to lower pH and to improve the availability of some soil nutrients. A major requirement in utilizing elemental sulfur to lower soil pH is the presence and activity of sulfur oxidizing bacteria (especially the Thiobacilli) in the soils.This investigation involved the effects of sulfur rates, Thiobacillus inoculant on sulfur oxidation trend and the subsequent release of iron and zinc in calcareous soils. In this study, a completely randomized factorial experiment was conducted using three replications, eight levels of sulfur, two levels of Thiobacillusinoculant, in two different calcareous soils. During three months incubation period, care was taken to keep the soil moisture at F.C and temperature at 28-30oC. Soil samples were taken at time intervals 0, 15, 30, 60, and 90 days after incubation. Then, soil pH, EC and available sulfate, iron, and zinc were measured in the samples. The analysis of data by SAS software showed that during the experimental period the nutrients availability, such as sulfate and iron, increased in both calcareous soils but available zinc increased in one of the study and reached maximum content 60 days after incubation.Also, application of sulfur increased the concentrations of sulfate, iron, and EC, but decreased soil pH. Additionally, increasing sulfur application rates, increased nutrient concentrations and EC, but decreased soil pH as compared with the control.

Plant growth is directly affected by soil water, soil aeration, and soil resistance to root penetration. Least limiting water range (LLWR), a proposed soil structural quality index, is the range of soil water content at which plant growth is least limited by water potential, aeration, and soil mechanical resistance. In this study, the effect of tillage on the physical factors controlling plant growth in the LLWR index was investigated. Sixty undisturbed soil samples were collected from two contiguous fields cultivated by no-tillage and conventional tillage. Then, soil water retention curve, soil resistance curve, and bulk density were determined. The results showed that in conventional tillage system LLWR was significantly higher (P<0.01). In no-tillage system, qSR (soil moisture equivalent to 2 MPa penetration resistance) was the lower limit of LLWR in 63% of the samples and replaced qPWP (soil moisture at permanent wilting point), while this value was 53% in conventional tillage.

Plant growth promoting rhizobacteria can enhance growth and yield of different crops through direct and indirect mechanisms. In this experiment, effect of phosphate solubilizing pseudomonads strains on yield, growth parameters and phosphorus uptake of three rice cultivars was studied. The experiment was carried out in a randomized complete design (RCD) in factorial experiment with four replications. Three cultivars of rice Tarom, Neda and Khazar, and six strains of Fluorescent pseudomonads GO11, GO12, GO15, GU10, MZ3 and MZ16 were used along with a control treatment. The collected data included weight of fresh shoot, weight of dry shoot and phosphorus uptake by plant at flowering stage, and yield of grain, 1000 seed weight, number of panicles, number of spikelets, number of grains per panicle, and phosphorus uptake in grain at maturity. Results of the experiment showed that all the parameters according to Duncan test (P≤0.05) were significantly affected in different cultivars. Maximum grain yield was obtained from Neda cultivar. Inoculation with strains increased all plant biometrical parameters, growth indices and yield of rice. Maximum grain yield (30.61g per pot) was obtained with P. fluorescens GO15 strain and showed a significant increase in comparison with the control, (24.5%.). Maximum grain yield and growth indices were obtained from inoculation of seeds of Neda cultivar with P. fluorescens GO15.Maximum rates of P uptake in plant and grain of rice were obtained from interaction of P. fluorescens GO12 with Neda and Khazar cultivars, respectively. Based on the obtained results, fluorescent pseudomonads could affect yield of rice and P uptake in plant and grain.

The effects of heavy metals, as soil pollutants, on Rhizobia and symbiotic system of Rhizobium -legume are not clearly known. The aims of this study were to determine the effects of Cd on nitrogen fixation of native isolates of Sinorhizobium meliloti in Zanjan province soils. To isolate and obtain pure cultures of sinorhizobium meliloti isolates, root nodules were collected from different alfalfa farms contaminated by heavy metals, especially Cd, in Zanjan province. Plant infection tests were carried out on different strains to identify Rhizobia, then, isolates capable of nodulating were determined. Based on effectiveness of symbiosis and shoots dry weight of alfalfa in greenhouse condition, nitrogen fixation efficiency of different isolates was examined and compared with each other. The results showed that different isolates had different nitrogen fixation efficiencies and the isolates were classified into four groups, namely, very effective, effective, partially effective, and not effective. In the second part of the experiment, resistance of different sinorhizobium meliloti isolates to Cd was examined using selective medium of HEPES-MES containing different amounts of Cd.The highest concentration of heavy metals supporting growth for each isolates was determined as the maximum resistance level (MRL) and, based on it, the isolates were classified into three groups, namely, sensitive, relatively sensitive, and tolerant. In the final experiment, the effective isolates (capable of nodulating) with low and high tolerance to heavy metals were selected and used for a pot experiment. In this experiment, the effects of five sinorhizobium meliloti isolates (S6, S12, S17, S41 and S51) as inoculants, and five concentrations of heavy metals were examined on growth of alfalfa plant in a mixture of perlite and sand as media. A control and a treatment receiving 70 mg/kg N were also included in this experiment. The highest and lowest biomass yields of alfalfa were obtained for control and those treatments inoculated with resistant isolates to Cd. The S51 isolates was tolerant to Cd and had higher nitrogen fixation ability than the other isolates. The S17 and S3 were the most tolerant and the most sensitive isolates to Cd, respectively.

This study was conducted in order to evaluate both temperature and rainfall (climatic factors) effects on soil properties and transformation of clay minerals.A climatic gradient was selected about 80 km in length, located between 55o 16’ 56” to 54o 55’ 46” longitude and 37o 03’ 26” to 37o 30’ 26” latitude in Golestan Province, from mountainous area in the south to the coastal plain of Caspian Sea in the north. Soil moisture and temperature regime varies across this climatic gradient as, respectively, udic, xeric, aridic, mesic and thermic.Seven soil profiles were studied on loess parent materials. Soil horizons were sampled for laboratory analysis. Soil characteristics including texture, pH, EC, organic carbon, CaCO3 and CEC were measured in the collected samples. Clay minerals were separated using sedimentation method. Results showed that there was a good positive relationship between soil development stages and rainfall increase and reverse with temperature decrease. In the areas dominated by aridic soil moisture regime, Entisols and weakly developed Aridisols prevailed, while in the areas with udic soil moisture regime, highly developed Mollisols with an argillic and calcic subsurface horizons were formed. Mineral studies showed that Illite, Chlorite, and some Kaolinite were the dominant clay minerals in the soils. Mineralogical studies showed that mineral composition of the clay fraction in the soils were, respectively, Illite, Chlorite, Smectite, Vermiculite, Kaolinite, and Interstratified clay minerals. Good reverse relationship occurred between Illite and Chlorite content of the soils with climatic index (P/ETo), however, Smectite had a positive relation. In arid region, clay minerals were mostly inherited from parent material. Vermiculite was merely found in the soils distributed in the region with udic soil moisture regime (profile 1). It seems that Vermicullite is unstable in other soil moisture regime condition because of high soil reaction, presence of Si4+and Mg2+and low solubility of Al3+, and is not found.