Iranian Journal of Soil Research
Year:2012 | Volume:26 | Issue:2|Papers Count:11

Analysis of the trends of the cultivated area, agricultural production, and water resources in the past 50 years shows that focus of agricultural development has to be on intensification to cope with the rising demands for food of the growing population in Iran. This means more pressure on soil resources, which threatens sustainable production and food security. It also shows the key role of soil fertility and balanced soil fertilization, which is the main concern of the agricultural sector as well. In this paper, fertilizer recommendation and forecast are investigated as the first and the main steps of fertilizer system including recommendation, forecast, supply, allocation and consumption. Considering soil and plant nutrient criteria and fertility evaluation of some 20, 000 soil samples revealed that more than 50 percent of the cultivated soils suffer from the deficiencies of one or more nutrients.Furthermore, the low soil organic matter content is the main limitation factor of sustainable soil fertility and production. Among the four fertilizer recommendation approaches based on soil test, fertilizer recommendation in Iran is more based on thesufficiency range approach. Due to the lack of adequate data, the other approaches includingbuild up, maintenance, and cation balancemethods have been ignored, but should be considered in the future. Fertilizer recommendation trend shows a transition from the general and regional recommendation towards the soil test recommendation along with more attention to research and soil analysis. In addition to soil test as a base of fertilizer recommendations, other factors such as climate (drought, temperature), soil (salinity), plant (uptake efficiency) and agronomic management (rotation) should be considered in the fertilizer recommendations system. Fortunately, the first steps for integration of these factors are gathered inautomated fertilizer recommendation program which needs more complete investigations. Among the five main fertilizers forecasting models in Iran, fertilizer estimation is more based oncrop based model and has a generation trend due to more availability of soil and plant analysis data. This trend shows more fertilizer requirement in the future.However, it is necessary to distinguish between the total fertilizer requirement and its consumption at the farm. This means fertilizers consumption is not balanced in general, while balanced fertilization should be the main policy. There should be anational soil testing program in a way to include all stakeholders (private soil test lab, producers, etc) in fertilizer program. With the preparation of soil test infrastructure and facilitation of farmers' access to soil lab and appropriate fertilizer, balanced fertilization and, consequently, sustainable soil fertility, food security, and environmental protection could be achieved.

There are many problems in crop production in calcareous soils. The main problems are due to high concentration of Ca+2 and high pH. There is a direct relationship among phosphorus and micronutrients absorption and high pH.Usually, micro nutrients in these soils are fixed and become unavailable for plants absorption. However, sulfur oxidation in these soils produces sulfuric acid and decreases soil pH, leading to higher absorption of other nutrients indirectly. To determine the exact amount of sulfur needed to avoid imbalance of nutrients and the effect of microbial sulfur fertilizer on nutrient uptake and yield of soybeans in a calcareous soil, an experiment was carried out in Qarakheil Agricultural Research Station in (RCBD) design with 3 rates of sulfur in 3 replications. Elemental sulfur powder at three levels (S0, S1.5, and S3) as zero, 1.5 and 3 t/ha along with Thiobacillus inoculation at all levels. For measuring rates of nutrients in plants leaves, we carried out sampling at flowering stage. Results showed that application of sulfur had significant effect on yield and concentration of P in leaf. The highest yield (2429 kg.ha-1) and concentration of P (0.58 %) were obtained in 3 t/ha sulfur treatment. Applying sulfur to soil increased the concentrations of P, Fe, Zn, Mn and Cu in leaf significantly. Also, the concentration of Fe, Mn, Zn and Cu of soil increased, but pH concentration of soil decreased when sulfur was applied to the soil.

The purpose of the present research was to study the role of morphometric, vegetation, and rain event factors on gully development in different stages.Research method consisted of sampling after every rainfall event of 10mm in 24-hr, during two hydrological years of 2008-09. Graduated rods were installed in different parts of the gully and were used to measure the morphometric characteristics and advance of the gully after the rain. Soil samples were taken at distances of 0, 25, 50 and 75 meters from the headcut.The results showed that the gully development was cavernous (a large hole) and, from its middle parts to lower layers, gully development was facilitated by frail and fragile layers and solubility of salts, thereby causing collapse of the gully roof. The results of statistical analysis showed that all factors investigated had an important role in gully development such that the correlation coefficient was in the confidence range between 87 to 92 percent.Also, gully development charts in different distances from the head-cut showed that the gully in stages 2 and 3 was more than stage 1.Besides, according to the results of mechanical analysis, clay content in the B and C layers were more than in A layer. Due to the clay swelling properties, it contributed to the formation and development of the gully. The results of this study indicated that soil physical and chemical conditions including vegetation and rainfall were effective in soil displacement and gully development both in length and width.

The purpose of this study was to investigate the effect of salt stress on growth, biological nitrogen fixation (BNF), and salinity tolerance of three soybean cultivars (Jk, Sahar, and Gorgan3). These cultivars were planted in a factorial experiment, completely randomized, with four replicates and two variables that included the aforementioned cultivars and four salinity levels (1, 4.2, 5, and 5.8 dS/m). The plants were grown in 48 pots and were harvested after 1 month and their nodule number, fresh and dry weight of root and shoot, biomass, nitrogen percentage, and nitrogen content were measured. Results showed that with increasing salinity, all traits decreased.Means comparison showed that cultivar Jk was better than the other cultivars with respect to nodule number, fresh weight and dry weight of root and shoot, biomass, nitrogen percentage, and nitrogen content. Accordingly, cultivar Jk had the lowest sensitivity to salinity and could be considered a promising genotype for breeding programs.

Cadmium (Cd) is one of the most toxic pollutants whose concentration in soil has been rising due to the increasing application of phosphorus fertilizers in agricultural fields. Phytoremediation, an emerging low-cost and ecologically benign technology for decontamination of soils, is defined as the process of utilizing plants to absorb, accumulate and detoxify contaminants in soil through physical, chemical and biological processes. One of the problems of this method is slow growth rate of the selected plant. Use of plant growth promoting Rhizobacteria (PGPR), especially those containing ACC deaminase, stimulates growth of plants and, thereby, improves bioremediation of Cd in contaminated soil. Therefore, to investigate the bacteria effect on the efficiency of Cd bioremediation by kale (Brassica oleraceae var. viridis), a pot-culture experiment was conducted in a completely randomized block design in the green house of agricultural college, Tarbiat Modares University, in 2009-2010. In this experiment, inoculants including: 1) control (un-inoculated), 2) Pseudomonas fluorescensstrain 169, 3) P. putida strain 108, 4) P. putida strain 11, 5)P. putida strain 159, 6) P. putida strain 4, and seven Cd concentration levels, i.e.0, 5, 10, 15, 30, 50 and 100 mg kg-1, were studied. Inoculated and un-inoculated seeds of kale were planted. Plants grew in green house for seven months.Afterwards, kale shoots and roots were harvested separately. In all treatments, Cd concentration was measured using flame Atomic Absorption spectrophotometer.The results were analyzed using SAS software and revealed that the inoculants and Cd concentration levels had significant effects on kale growth and Cd concentration in both shoots and roots (a=1%). By increasing Cd concentration, shoots and roots growth decreased, but inoculants, especially inoculant (5), decreased this effect.Maximum Cd concentrations were 136 and 58 mg kg-1 in roots and shoots, respectively, in 100 mg kg-1 Cd concentration treatment accompanied by inoculant (6). Maximum root dry weight was 1.96 gr for inoculant (4) in 15 mg kg-1 Cd concentration treatment and maximum shoot dry weight was 12.53 gr for inoculant (3) in 30 mg kg-1Cd concentration treatment. According to the noticeable amount of Cd uptake in case of the combination of the plant and the inoculants, kale accompanied by the bacteria can be considered as a reliable option for the remediation of low to moderate Cd-polluted soils (<50 mg kg-1). In high Cdpolluted soils, however, due to severe decrease in Cd translocation, kale is not a suitable plant for phytoremediation in highly Cd contaminated soils, even if inoculated with bacteria.

The role of biological fertilizers in improvement of soil physical and chemical properties is important. A field experiment was carried out as factorial in randomized complete block design with four replicates during 2006-2007 at National Bean Research Station in Khomein, Iran. Treatments included five different rhizobium strains, nitrogen fertilizer (100 kg N ha-1), control (without inoculation and N-fertilizer) and three red bean varieties.The results showed that rhizobium treatments were significantly effective on plant height and pods per plant. Varieties were significantly effective on the number of days to maturity, number of days to flowering, plant height, 100 grain weight, pods per plant, grain per pod, grain per plant, grain yieldو and N concentration. Interaction between rhizobium strains and varieties were significantly effective on pod per plant and green area percentage. Among the bacteria strains, the maximum yield was obtained from L-120 rhizobium strain (2950 kg ha-1), however, there was no significant difference between these treatments. The maximum grain yields were obtained from Goli variety (3190 kg ha-1) inoculated with L-39 rhizobium strain, L-120 rhizobium strain and Akhtar variety (2692 kg ha-1) and L-58 rhizobium strain and D81083 line (2678 kg ha-1(.

Pseudomonads fluorescent is one of the most important plant growth promoting bacteria that increase plant yield and growth through several different mechanisms.They have been reported many times for their ability to dissolve the zinc insoluble compounds. In this research, 40 isolates were evaluated for their ability in solubilization of ZnO, ZnS, and ZnCO3 compounds. The results indicated that 20 percent of the examined isolates could dissolve ZnO and ZnCO3 salts, but none of them could dissolve ZnS. Zinc solubilizing isolates were investigated for their growth stimulating factors. The results demonstrated that all of the zinc solubilizing isolates could produce auxin and siderophore and they also could dissolve phosphate insoluble compounds in both solid and liquid media. ACC-deaminase was not produced in all of the isolates, except P1. None of the strains could produce HCN except for GRP3. The effect of the selected strains on zinc uptake was determined in greenhouse condition. P19 was selected as the most effective strain. It could increase zinc concentration up to 50.1 mg.kg-1 in shoot, at 500 mg.kg-1 concentration of ZnCO3.

Salt accumulation in arid and semiarid areas of the world is one of the most common abiotic stresses that can have a wide range of effects on crop yield.The objective of this research was evaluation of the effect of fluorescent pseudomonads containing ACC-deaminase on nutrient uptake and growth of canola (Brassica napus L.) in saline condition. The experiment was conducted in factorial arrangement with completely randomized design with four replications. The experimental variables were: water salinity at four EC levels of 0.335 (control), 5, 10, and 15 dS/m (natural saline water) and five levels of bacterial inoculants including Pseudomonas putida strain P.p.169, P.p.196 and Pseudomonas fluorescen s strain P.f.108, P.f.11 and a noninoculated control. The results showed that inoculation with the selected strain was effective at alleviating salinity stress during different growth stages of canola. By increasing the salinity, uptake of K and Ca decreased, while uptake of Na and Cl increased. At salinity levels, inoculation with the selective strain, decreased the effects of salt stress, hence, inoculation of canola seeds with fluorescent pseudomonads strain may alleviate the stress effects of salinity on canola growth and nutrient uptake.