Iranian Journal of Soil Research
Year:2012 | Volume:26 | Issue:1|Papers Count:12

Phosphorus adsorption in soils is one of the most important processes that determine its availability to plants. Many studies have revealed that phosphorus fertilizer recommendation can be improved based on soil adsorption properties. Phosphorus adsorption isotherms were constructed for different soils under wheat crop. The sorption curves were used as a basis for fertilizing soils in pots suchthat phosphate in soil solutions varied from about 0.075 to 1.2 mgl-1. Wheat was grown for 6 weeks. Adsorption data were successfully described usingFreundlich and Van Huay sorption models (R2= 0.927-0.997 and R2=0.949-0.999 for Ferundlich and Van Huay models, respectively). In most soils, yield approached more than 85% of the maximum when phosphate in the soil solution was adjusted to 0.3 mgl-1.The standard phosphorus requirement varied from 19 to 157 mgkg-1. There was linear relation between added P and bicarbonate- extractable P (Olsen P) in all soils (R2=0.96-0.99, andmean of0.98) and the slope of this linear equation (by plotting added P against Olsen P) varied from 0.23 to 0.47 with 0.38 as an average. The recovery of phosphorus varied from 12 to 50% with 37% as an average. This means that 63% of the added P was unavailable. There was no significant difference between the mean recoveries in the different treatments. The phosphorus critical level for sodium bicarbonate extractant (Olsen P) based on was determined at 13 mg P kg-1 soil.

In order to investigate the effects of corn-wheat rotationon the available-P and inorganic phosphorus fractions of soil, with and without P application, agreenhouse study was carried out as a 2 x3 x2 factorial experiment in a randomized complete blocks design. Treatments included two types of soil, 3 levels of P, and two planting treatments (corn-wheat rotation vs fallow land), with 3 replications. In a period of 5 months, variations of Olsen-P and soil inorganic phosphorus fractions were studied. The results indicated that effects of soil P application and planting treatment on Olsen-P and soil inorganic phosphorus fractions were significant.Within creasing P application, soil inorganic phosphorus fractions increased, but, with balanced P application, P fixation in soil was decreased. In corn-wheat rotation, suitable P application rates at the time of planting corn will also meet the requirement of the next crop of wheat.

The objective of this research was to compare the effects of fertigationand soil application methods of nitrogen, iron, manganese, and zinc on wheat production and its growth parameters. The study was conducted in a stripe statistical design by use of 5 pipelines as triple line-source sprinkle irrigation. Treatments were: T1= fertigationin 3 meters distance from fertilizer injection line, T2= fertigationin 6 meters distance from injection line, T3=fertigationin 9 meters distance from injection line, T4=soil application in 3 meters distance from irrigation line, T5=soil application in 6 meters distance from irrigation line, and T6 were nutrients soil application in 9 meters from irrigation line. In fertigation method, nitrogen source was ammonium nitrate while iron, manganese and zinc were chelated sources injected into the middle pipeline by use of a Venturi system. In soil application method, 425, 110, 100 and 20 kg.ha-1 of Urea, Triple Super Phosphate, Potassiun Sulfate and Zinc Sulfate, respectively, were applied to the soil and were watered with a sprinkler system. Fertilizers used were based on the soil test.The results showed that by increasing ammonium nitrateconcentrations, total yield, grain yield, and 1000 grain weight increased. The highest yield (7623 kg ha-1), the highest 1000- grain weight (36.3 g) and the highest grain protein content (15.4%) were obtained from the first fertigation treatment i.e. fertigationin 3 meters distance from injection pipelineand application of 170 kg ammonium nitrate ha-1.The results showed that the rate of nitrate applied in fertigation system was highly correlated with1000-grain weight, grain yield, and total yield. The results also indicated that zinc and manganese foliar fertilization were more effective than soil application. More detailed studies about the economic aspects seem to be necessary.

Amount and distribution of iron and manganese and their concretion sreflect a lot of processes involved in soil genesis. Fe-Mnc on cretions show different characteristics of soil matrix and occur in different environmental conditions and are important in soil genesis, classification, and environmental aspects. The objective of the present study was to investigate abundance and distribution of Fe and Mn chemical forms and the factors affecting them and to compare characteristics of Fe and Mn concretions with their adjacent soil matrix. To this end, seven profiles affected by redox conditions and five horizons were studied. Four forms of iron, including total iron (Fet), free iron oxides (Fed), amorphous (Feo) and DTPA extractable iron, and two forms of Mn, including total Mn (Mnt) and DTPA extractable Mn, were measured.Also, to studythe concretions and their mineralogical properties, Scanning Electron Microscopy (SEM) was used. Results showed that organic matter and clay content werethe most important factors influencing different forms of Fe and Mn in the studied soils. Distinct contradictory conditions of micro zones of the Fe and Mn concretions with their adjacent environment caused higher concentrations of Fed, Fet, Feo, MntandFeo/Fed ratio in Fe- Mn concretions compared to the adjacent soil matrix.

Because of the scarcity of in situ measurements, simulations of soil moisture and temperature are very important for irrigation management and scheduling and evapotranspiration estimation in different field conditions. This paper aims at evaluating the efficiency of the COUP model in simulating soil temperature and moisture dynamics in two plots under maize canopy and with no vegetation cover in Karaj climate. Soil physical parameters, estimated based on the soil analysis (soil texture, bulk density), and daily meteorological parameters (including maximum and minimum temperature, wind speed, pan evaporation, sunshine hours and rainfall) and cropdata (crop height, root depth, and leaf area index) were used to run the model over the growing period. Soil temperature was measured using standard soil thermometers at depths of 10, 30, 50 and 70 cm and soil moisture was measured by means of a theta probe installed at the same depths. Statistical criteria were used to compare the simulated soil temperature and moisture with those observed. Results showed that the COUP model was highly efficient in simulating soil temperature. The simulated soil moisture was comparable with observations. However, the model was less skillful in simulating soil moisture than temperature. Further scrutiny is needed to assess the possible reasons for this discrepancy.

The power-law functions, especially the mass-based fractal models, have been widely used to quantify and describe the particle size distribution (PSD). Many researchers have shown that the ratio of cumulative mass fraction to particle size will change with the invariant scale, called fractal dimension (D), if the particle density is constant across the entire size fractions. However, some reports show that the application of these models has some limitations. This research was carried outfor investigating the limitations and evaluation of the best size ranges for application of power law functions (two mass-based fractal models). Thirty two soil samples with eight different textural classes were used for particle size distribution experiment using the hydrometer method. Fitting the models on PSD data sets showed that these models were not able to accurately represent the PSD curve across the entire range of particles under the size of 2000 µm (R2= 0.7461).The best applicable size range was less than 54 µm (R2=0.9716).These conditions can limit the use of power functions in sandy soils. The results showed that the application of the fractal models in clayey soils is valid for particles smaller than 24 µm. Also, these results showed that approximately 70% of changes in fractal dimension were controlled by the silt to clay ratio in the soil samples.

Increase in the price of agricultural inputs, especially chemical fertilizers, has influenced agricultural production in recent years. Thus, overuse of fertilizers, which is utilization of large amounts of fertilizers, has no economic and environmental justification. Environmental hazards of chemical fertilizers, including degradation and compaction of soils and declining soil organic matter, have also important role in this trend. The idea of green revolution and minimum utilization of chemical fertilizers and pesticides and the increasing social attitude toward consumption of “organic” products have led to increasing interest in biofertilizers. Global changes in fertilizer economy and the necessity of paying attention to soil, crop, and public health have also placed biofertilizers in focus. Production of biofertilizers in Iran began a decade ago and although there is now a good condition for biofertilizers, it has experienced much fluctuation. However, there are scientific and executive challenges regarding different aspects of biofertilizers. Academic education here still lacks a clear stance on the subject and the research section does not have a road map for expanding the use of biofertilizers. On the other hand, most of the national biofertilizer producers are suffering from lack of Research and Development section and this negatively affects the quality of their products. Also, intellectual property right of producers has been influenced by lack of quality inspection agencies. While for many years there was huge governmental subsidy for chemical fertilizers, there was little opportunity for biofertilizers to be adequately introduced in the country. Most of the biofertilizers introduced during those years have faced different problems in spite of passing all steps of research, development and commercialization. However, lately, when providing subsidies for chemical fertilizers was limited, biofertilizers became more in focus. According to the governmental legislation N42963t/90765, 10 percent of the subsidies for chemical fertilizers are to be allocated to biofertilizers for more support and promotion of their use. Obviously, both approaches i.e. neglecting biofertizers or excessive promotion and attention are not wise and may not lead to a sustainable production. It seems that the best approach is to gradually increase the use of proper types of biofertilizers. This paper discusses the conditions of biofertilizers in Iran and its challenges from point of view of research, training, production, quality, and intellectual property right.

The aim of this study was to investigate the effectiveness of isolates capable of producing IAA and utilizing ACC as the sole source of nitrogen on growth of pistachio seedlings. In the present study, based on fluorescent properties of isolates in King B medium, 52 colonies of fluorescent pseudomonad were randomly isolated from the rhizosphere of pistachio seedlings and then purified. These strains were identified according to the microscopic, physiological, and biochemical characteristics tests related to species determination. Study results showed that 49 of the 52 isolates belonged to Pseudomonas fluorescens species and, due to the lack of conformity with the characteristics in the Bergey book, three isolates were identified as Pseudomonas sp. Then, isolates were evaluated for the ability to produce IAA and utilize ACC. The results indicated that all the strains were able to produce IAA and 62% of which were able toutilizeACCas the sole sources of nitrogen. In a greenhouse experiment, the effectiveness of the six isolates that were able to utilize ACC and produce different amounts of IAA were tested on the pistachio seedlings. The results showed that application of most of the strains significantly increased leaf number, leaf area, and shoot fresh and dry weight of pistachio seedlings.

Nitrate is the primary source of nitrogen that is essential for the survival of plants. Therefore, nitrogenous fertilizers are used to improve plant growth. Increased use of nitrogen fertilizers causes migration of nitrate to surface and groundwater resources, resulting in their contamination. The objective of this study was to investigate the effect of potassium zeolite on nitrate and ammonium ions sorption and retention in a saturated sandy loam soil under laboratory condition. The experimental design was complete randomized block with four treatments consisting of potassium zeolite applications of 0, 2, 4 and 8 g zeolite per kg soil, with three replications. Ammonium nitrate fertilizer with concentration of 10g per liter was added to soil columns and then leaching was performed. Results of the study showed that with increasing the amount of potassium zeolite to soil, the leaching of nitrate and ammonium ions decreased and their retention in soil increased. For the control treatment and use of 2, 4, and 8 g zeolite per kg soil, the amounts of nitrate exiting the bottom of the soil columns were 93.88%, 73.91%, 59.62%, and 53.61 percent of the amount of nitrate added to the soil, respectively. The respective values for ammonium were 4.74%, 4.12%, 3.37% and 3.24 percent, respectively. Based on the results obtained, application of 2, 4, and 8 g zeolite per kg soil reduced the average pore water velocity in soil to 43.79, 58.43 and 60.52 percent compared to the control treatment, respectively. Generally, increasing the amount of zeolite application to the soil decreased the hydrodynamic dispersion coefficient of nitrate ion.

Potassium is an essential element for plant growth that is mostly supplied by K-bearing minerals in soils. The role of these minerals, which are mostly mica, in K supply for plants is well known. However, little information is available on the rate of K release from micaceous minerals with time. The objective of this study was to investigate the temporal changes of concentration and uptake of potassium from phlogopite by alfalfa. A pot experiment was conducted under greenhouse conditions. Growth medium was a mixture of quartz sand and phlogopite. The experimental design was a completely randomized factorial with 3 replicates. During 200 days of alfalfa cultivation, plants were irrigated with either a complete or K-free nutrient solution and distilled water as needed. At 40, 75, 110, 140, 165 and 200 days after cultivation, 3 replicates of each treatment were harvested and their K concentration and uptake were measured by flame photometer following dry ash extraction. Results indicated that the K concentration in plant tissues significantly decreased with time. In addition, phlogopite was able to maintain plant potassium concentration for more than 110 days in the sufficient range. Also, the parameters of growth and uptake rates showed significant changes with time. At the early stage of plant growth, both growth rate and K uptake were low. These parameters increased with time as the ability of root to extract potassium increased. At the end of the experiment, because of the plant age and also decline in potassium source, root power for potassium uptake diminishedand, thus, the amounts of plant growth rate and K uptake rates also decreased.