Iranian Journal of Soil Research
Year:2003 | Volume:17 | Issue:1|Papers Count:14

Canola (Brassica napus L.) is an oilseed crop that is getting more attention as a source of vegetable oil in the country. Canola requires high rates of nitrogen and is regarded as a nitrogen-demanding crop. Nitrogen affects the growth, plant height, flower bearing branches, and the total dry matter production. Nitrogen fertilizer also affects the canola plant density. The principal effect of nitrogen fertilizer on the canola yield components can be seen in the increased number of the seedpods per plant, which is the main factor in improving the yield of canola seeds. The level of glucose inolate in canola is considered as an important canola quality index, which seems to be affected by the level of nitrogen supplements. Manganese Plays an important role in canola crop quality, especially the oil content of the seeds. A completely randomized block experiment with 24 treatments and 3 replications was carried out during 2000-2001 growing seasons in Ahar region to investigate the effects of the rates of manganese and nitrogen applications on the yield and quality of two winter canola varieties. The experimental factors were: four rates of nitrogen (50, 100, 200, and 300 kg/ha) applied as urea; three rates of manganese (5, 10 and 15 kg/ha) applied as manganese sulfate; and two winter canola varieties of Okapi and SLMO46. The analysis of variance showed that nitrogen rates significantly (at 1% level) affected canola yield. The highest yield was obtained with 300 kg N/ha. Likewise, the highest yield of canola oil was obtained with 200 and 300 kg N/ha N/ha. The highest oil content in the seeds was obtained with the applications of 200 and 300 kg N/ha plus 15 kg Mn/ha. The canola seed meals content of glucose inolate decreased significantly with increasing nitrogen rates so that 200 and 300 kg N/ha produced the lowest levels of glucose inolate. The main effects of nitrogen and manganese on the thousand kernel weight index were found to be significant a 1% level. The greatest value for the index of the weight of a thousand seeds was obtained with the application of 200kg N/ha and 15 kg Mn/ha. The largest number of seedpods per plant was obtained with 200 kg N/ha. None of the treatments had any significant effects on the number of plants per unit area. The most favorable protein content, Taking the crop yields and % oil into account, was obtained with a combined application of 200 kg N+15 kg Mn per hectare. Furthermore, the treatment effects were not statistically different for the two varieties.

Iron deficiency which usually appears as chlorosis in young leaves, is considered to be one of the most important nutritional disorder in citrus trees, particularly in calcareous soils. This experiment was conducted to study the effect of ethephon 37% (as an ethylene releasing agent) with two precultural roots application levels of 800 and 1600 µl/l and four foliar application levels of 0(control), 200, 800 and 1600 µl/1 on morphological characteristics of roots, iron absorption, chlorophyll concentration, leaf area, leaf iron concentration and iron content per 2individual leaf, leaf fresh and dry weight and specific leaf weight (SLW) of sour lime (Citrus aurantifolia Swing) seedlings. The precultural roots application of 800 and 1600 µl/l ethephon, not only significantly increased roots expansion by auxiliary roots development, but also induced roots hair formation and subapical root swelling. These two levels also considerably increased iron uptake by roots. In this experiment, ethylene increased leaf chlorophyll concentration in two different ways, so that, the precultural roots application level of ethephon enhanced the chlorophyll concentration by increasing iron uptake from soil, while foliar application of ethephon most likely induced chlorophyll concentration by increasing iron uptake in leaves, In this experiment, a better correlation between chlorophyll and Fe in leaves was obtained by calculating the leaf iron content per individual leaf rather than iron concentration per dry weight. However, this index is not very accurate because of SLW variations, especially under the roots treatment by ethephon. The results indicated that in the case of plant fortification with iron, ethylene plays a very important role in root morphology and in the case of iron chlorosis paradox in leaves, it has an important role in root morphology and in the case of iron chlorosis paradox in leaves, it has an important effect on increasing chlorophyll concentration and correcting the chlorosis incidence.

Soils in arid regions are very poor in organic matter content. The application of municipal compost enhances crop yields by improving soil physical and chemical conditions. A field study was conducted in a complete randomized block design with four replicates. The factorial combination of 0, 25, 50 ton/ha municipal compost and 0, 60, 120 kg N/ha was used with sugarbeet-wheat rotation in permanent plots for two years. Compost analysis showed that the lead level was higher than the permissible level. The effect of compost treatment, especially in the second year, on the yields of sugarbeet and wheat was significant (P< 0.01). Due to high concentrations of N-NO__3 in irrigation water, the effect of nitrogen levels on the yields was not significant. However, the effect of municipal compost on the availability of P, K, Fe, Zn, Cu and Pb was statistically significant.

To determine the proper time of N fertilizer application for wheat, 2 field experiments were carried out with 3 replications in Maragheh Dryland Research Station. The first experiment had 4 treatments: N__0 (control), N__(30+30) (30 kg N ha^-1 in autumn +30 kg N ha^-1 in spring), N__60 (60 kg N ha^-1 in autumn) and N__(60+60)(60 kg N ha^-1 in autumn + 60 kg N ha^-1 in spring) replicated for four years (1992-1997). The second experiment was conducted to determine the effects of rates and times of application of urea and ammonium nitrate on the yields of wheat crop. Results showed that the application of 60 kg N ha^-1 (without mixing with seeds) produced the maximum grain yield. With an increase in total precipitation and seasonal rainfall, the yield increase for N__60 treatment was higher than for N__(30+30) (30 kg N ha^-1 in autumn and 30 kg N ha^-1 in spring). Grain protein yield was higher for N__60 than for split applications of nitrogen. However, grain protein content for N__60 treatment was lower. By increasing the application of nitrogen as topdressings, harvest index decreased significantly, a disadvantage of top-dressing for cereal production in dryland farming.

This research was conducted in two separate laboratory experiments to compare the effects of NaCl, PEG 6000. And distilled water on germination traits and salt tolerance (EC=13.7 dS/m) of Sefid Kashan onion seeds as compared with dry untreated seeds. Priming was done by NaCl at 5 concentrations and 3 periods and PEG6000 at 4 concentrations and 2 periods. The seeds after priming were rinsed and dried. Then planted in Petri dishes under saline conditions Germination study was done in an incubator with 20°C temperature and 65% relative humidity in darkness. The traits studied were: germination percentage after 4.8 and 12 days. Plantlet F.W. and D.W., radicle and shootlet length. In this study, RCBD experimental design was used for the analysis of experimental factors. The results showed that hydration of seeds in distilled water significantly increased germination % and plantlet F.W. in comparison with hydration in NaCl solutions. PEG6000 at 25g/l concentration significantly increased germination percentage and radicle length in comparison with other PEG concentrations. It is concluded that PEG6000 has a positive effect on increasing salinity tolerance of onion at germination stage.

The relation between soil moil moisture and matric potential referred to as soil moisture characteristics curve, is one of the most fundamental soil physical properties. Field and laboratory methods of measuring this relationship are time-consuming and costly. Therefore, developing methods that estimate soil moisture (q#) at specific suctions from easily available and simple properties of soil will be advantageous to researchers and general users. The one-parameter model of Gregson et al. (G.H.M) is based on log-log form of soil moisture characteristics curve as ln z# =a+b ln q#. In this equation (a) and (b) are constants and have a negative correlation as a=p+qb. Using this equation and substituting it in the first equation results in the Gregson et al one-parameter model:lnz# =p+q(q+ln q#). In this equation (p) and (q) are regression coefficients and have specific values for each textural class, and only the parameter (b) is unknown. This parameter was estimated by Shirazi-Boersma soil textural diagrams values (geometric mean diameter and geometric standard deviation). To develop this model, 290 soil sample data from different laboratories were used and also 30 undisturbed soil samples were used to test the model. These samples were grouped into 8 textural classes and finally. (p) And (q) and (b) were calculated for each one of the 8 textural classes. Results showed that estimating soil moisture at specific matric potentials with the model has R__^2 greater than 0.9 for each textural class.

Determining water retention curve (WRC) is time consuming and expensive. Other soil parameters, like particle size distribution, organic carbon, bulk density and soil moisture in particular matric potentials can be used to estimate WRC. The objective of this study was to compare the abilities of van Genuchten and Brooks-Corey and two regression models (power and exponential) in WRC prediction with the coefficient of van Genuchten and Brooks-Corey estimated by using inverse solution method. A sandy loam and a clay loam soil incorporated with 60 Mgh^-1 cow manure were used. Three months after manure application, WRC was determined at 18 matric potentials (from 10 to 1500 kPa). The experimental data were used for van Genuchten and Brooks-Corey coefficients estimation using inverse solution (by RETC computer program), and also for the determination of the regressions coefficients. Two data set sizes were used in all models: I) water content at exactly 30 and 1500 kPa (2p), and II) water content at 18 water potential ranging from 10-1500 kPa(18p). Sum of square of deviations (SSD) and R, between measured and predicted water contents were compared for all the models just mentioned. Using 2p data set, regression equations (particularly exponential equation) and van Genuchten models produced similar results and were more accurate than Brooks-Corey model, especially for the SL soil. But when 18p data set was used, van Genuchten and Brooks-Corey models predicted WRC better than the regression models, especially for the CL soil.

The chemical oxidation of sulfur in soils is generally very slow. The activity of some soil microorganisms enhances the oxidation of sulfur, which results in pH reduction. A wide spectrum of microorganisms are capable of oxidizing sulfur in the soil environment. In a number of studies and reviews, it has been suggested that heterotrophs play an important role potential by heterotrophic microorganisms and their effects on pH reduction of different soils. Soil samples with different TNV values and organic matter contents from agricultural areas of Gilan province, were collected, sieved (2 mm) and incubated in one kg polyethylene bags at 60% of FC and 20-30 °C. Laboratory studies were performed based on Completely Randomized Design (CRD) in a factorial experiment with 30 treatments in 3 replications. The treatments consisted of three levels of sulfur (s__0=0%, s__1=0.2% and s__2=0.4%), two levels pH and electrical conductivity. Results showed that elemental sulfur lowered the pH values of some soils by 0.2 units after incubation for 80 days. In soils number 3 and 4, the addition of glucose with sulfur significantly stimulated sulfur oxidation and pH reduction in comparison with the same treatment without glucose, while in soils number 1, 2 and 5 the effect of glucose on soil pH was not significant. Addition of glucose to soils amended with sulfur, significantly decreased soil EC levels compared with soils amended just with sulfur. It can be concluded that the addition of 0.2 % sulfur can reduce the pH in some soils while in some other soils organic substrate should also be added along with sulfur.

Investigations on some thirty rainfed wheat fields in East Azarbayjan have shown that the soils were recently developed or consisted of materials with conditions such as low levels of essential nutrients and organic matter, and insufficient moisture that limit rainfed wheat cultivation in that province. Estimates of spore populations, and of total indigenous as an index of the soil mycorrhizal potential, showed that the populations in the rainfed wheat fields were lower than those of forage crops such as alfalfa. The greatest levels of spores and MIP (Mycorrhizal Infectivity Potential) for the investigated wheat fields were 110 and 209 per 50 grams of soil samples, respectively. The respective populations for Alfalfa fields were in the order of 135 and 245 per 50 grams of soil samples. MIP values increased significantly due to increases in the level of asexual Arbuscular mycorrhizal spores, the organic carbon, mineral nitrogen content of the soil, soil available potassium, manganese, and zinc, while increases in the level of available phosphorus significantly reduced MIP levels in the soils.

Dasht-e-Room is located in the south-west of Yassoj (capital of the province). It has an elevation of 2090 m above mean sea level with an annual precipitation of 1029 mm. In this study, the influence of climatic indices and some soil properties on grass covering development and formation and genesis of mollic epipedon were investigated. To answer the question of "which soil properties and climatic indices are more effective on the mollic organic carbon content of the topsoil and consequently on the genesis of the mollic epipedon?" many factors were investigated. In this study, a set of soil properties and climatic indices were identified. Amount and distribution of precipitation results in extenuation of grass cover. High elevation above mean sea level of this area (through increasing the precipitation and decreasing the air temperature), causes significant increase in soil organic matter. Clay content by forming organic and inorganic complexes and adsorption of humic substances helps in retention of organic matter in soil. Ali these indices are important in fulfilling the requirements for mollic epipedon in soil surface horizon.

Iran is located in an arid and semi-arid region of the world and its annual average rainfall is one-third of the world rainfall. Too little rainfall and long lasting drought during recent years have intensified the problems caused by water shortage and salinity of water resources. In such situations, saline and moderately saline waters can be used by considering proper management strategies to obtain optimum yields. In this paper, a series of studies on methods of using saline water such as substitution of crops, using proper leaching, alternate use of saline and fresh water and use of saline water after seed germination and plant establishment will be presented. The crops under study were wheat, barley, cotton and sunflower. The water use efficiencies with respect to water qualities and specific management practices were measured. The results showed that maximum water use efficiency with respect to the amount of fresh water used in the treatments was obtained by using 28 percent of total water used as fresh water in barley, 14 germination and establishment stage. In this case, the remaining water requirements of the crops were met with saline and slightly saline waters. Intermittent use of fresh and saline or slightly saline waters also produced high water use efficiencies, and in the meantime saved about 50 percent of the fresh water, which can be used to increase the cultivation of salt sensitive crops with high economic returns.

The effects of rainfall and temperature on the yield of dryland wheat were evaluated. The main objective was to develop a model that could predict dryland wheat yield before harvest by using the yield at fanner"s field and climatic data (temperature and rainfall) during the past 13 years. The following equation was developed: Y= 95+ 7.6 M.R+ 5.2 S,T.W,>4 °c +5.2 A.R- (4.6 FSP+25 mm), in which: Y = Yield (kg/ha), M.R = May Rainfall (mm), S.T.W>4 °c = Sum of Temperature>4 °c in winter, A.R = April Rainfall (mm), and FSP+25 mm = First Significant Precipitation + next 25 mm rainfall. From above equation it is concluded that rainfall has stronger effect on the yield than temperature. The increase in rainfall at the end of growing period is more effective than at the beginning of growing period. S.T.W. has a positive effect on yield, while temperature increase at the end of growing period has a negative effect on yield.