Journal of Agricultural Science and Technology
Volume:10 Issue: 1, Jan 2008

Knowledge of airflow resistance is an important consideration in designing an appropriate ventilation system and for proper fan selection. An airflow resistance device was designed and fabricated to measure the airflow resistance of potatoes. The device the composed of an air compressor, a rotameter, a cylindrical bin to contain the potatoes and an inclined u-tube manometer. Airflow resistance of potatoes was measured as a relationship between the airflow rate and pressure drop per unit depth (Pa/m) at 12 airflow rates of 0.085 to 0.55 m3 s-1 m-2. Two airflow resistance models, namely, Shedd’s and Hukill and Ives’, were fitted to measured data by using PROC NLIN of SAS. The effect of potato size below 120 g (small), at or above 120 g (large) and unsorted (mixed size), and bed depths of 25, 50, 75 and 100 cm of potatoes on resistance to airflow was determined. Results showed that the airflow resistance of small size potatoes for a 100 cm bed depth was 1.6 times higher than that for large size potatoes, and as the bed depth of potatoes was increased, the airflow resistance was increased.

Nitrate concentration of the soil, at the start of growing season, is high due to mineralization of soil organic N during the Fall and the addition of N fertilizers. It may be useful to exploit this N form as much as possible. Therefore, the nitrate uptake, assimilation and dry matter production of several wheat cultivars were examined in a series of experiments using a hydroponic culture system. Seedlings were grown at two rates of nitrates (0 and 1.0 mM) and the experiments lasted for 26 days. Significant genetic variation in the growth and nitrate uptake were observed. The Atila and Yavarous cultivars consistently produced large seedlings absorbing higher quantities of nitrate from the nutrient solution, compared to the Falat, Star and Seri 11 cultivars which produced smaller seedling and took up lower amounts of nitrate. However, apart from seedling vigor, there was evidence that some cultivars were more efficient physiologically in assimilating nitrate. For comparable amounts of nitrate taken up from solution, total dry matter production in this group of cultivars was considerably greater than others. Results of this work revealed that genetic differences among wheat cultivars affect nitrate uptake, which in turn indicated the influence of plant status and in particular root system on the potential of nitrate uptake.

To evaluate the yield and quality of barley (Hordeum vulgare)–vetch (Vicia desycarpa) intercropping, a series of experiments were conducted at the Experimental Field of the College of Agriculture, University of Tehran, in Karaj (Iran) from 2003 to 2005. The experiments were arranged in a randomized complete block with a split plot design and four replications. Three levels (0, 45 and 90 Kg N ha-1) of nitrogen fertilizer and three cropping systems (sole barley, sole vetch and barley-vetch intercropping) were allocated to the main and sub plots, respectively. The barley-vetch intercropping treatment had a replacement arrangement (50: 50) with single alternate rows. Land equivalent ratio (LER), was used to compare sole cropping with intercropping systems. Results showed the supremacy of intercropping of barley and vetch over single crops. Generally, increasing nitrogen fertilizer caused a decreasing trend in the biological efficiency of intercropping. The highest LER for grain was obtained in control (N fertilizer free) plots (LER= 1.145). Nitrogen fertilizer increased the forage yield, grain yield, crude protein content, and crude protein yield of barley and vetch in sole and intercrops. Nitrogen application increased water use efficiency. In this study, barley was the dominant crop. The intercropping vetch and barley had the highest productivity and crude protein yield.

Ten Solanum tuberosum cultivars and accessions from 11 wild Solanum species were evaluated for their tolerance to salt (200 mM NaCl or 100 mM Na2SO4), drought (35% PEG), cold (-4ºC) and heat (37ºC). Evaluation was based on electrolyte leakage from detached leaves of in vitro plantlets. Testing involved a rinsing treatment with three changes of distilled water to remove electrolytes from leaf and petiole surfaces, an exposure period of 24 hours for salt and PEG stress and four hours for temperature stress and a rehydration period of 24 hours in distilled water followed by measurement of electrical conductivity into distilled water to determine the effects of stress. Significant differences were observed between Solanum genotypes for all types of stresses. Among the S. tuberosum cultivars, stress tolerance was great to NaCl and PEG in Alpha and Bintje; to Na2SO4 in Agria and to heat and cold in Norland. Among the wild species, tolerance to all stresses was great in S. demissum, to all stresses except heat in S. acaule and to heat and cold in S. commersonii. The correlations among types of stress tolerance were significant for all stresses except for heat and drought. The level of tolerance in some wild species was significantly greater compared with the cultivars tested. There appears to be a wide genetic base available to improve the stress tolerance of cultivated potato.

Environmental variables, including soil water content (SWC), act as constraints on crop growth and productivity. Therefore, open air (E0), perforated (E1) and nonperforated (E2) plastic housings were used with well-watered (W0), moderately-watered (W1) and water-stressed (W2) bush bean plants to explore the relationships between water- use efficiency (WUE), carbon isotope discrimination (Δ) and isotopic composition (δp), leaf assimilation rate (A) and leaf Kjeldahl nitrogen (N) under diverse environments. The CO2 concentration and air carbon isotopic composition (δa) varied with the environment. The δa values were reduced by about 0.8 × 10-3 and 3.8 × 10-3 in E1 and E2, respectively, compared with that in E0. SWC significantly affected WUE, Δ, δp in both E0 and E1 but not in E2. The decoupling of plants from the outside atmosphere might have contributed in maintaining the above quantities almost constant in E2. The Δ-value increased by about 2.2 × 10-3 in E0 and 1.7 × 10-3 in E1 compared with E2. Water stress reduced the Δ-value by about 1.1 × 10-3in both E0 and E1. WUE and Δ were significantly correlated in E0 and E1 (r = - 0.72, and - 0.75, respectively) whereas there was no definite relationship between WUE and Δ in E2 indicating that stomatal conductance was almost independent of SWC. The N-content had little effect on Δ. Leaf N significantly increased in water-stressed plants depending upon the time of harvest and the environment. The mean leaf assimilation rate was significantly higher in E0 than in either E1 or E2.

Detention rockfill dams are an easy and common tool for flood control. Due to their coarse pores, the flow in void spaces is turbulent and non-Darcy. Different relationships introduced by researchers are used to define the hydraulics of the flow within the rockfill materials. The present research is aimed at gaining a better understanding of the difference among these relationships and the sources of uncertainty associated with the different parameters of each of the relationships. To examine the importance of various factors on the uncertainty of the outflow hydrograph, sensitivity analysis was conducted. For this purpose, a rockfill mass was provided, fifteen random samples of the mass selected, and then the physical characteristics of the material were measured or estimated. Also, some flood routing tests have been conducted. In these tests a physical model of a dam was installed and downstream water level was measured for different outflow rates. While the downstream water level was considered as certain variable but other parameters were seen as stochastic (stochastic parameters are considered as random variables) and outflow discharge as an output uncertain parameter. Uncertainty analysis has been conducted for different points of the outflow hydrograph by employing available methods. The results show that the Samani et al. and McCorocoudale et al. relationships have the lowest and highest uncertainty, respectively. The sensitivity analysis demonstrates different levels of sensitivity accompanied each of the relationship parameters which results in different effects on the total uncertainty of the relationships.

The stripe (Yellow) rust in wheat is one of the most important plant diseases in Iran. Since 1993 several epidemics have occurred in Iran causing the breakdown of widely utilized sources of resistance in wheat cultivars. Twenty-seven pathotypes were identified during 2003 and 2004 in greenhouse tests. Pathotypes 6E6A+, 6E22A+, 6E130A+, 6E134A+, 6E142A+, 6E158A+, 134E130A+ and 134E142A+ were more common during the course of this study. Virulence on plant/s with gene/s Yr2, Yr6, Yr7, Yr8, Yr9, Yr24, Yr25, YrSD, YrSP, Yr3N, Yr2+, Yr6+, Yr9+, Yr7+, Yr32+ and YrA was detected under greenhouse conditions. The majority of isolates with a high frequency (more than 88%) showed virulence on plant/s with Yr2, Yr6, Yr7, Yr9, YrA and Yr24 genes. No virulence was detected on plant/s with Yr1, Yr3V, Yr4, Yr5, Yr10 and YrSU genes. In a greenhouse test, frequency of virulence to wheat genotypes with the Yr32+, YrSP and YrSD gene was less than 7%; frequency of virulence to all other wheat genotypes was between 19 and 100%. During three years of field study, virulence on wheat genotypes Heines Kolben (with genes Yr2 and Yr6), Kalyansona (Yr2), Lee (Yr7), Avocet R (YrA), Federation*4/Kavkaz (Yr9) and TP1295 (Yr25) was common. No virulence was observed on plants with Yr1, Yr3V, Yr3N, Yr4, Yr5, Yr8, Yr10, Yr18, Yr24, Yr32+, YrSP, YrSD and YrSU genes in the trap nurseries. The coefficient of infection (C. I.) of the adult plant resistance gene, Yr18, was between 16-64 with moderate susceptibility and is going to be used in the breeding program in combination with other resistant sources.

Hairsine and Rose (1991) developed a process-based soil erosion model which described the erosion transport of multiparticle sizes in sediment for rain-impacted flow in the absence of entrainment in overland flow. In order to test this model laboratory experiments were carried out in a detachment tray using simulated rainfall. Three contrasting soil types were subjected to simulated rainfall at different rates (25-110 mm h- 1) in a 35×30 ×10 cm detachment tray. Rainfall was applied using a rainfall simulator with a single scanning nozzle located four meters above the soil surface that emitted drops with a mean diameter (volumetric D50) of 1.5 mm. Results showed that the Hairsine and Rose model can clearly describe the sensitivity of different soils to erosion by introducing three terms of detachability, re-detachability and settling velocity, though the model is unable to describe aggregate breakdown which takes place in one of the soil at higher rainfall rates. The experimentally observed relationship between ponding water depth and soil detachability parameters did not agree with previously proposed theories. In addition, the results showed that the Hairsine and Rose model tends to over-predict values at the lower end of the scale, and under-predict values at the upper end, although the average sediment concentration predicted for the entire data set is not greatly different from the average measured values.

This paper presents an analysis of annual precipitation trends in Iran. Mean annual rainfalls were collected from 30 synoptic stations with a reasonable geographic distribution and with data equal to or less than 50 years. Trend analysis was investigated using a "regression line slope" method (annual rainfall as a dependent variable and year as an independent variable). The results showed that for the entire period, and at a 95% level of significance, seven stations showed a negative trend, while a positive trend was found at six stations. The same data over the period of last 40 years demonstrated that four and 8 stations had negative and positive trends, respectively. Decreasing the record length, up to the last 30 years, resulted in fewer stations with any significant trend. The results identified that, in any case, the trend did not depend on the mean annual rainfall but rather record length could have some effects on it.