نشریه یافته های نوین کشاورزی
پیاپی 1 (پاییز 1385)

Application of allelopathic plants for the control of weeds in many crops has been proved. This field study was conducted for two years (2001-2002) at Hamadan agricultural research center. Experiments were a factorial design based on randomized complete block with 8 treatments and 4 replications. Three crops (Brassica napus، Vicea sativa، Secal cereal) as allelopathical crops were cultivated by alone، double and treble at autumn season and as green manure، mixed with soil at spring، and then a week after، potato (Agria) was planted in plots. Results showed that، there were significant differences in all measured parameters include of fresh weight of cover crops (g/m2)، fresh weight of weeds (g/m2)، number of weeds per square meter and potato yield (t/ha). S. cereal treatment has the highest fresh weight between cover crops. All of treatments could reduce number and weight in weeds at comparison with check treatments (without cover crop). Yield of potato increased by 40% in top treatment (S. cereal) in comparison with check treat. The final results revealed that، the allelophathical plants as cover crops، before potato، not only increases yield، but also decrease weed population in potato field without usage of herbicides.

This study was carried out in 2004 in Damavand region to evaluate the effect of plant density and nitrogen fertilizer amounts as top dressing on yield and yield components of potato (Agria cultivar) on a split plot design of the study comprised of randomized complete blocks design with four replications. In this experiment, plant densities (7.97, 5.29 and 3.32 plant /m) and nitrogen fertilizer amounts (0, 100, 200 and 300 kg urea/ha) were levels of main plot and sub plot respectively. Characteristics such as number of tuber per plant, average tuber weight, weight of tubers per plant, tuber yield (t/ha) and dry matter percentage after harvesting were recorded and statistically analyzed. The results showed that there were significant differences between plant densities and nitrogen fertilizer levels for all traits(Duncan 1%). Means comparison showed that density of 5.29 plants per square meter and fertilizer levels (200 and 300 kg urea/ ha) from the point of view of all traits were superior to the others. Also interaction effects of plant density and nitrogen fertilizer statistically were significant for all characteristics.

In order to investigate the effect of between and within row distance on the quantitative and qualitative traits of three soybean cultivars, a field study was conducted at research field of the Faculty of Agriculture, urmia university. The factorial-split plot design of the study comprised of randomized complete block with three replication. Main plots were including two row spaces(45 and 60 cm) and three within row distance (5, 10 and15 cm) that located in factorial arrangement. Subplots were allocated to three cultivars; WILIAMS, AS3925 and CLARK-63 (maturity group II, III, IV) respectively. Results showed that increasing between and within row spacing about all cultivars caused to decreasing in plant height and height of first pod, but increased the number of nods, number of pods per main stem, branches and per plant, diameter of stem and number of branches per plants. The highest total dry matter, yield and harvest index were obtained from between and within row spacing 45*5 cm. In comparison with other cultivars, AS3925 with 3510.8 kg/ha showed superiority over the two other cultivars. The between and within row distance did not show significant effects on oil and protein content, but there were significant difference among cultivars. Williams and AS3925 cultivars with 36.85 % and 19.36 % respectively showed the highest protein and oil content.

In order to evaluation of water stress at silique and grain filling stages on rapeseed cultivars, This experiment a factorial design of the study comprised of randomized complete block with four replications. There were two levels of conventional irrigation periods. Normal irrigation at 80 millimeter evaporation pan class A and water stress condition (discontinuing irrigation before siliqua formation). There were twelve cultivars of rapeseed: Celsius, Elvis, Sahara, Sunday, Slm 046, DS29955, Banjo, Olpro, Okapi, Opera, Herkules, Hyola 401. In this evaluation, most stages of plant phenology such as plant height, silique number in plant, seed number in silique, mean kernel weight, kernel yield, seed oil percentage and oil yield were measured. Results showed that Elvis with mean yield 5312 kg/h and oil 2270 kg/ha had superior points during two irrigation conditions. The difference of seed yield in two irrigation was 12% and in about oil yield water stress decrease 6% soil yield. Result showed that four genotypes of rapeseed including Elvis, Olpro, Sahara and Sunday were better than other in speed yield and oil seed during two type of irrigation.

The effects of salinity levels of NaCl were examined on seed germination of three clover species: Trifolium pratense, T. resupinatum and T. repens. Salinity levels comprised of 0 (control), 50, 100, 150, 200, 250 and 300 milimolar NaCl. Treatments were arranged factorial design and were compared in a Completely Randomized Design (CRD) with three replications. Results showed clover species, salinity levels and their interactions had a significant effect on germination percentage of clovers. As the level of salinity increased, seed germination decreased. In regard to salinity tolerance at germination stage,T. resupinatum was the most tolerant species and T. pratense and T. repens, were ranked as the second and third grade respectively. As the level of salinity increased,the percentage of abnormal seedling on T. resupinatum, the percentage of hard un-germinated seeds On T.pratense and the percentage of smooth un-germinated seeds on T. repens, were increased.

The predatory bug Orius albidipennis is one of the most important biological control agents of some orchard, cultivated and ornamental crop pests in Iran. Therefore, determination of its biological characteristics is important. In this research, life table and population parameters of O. albidipennis were investigated in a growth chamber at temperature of 25±1ºC, 65± 10% relative humidity and a photoperiod of 14:10 (L:D) hours on different developmental stages of Tetranychus urticae. The experiment was carried out using 100 one day old eggs of O. albidipennis and mortality of different developmental stages was estimated daily. The results indicated that age specific mortality of O. albidipennis on different developmental stages of two-spotted spider mite was started from 4th day and increased gradually with regular fluctuations. Life expectancy was increased after emerging of nymphs and then was decreased regularly. Life expectancy was estimated 12.97 and 18.86 days in nymph and adult emerging time, respectively. The gross fecundity rate, gross fertility rate and gross hatch were determined 76.45±0.42, 60.12±2.29 and 0.79, respectively. The mean numbers of eggs per female per day was estimated 4.25 eggs.

Lacewings are the predatory insects that widely used in biological control programs. Among them, Chrysoperla carnea (Stephens) (Neu.: Chrysopidae) is a promising biological control agent in releasing against pests in greenhouses and fields. In this study, two release methods of lacewing’s eggs were compared: distribution of eggs mixed with sawdust as an egg carrier and dispensation of the eggs using chrysobag (the special net bags). Experiments were conducted on the cucumber Cucumis sativum L., against cotton aphid, Aphis gossypii Glover in netted cages. Ratio 1:5 was compared in two methods in a condition that each cage contained 4 plants and density of aphids was higher than that of the last experiments. This experiment was conducted in a randomized complete block design. First egg release showed no significant difference between two methods. Approximately 80-84% reduction in population density of aphids was observed compared with control treatment. However 2nd egg release, 7 days after 1st release, showed 94-95% reduction in aphid population. Better control of aphids was observed with repeated egg release. If experiments conducted in cage without presence of generalist predators (such as ants) of eggs, two methods had the same effect to control aphids. Although two methods had the same efficacy without presence of ant, if eggs released in greenhouses and fields, chrysobag protects eggs from ants and other predators. Therefore, chrysobag with a high efficiency and without bad affect on host plant. Chrysobag method suggested to be used in commercial greenhouses and field.

At the present research the connecting rod of universal tractor (U650) was simulated using ANSYS software and with its fatigue analysis, longevity after a 1000000-cycle load, was assessed. The goal of the investigation was analyzing connecting rod behavior against repetitive loads for fatigue phenomena. The results not only save cost and time but also optimize design process. By sophisticated analysis, critical nodes which probability of crack growth is more were finding. Results show that the critical point of crack growth obtained with 26.793 Mpa. This point in both tensile and compression test shows critical attitude. With fully reversed loading condition, load fluctuation cycle is about 108 so that with less stress concentration factor, it could be increase. The results obtained from the present paper can be used to bring up modifications in connecting rod manufacturing.