جستجوی مقالات مرتبط با کلیدواژه « nitrogen fertilizer » در نشریات گروه « گیاهپزشکی »

 The functional response is one of the important components of predator-prey interactions. It can be affected by different factors such as host plant quality. In this research, the functional response of the predatory gall midge Aphidoletes aphidimyza larvae to the nymphs of the melon aphid, Aphis gossypii reared on cucumber plants amended with different levels of nitrogen fertilizer (0, 100, 150 and 200 kg/ha) was investigated. The experiments were carried out at 25±1 °C, 60±5 % RH and a photoperiod of 16: 8(L: D). Different densities (2, 4, 6, 8, 12, 16 and 24) of mixed 2- and 3-d old nymphs of the aphid were separately offered to 4-d-old predator larvae. The numbers of killed preys were recorded after 18 h. Logistic and nonlinear regression analyses were used to determine the type of functional response and estimate of attack rate (a) and handling time (Th) parameters, respectively. At all treatments, the predator exhibited a type II functional response to change in A. gossypii density. The attack rate and handling time of the predator were ranged from 0.0623 to 0.1512 h-1 and 1.4646 to 1.8716 h, respectively. The highest value of attack rate and the lowest value of the handling time of A. aphidimyza were obtained at treatment of 200 kg/ha nitrogen. This study revealed that adding nitrogen to the soil in cucumber cultivation can improve the predatory ability of A. aphidimyza on A. gossypii. However, for understanding further details of the effects of different levels of nitrogen fertilizer on cucumber- A. gossypii- A. aphidimyza interactions, further studies need to be carried out.

Increasing crop competitive ability is an important part of integrated weed management (IWM). In this regard, identifying weeds reaction to soil fertility status for developing fertilizing methods, as components of IWM programs, is a necessity.
In order to evaluate the growth characteristics of purple nutsedge under the conditions of interference with onion, a factorial experiment based on randomized complete block design was conducted with three replications at the Research Greenhouse of University of Birjand in 2013. The first factor included three sowing methods of onion (seed sowing, onion set and transplanting) and the second factor included three levels of nitrogen (50, 100 and 150 kg N ha-1, equivalent to 25, 50 and 75 mg N kg-1 soil), urea fertilizer with a purity of 46% was used for this purpose.
The results of analysis of variance showed that sowing method and nitrogen levels had significant effects on plant height, leaf area, aboveground dry weight as well as tuber number and underground dry weights. Moreover, the interaction between sowing methods and nitrogen levels had a significant effect on plant height, leaf area, aboveground dry weight as well as tuber number and underground dry weights. The results of the comparisons of the mean for the interaction of planting methods and different levels of nitrogen indicated an increased weeds growth in direct seeding method and high levels of nitrogen in weed height trait, so that the greatest nutsedge height during the growing season (92.33 cm) was obtained at direct seeding method and high nitrogen levels . Moreover, the lowest weed height during the growing season was obtained at onion set planting method and 50 kg ha-1 nitrogen. The highest leaf area of purple nutsedge at ten weeks after planting (446.65 cm2), was obtained in direct seeding method and high levels of nitrogen, and the lowest value for this trait (203.38 cm2), was observed in onion set planting method. The greatest shoot dry weight of purple nutsedge during the growing season was observed in direct seeding method and high levels of nitrogen. The maximum amount of this trait at eight and ten weeks after planting was achieved in the level of 100 kg N ha-1 which was about 3.797 and 7.306 gr plant-1, respectively. Also the minimum shoot dry weight of weed was produced in onion set planting method and their amounts were about, 1.161 and 4.229 gr plant-1 at eight and ten weeks after planting, respectively. The greatest tuber number of purple nutsedge during the growing season were observed with seed planting method which were 7 and 15.33 tuber per pot at eight and ten weeks after planting, respectively. Moreover, the minimum tuber number of weed was produced in onion set planting method and were about 1.66 and 5.66 tuber per pot at eight and ten weeks after planting, respectively. The maximum underground dry weight of purple nutsedge during the growing season was obtained at direct seeding method and high levels of nitrogen. The maximum amount of this trait at eight and ten weeks after planting was obtained in the level of 100 kg N ha-1 which were about 2.472 and 5.396 gr plant-1, respectively .The minimum underground dry weight of weed was achieved in onion set planting method which were about, 0.888 and 1.873 gr plant-1 at eight and ten weeks after planting, respectively.
Overall ANOVA results showed that the sowing method and level of nitrogen as well as their interaction had a significant effect on all studied traits of purple nutsedge. Evaluation of growth characteristics of purple nutsedge under the conditions of interference with onion showed that the greatest and lowest growth of purple nutsedge were obtained where seed and onion sets planting methods were implemented, respectively. Moreover, the results indicated a positive response of purple nutsedge to high levels of nitrogen. Thus, in order to minimize the damage caused by purple nutsedge, the application of 100 kg N ha-1 nitrogen in onion set method is recommended as the most appropriate treatment for the management of purple nutsedge in infected onions farms. However, this study was conducted under greenhouse conditions and there is no doubt that repeating the test in the field is essential for verifying the results.

To study of environmental effects on sugar beet traits, population dynamism of Empoasca decipiens and Thrips tabaci, effects of three irrigation regimes (irrigation after 70, 105 and 140 mm cumulative evaporation from class A pan) and three fertilizer levels (200, 150 and 100 kg/ha net nitrogen) were evaluated in a complete randomized block design with 4 replication. The results showed that percentage of water and protein content and dry weight of crop foliage were affected by irrigation regimes and fertilizer treatments and these changes influenced the population of the pests. Irrigation after 70 mm in comparison to 140 mm, increased percentage of the foliage water 78.6%, but its protein content decreased 31.1%. Increase of nitrogen fertilizer from 100 to 200 kg/ha, increased protein content 12.25%. The highest and lowest mean of the pest population were observed in 105 and 140 mm irrigation treatments respectively. Irrigation after 105 mm in comparison to 140 mm, increased population of leafhopper and thrips as much as 3.37 and 3.51 times respectively. Increase of nitrogen fertilizer from 100 to 200 kg/ha, increased population of leafhopper and thrips 37.5% and 48.66% respectively.