weed density

Oilseeds are very important as the raw material for the production of vegetable oil (one of the basic needs of the society in the food field). Therefore, achieving any success in increasing the amount of production and supplying as many of these products as possible to meet the domestic needs of the country is considered a valuable and great success. Safflower, with the scientific name Carthamus tinctorius L., is an annual long-day plant from the chicory family. Wild mustard (Sinapis arvensis L.), which is also called Brassica kaber in some literatures, is one of the most important weeds belonging to the Brassicaceae family. Competition can perhaps be considered the most important biological interference factor effective in determining crops productivity.Effective management of weeds in agricultural systems is very decisive. Extensive and repeated use of herbicides has led to the emergence of resistant weed biotypes, which has often increased the cost of control. It has also caused some concerns about the negative environmental effects of herbicides. When the competition is for light, the competitive ability of the species is first determined by the morphological traits. The response of crop height to weed competition is related to the density and intensity of competition and the type of weeds and can be positive or negative.

An split plots experiment based on randomized complete block design with three replication was carried out in the Research Farm of University of Birjand during the 2018-2019 cropping year. The treatments include four level of phosphorus fertilizer (0, 25, 50 and 75 kg P 2O5 ha-1) as the main plot and the four wild mustard densities (0, 7, 14 and 28 pl m-2) as subplots. Plant growth characteristics were measured from 150 to 210 days after planting (DAP) in five stages at 15-day intervals. Also, at the harvest maturity, the yield and yield components of the crop were determined.

According to the results, the highest (35.48 g m-2) and lowest (28.23 g m-2) safflower leaf dry weights were obtained from control (no-mustard) and 28 pl m-2 mustard densities at 165 DAP, respectively. The highest (1.67) and lowest (1.19) leaf area index of safflower were achieved at 210 DAP using 25 and 50 kg P 2O5 ha-1, respectively. Based on these results, it can be concluded that the most effective level of phosphorus on the improvement of safflower growth traits (e.g. leaf area and dry weight and stem dry weight) and its competitive ability was 25 kg P2O5 ha-1, although the its effects were not significant for many traits, and as phosphorus levels increased, the competition shifted more in favor of wild mustard. In accordance with these results, and probably due to luxury consumption by weeds, it has been observed that when weed density is high, adding fertilizer leads to superiority of weed growth over crop (Blackshaw et al., 2008). Also, the highest leaf area index of mustard (0.63) was obtained at a density of 56 mustard pl m-2 at 165 DAP and the lowest one of (0.26) was observed at a density of 14 pl m-2 at the same time. It was also observed that the height and leaf area index of wild mustard were the highest in all measuring stages at higher weed densities, indicating the competitiveness of the weed. The increase in weed density had a negative impact on the safflower, although insignificant in many cases, which could be the result of the competitive effect of mustard for resources such as radiation and nutrients (Wright et al., 1999).

In general, the increase in weed density had a positive effect on the yield and its components in wild mustard and a negative effect on the safflower, and under these condition, the application of more than 25 kg P2O5 ha-1 does not have a positive effect on the crop. Thus, it seems that the revision in weed management and the use of fertilizer as an agronomic strategy can be effective in reducing the crop losses caused by the presence of high densities of weeds (Clements et al., 2014).

Vicia hyrcanica grows in crop fields and field margins, pastures, meadows, orchards, vineyards, uncultivated areas, and other open areas in western parts of Iran. This is an annual, cool-season weed, which can reduce crop yield substantially. The population of this weedy species during last yeard has been increased and it is now considered as an invasive weed in the cuktivated areas of west of Iran. Hence, the aim of this study was to determine the diversity, density and dominance of Vicia hyrcanica compared with other weed species infesting wheat and chickpea fields in Kuzaran city in Kermanshah province, Iran. Furthermore, another aim of this experiment was to prepare the map of contaminated areas with V. hyrcanica as well as the endanger fields for being invaded by this weedy species.

 For conducting this study, a list of important areas for growing wheat, chickpea, rainfed and irrigated in Kuzran city was prepared, then the distribution of this weed was evaluated during growing season of 2020. 300 farms of both irrigated and rainfed wheat and chickpea farms of Kuzaran city, Kermanshah province, Iran were selected for sampling. The selected fields were monitored in such a way as to cover all important areas of wheat and chickpea production areas in Kuzran city. The selection of farms at a distance of approximately 3-5 km before the emergence of wheat spike gradually began in late April from different parts of the city and continued until late May. Sampling time in different parts of the province was from the beginning of stem emergence to the end of wheat clustering. In order to identify seedlings, they were labeled in the field and seedling identification keys were used to identify them. Parameters related to relative abundance, species richness, density and relative uniformity as well as diversity and dominance indices were measured to determine the importance of the mentioned weed species at the farm level. Through using GIS technique, the distribution map of yellow flower vetch in these areas was drawn.

 In addition to yellow vetch, another 21 species of geraminae weeds were observed. The highest average species density with 35.2 plants per square meter and the highest relative abundance of 36.3% is related to Vicia hyrcanica and two species Tragopogon major and Melilotus officinalis both with 0.27 and 0.26, respectively, had the lowest mean species density and relative abundance. In adition, the most common broadleaf species included Catchweed bedstraw (Galium tricornutum Dandy), yellow vetch (V. hyrcanica), wild mustard (Sinapis arvensis L.) and Makhobeli (Cephalaria syriaca (L.) Roemer & Schultes). Uniformity index in irrigated and rainfed wheat fields of Kuzran city of Kermanshah province shows that the differences between species were very close in terms of uniformity and ranged from 0.53 (Sinapis arvensis) to 95% (related to Silybum marianum).

 The highest prevalence index was related to species (V. hyrcanica) and all other weed species had a dominance index of less than 100. Based on the results obtained, among the species identified in wheat and chickpea fields of Kuzran city, five species with the highest prevalence of Simpson species were introduced as the species with the highest relative importance. Differences in species diversity and dominance indices were related to the amount and type of management operations on farms. Caspian vetch and Catchweed bedstraw were identified as the main invasive species. The predominance of these weeds, especially the Caspian vetch, as a weed, creates problems for farmers in the production of important crops, such as peas, because these crops are similar to vetch, and they separate it from the seeds of the crop. It is difficult and somewhat impossible by Bojari devices. Therefore, presence of this weed in these fields is critical and their spread should be prevented. In addition to seed contamination, endrils of vetchs allow V. hyrcanica to attach to crop plants, which results in hindering crop harvest and reducing its yield. Finally, totally, these attributes help to increase the infestation area by this weedy species and my explain its invasion status in the region.

Rapeseed is one of the most important crops cultivated for oil extraction and has the highest annual growth rate (in terms of production) among the essential oilseeds in the world. Due to its slow growth rate, the rapeseed plant has little competitive ability against weeds in the early growing season, which causes it to be severely damaged by weed interference. Since the long-term presence of weeds in rapeseed could reduce its quality and yield, early weed control is essential to achieve economically acceptable yields.

In order to control broadleaf weeds in rapeseed fields, a factorial experiment based on a randomized complete block design with three replications was conducted in winter 2019 in Benvar Nazer region, Andimeshk county, Iran. The experimental factors included two types of rapeseed hybrids (Hayola 50 and Agamax) and clopyralid herbicide (1.5 L ha-1 recommended dose, EC30%, Aryashimi, Iran) application with a fixed dose of 1 lit ha-1 for all treatments along with oxadiazon herbicide (recommended dose of 3 L ha-1 for using in rice as pre-plant before the two leaved barnyard grass, EC12%, Shimagro company, Iran) at doses of 100, 175, and 200 ml ha-1, and oxadiargyl herbicide (recommended dose of 3-3.5 L ha-1 for using in rice as pre-emergence or at the beginning of weed emergence in transplanted rice, SC3%, Herbicide Production Company, Iran) with doses of 100, 125, and 150 ml ha-1. Weedy and weeding control (complete control by manual weeding) were considered as control treatments. Herbicides were applied by a 12 liter back sprayer equipped with a TJET 11003 nozzle, which was calibrated for spraying 200 liters per hectare, in the initial 2-leaf stage to the beginning of 4 true leaves for chemical control of weeds in the plots. The grass weeds were removed by hand. Broadleaf weeds were counted separately according to the weed species at before spraying, three and six weeks after spraying and were cut at the soil surface and dried at 70 °C in oven. Then, weed dry weight was measured with a digital scale 0.01 and the percentage reduction in density and dry weight of weeds were calculated. In addition, the amount herbicides used on rapeseed was visually assessed using the EWRS standard table. Then, yield and yield components of rapeseed including number of siliques, seed no. per silique, 1000-seed weight, seed yield, biological yield and harvest index were measured.

Results showed that the predominant weed species in the experimental plots included wild clover, queen anne᾿s lace, mallow, Anagalis spp., wild mustard, and field bindweed, which the highest frequency (31.29%) belonged to wild clover and the lowest frequency (1.03%) belonged to field bindweed. The ANOVA results showed that the reduction percentage of density and dry weight of weeds and seed yield were affected by experimental treatments; as the treatments of clopyralid + oxadiazon 100, clopyralid + oxadiazon 175, clopyralid + oxadiargyl 125 in Hyola50 hybrid and clopyralid + oxadiazon 175 in Agamax hybrid reduced the density and dry weight of weeds by 100%. While, the lowest reduction percentage of weed density and dry weight (44.74 and 55.33%, respectively) was observed in Agamax hybrid and clopyralid (1 L ha-1) treatment. Also, the highest and lowest herbicide injury on weeds were observed in clopyralid+oxadiazon 100 (9.67%) and clopyralid alone and combination of clopyralid+oxadiargyl 100 and 150 in Agamax hybrid (0%), respectively. The highest seed yield, biological yield and 1000-seed weight of rapeseed were observed in clopyralid+oxadiazon 200, oxadiargyl 125 and 150 (3377.6 kg ha-1, 11295 kg ha-1, and 3.27 g, respectively), and the lowest was observed in weedy control treatment (2064.2 Kg ha-1, 7458 Kg ha-1 and 2.87 g). 1000-seed weight is less affected by treatments and is a genetic trait. The highest and lowest number of seeds per silique under the influence of herbicide treatment were related to clopyralid+oxadiazone 175 and clopyralid+oxadiargyl 100 (23.33 and 18.17), respectively. An increase in the number of seeds per silique was observed with increasing the dose of herbicide oxadiazone in combination with clopyralid up to 175 ml ha-1. The highest number of siliques per plant was obtained in weeding treatment in Agamax hybrid with 189.33 silique per plant, which was significantly different from weedy control treatment. Also, the lowest number of weed control silique was obtained with Hayola 50 hybrid, which was not significantly different from clopyralid+oxadiazone 100 in Agamax hybrid.

According to the results, mixing herbicides is a solution to eliminate the competition of weeds with rapeseed and increase the yield so that the yield of up to 3.3 tons is obtained, which compared to clopyralide only as a control treatment. In general, the highest yield of rapeseed from plots treated with clopyralid+oxadiazon 200, oxadiargyl 125, and 150 were the best treatment in comparison with the applied treatments. The best treatment is the one in which rapeseed yield has been the highest. In addition, since clopyralid is a selective herbicide in rapeseed, it did not have sufficient efficacy due to poor control of important weeds such as wild mustard. It should also be noted that further testing of the above herbicide mixtures on rapeseed fields throughout the country is necessary in order to obtain the results that are the basis for recommending these mixtures in rapeseed.

Phaseolus vulgaris L., known as the common bean and green bean among other names, is a herbaceous annual plant grown worldwide for its edible dry seeds or unripe fruit. Weeds are one of the most important factors in reducing the yield of common bean. Since tillage promotes germination of many weed species, tillage followed by destruction of weed seedlings with minimal further soil disturbance often leads to lower weed density in the crop. This is referred to as the stale seedbed method of planting. In false seedbed technique, preparation of a seedbed is followed by one or more superficial cultivations as about one-week intervals prior to planting the crop. Although these procedures are widely used by farmer, they have received little scientific study. This experiment was conducted to investigate the combined method of using seed bean bed preparation with application of herbicides such as EPTC, linuron, and trifluralin, in order to bean weeds control in Aleshtar region.

In order to investigate the effect of seedbed preparing methods and soil applied herbicides in weed management and yield of common bean, an experiment was carried out as factorial in a randomized complete block design with four replications in 2015-2016 growing season in Hatam Abad village, Selseleh, Aleshtar, Lorestan, Iran. Experimental factors included seedbed at two levels (fasle seedbed and stale seedbed) and soil applied herbicides at three levels (EPTC (3 L ha-1), linuron (1.5 L ha-1), and trifluralin (1.5 L ha-1)). Two treatments including weed infested (as control) and weed free (as treatment), are also considered. Each plot was divided into two parts, one infested with weed (as contaminated control) and the other treated with herbicide. The percent reduction of weed density and dry weight were calculated at 30 and 60 days after spraying. The studied traits were plant height, number of pods per plant, number of branches per plant, length of pod per plant and number of seeds per pod, economic and biological yield and harvest index. The SAS9.2 software was used to analyze the data.

The results showed that weed dry weight reduction (79.09% and 78.57%) was greatest in stale seedbed plus EPTC and trifluralin at 30 days after herbicide application (DAHA), respectively. While, the lowest reduction in weed dry weight (28.27% and 35.41%) was observed in stale and false seedbed with linuron application. Weed dry weight reduction at 60 DAHA in false seedbed (76.58%) was lesser than stale seedbed (84.34%). The highest and lowest weed density and dry weight reduction percentages (90.38% and 89.69%) and (64.48% and 64.48%)) were obtained trifluralin and linuran, respectively. The highest percentage of increase in number of pods per plant belonged to weed free (52.01%), followed by linuron (42.5%), EPTC (40.43%) and trifluralin (34.34%). The highest percentage of increase in the number of seeds per pod belonged to weed free (36.14%) and then EPTC (29.54%), linuron (28.06%), and trifluralin (28.06%). Regarding grain yield, the highest percentages were weed free (52.92%), EPTC (44.11%), linuron (31.13%) and trifluralin (30.30%), respectively. The highest percentage of biological yield increase belonged to weed free (32.46%), linuron (25.5%), EPTC (20.81%), and trifluralin (17.83%), respectively. The highest percentage of harvest index belonged to weed free (34.33%), followed by linuron (21.37%), EPTC (19.55%), and Trifluralin (18.23%).

The result of present study showed that trifluralin could control weed more than EPTC and linuron. The weed dry weight reduction percentage in the stale seedbed was also higher than that of the false seedbed. In all treatment, the percentage of yield increase of weed free was higher than the other treatments. Except for grain yield, which showed a significant difference in herbicide treatments, other treatments did not differ significantly. Totally, the false seedbed technique has several limitations. First it can only be effective if the soil is warm and moist enough to allow germination of weed seeds. A second limitation is that the soil is kept bare and loose for a more period, and this may lead to more erosion. A third limitation is that yield may be lost if planting is delayed by the pre-plant cultivation. A fourth problem is that although cultivation prior to planting may greatly reduce one set of species, if planting is delayed, a new set of species may become physiologically ready to germinate.

Introduction Potato is globally the fourth important food crop after rice, wheat, and maize and is cultivated in several countries worldwide like Iran. Weeds are the most important restriction factor for crop development in agricultural systems and the absence of weed control lead to crop yield reduction between 10 to 100 percent and this reduction could be a serious threat for a growing world population to be considered. Rimsulfuron is a sulfonylurea herbicide for control of weeds in potato, corn, wheat, barley and canola. It can be used as pre or post emergence in potato. These herbicide act through inhibition of enzyme acetolactate synthase (ALS), which catalyzes key reactions in the biosynthesis of basic branched-chain amino acids that are essential components of the growth process in plant cell division such as valine, leucine, and isoleucine
Materials and methods In order to study rimsulfuron (Titus 25% DF) effect on weed biomass as a postemergence herbicide, a field experiment was carried out in the farm located 3 km out the city of Ardabil during 2014. The factorial experiment was performed based on randomized complete block design with three replications. Potato cultivar was Agria (common cultivar in Ardabil). The first factor was rimsulfuron doses with six levels (5, 10, 20, 30, 40 and 50 gr a.i. / ha), and the second factor was time of application based on different potato growth stages, (Potato emergence, stoloning and tuber bulking). Also two treatment (with and without weeding) were considered as control. Tubers were hand sown on 22th May in rows 75 cm apart and 20 cm in the rows at 10 cm depth. Rimsulfuron was applied by backpack sprayer fitted with 8001 flat fan nozzles. Three weeks after treatment, weed sampling was carried out by a quadrate sized 0.375 m2. Tubers were harvested from two center rows to determine total tuber yield per hectare. Two models fitted to the data were three parameter logistic and three parameter sigmoid.
Data were analyzed using SAS 9.1 and MSTAT-C. Analysis of variance was used to test the significance of variance sources, and Duncan’s Multiple range test (P ≤ 0.05) was used to compare the differences among treatments.
Results and Discussion Results showed that the maximum reduction percent of redroot pigweed (Amaranthus retroflexus L.), field bind weed (Convolvulus arvensis L.), lambsquarter (Chenopodium album L.), total weed biomass and density achieved by 40 and 50 gr a.i. / ha application. So that 40 and 50 gr a.i. /ha of rimsulfuron compared to control reduced weed density up to 49.47and 55.38 % and biomass up to 89.97 and 94.63 %, respectively. Also results showed that 40 and 50 gr a.i. /ha of rimsulfuron compared to control reduced biomass of redroot pigweed 89.91 and 95.50 %, Field bind weed 84.28 and 94.79 % and lambsquarter 92.75 and 96.87 percent respectively. That there was not statistically significant difference between 40 and 50 gr a.i. /ha of rimsulfuron.
Among rimsulfuron application times, potato emergence stage reduced total weed density and biomass 36.45 and 68.04 %, respectively which is compared to control (weedy). Rimsulfuron application at potato emergence stage reduced biomass of redroot pigweed and lambsquarter 62.51 and 71.08 percent respectively. However it had no significant effect on biomass of Field bind weed.
The results showed that potato tuber yield was 46.31 and 45.96 ton/ ha while rimsulfuron applied 40 and 50 gr a.i. / ha. Among rimsulfuron application times, potato emergence stage had total tuber yield 47.58 ton/ha.
Conclusion Results showed that the maximum reduction percentage in weed density and biomass was observed for treatments in which were used 40 and 50 gr a.i. / ha application. Application of rimsulfuron at potato emergence reduced weed density and biomass and increased total tuber yield. Itproves the effectiveness of the rimsulfuron for potato emergence without damage. Furthermore the effective dose of rimsulfuron for 50 percent reduction in biomass of redroot pigweed, field bind weed and lambsquarter were 14.36, 12.26 and 10.17 g a.i. /ha, respectively. The results also showed that rimsulfuron application 40 and 50 gr a.i. /ha increased total tuber yield by 19.90 and 20.51% respectively. Application of 40 and 50 gr a.i. / ha at potato emergence stage produced maximum total tuber yield per hectare. The result of this study showed that 40 and 50 gr a.i. /ha rimsulfuron application at potato emergence assessed as the best treatment to control weed and increase total yield.

Elimination or reduction of tillage in conservation agricultural systems has led to wide variations in germination, emergence, and growth of weeds and has caused variations in the density and diversity of weeds under such systems. Maintaining crop residues on the soil surface has many potential benefits in agricultural production systems; such as reducing water and wind erosions, increasing the soil organic matter content, improving the soil structure and sowing conditions, as well as a better weed management through allelopathy or physical interference provided by the crop residues. Crop residue and tillage system cause potential changes in the soil temperature and water content, which influence soil density, structure, moisture, as well as soil temperature and nutrients. Crop residues act as mulches and can effect on weed seed germination and seedling emergence. Therefore, the objectives of current study were to evaluate the effects of no-tillage systems on: (i) narrow- and broadleaved weed densities, (ii) crop yield and (iii) water productivity (WP).
A two-year field study based on a split plot experiment in a randomized complete block design with four replications was carried out in Zahedshahr, Fars province, Iran (latitude 28˚44΄N, longitude 53˚48΄E, 1180 m altitude) during 2009-10 and 2010-11 growing seasons. The planting practices including moldboard plow, disk and leveler were practiced in conventional tillage plots and crop planting was performed using a drill seeder (made by Kohorasan Co., Iran). The no-tillage plots were directly planted without any soil disturbance and removing wheat residues of the last year using a direct planter machine (model Berteni, Argentina). Furrow irrigation was used at both systems and a water counter (model WD, size DN100) was applied to measure the amount of used water based on m3 ha-1. 1 x 1 m quadrates that were installed at the center of each plot. Crop density, narrow and broadleaved weed densities were recorded at 30 days after the beginning of crop emergence. Wheat grain yield was calculated at harvest time. Comparison of the means was conducted based on protected LSD (PLSD) at 0.05 significant levels.
Tillage systems indicated a significant effect on wheat density. The average number of crop seedlings in no-tillage plots was 27 % higher than in the conventional tillage plots. Maintaining crop residues on the soil surface provided a better site for crop germination and emergence. The response to tillage system and year effects varied depending on the weed species. Results showed that the effect of tillage systems, year and their interactions were significant on the density of Lolium temulentum and Sinapis arvensis, while in the case of Phalaris minor and Hordeum spontaneum just the tillage regimen significantly influenced the weed density. L. temulentum and S. arvensis plants showed an almost similar pattern in their response to tillage systems and year effects. The density of these two species significantly decreased under no-tillage system compared with conventional tillage operations. Moreover, their densities in conventional tillage plots were significantly greater in the second year of the experiment than the first year. The lower seedling emergence of P. minor and H. spontaneum under no-tillage circumstances is not surprising, as crop residues prevent from reaching the light on the soil surface and the light requirement for germination of these species has been reported in several studies. The water productivity of the no-tillage plots was greater than of the conventional ones at both two years of the experiment. Preservation of wheat residues on the soil surface decreases soil temperature via shading and causes reduces the evaporation rate from the soil surface. Although there was no significant difference between wheat yields in the two growing seasons under conventional tillage environment, wheat yield in no-tillage plots was significantly greater in the second year of the experiment than that of the first year. Low weed densities and high WP were observed under no-tillage conditions, although the crop yield was greater in conventional tillage plots. It seems that this yield reduction in no-tillage plots is mostly due to greater C/N ratio in no-tillage plots than conventional tillage ones.
According to the results, although wheat yield decreased under no-till system, increased water productivity, weed control and reduced cultivation costs might justify the adoption of no-tillage cropping systems by local farmers. Other principles of conservation agriculture including suitable crop rotation systems and planting cover crops must be incorporated into the no-till cropping system. As the occurrence of autumn rainfall is usual in these dry regions, employment of the stale seedbed might be another promising technique which controls early season weed species in no-tillage systems.

Corn (Zea mays L.) is one of the most important crops in the world that need high water requirement during its developmental stages. Improvement of water management system increases crop production all over the world, especially in aired and semiarid climates. For instance, drip irrigation system can be used to provide accurate and adequately nitrogenous fertilizers while conventional systems such as flood irrigation has lower efficiency in the use of nitrogen fertilizers. An improved understanding of the effects of nitrogen (N) on crop–weed interactions is needed for development of integrated weed management systems where reasonable application of N fertilizers is considered too. Moreover, maize competition with weeds is another important factor that affects its yield. So this study was conducted to evaluate the effect of nitrogen on yield and yield components of corn and weed interference under two systems of flood and drip irrigation. In order to evaluate the effect of irrigation methods and nitrogen under weed-infest condition on yield and yield components of maize, a field experiment was conducted in split-split plot design based on randomized complete blocks during 2012 growing season at the Collage of Agriculture, Shiraz University. Factors were irrigation type as main plots (flooding and drip), nitrogen levels as sub plots (0, 75 and 150 kg ha-1) and weed interference as sub-sub plots (weed infest and weed free). Drip irrigation system was carried out by using strips with 20 cm output, 0.175 mm thickness and 16.5 mm internal diameter. Urea 46% was used to supply nitrogen. A control (weed free) was used in this experiment. Statistical analysis of the data was performed by using SAS 9.1 software and comparing of the means was done by the least significant difference test (LSD) at 5% level. The results showed that under weed interference, grain yield (51.0%) and yield components (number of rows and kernels per ear, ear length and diameter and seed weight) decreased significantly. In the former studies weed competition had been expressed a major limitation for corn production. It seems that weeds caused corn yield losses indirectly through their influence on the resources required for crop growth and competition for light and belowground resources. It was also shown that weeds are high nitrogen consumers cause to reduce the amount of available nitrogen for crops growth. Therefore when corn and weeds emerge simultaneously in a mixture, weeds competitiveness increases with increasing nitrogen supply. However, nitrogen addition has a positive effect on both corn and weeds growth, but weeds tends to respond more to nitrogen addition than corn. In this study we observed similar results and increasing of nitrogen application from 75 to 150 kg ha-1 which increased grain yield by 44.4% and ear length by 4.9 %, but under weedy condition decreased ear length by 25.8%. Nitrogen application caused a different response in each irrigation system, so that the application of 75 and 150 kg ha-1nitrogen under drip irrigation system reduced weed biomass by 62.6 % and 64.4 % compared to flooding system respectively. Applying drip irrigation system also reduced weed density (56.8%) and biomass (54.3%) and increased corn grain yield compared to flooding irrigation system. Under weed free condition and using of drip irrigation system number of grain per ear increased by 50.1% significantly. In drip and flooding irrigation systems under weed free condition compared to weedy plots, number of grain per ear increased by 17.0% and 7.9% respectively whilst drip irrigation system compared to flooding irrigation system increased ear diameter by 50.5%. However hundred grain weights were affected by all treatments, under weed free condition compared to weedy condition, in drip irrigation system hundred grain weights increased by 18.2 %, but in flooding irrigation system no significant differences was observed. Performance comparison of grain yield under irrigation systems revealed that drip irrigation increased grain yield by 62.0 %. The results showed that the effectiveness of nitrogen was much higher under drip irrigation compared to flooding irrigation. It can be because of that drip irrigation system directly provide water for plants and prevent from water availability for weeds. Therefore, appropriate irrigation system as an agronomical practice affects the growth and weed competition ability in corn.

In order to evaluate the effect of planting date of soybean cultivars in weed management، experimental design in the form of strip split plot as a randomized complete block design with three replications was conducted in Dasht-e-Naz Company Sari-Iran، in 2008. Treatments studied included three planting dates with a 20 days intervals (5 / 17، 6/ 6 and 2008/6/ 26) soybean cultivars (BP، JK، 032، 033 and Sahar) and weed control، including: 1 - Sonalan as pre-planting (3lit/ha) 2 - Sonalan as per-planting (3 lit/ha) + Sencore (Sonalan coincident) (700 g/ ha) 3 - Sonalan as per-planting (3 lit/ha) + Sencore (Metribuzin) as per-emergence (700 g/ ha) 4 – Control + Basagran as per-emergence (3 lit/ha) 5 – Treflan (Trifluralin) as per-planting (3 lit/ha) + Basagran as per-emergence (3 lit/ha) 6 – control. The results showed that planting date had a different effect on the density of either weed. The result also showed that Ethal-fluralin (Sonalan) can control narrow leaf weeds by alone. But combination of Ethal-fluralin (Sonalan) with Sencore (Metribuzin) whether pre-planting or pre-emergence can be control broadleaf weeds including wild melon (Cucumis melo)، velvetleaf (Abutilon theophrasti)، Sow thistle (Sonchus oleraceus) and nightshade (Solanum nigrum). These treatments also gave the highest seed yield. Between experimental cultivars، JK and 033 reduced density of wild melon. 033 also reduced the Barnyard grass (Echinochloa crus-galli) density. BP، Sahar and JK produced the highest yield، but BP had the highest yield in presence of weeds.