Evaluation of ultrasound technology to break seed dormancy of common lambsquarters (Chenopodium album)

Although seed dormancy is advantageous for annual plants in the wild, unsynchronized germination in the laboratory leads to increased error in measurements. Therefore techniques to promote and synchronize germination are routinely used. Ultrasound is one of the newest methods for breaking dormancy in weed seeds. We have investigated whether ultrasonic waves can be used to break seed dormancy of common lambsquarters (Chenopodium album), a highly competitive annual weed that leads to significant reduction of yields of corn, soybeans, and sugar beets. Ultrasonic waves with frequency of 35kH were applied for 0 (control), 5, 10, 15 and 30 minutes using a completely randomized design. The results showed that the use of ultrasound waves generally enhanced the traits under investigation in the treated samples compared to the control sample. The maximum enhancement of germination percentage (180%), seedling dry weight (78%), and seedling vigor index I (271%) and II (392%) was seen in the common lambsquarters samples treated with ultrasound for 15 minutes and seedling length (40%) at 30 minutes compared to the control samples. Radical lengths were not statistically different from controls under any treatment and plumule length only increased marginally. These changes are reflected in seedling vigor index I and II measurements. For some of these traits, increasing the length of ultrasound treatment to 30 minutes had negative effects. These results demonstrate that ultrasound technology can be used as a quick, and efficient non-destructive method to break seed dormancy in common lambsquarters

Redroot pigweed (Amaranthus retroflexus L.) and lamb's quarters ‎‎(Chenopodium album L.) populations exhibit a high degree of ‎morphological and biochemical diversity

Amaranthus retroflexus L. and Chenopodium album L. are noxious weeds that have a cosmopolitan distribution. These species successfully invade and are adapted to a wide variety of diverse climates. In this paper we evaluated the morphology and biochemistry of 16 populations of A. retroflexus L. and 17 populations of C. album L.. Seeds from populations collected from Spain, France and Iran were grown together at the experimental field of the agriculture research of University of Mohaghegh Ardabili and a suite of morphological traits and biochemical traits were assessed. Among the populations of A. retroflexus L. and of C. album L. were observed significant differences for all the measured traits. The number of branches for A. retroflexus L. (12.22) and inflorescence length (14.34) for C. album L. were the two characteristics that exhibited the maximum coefficient of variation. Principal component analysis of these data identified four principal components for each species that explained 83.54 (A. retroflexus L.) and 88.98 (C. album L.) of the total variation. A dendrogram based on unweighted neighbor-joining method clustered all the A. retroflexus L. and C. album L. into two main clusters and four sub-clusters. Canonical correlation analysis was used to evaluate relationships between climate classification of origin and traits. Similarly, the measured characteristics did not group along Köppen climate classification. Both analyses support the conclusion that A. retroflexus L. and C. album L. exhibit high levels of diversity despite similar environmental histories. Both species also exhibit a high diversity of the measured biochemical compounds indicating they exhibit different metabolic profiles even when grown concurrently and sympatrically. Several of the biochemical constituents identified in our study could serve as effective indices for indirect selection of stresses resistance/tolerance of A. retroflexus L. and C. album L. The diversity of the morphological and biochemical traits observed among these populations illustrates how the unique selection pressures faced by each population can alter the biology of these plants. This understanding provides new insights to how these invasive plant species successfully colonize diverse ecosystems and suggests methods for their management under novel and changing environmental conditions

Composite patch reinforcement of a cracked simply-supported beam traversed by moving mass

In this study dynamic analysis of a metallic beam under travelling mass was investigated. A beam with an edge crack was considered to be reinforced using composite patch. Euler-Bernoulli beam theory was applied to simulate the time-history behavior of the beam under dynamic loading. Crack in the beam was modeled using a rotational spring. Dimension of the composite patch, crack length, stress intensity factor at crack tip and beam deflection are some parameters which were studied in details. Results were validated against those which were found through Finite Element Method

The effect of species, planting date, and management of cover crops on weed community in hybrid sunflower (Helianthus annuus)

Introduction: Studies showed that if mixed populations of annual weeds grow with the sunflower, for every 10% increase in weed biomass, seed yield would decrease by 13% (Van Gessel & Renner, 2000). In addition to control weeds using herbicides multi-stage spraying is required. In organic farming systems mulch is used to control weeds, protection, fertility and improve soil quality (Glab & Kulig, 2008; Kuchaki et al., 2001). Surface mulches from cover crops suppress weed growth by reducing light levels at the soil surface, thereby slowing photosynthesis. In return, these conditions reduce seed germination and act as a physical barrier to seedling emergence and growth (Teasdale et al., 2007). Materials and Methods: The experiment was carried out in Ardabil Agricultural Research Station, as a factorial experiment based on randomized complete block design with three replications during 1390-1391. The first factor was considered four types of cover crops including winter rye (Secale cereal), spring barley (Hordeum vulgare), winter wheat (Triticum aestivum) and control (no cover crop, no weeding).The second factor was mulch management at two levels (living mulch and dead mulch) and the third factor was two planting dates for cover crops (synchronous with sunflower planting and 45 days after sunflower planting). Sunflower seeding performed manually on 23 May on the ridges with 50 cm row distance and spacing between plants was 25 cm in depth of 5 cm. Cover crops seeds, rye, barley and wheat, were planted between rows of sunflower. Due to the low density of weeds in study field, complete weeding and sampling of weeds in one session was performed (60 days after planting date sunflower). Statistical analysis of data performed using SAS software and mean comparison performed using Duncan's test with probability level of 5% and 1%. Diagrams drawn using Excel (Version 8.2). Results and Discussion : Density and dry weight of Field bindweed (Convolvulus arvensis L.): Results of the study indicated that the interaction between cover crop and planting date on density and dry weight of bindweed was significant at probability level of 5% and 1%, respectively. The best condition of reduced density of bindweed was related to the time of using rye cover crop where reduced Field bindweed density to 64% compared to control (without cover crop, no weeding). Date of simultaneous planting of cover crop, reduced bindweed density from mean 15/7% plant.m-2 to 11/62 plant.m-2, compared to 45 days after sunflower planting. Hasannejad and Alizadeh, (2005) reported that rye significantly controlled the weeds of redroot pigweed, common lambsquarters, knotgrass, russian thistle and field bindweed compared to controls with no cover crop. All three cover crops had significant effect on reducing the dry weight of bindweed. Cover crops showed the potential to reduce density and total dry weight of weeds compared to no control weeds and increase the plant yield. In a study, the density and dry weight of field bindweed in treated living rye and dead rye reduced 100% and 85% respectively (Samadani & Montazeri, 2009). Density and dry weightof Pale bugloss (Anchusa italica Retz): The interaction (cover crop × planting date) on pale bugloss density and dry weight was meaningful in probability level of 1%.All three cover crops with simultaneous planting date showed lowest density of pale bugloss. Rye with proper ground cover in the beginning of season, and due to the long-term preservation of residues in the ground level, inhibited germination and growth of weeds for longer times. Results of the studies by (Abdollahyan Noghaby et al., 2011) on sugar beet showed that the effects of planting cover crops of triticale, wheat, rye and barley, between rows where sugar beet planted, to control weeds population would be the same as when herbicide used to control these weeds. Density and dry weight ofRussian thistle (Salsola kali L.): Results indicated that the interaction effect (cover crop × planting date) on density and dry weight of russian thistle was meaningful at probability levels of 1% and 5% respectively. The best result on the reduced density and dry weight of russian thistle observed when rye cover crop was used. Elmore, (1980) in a study observed that rye stubble, has more potential in reducing the biomass of wide spectrum of weeds, particularly the annuals. Density and dry weight ofCommon reed (Phragmites australis L.): Density of common reed on main effect of cover crop and its dry weight on main effect of cover crop and planting date showed meaningful difference with probability level of 1%. Cover crop of rye, due to the increased biomass, initial growth vigor, high tillering and in fact because of high allelopathy showed better performance in reducing density of perennial weeds such as common reed when planted simultaneously with sunflower, compared to wheat and barley. Samedani et al., (2005) reported that rye and wheat can better control the weeds due to high biomass. Dry yield of sunflower seed: Regarding the results of data analysis, the yield of sunflower seed influenced by cover crop treatments (P≤0.05). Sunflower seed yield in treatments of rye and wheat cover crops with control 1 treatment (no cover crop, complete weeding) showed no meaningful difference. Among cover crops, highest yield of seed related to wheat with 3916/7 kg.ha-1. Cover crop of barley showed poor yield compared to rye and wheat that was likely due to lower growth of barley and the lack of producing sufficient biomass and proper control of weeds. Cover crops can have positive or negative effects on grain crop yields, depending on environment, cover crop species and management (Miguez & Bollero, 2005). Conclusion: Results showed that cover crops, particularly rye, are very effective in reducing the density and dry weight of weeds so that the application of cover crops even resulted in increased yield of sunflower seed. Therefore, use of cover crops between planting rows of crops can be a good option to replace herbicides and conventional tillage and as a new and proper approach for sustainable management of weeds

Evaluating Rimsulforon Efficiency on Controlling Weeds in Potato at Different Growth Stages

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

Predicting Emergence of the Most Important Weed Species in Soybean (Glycine max L.) under Different Management Operation

Introduction: Summer annual weeds typically germinate in spring and early summer, grow throughout the summer, and set seeds by fall. Summer annual weeds are a persistent problem in summer annual row crops, competing directly for water, light, and nutrients, causing yield losses in quantity and quality. Although agriculture is increasingly relying on modern technology, knowledge of the biological systems in which these technologies are used is still critical for implementation of management strategies. Biological information about weeds is valuable and necessary for developing management strategies to minimize their impact. Scouting fields for pest problems are essential in any cropping system and knowledge of the timing and sequence of weed species emergence could increase the effectiveness of weed scouting trips and subsequent management practices. The success of any annual plant is directly correlated to its time of seedling emergence because it determines the ability of a plant to compete with its neighbors, survive biotic and abiotic stresses, and reproduce. The period and pattern of emergence of the weed community depend on the species present in the seed bank and their interaction with the environment. Therefore, knowledge of the weed species present in the soil seed bank and when these species are most likely to emerge is important in planning effective weed control programs. Temperature has been reported to be the main environmental factor regulating germination and emergence of weed species. Scientists have developed TT models to predict the emergence of weed species based on a daily accumulation of heat units or growing degree days (GDD) above a minimum base threshold value (Tbase). The predictive models for weed emergence based on the accumulation of TT appear to be accurate enough for projections of weed emergence time (Grundy 2003). Moreover, soil temperature data are easily accessible, making this type of model practical and useful to farmers. Many studies of weed growth, and thus predicting models for areas outside of Mazandaran is performed as a particular study. Because the differences in soil conditions, climatic, geographic and weed species there is a possibility that these models are not appropriate to predict weed species in Mazandaran province. Furthermore, the purpose of this experiment is investigation growth of weeds and develops an empirical model based on GDD to predicting the growth of several species of summer weeds in soybean. Materials and methods: The experiment was conducted as split split-plot in a randomized complete block design with three replications in the summer of 2016 in Dasht-e-Naz Company Sari-Iran with geographical coordinates 36º 39´ N 53º 11´ E, and 1 meters above sea level. The treatments included two tillage system (No Tillage, Tillage), three densities of 20, 30 and 40 plants per square meter of soybeans and Pursuit-doses (imazethapyr) (0, 50%, 75%, standard dose and 25% of the standard dose, respectively). To predict the growth pattern in each plot a fixed 50 × 50 cm quadrat fixed in the center of each plot and since the beginning of the season and after the first irrigation, counting of new grown seedlings was began based on weeds species. The Counting was performed weekly and then counted seedlings were eliminated after in any stage as long as new emergence was not seen. Non-linear regression (Sigma Plot 12.5) was used for the expression pattern of cumulative emergence of seedlings. The 3 parameter logistic function was fitted to the data. where y represents the predicted cumulative percent emergence, X0, GDD to reach the %50 cumulative emergence, a is the upper asymptote (theoretical maximum percent emergence), b is the slope of the curve. We considered that soil water was not a limiting factor for weed emergence, using soil temperature (growing degree days, GDD) as the only independent variable for predicting cumulative emergence. Thus, GDD were calculated with the soil temperatures by using the formula: where Tmax and Tmin are the daily maximum and minimum temperature, respectively, and Tb is the base temperature. Base temperatures used in the calculations of GDD were: 9.0ºC for A. theophrasti, 12.0ºC for S. halepense, 22.3ºC for A. retroflexus, 8.1ºC for E. maculate, 7.5ºC for P. oleracea, 4.0ºC for B. napus. From the emergence count data, mean emergence time (MET) and emergence rate index (ERI) were calculated as follows: where N1, ..., Nn is the number of newly emerged seedlings since the time of the previous count, t1, ..., tn are the GDD after sowing, and n is the number of sampling occasions. These two indices give us a simple indication of the emergence process, providing a useful tool to compare the progress of seedling emergence of each species in the two sites. However, they cannot provide more detailed information on emergence duration and speed. Results and Discussion: The results showed that except sorghum that in tillage treatment had the lowest cumulative emergence, other species in no-tillage treatment had the lowest cumulative emergence. At the end of the sampling patterns of emergence has been specified, all species of weeds, in the density of 40 plants per square meter of soybean and dose of 1.25 liter per hectare of herbicide Pursuit had the lowest cumulative emergence and in the density of 20 plants per square meter of soybean and dose of 0 liters per hectare of herbicide Pursuit had the maximum cumulative emergence. Among other species, Amaranthus retroflexus needed the lowest mean emergence time (MET) and the lowest growing degree days (GDD) to reach 50% emergence. Whereas, among the species, Abutilon theophrasti needed maximum mean emergence time (MET) and maximum growing degree days (GDD) to reach 50% emergence. On this basis, growth stage suitable for controlling pigweed, when the main wave of seedlings of other species still have not found growing. The best management practice used to manage weeds will depend upon the weed species present in the soil seed bank, and diversity of management tactics (e.g., planting dates) will result in fewer shifts in species composition