جستجوی مقالات مرتبط با کلیدواژه « competitiveness » در نشریات گروه « زراعت »

In order to study the competitiveness of potato cultivars with weeds, an experiment was conducted in 2016 at field research of Ardabil Agriculture and Natural Resources Research Station. For this purpose a randomized complete block has been used with three replications. The treatments include ten potato cultivars, grown with and without natural weed competition, with yield loss ranging from 3% in Satina to 84% in Agria in weedy condition. Also, the Competitive Ability (CA) of the cultivars differs. It is observed that satina cultivar has had the highest competitive index (CI) and could reduce the weed dry mass by two folds in comparison to Spirit as a poor cultivar. Also, stem diameter is seen to be negatively correlated with weed dry mass and positively correlated with tolerance and competition indices. Stem diameter in Satina has significantly stodd higher than Spirit cultivar. In general, the results of this study declare that Satina cultivar is considered as a tolerant and recommendable option for cultivation in Ardebil region than other cultivars, less susceptibility index (SSI) and more stable than weed, and can be introduced as a competitive cultivar in non-chemical weed management programs.

Recent multi-year experiences in Iran show that reliance on income from the sale of crude oil leads to instability in export earnings.  In order to reduce the dependence of the Iranian economy on crude oil exports, export policies should be directed towards export of non-oil commodities, including exports of agricultural products. Saffron is one of the most important export items of the agricultural sector and medicinal plants. However, its production and export has not grown exponentially in recent years despite growing allocation of land and production. The results of various studies in  have shown that one of the main reasons for failure of Iranian companies in the world market for exporting medicinal herbs is decline in competitiveness in these markets in recent years. Therefore, this study seeks to examine factors affecting competitiveness of Iran's saffron exporting companies in global markets. Competitiveness measurements using symmetric revealed comparative advantage index and analysis of its influencing factors were analyzed using the Porter Diamond Competitive Model and Fractional Logit Panel regression model. The statistics and data were collected through collecting questionnaires from 35 saffron exporter companies for 2011-2016. The results showed that the six components of the Porter diamond model including demand conditions, factor conditions, supporting industries, firm strategy, state and unpredictable events affect the competitive situation of the companies under study. Accordingly, observance of quantitative and qualitative export standards, prevention of fluctuations in the price of saffron, reduction of exchange rate fluctuations in line with government policies, reduction of production fluctuations due to climate change by providing technical solutions and sufficient attention of companies to marketing strategies are proposed as new ways to improve the competitive situation of the companies being studied.

The cultivation of crops in most parts of the world, in addition to competing with different weed species, is affected by a variety of environmental stresses, including salinity stress. The changes in the growth rate and production of crops under the influence of salinity stress and competition with weeds have been extensively studied. However, what is currently less investigated is the competition of several species of weeds with crops and the competition of crops with weeds under salt stress. Therefore, the aim of this experiment was to evaluate the competition between tumble pigweed, common purslaneand and common millet under soil salinity stress. This study was conducted as a factorial experiment based on a randomized complete block design with three replications. Experimental treatments consisted of two rates of soil salinity (3 and 10 dS.m-1), and different ratios of interference of the three species (tumble pigweed, common purslaneand, millet) including 0-0 -100, 0-25-75, 12.5-12.5-75, and 25-0-75, 50-0-50, 25-25-50, 0-50-50, 75-0-25, 37.5-37.5-25, 0-75-25, 0-100-0, 50-50-0 and 0-100-0. The desired density in each pot was constant and equal to 8 plants. After preparing the soil and passing through a 2 mm sieve, fertilizer and saline solutions were added to the soil and the soil was transferred to 5 kg pots. Then all three plants were planted and attained to intended density at the four leaf stage. At the end of the experiment, each plant species was separately harvested from each pot and were weighed after complete drying. Finally, for analyzing the results of the experiment, relative yield indicators, total relative yield (Land Equal Ratio), relative crowding and agressivity indices were used. The results showed that increasing soil salinity decreased the dry matter produced by common millet, tumble pigweed and common purslane by 19.5, 4.7 and 27.8 percent, respectively. Comapring the relative yield of millet with those of tumble pigweed and common purslane and also both weeds together by different ratios of planting showed that these values were more than predicted ones under either 3 or 10 dS.m-1 salinity level, which indicates the weak competitive ability of these two weeds against millet. The results of the relative crowding index of species showed that in the ratio of 75% of millet and 12.5% tumble pigweed and 12.5% of common purslane, the greatest rate of relative crowding index was achieved for millet under salinity level of 3 dS.m-1. Also, the greatest relative crowding index of tumble pigweed and common purslane under either salinity level was observed with the cultivated ratio of 75% for both weeds and 25% for millet, suggesting an increased competitive ability of these two weed species through increasing their density even under a higher level of soil salinity. By evaluating the agressivity index between tumble pigweed and purselane, it was found that this value was negative for purselane under the salinity level of 3 dS.m-1. Therefore, it seems that tumble pigweed is more competitive than the common purslane where both weed species grow together. In general, the results of this study showed that in conditions of salinity of 3 and 10 dS.m-1, common millet had more competitive ability than the two studied weeds, but with increasing salinity level, competitive ability of millet was reduced, while it increased weeds competitiveness. Therefore, in the situation of high weed densities, we may expect a greater damage to crops under salinity stress.

Grass pea is an annual plant which produces adequate yield in unfavorable conditions. South Khorasan is one of the areas where grass pea cultivation has been spread, but due to rainfall rate and high evaporation and transpiration in this region, plants are facing drought stress; On the other hand, Amaranthaceae family weed (pigweed and tumble pigweed) also among the most important weed in farm fields in this region of Iran. Since the studies of multi-species competition provide more detailed information about relationships circumstance between plants, the aim of this study is to evaluate the competitiveness of pigweed, tumble pigweed and grass pea under drought stress using experiments with replacement series. The experiment was carried out in a factorial based on RCBD with three replications. Experimental treatments consisted of two levels of water stress (80 and 50% of soil water field capacity), different weed interference ratios with grass pea (tumble pigweed + pigweed- grass pea) including (0-100, 75-25, 50-50, 25-75 and 100-0%), as well as different two weed interference ratios with each other (tumble pigweed - pigweed) containing (0-100, 50-50 and 100-0). Optimum density of eight plants per pot was fixed. Plants were cultivated after soil preparation and addition of chemical fertilizers and at four leave stage, the desired density was reached. At the end of the experiment, all plants were harvested from each species separately and weighed after drying. Finally, for results analyzing of the experiment, relative yield indices, total relative yield (LER) were used and relative competition Intensity index and aggressiveness index were used. The results showed that grass pea, pigweed and tumble pigweed dry matter, decreased with reducing soil water content of 80 to 50 % of field capacity by 33, 30 and 12 % respectively. Also, the results showed that predicted yield of tumble pigweed was close to the actual yield. The results of relative yields showed that in sowing ratio of 50-50% grass pea and pigweed, 50-50% of grass pea and tumble pigweed, also 50-50% of grass pea and both two weed together in 80% treatment of soil water field capacity, the relative yield of grass pea were 0.33, 0.36 0.39 respectively, that with drought stress increasing to 50% of soil water field capacity, increased by 36, 50 and 31% reached to 0.45, 0.54 and 0.51 respectively. Changes in relative yield curve of grass pea under 80% treatment of soil water field capacity irrigation, in competition with tumble pigweed, pigweed and both weeds together was convex; which indicates that with enough water in the soil, grass pea competitiveness is less than Amaranthaceae family weed. The results of relative competition Intensity index showed that numerical value of this index for grass pea, tumble pigweed and pigweed, in all sowing ratios is a positive value, which shows higher inter-specific competition than intra-specific competition in different sowing ratios. Also the results showed that in the sowing ratio of 50% grass pea with 25% tumble pigweed and 25% pigweed in 50% treatment of soil water field capacity, Grass pea aggressiveness index against both weed separately and together was positive value, which indicates a relative superiority of grass pea under drought stress in competition with these two weed. In generally, the results of this study showed that water stress reduced all three plants growth but, decline in tumble pigweed was lower. The results also showed that the competition formed between these three species was Inter-specific and have negative effects on all three plants. Although the aggressiveness index indicates that the grass pea was beaten in most sowing ratios, but with the increase of drought stress and water deficit, due to inter-specific competition between weed, competition between weed and grass pea has been reached to lowest level.

IntroductionConservation agriculture (CA) has been proposed as a set of principles that could help reverse widespread soil degradation in the region and help farmers stabilize yields by mitigating the effects climate variability. Though numerous questions remain on how CA practices might fit in a complex mix grain- grazing farming systems, where limited land, cash and labor impose severe constraints on farmers’ options. Intercropping is a CA approach that has been traditionally practiced in many parts of world and has some advantages over monocultures. One of its obvious advantages may be to increase forage protein, the principle being improvement of forage quality through the complementary effects of two or more crops grown simultaneously on the same area of land. Intercropping supplies efficient resource utilization, reduces risk to the environment and production costs, and provides greater financial stability, making the system more suitable particularly for labor-intensive, small farmers. Morpho-physiological differences and agronomic factors such as the proportion of crops in the mixture and fertilizer application regulate competition between component crops for growth-limiting factors. Greater total uptake of nutrients and other growth factors by the component crops in the intercropping is the primary cause of obtaining intercropping advantage. Intercropping research studies involving a cereal and a legume have not considered the combined effect of fertilizer application and plant population variation. Maize and beans are important food crops, mostly grown by resource- poor farmers in complex and risky farming systems. Morgado & Willey (2003) showed that competitive effect of intercrop beans on maize yields was high at higher plant populations.
Materials & MethodsIn order to study the production potential and competitiveness of sweet corn and bean varieties, an experiment was carried out based on a randomized complete block design with three replications in the Agricultural Research Station, Ferdowsi University of Mashhad, during growing season of 2014-2015. Treatments included different combinations of bean (B) and sweet corn (C): 25%B%C, 50%B%C, 75%B%C and bean varieties and their monoculture. Bean varieties consisted cowpea, white, red, pinto and landrace and chase sweet corn. Studied criteria were yield components (pod number per plant, seed number per pod and 100-seed weight), biological yield, seed yield and harvest index (HI) of bean and biological yield, seed yield and HI of sweet corn and land equivalent ratio (LER).
Results & DiscussionThe results indicated that effect of intercropping ratios were significant (p≤0.05) on seed yield, biological yield, HI, pod number per plant and seed number per pod and biological yield and seed yield of bean. The highest seed yield of bean was observed in 75%B 25%C with 1675 g.m-2 and the lowest was related to 25%B 75%C with 778 g.m-2. The maximum seed yield was obtained in pinto (2342.33 g.m-2) and the minimum was achieved in landrace (847.75 g.m-2). Seed yield of sweet corn in monoculture was higher than intercropping ratios, but by increasing density in intercropping ratios with bean varieties it significantly enhanced. The highest and the lowest seed yield in intercropping ratios were observed in 75%C 25%B with 7348.1 g.m-2 and 25%C 75%B with 3466 g.m-2, respectively. In all combinations of intercropping ratios LER was higher than 1, that it represents intercropping is better than monoculture. The maximum land equivalent ratio was calculated with 1.47 for 25%B (landrace) 75%C. The results showed that landrace was competitive than other varieties.
ConclusionThe effect of intercropping ratios of sweet corn with bean landraces were significant (p≤0.05) on seed yield, biological yield, HI and yield components of the crops. The maximum seed yield was obtained in pinto and the minimum was achieved in landrace. Seed yield of sweet corn in monoculture was higher than intercropping ratios, but by increasing density in intercropping ratios with bean varieties it significantly enhanced. According to the results, intercropping of plants of 25%B (landrace) 75%C can be beneficial in term of ecological management.

Water is one of the most important factors for plants growth and development and both weeds and crops compete for it. To investigate the influence of drought stress on competition between grass pea and pigweed, a greenhouse experiment was conducted as randomized complete block design with three replications based on replacement series arrangement at Faculty of Agriculture, University of Birjand in 2012. Treatments were different planting ratio of grass pea– pigweed (100-0, 75-25, 50-50, 25-75, 0-100%) and four water regimes (100, 75, 50 and 25% soil field capacity, FC). Results showed that a reduction of soil water content from 100 to 25% of FC (pot) caused a 95% (P <0.01) in dry matter production of both species in their pure cultivation. The relative yield index, relative invasion index and relative dominance index of these species indicated that, where both plants were competing, pigweed was more competitive than the grass pea at high soil moisture levels (100 to 50% of the soil (pot) field capacity). Although with further soil water reductions to 25% of field capacity, grass pea showed the superiority over wild amaranth, it seems that growing grass pea is not economically justifiable under these circumstances.

One component of integrated weed management is use of cultivars with high competitive ability against weeds. Balance between competitiveness and productivity of rice under condition of presence or absence of weeds, is complicated the breeding of rice cultivars to increase competitiveness against weeds. Path coefficient analysis has been widely used in crop breeding to determine the nature of relationships between the grain yield (GY) and its contributing components. To study the weed-suppressive ability by rice, an experimental was conducted in a randomized complete block design with four replications in Chprsr, Tonekabon Rice Research Station at 2009. The experimental treatments include seven varieties (Daylamani, Khazar, Sepeedrud, Neamat, Dorfak, Fajr and Shiroodi) and three lines (830, 841 and 843) of rice that were cultured in the presence of barnyard grass. The results of path analysis showed ability withstands competition (AWC), thousand grain weight (THGW), fertile tiller number m-2 (FT), filled grain number panicle-1 (FG) and competitive index (CI) as the first-order variables for GY. The traits such as specific leaf area of rice at 25 days after transplanting (Rsla25), ear length (EL), Filled grain percentage (FGP), specific leaf area of rice at heading stage (RslaHD) were as the second-order variables for GY and influenced positively this response variable. Dry weight of barnyard grass biomass was negatively correlated with CI and RslaHD. However, these traits have a positive effect on grain yield, but fertile tiller number and specific leaf area at heading stage are measurable before maturity of grain. Thus, select of cultivar with high grain yield is possible before heading of grain, through these two traits. The variety of Shiroodi and line of 843 with highest value of specific leaf area at 25 days after transplanting and heading stage, high ability withstands competition and competitive index have a high capacity to compete with barnyard grass and can be considered as a suitable cultivar in selection processes and are also used as crosses parents.