Flora and Structure of Weed Communities of Agro and Orchard Ecosystems in Bardaskan

Weeds are among the major constraints to crops growth that can affect yield based on their species composition and density. Weed competition reduces yield and consequently farm income. Weeds infestation also encourages disease problems, serves alternate host for deleterious insects and diseases, slows down harvesting, restricts operations, increases the cost of production and reduces the market value of crops. Weed flora composition is strongly associated with regional climate, soil and irrigation water characteristics, and management methods. Weeds dispersal power is amongst the major factors affecting the agricultural plants success. Diversity reflects the complexity of a system and can maintain its sustainability. Higher diversity results in higher inherent complexity of agro-ecosystems and strengthens their processes. It is necessary to realize the spatial distribution and temporal properties of the biodiversity components in agro-ecosystems, for the conservation and optimal utilization. Since weeds as complementary components of agro-ecosystems are inseparable, studying species and their functional and structural diversity plays an important role in weed management and balance of ecological systems. Weeds are highly problematic in agricultural systems in Bardaskan county reducing yield quality and quality. However, the first step in weed management is identifying the flora. Therefore, this study was conducted to determine the flora and structure of weed communities of agricultural and horticultural products in Bardaskan-Iran.

In order to study flora and structure of weed communities of fields and orchards in Bardaskan county, this research was conducted on wheat, rapeseed, autumn sugarbeet, cotton, cumin, melon, pistachia, vineyard, pomegranate and saffron during 2016. Sampling was performed using the W systematic method proposed by Thomas (1985) and McCauley et al. (1991) by using 0.5×0.5-meter quadrate with a slight modification (random systemic method of W instead of systemic of W method). The basis of sampling was systematic, but after determining the main sampling points with intervals of 20 steps on the W system as the main sampling points, other sampling points were randomly selected as sub-sampling points within a radius of 5 to 10 m from the main sampling points to increase the sampling accuracy. Sampling was not performed to remove the marginal effects depending on the farm and garden up to 20 meters from the farm margin. The weeds in each quadrat were counted and their genera and species were identified and weed population indices including mean relative density, relative uniformity and frequently were calculated.

In this study, 106 weed species belonging to 30 families were identified which the most species were from Poaceae with 22 species, Brassicaceae with 15 species and Asteraceae with 13 species. From the 106 identified weed species, 80 species (75.47%) were broad-leaf and 26 species (24.53%) were grassy weeds. In terms of life cycle, 82 weed species (77.36%) were annual and 24 species were perennial. Based on photosynthetic pathway, 82 species (77.36%) had C3 photosynthetic pathway, 23 species (21.7%) C4 and one species (0.94%) was CAM photosynthetic pathway. Among the studied crops, the largest number of weed species were observed for saffron (61 species) and pistachia (55 species) and the lowest species were found for cotton (26 species) and rapeseed (28 species). The broadleaf species of Russian knapweed, hoary cress, African rocket, lambsquarters, camel thorn, mesquite, prostrate knotweed, field bindweed, Russian thistle, common orach and the grassy weed species of mouse barley, wild barley, ryegrass, wild oat, bermudagrass and lesser canarygrass had the highest relative dominance, frequency and density (plant m-2).

In general, a wide range of broadleaf and grassy weeds especially Poaceae and Brassicaceae families was found in the studied area. Overall, the results showed that most weeds identified in this study can grow in different environmental conditions and their growth is less dependent on growth condition. Therefore, presence of some weed species in all studied fields and orchards indicates the possibility of their growth under different environments and managements. Therefore, difference in management strategies and climates can be considered as one of the important factors of differences in the flora and population structure of weed communities in Bardaskan. It seems that weed management in Bardaskan county is inappropriate for various reasons including farmers' lack of knowledge on weeds control, application of inappropriate chemical technologies, and the lack of specific herbicides in some products.