عنوان مقاله [English]
نویسندگان [English]چکیده [English]
Kermanshah province, Iran, comprises an area, of 24640 km2 and is located between 33°37′-35°17′N and 45°20′-48°1′E. The average annual precipitation is 450 mm. Most of the fields surveyed in this study lie between 542 and 1554 m a.s.l. Among the factors decreasing the wheat yields, weeds have an important role. The results of some researches show that the weeds flora depends on climatic conditions, temperature and amount of rainfall in spring and in summer. Environmental factor splay a key role in the weed cover. These differences affected by climatic conditions, latitude and longitude. Multivariate statistical methods that have been addressed in this study area powerful tool to study the relationship between environmental factors and ecological weed community composition (Hassannejad & Pourhaydar Ghafarbi, 2013; Lososova et al., 2004). Correlation and regression of data floristic and environmental factors were used in the CCA (Canonical Correspondence Analysis) technique (Legendre & Legendre, 1998).
Materials and methods
A survey was conducted to study the effects of soil and climatic factors on distribution of weeds in 85 irrigated wheat fields in 11 counties based on its area under irrigated wheat. An Experiment was conducted in Kermanshah province during 2011-2012. After choosing the field to be surveyed, the surveyor followed a “w”-designated set pattern to enumerate the weeds in each type of field. The pattern and number of 0.25 m2 quadrats varied according to the size of the fields. The field surveys were made during the wheat tillering to stem elongation stages. Frequency, density and mean density index of species in each county were calculated. After weed species were collected in the fields, we arranged the samples into the first matrix where weed species are represented by columns and fields of different districts by rows. Also, in the second matrix, environmental factors are represented by columns and fields of different districts by rows. Data on weed communities and environmental factors of all districts were analyzed through with ordination methods like canonical correspondence analysis (CCA) and weed species distribution and environmental factors displayed in ordination diagrams. These ordination methods were done with mean density of 29 abundant weed species for CCA using CANOCO (Version 4.5). Ordination plots were produced for both sampling sites and weed species associated with environmental factors. For CCA, we used site elevation, humidity for 10 years period, daily raining for a 10 years period. Soil characteristic included calcium, phosphor, potassium, nitrogen, sodium, magnesium, pH were determined. Sand, clay and silt in soils were measured and elevation of each field was gained by GPS.
Results and discussion
162 weed species belonging to 33 plant families were identified in these fields. Multivariate analyses with canonical correspondence analysis (CCA) showed that changes in the weed species distribution were due to soil characters (pH, Calcium, Magnesium, Phosphorus, Nitrogen, Sodium, Potassium, silt percent, clay and loam in soil tissue, cation exchange capacity, EC) and environmental conditions during former years. The first and second RDA axes described 64% of variations in the weed populations affected by climatic factors. Winter wild oat (Avena ludoviciana L.), ryegrass (Lolium rigidum Gaud.), wild mustard (Sinapis arvensis L.) and canary seed (Phalaris brachystacys Link.) in areas of high temperature and low altitude, had a wide distribution. High evaporation increased wild barely (Hordeum spontaneum C. Koch.), Corn cleavers (Galium tricornutum Dandy.) and Vetch (Vicia assyriaca Boiss.) density during last decade. Where the soil nitrogen and phosphorus rates were high, Wild barely (Hordeum spontaneum C. Koch.) density was found frequently in wheat fields of Kermanshah. In the wheat fields of Kermanshah, Bindweed (Convolvulus arvensis L.) and wild safflower (Carthamus oxyacantha M. B.) were more abundant in clay soils. High Corn cleaver (Galium tricornutum Dandy.) density was found in alkaloid and sandy soils.
Generally predict that if the temperature rise over the next few years, weed density and abundance of wild oat, ryegrass and wild mustard will be increased in irrigated wheat fields.
The authors acknowledge the financial support of the project by agricultural Research education and extension organization and College of Agriculture and Natural Resources, Tehran University.