جستجوی مقالات مرتبط با کلیدواژه "dominance index" در نشریات گروه "زراعت"

In conditions where don't have enough water for irrigation, intercropping of forage plants is one of the ways to achieve sustainable agriculture. Biochemical and physical properties of soil tillage system can affect the yield of plants in intercropping. Therefore, with the aim of investigating the forage yield and competitive indices of intercropping, this experiment was performed in the cropping seasons of 2020-2021. Treatments included conventional, minimum, and no tillage system. Intercropping patterns also included monoculture of forage sorghum and maize, alternate row cultivation maize and forage sorghum and alternate cultivation on planting rows. The results showed that the highest plant height (295 cm) and leaf area (6.88) was obtained in intercropping and conventional tillage. The highest forage yield was also observed in sorghum monoculture. However, the land equivalent ratio of mix intercropping with 1.17 showed the superiority of intercropping over monoculture. Evaluation of competitive indicators such as dominance index, relative crowding coefficient, and competitive ratio showed that forage maize is the predominant plant in intercropping conditions. The system productivity index with 8.11 showed that intermediate cultivation on planting rows was superior to other treatments in conventional tillage conditions. The results showed that in conventional tillage and intercropping conditions, acceptable yield was obtained; this advantage can increase water efficiency and use of sorghum in intercropping.

By understanding the diversity and dominance of weed species, which is affected by changes crop management systems and weed control practices, these plants can be managed more efficiently. In this study, the diversity of weed species of irrigated wheat fields was studied in an area of ​​less than one, one to two, two to four, four to eight and more than eight hectare in the central region of Arak, Iran, in 1919. A total of 74 weed species were identified from 25 plant families, of which 61 species were dicotyledons and 13 species monocotyledons, 78.38% annual and 21.62% perennial as well as 95.95% C3 and 4.05% C4. Also, Asteraceae and Brassicaceae families among dicotyledons and Poaceae family among monocotyledons had the highest species diversity. According to the dominance index, ten dominant weed species were flixweed (Descurainia Sophia), binweed (Convolvulus arvensis), foxtail grass (Alopecurus myosuroides), common thistle (Cirsium arvense), Iranian knapweed (Centaurea depressa), lowgrass (Polygonum aviculare), corn cleavers(Galium tricornutum), Syrian mustard (Eeuclidium syriacum), goldbachi (Goldbachia laevigata) and nodding hypecoum(Hypecoum pendulum). There was a significant inverse relationship between field size with Shannon-Wiener and Pielou's uniformity indices and their highest values (2.58 and 0.84, respectively), was obtained in the fields less than 1 ha and the lowest values (1.48 and 0.61, respectively), in the fields more than 8 ha. In contrast, the relationship between field size and Simpson's dominance Index was positive and significant and its value was calculated 0.1 and 0.33 for fields less than 1 ha and more than 8 ha, respectively. In total, the results of this study showed that a few weed species in most wheat fields in this region were well distributed and had high density, abundance, uniformity and dominance index and if the usual farm management methods continue, there is a possibility that species diversity will decrease and the problematic weeds will dominate.

The Khorasan Razavi province is the center of saffron production in Iran and the world. Among factors affecting saffron gap yield, weeds are the most important one. However there is no compiled information about saffron weed flora population and its structural characteristics in the Khorasan Razavi province. In order to identify and determine the density and frequency of weed species on saffron fields in the Khorasan Razavi province, 118 fields in 6 counties during two years (2014 and 2015) were selected based on the cultivation area and yield per area. In each field, weed species were counted in each sampling point and weed population indices including mean relative density, relative uniformity and frequently were calculated and latitude and altitude were recorded by GPS. By using recorded data, population indices of different weed species in the studied saffron farms including mean relative density and relative frequency of species were calculated. During 2 years, a total of 52 weed species were identified and observed within the saffron fields. Between plant families, Brassicaceae, Asteraceae, Poaceae, Fabaceae and Charyophilaceae were the most abundant families, respectively. The results showed that the highest and lowest number of weed species belong to Kashmar and Gonabad counties, respectively. Based on the frequency index, the important annual weed species on saffron fields of the Khorasan Razavi province wereMouse Barle (Hordeum murinum) and London Roket (Sisymbrium septulatum) and perennial species were Hoary Cress (Cardaria draba) andCommon yarrow (Achillea millefoliam)

In order to compare the weed flora and determine the abundance and distribution of weed species in dryland wheat fields, a study was conducted in Ilam province in the spring of 2014. Sampling weeds in wheat farms of 50 ha at the tillering stage of wheat was done. After monitoring the wheat fields of Ilam, 51 weed species were observed in no control conditions and 27 weed species in control conditions, which the results showed that narrow leaves were more abundant compared to the broad-leaved weeds in the studied fields. Winter wild oat with frequency 38.5 and wild barley with frequency 30.5 were most important of narrow leave weed, and London rocket with frequency 37 and Canada thistle with frequency 33 were most important of broad leave weeds in wheat farms of Ilam. Also the species of bermudagrass, shortspike canarygrass, annual bluegrass, cypress spurge With C4 photosynthetic pathway and the remaining monitored plants have been C3 photosynthetic pathway. Finally, it was observed that the Ilam farms have been highest diversity index of Shannon-Wiener (2.52) and Rika had the lowest rate Shannon-Wiener diversity index (1.81). In control conditions, areas with higher diversity index had most uniformity and species richness index. The areas with higher diversity index had a higher species abundance and richness.

A study was conducted to assess the weed flora changes in the irrigated wheat fields during the last decade in 52 fields located in seven cities at Tehran province in 2015. The frequency, Unifromaty and dominance index of species were calculated and they were compared with the mentioned indices from 2005. In 2015, 66 species of weedsfrom 26 families were identified, of which, 55 species were broad-leaf and the others were grasss. 10 species that had been observed in 2005 had been omitted from the fields and 15 new species from 11 families were identified. Amaranthaceae, Dipsacaceae, Plantaginaceae, and Solanaceae were the four families that were for the first times observed in the fields of the province for the first times. Brassicaceae, Poaceae and Asteraceae families were dominant families in the fields. The broadleaf species of flixweed, knotweed, bindweed and fumitory with dominance indices of 117/94, 97/82, 81/09 and 46/11 and the grasss of wild oat,wild barley,annual ryegrassferalrye with dominance indices of 86/59, 50/94, 27/64 and 15/41 had the greatest dominance indices respectively. The differences of dominance index of the most species were negative. The results of study indicated the dominance reduction of the most weeds and their control improvementy although in a few number of weeds such as wild mustard and catchweed, an increase in the dominance index was observed.

In order to identify weedspeciesand their community structure in saffron fields of Kashmar and Khalil-Abad counties, 45 farms were selected randomly based on cultivation area during 2014- 2015. In each farm weed species were counted separately and also the geographical information of each farm was recorded by GPS. These data were used for mapping of weed species and geographic distribution in ArcGIS software. The results showed that 82 weed species belong to the families of Astraceae, Brassicaceae, Poaceae and Caryophyllaceae had the highest frequency, respectively. The most important weeds in the surveyed area based on the abundance index were: downy brome (Bromus tectorum L.), Hordeum spontaneum C. Koch, from grasses and hoary cress (Cardaria draba (L.) Desv.), Holosteum glutinosum F.et M, Russian knapweed (Acroptilon repens (L.) DC), Sisymbrium subulatum E.Fourn , creeping thistle (Cirsium arvense (L.) scop) from Broad leaves. Annual weeds had the greatest species diversity (53 species), biennial weeds had the lowest species diversity (4 species), and perennial weeds were intermediate (25 species). 82 percent of weeds were broadleaf, and 18 percent were narrow leaf weeds. The weeds such as Bromus tectorum L., Holosteum glutinosum F.et M, Acroptilon repens (L.) DC, Descurainia sophia (L.) Schar, and Cardaria draba (L.) Desv., were dominant species in Kashmar, while Cardaria draba (L.) Desv., Hordeum spontaneum C. Koch, Sisymbrium subulatum E.Fourn, Hordeum murinum L., Cirsium arvense (L.) scop, and Malcolmia africana (L.) R.Br., were dominant species in Khalil-Abad . Cardaria draba was problematic and dominant species at both locations.

In order to identify and determine weed population in sugar beet fields, 92 fields from five counties of Kermanshah province in Iran were selected and evaluated at two growing stages (early May and late September) in 2014. The weed population indices were calculated by counting the number of weeds separated on othe basis of genus and species. For all fields, the latitude, longitude and altitude were recorded using GPS device. Eighty-five weed species belonging to 31 families were identified in different sugar beet fields. The dominant broad-leaf weeds identified at the beginning of the growing season (first sampling stage) were lamb's quarters (Chenopodium album L.) and field bindweed (Convolvulus arvensis L.) with 189.22 and 124.09% dominance index, respectively, whereas at the second sampling (late September), the dominant broad-leaf weeds identified were lamb's quarters (Chenopodium album L.), pigweed (Amaranthus retroflexus L.) field bindweed (Convolvulus arvensis L.), and cocklebur (Xanthium strumarium) with 207.92, 194, 111.22, and 107.93% dominance index, respectively. Green foxtail (Setaria viridis L.) was the dominant narrow-leaf weed in both samplings at the beginning and end of the growing season with 79.73 and 176.35% dominance index, respectively.

Agrobiodiversity is an issue that has been considered for the last decade. There are few reports on diversity of orchard species in Iran and some available reports have not mentioned the relevant indices and analysis results. In the current study, based upon data collected from 29 provinces of Iran along with 23 counties of Khorasan provinces, a comprehensive analysis was made and different diversity indices such as Shanon- Weaver, Evenness index, Margalof richness index as well as two dominance indices including Sympson and Berger-Parker were calculated. The results indicated that Kerman, Fars and Khorasan provinces cover 40% of orchard areas in the country. Species richness in all provinces was relatively high but the evenness index was not so (average evenness for all provinces is 0.55). Therefore, in some provinces such as Boshehr and Kerman, species dominance is observed due to Date and Pistachio, respectively. Also, Stone fruits among Khorasan orchards provided the highest richness and diversity. The highest area of orchards in Khorasan are belonged to nuts including Pistachio, Almond, Walnut and Oleaster. Kashmar district has the highest orchards area in Khorasan province. According to the Shanon-Weaver index, the highest and lowest diversity were observed at Nahbandan- Birjand and Fariman counties. Results also indicated that the Berger-Parker dominance index is highest at Fariman and Shirvan districts of Khorasan because of apple and grape species dominance.

Agricultural production in arid and semi-arid regions always is affected by soil salinity and weeds competition. In order to study the effect of soil salinity on competition between wheat and rye, a factorial replacement series experiment based on completely randomized design with 3 replications was conducted in research greenhouse of faculty of Agriculture, at University of Birjand, in 2012. Four different ratios of wheat-rye (100-0, 75-25, 50-50, 25-75, 0-100 percentage) and 4 levels of soil salinity (2, 4, 8 and 16 dS.m-1) were used as experimental factors. The results indicated significant (P<0.01) effect of salinity on dry matters of wheat and rye. Increasing soil salinity from 2 to 16 dS.m-1 decreased 84% and 90% of the dry matter of rye and wheat, respectively. Competitive ability were more at salinity levels of 2 and 4 dS.m-1 in rye and 8 and 16 dS.m-1 in wheat. Investigation of competition by several indices indicated that increasing of salinity level can decrease competitive ability of rye versus wheat.