جستجوی مقالات مرتبط با کلیدواژه « Stability coefficient » در نشریات گروه « زراعت »

In order to investigate the effect of different sources of nitrogen fertilizer on the relative frequency, density and biomass of safflower, a factorial experiment was conducted in a randomized complete block design with three replications located in the research farm of faculty of agriculture university of Jiroft in 2018-2019 year. The first factor at two levels included the use of manure and non-use of manure, the second factor included different nitrogen fertilizer sources at five levels of control, urea fertilizer, urea fertilizer with sulfur coating, ammonium nitrate, nitroxin and nano nitrogen. The results showed that in all three stages of sampling weeds, Clover (Trifolium repens L.) and Umbrella sedge (Cyperus rotundus L.) weeds had the highest and Bermudagrass (Cynodon dactylon) and Sorrel (Rumex crispus L.) had the lowest relative abundance. Different sources of fertilizer had a significant effect on biomass weeds of clover, umbrella sedge, common mallow and other weeds during three sampling stages. Based on the results of mean comparison, the highest biomass was obtained of clover weed in the first stage in the treatment of manure with chemical fertilizers urea (17.04 g). The lowest biomass was obtained in no manure in control (6.47 g) and nano nitrogen fertilizer (4.63 g). Shannon and Margalef indices in the first stage of sampling 0.96 and 0.94, the second stage of sampling 0.79 and 1.06 and the third stage of sampling 0.63 and 1.11 respectively in the treatment of manure was more than to non-use manure. Sources of urea and urea fertilizers with sulfur coating had higher weed diversity index than other treatments. According to the results of this study, it is suggested to use biological sources of nitrogen in order to prevent weed infestation and competition with the target plant.

Weedy flora of agroecosystems is composed of many species that have evolved in response to cropping system practices by occupying the niches left available in agroecosystems. In order to study weed species diversity and community structure in the saffron fields of Khorasan province, a survey trial was carried out in seven counties (including Mashhad, Neyshabur, Birjandn, Ghaen, Gonabad, Torbat-e Jam and Torbat-e Heydari) during 2014 and 2015 from vegetative growth, dormant to flowering stages of saffron randomly dropped 1×1 m2 quadrates in 50 fields based on a systematic method as W pattern. The counties were clustered by the hierarchical complete linkage method based on Euclidean. Biodiversity indices such as stability coefficient, Simpson, Shannon–Wiener, Margalef and Menhinick were computed. The results indicated that the dominant weeds in saffron fields belong to 19 families and 50 species. Poaceae, Brassicaceae, Asteraceae and Fabaceae were dominant families with 11, 9, 8 and 6 species, respectively. The majority of weed species were dicotyledonous, C3, noxious and annual plants. The highest stability coefficients in the stages of growth of saffron were calculated in Alhagi camelorum, Avena fatua and Achillea millefolium to be 30.81, 24.11 and 12.14, respectively. All weed species except for Alhagi camelorum (sustainable species) and Avena fatua (temporary species) were recognized as causal species. The maximum diversity indices for weed species were recorded at the vegetative phase of saffron. Correlation coefficient between weed density and yield loss of saffron was computed as R2=0.98. Based on diversity indices for weed species, different counties were clustered in three groups at 75% similarity level.