الفهرس 
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Abstract
SUMMARY
The main objectives of this study are to study the floristic and vegetation analyses of wheat and maize crops and their associated weeds and the environmental variables affect them. It also evaluates the weed-crop interaction, in terms of density and biomass, and its impact on the crop yield, in addition to the impact of nutrients and trace metals captured by weeds on the nutrient absorption and production of the study crops. Moreover, the impact of weeds on the functional traits of wheat and maize plants was also investigated.
The weed flora associated with wheat and maize crops were surveyed through randomly selecting a number of stands (each 10 × 10 m) in Menofia Province. A visual estimate of the total cover and the cover of each species (%) of weeds was assessed; in addition to life forms and global geographical distribution. Two-way indicator species analysis (TWINSPAN) and Detrended Correspondence Analysis (DCA), as classification and ordination techniques, were applied to determine the different communities associated with the crops. Four crop cultivated farms were selected during winter for wheat and summer for maize. Farm I was not subjected to weed management practices, but supplied with fertilizers, while farms II, III and IV were subjected to chemical weed control with herbicides and application of fertilizers. For wheat farms I and II were sown by drilling (pitting), while farm III by broadcasting (dispersion); and farm IV by furrowing (striation) methods. On the other hand, all maize farms were sown by pitting. At each farm, five quadrats (0.5 x 0.5 m) were randomly selected for determining the number of cereal shoots (tillers for wheat) as well as the number of individuals of each of the common associated weeds, the shoot height; stem diameter; leaf length, width and area; and spike (cob for maize) length and diameter for cereals and their common grasses. Then the shoots of cereal plants and their common associated weeds were oven dried for estimating their biomass.
Three composite samples (shoot and root), representing the cereal crops and their common associated weeds, in addition to cereal grains, were collected for the analysis of total N, P, K, Fe, Cu, Mn, Cd, Zn, Pb, Ni, Co and Cr. Moreover, three composite soil samples were collected from each farm at the end of the growing season for mechanical and chemical analysis (pH, EC, HCO3, Cl, SO4, total N, P, Ca, Mg, Na, K, Fe, Cu, Mn, Cd, Zn, Pb, Ni, Co and Cr). The produced data were treated statistically as well as the bioaccumulation and translocation factors for heavy metals were also investigated.
Forty-five species (38 annuals and 7 perennials) belonging 42 genera and 21 families were recorded associated with wheat and maize crops. Therophytes were the dominant life form, while pluri-regional and mono-regional taxa were the dominant elements in wheat and maize, respectively. By the application of TWINSPAN, 8and 7 vegetation groups were recorded as common communities in wheat and maize, respectively.
It was found that, wheat plants from the untreated farm were characterized by the highest values of plant height, leaf length and leaf area, but the lowest of culm diameter, number of leaves, number of spiklets per spike, and number of grains per spike. The highest number of wheat grains was recorded in treated pitted farm characterized by the lowest number of tillers and leaf area. Wheat plants produced grains during the fourth month, however all morphological variables were significantly different among the different farms, except the number of tillers during January; leaf width during February; sheath length in March; number of tillers, spiklets per spike, spike length and number of grains per spike in April.
In a comparative study with the common associated species with the same life form of T. aestivum (wheat), significant variations in all morphological characters were recognized. It was found that wheat had the higher number of tillers than A. fatua and P. monspliensis. In addition, A. fatua had the highest values of plant height; culm diameter; number of leaves; leaf length, width and area; and sheath length, while wheat had the lowest of plant height, number of leaves, leaf length and sheath lengthand P. monspliensis had the lowest of culm diameter, leaf width and leaf area.
Maize plants from the treated farms were characterized by the higher values of plant height; stem diameter; leaf length, width and area; sheath length; cob weight, length and diameter; and number of grains per cob, but lower number of shoots and leaves than untreated one. The plant produced grains during the third month. The number of maize shoots had its highest value during June, and then decreased to reach in August in contrast with the plant height, which had its highest value during August and the lowest during June.
The highest wheat density was recorded in treated striated farm, associated with the highest of A. arvensis, C. arvensis, C. niloticus, and S. oleraceous, but the lowest of C. bursa-pastoris, while the lowest was recorded in treated pitted farm associated with the highest plant density of A. fatua and P. annua, but the lowest of C. murale and S. oleraceous. On the other hand, the highest maize plant density was recorded during June and then decreased gradually until reach its minimum value during August associated with the highest plant density of E. colona, D. sanguinalis, S. viridis and P. oleracea.
The highest wheat biomasswas recorded in treated striated farm, associated with the highest of A. arvensis, C. arvensis and C. niloticus, but the lowest of C. bursa-pastoris, C. rotundus, P. annuaand P. monspliensis, while the lowest wheat biomass was recorded in untreated farm associated with the highest biomass of A. fatua, C. murale, P. monspliensis and S. oleraceous, but the lowest of C. arvensis. The production of wheat crop indicated that treated striated farm had the highest grain production, followed by treated pitted, treated dispersed and untreated farms. On the other hand, maize plants attained their highest biomass associated with the lowest biomass of E. colona, D. sanguinalis, S. viridis, T. portulacastrum, C. arvensis and C. rotundus, while the lowest biomass was associated by the highest E. colona, P. oleracea, T. portulacastrum and C. arvensis.
The highest values of N and P were recorded in the treated wheat grains characterized by the lowest K.In addition, the highest concentrations of Cr, Ni, Mn and Fe were recorded in the plant roots from treated farms, while the highest Cu was recorded in treated shoots. C. niloticus roots accumulated the highest N, Pb and Zn, while C. murale roots accumulated the highest P, K and Cu, but the lowest of Ni and Mn. In addition, A. fatua roots had the highest concentrations of Cr and Cd, while that of P. annua had the highest Co, Ni, Mn and Fe. On the other hand, the highest values of N and P were recorded in the treated maize grains characterized by the lowest K, while, the highest K was attained in untreated root. In addition, the highest concentrations of Cu, Pb, Mn and Ni were recorded in the plant shoots from untreated farms, while the highest Fe was recorded in treated roots. Moreover, P. oleracea roots accumulated the highest N, while S. viridis roots accumulated the highest K, but the lowest N, Cu, Cr, Ni and Mn. In addition, D. sanguinalis roots had the highest concentrations of Cu, Pb, Cr, Cd, Ni, Mn, Zn and Fe.
The bioaccumulation factor (BF) of trace metals from soil to wheat plantindicated that all trace metals had BF less than unity, except Cu and Cr.While, the translocation factor (TF) showed that all metals had TF less than unity, except Cu. The BFof trace metals by the common weeds associated with wheat plants indicated that these weeds had BF less than one for Co, Cd, Ni and Fe, while had BF more than unity for Mn and Cr. A. fatua had the highest BF for Cr, while P. annua had the highest of Mn. In addition, C. niloticus had the highest BF for Pb and Zn, while C. murale had the highest of Cu. On the other hand, the BF of trace metals from soil to maize plant indicated that all trace metals had BF less than unity, except for Co and Cr, while the TF showed that all metals had TF less than unity, except Pb, Cd and Ni. Moreover, the translocation of trace metal from shoot to the grains indicated that Cr and Zn had a value more than one. D. sanguinalis had the highest BF for Cu, Pb, Cr, Cd, Ni, Zn and Fe, while C. arvensis had the highest of Co