الفهرس 
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Abstract
The present study aimed at evaluating the weed-crop interaction of the rain-fed barley fields at Marsa-Matrouh Governorate, Egypt. The associated flora with rain-fed barley (Hordeum vulgare L.) crop was surveyed in 48 permanent stands during period (2016-2017). Seventy-five species belonging to 63 genera and 24 families were recorded as associated species with rain-fed barley. The most dominant families were Asteraceae followed by Poaceae, Chenopodiaceae, Fabaceae and Brassicaceae. A total of 48 species were recorded as annuals, while 25 species were perennials and two species were biennials. Therophytes were the dominant life form. The application of TWINSPAN on the cover estimates of 75 associated species recorded in the 48 sampled stands of barley, led to recognition of eight vegetation groups.
Significant variations were recognized in density between barley and its common associated species (Glebionis coronaria, Achillea santolina, Erucaria microcarpa, Carrichtera annua and Vicia lutea). The highest density was recorded for barley, followed by A. santolina. On the other hand, V. lutea had the lowest density. There was significant variations in the shoot and root length among the different species. It was recorded that V. lutea had significantly the highest shoot length, followed by rain-fed barley, E. microcarpa, G. coronaria and C. annua, respectively, while A. santolina had significantly the lowest shoot and root length. The highest shoot and total biomass was recorded for barley, followed by E. microcarpa and C. annua while A. santolina had the lowest values.
Field experiment was conducted under controlled conditions to estimate the effect of weeds on the growth of barley and its yield. In addition, it used to determine the beginning and end of the critical period of weed control. The growth measurements of barley in experimental irrigated weedy and non weedy plots indicated the significant impact of weed interference on the growth properties of barley plants. It was found that the growth measurements of barley in the weed-free periods were higher than those in the weed-infested periods. The shoot length of barley and its common associated weeds in irrigated field indicated that the barley plant continues to increase in height until reach its maximum at the end of weed infestation period, while Medicago polymorpha reached its maximum height after 60 Days After Emergence of barley (DAE). In addition, the maximum height of Euphorbia peplus was recorded after 75 DAE.
It was found that the density of barley plants in the presence of two common weeds (M. polymorpha and E. peplus) showed sharp increase until it reach its maximum value after 60 DAE, and then exhibited slight increase until the end of weed infestation period (75 DAE). However, M. polymorpha and E. peplus started to emerge after 45 DAE, then it reached their maximum after 60 DAE corresponding to the maximum barley density. It was found that the average plant density in the control weed-free plot was higher than that in the control weed-infested plot at harvest time, with a reduction percentage of 16%.
In this experiment, the aboveground biomass of barley showed gradual increase until the end of the weed infestation period. Meanwhile, the biomass of M. polymorpha and E. peplus had its maximum after 45 DAE, and then started to decrease by increasing the biomass of barley. The present study showed that the beginning of the Critical Period of Weed Control (CPWC) based on 10% yield loss occurred by 63 DAE, while the end of CPWC occurred by 79 DAE. According to 5% yield loss, the beginning of the CPWC occurred by 41 DAE, while its end occurred by 102 DAE.
It was observed that the optimum condition for the germination of barley grains was that of variety Giza 126 at 20˚C under dark conditions. The study of the allelopathic potential of most common associated native species with rain-fed barely (G. coronaria, A. santolina, E. microcarpa, C. annua and V. lutea) indicated that 10 and 30% of A. santolina extract had the highest inhibition percentage on germination of barley grains, while that of E. microcarpa had the lowest. For concentration 50%; it was observed that C. annua had the highest inhibition percentage, followed by E. microcarpa, while V. lutea extract had the lowest. It is worth to note that G. coronaria and V. lutea extracts inhibited completely the barley grains germination at concentrations of 80 and 100%. Moreover, E. microcarpa, C. annua and A. santolina had 100% inhibition at 100% of the donor extract.