The Interference of Wild Oat (Avena fatua) on Yield and Yield Attributes of Wheat in the Sistan

Introduction: Wild oat (Avena fatua L.) is an important winter annuals weed and is known as one of the most important weeds in wheat fields (1). The ability of wild oats in yield loss of wheat crop is attributed to greater height and better distribution of leaves which reduces light penetration in the canopy (5). Competitive effects of oat and wheat affected by the density of both species. Resources will be divided between competing species with changes in plant density. Increasing plant density increased competition for light and affect other growth factors (4). In this study, the effect of different densities of wild oat was examined on the yield, and yield components in what. Material and Methods: The experiment was conducted in 2010 at the Zabol University research farm in Zabol (61°29 N, 31°2 E, 450 m a.s.l.), south Iran in a sandy loam soil with pH 7.8. The experimental site is located in warm and arid region with mean annual precipitation of 63 mm and annual mean long-term average temperature of 23°C. The experimental design was randomized complete block with monoculture of wheat and wild oat densities at 7 levels (0, 10, 20, 35, 70, 140, 280 and 350 plants m-2), that were applied with three replications. Wheat crop density was constant rate of 400 plants m-2. The treatments were laid out in 2*2 m plots and wheat were sown at a spacing 0.2 m between rows and 0.012 m within rows. Wild oats were sown between the wheat rows. Adjacent plots were separated by a 0.5 m wide ridge and blocks were separated by a 2.0 m wide ridge. At the end of growth period five plants were sampled and the number of grains per spike, spike length, 1000 grain weight, plant height and number of leaves were recorded. At maturity plants were harvested from each plot, sun dried, threshed and weighed to determine grain and biological yield. Total N concentration in plant samples were estimated at the end of growth season following micro- Kjeldhal method. Data collected were subjected to the analysis of variance (ANOVA) and the significant differences between treatments were compared with the critical difference at 5% level of probability. Results and Discussion: The interference effect of wild oats was significant on vegetative growth (plant height, number of Leaves, Spike length) of wheat at 1% level of probability (Table 1). Plant height varied significantly between different densities of wild oats and interference of wild oat until medium density increased plant height of wheat (Table 2). Among different treatments the least leaf number and spike length was observed at plant cultivated along with the highest wild oat density. The effects of different density of wild oat on grain numbers per spike and 1000 grain weight was significant (Table 1). Wild oat interference significantly decreased yield component in comparison with weed free condition. Grain number per spike and 1000 grain weight decreased by 69 and 21%, respectively in weed free condition in comparison with the greatest wild oat density (Table 2). The grain and biological yield of wheat significantly affected by the presence of wild oat. The grain and biological yield of wheat was 44 and 61% greater at weed free condition in comparison with the highest density of wild oat (Table 2). Reduction of yield and yield components as a result of weed infection has been reported by several researchers (3, 7). Kemp and Whingwiri (6) imputed yield loss at wild oat presence to plant structure of wild oat. Pourazar and Ghadiri (2) stated that wild oat increasing density at wheat farm reduced wheat grain and biological yield. There was significant difference among different densities on nitrogen concentration in wheat grain (Table 4), and wild oat presence significantly reduced nitrogen concentration in grains. Potassium concentration of wheat grain was greater at weed infection in comparison with weed free condition (Table 2). Light absorption significantly influenced by different wild oat densities (Table 1). The greatest and the least absorbed light were observed at weed free condition and 350 wild oat plant, respectively (Table 2). Intense radiation interference was due to wild oat leaves development. Conclusion: The experimental results indicated that the greatest grain and biological yield were obtained in weed free condition. In the presence of wild oats the least density of weed produced the highest yield, and with increasing density of wild oat wheat grain and biological yield decreased linearly and significantly. Reduction in grain and biological yield at the highest density of wild oat was 61 and 44 %, respectively. Increasing wild oat density increased plant height and decreased number of leaves, spike length, number of grains per spike and one-thousand grain weight. Furthermore, increasing wild oat density decreases nitrogen concentration in grains and increases the absorption of light. These results suggested that wild oat density reduction to 35 plants m-2 may perform better grain yield of wheat under wild oat infection.