عنوان مقاله [English]
Introduction: Emergence is one of the most important events in the life cycle of annual species, because of its role in survival of the plant. Weed emergence timing has an important effect on the competition outcome of weeds with crops. Knowledge of weed emergence in the field could help reduce the loss from weeds. Many studies aim to develop prediction models that can provide information to farmers about methods and timing for weed management. Prediction of weed emergence could enhance crop management, facilitating implementation of effective strategies by optimizing the timing of weed control; this is becoming relevant for farmers because of current pressure to reduce herbicides and adopting nonchemical weed control methods.
Materials and Methods: Seed dormancy state, after-ripening, and emergence pattern of wild wheat (Triticum boeoticum Boiss) and wild barley (Hordeum spontaneum C. Koch), the most important grass weeds were studied underLorestan dry conditions. Wild wheat and wild barley weed emergence pattern in three stages during the fall, winter and spring were studied by split plot arrangement in a randomized complete block design with four replications. Furthermore, wild wheat and wild barley seed emergence trends was investigated in 12 stages with intervals of about two weeks from late November to mid-May.
Results and Discussion: Results showed that the presence of seed coat (Lemma and palea) acted as a serious obstacle for germination in both weeds. Regardless of treatment conditions, seed germination of wild wheat did not happen in intact seeds, up to 130 days after harvest. For wild barley, seed coat was also a serious obstacle for germination up to 130 days after harvest. Intact seeds of wild barley, generally did not germinate until two months after harvest, on the other hand, after about three months germination was less than 10%, while the germination of the seeds after 140 days under both conditions, including exposure to sun and stored at room were promoted to 87 and 37%, respectively. Both wild wheat and wild barley weeds, emergence rate during autumn dramatically exceeds the emergence rate during winter and spring. Spike number of grasses were significantly affected by planting season. Underthe spring sowing, wild wheat and wild barley as well as wheat crop, generally did not produce grain. The number of spike per area for autumn sowing was significantly more than the winter sowing up to 64.6 percent. Based on the equations fitted to the emergence of wild wheat and wild barley intact seeds planted over 12 stages from late November to mid-May of the growing season of 2013-2014, the minimum emergence in both grass weeds were estimated 75% and 56 %, respectively. Average emergence of before winter, during winter and in the spring for the wild wheat was estimated to 90, 86 and 89 percent and for wild barley 62, 77 and 69 percent, respectively. With the onset of the cold season in the late of autumn, the emergence rate of this grass weeds were reduced, but subsequently, with elimination of cold condition in late of winter emergence rate became more prominent, until deal with high temperatures in late spring that emergence declined. Considering the temperature changes during the growing season indicates that the correlation of emergence rate with the fluctuations in temperature. Emergence rate of wild wheat grass weed in autumn and spring seasons were 2.8 and 3.5 times more than the emergence rate in spring season, respectively. In the case of wild barley, grass weed emergence rate in autumn and spring seasons were 1.3 and 2.1 times more than that of winter. After four months of harvesting wild wheat seeds, the germination of seeds exposed to sunlight and stored under room temperature, on average, was 8.4 times more than the germination ability of seeds stored in the freezing condition. Germination rate of wild barley weed seeds exposed to sunlight and stored at room conditions during after-ripening period rose sharply. The germination rate for seeds placed in the sun and stored at room conditions, were 56 and 61 times more than seeds stored in freezing condition, respectively, after about five months of harvesting seeds.
Conclusions: The results of this study suggest that physiological dormancy, physical dormancy (seed coat), and after-ripening during the summer season play an important role as an obstacle in germination of both wild wheat and wild barley in rain-fed conditions. In case of soil moisture availability, the required time window to achieve 50% of achievable germination of wild wheat and wild barley in autumn, winter and spring seasons were estimated 9, 18 and 3 days, respectively.