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    Critical period for weed control in sesame production
    (Wiley-Blackwell, 2019) Karnas, Zeynep; Işık, Doǧan; Tursun, Nihat; Jabran, Khawar
    Planning effective weed control in cropping systems requires exact appraisal of the weed intensity and duration of their competition with the crops. This 2-year study was carried out in order to determine the critical weed control period in sesame fields. Related and relative crop yields were monitored and analyzed using a four-parametric log-logistic model. We recorded data from weed-free plots and compared these with data from different periods of weed interference. In both the study years, the longer period of weed interference decreased the relative yield of sesame, whereas the yield was increased with increasing duration of the weed-free period. A 51-78.7% decline in sesame yield was noted if the weeds were allowed to compete with the crop from planting to harvest. In the first year, the duration of the critical period for weed control (CPWC) was 177-820 growing degree days (GDD), which corresponded to 14-64 days after crop emergence (DAE), and between 170 and 837 GDD (13-64 DAE) in the second year; this was based on a 5% acceptable yield loss. The results of this study clearly elaborated that maintaining weed-free conditions is compulsory from as early as the second week after the emergence of sesame plants, and this should be maintained at least until the ninth week to avoid sesame yield losses by more than 5%. These findings show that growers can benefit from CPWC to improve weed control in sesame production, including the efficacy of a weed control program and its cost.
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    Effects of Elevated Temperature and Carbon Dioxide Concentrations on Aromatic Compounds of Stevia rebaudiana
    (Springer, 2021) Tursun, Ayşe Özlem; Jabran, Khawar; Gürkan, Hacer; Telci, İsa
    A global rise in CO2 concentration and temperature levels can impact the living part of the earth including the plants. Stevia or candy leaf (Stevia rebaudiana Bertoni) is a medicinal aromatic plant that produces several useful chemical compounds. Studies were carried out in a fully automated greenhouse in order to determine the response of aromatic compounds of stevia leaves to different CO2 concentrations and temperature levels. This study had four treatments including (1) 26?±?1/16?±?1 °C day/night temperature plus 400?±?50 ppm CO2 concentration [control], (2) 29?±?1/19?±?1 °C day/night temperature plus 600?±?50 ppm CO2 concentration, (3) 32?±?1/22?±?1 °C day/night temperature plus 800?±?50 ppm CO2 concentration and (4) 35?±?1/25?±?1 °C day/night temperature plus 1000?±?50 ppm CO2 concentration. Results of the study showed that yield of total aromatic compounds ranged between 12.65 and 13.65 ?g/g for stevia . Generally, concentrations of the compounds such as ketones, aldehydes and alcohols were decreased with increase in concentration of CO2 and temperature. Terpenes were the compounds whose concentrations were increased with increase in concentration of CO2 and temperature. The climatic conditions did not cause a significant change in the aromatic compounds of stevia.
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    Use of living, mowed, and soil-incorporated cover crops for weed control in apricot orchards
    (Multidisciplinary Digital Publishing Institute (MDPI), 2018) Tursun, Nihat; Işık, Doǧan; Demir, Zeynep; Jabran, Khawar
    Apricot fruits provide important health, economic, and nutritional benefits. Weeds damage apricot production directly and host the pests that cause damages to apricot trees. However, very few studies are available on weed control in apricot orchards. This research work was aimed at evaluating five cover crops for weed suppression in apricot orchard. The effect of living, mowed, and soil-incorporated cover corps on weeds was recorded and compared with glyphosate application and mechanical weed control. The cover crops were Vicia villosa Roth., Vicia pannonica Crantz, Triticale + V. pannonica, Phacelia tanacetifolia Benth., and Fagopyrum esculentum Moench. Five major weed species in the experimental area were Amaranthus retroflexus L., Convolvulus arvensis L., Tribulus terrestris L., Sisymbrium officinale (L.) Scop., and Sorghum halepense (L.) Per. The highest biomass production was noted for Triticale + V. pannonica in 2015 and for P. tanacetifolia in 2016. Living cover crops were effective in decreasing the weed biomass compared with the control. Both mowing and soil incorporation of cover crops were effective in decreasing weed richness and density over control. Mowed or soil-incorporated cover crops were more effective than herbicide or mechanical weed control, while F. esculentum was the least effective cover crop for suppressing weeds in apricot orchard. The results of our studies implied that cover crops could be used for weed control in apricot, and their mowing or soil incorporation could enhance their efficacy.