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Possible use of cereal cover crops as a sustainable alternative weed control option in canola fields through optimizing cover crop and its density in canola-weed-cover cropping tripartite systems was modeled using a gamma density function with four parameters. The effect of competition between main crop (canola), cover crop (wheat or barley) and weeds on canola yield was studied in an experiment conducted in 2012/2013. Each cover crop was sown in four seeding rates: 0, 25, 50 and 75 percent under two nitrogen rates of 75 and 150 kg ha-1 . Weed suppression measured as canola relative yield was associated with the increase of seeding rate of cover crop according to a modified gamma density function. Parameters alpha, kappa, eta and lambda summarized the effect of N application on yield response under no cover crop conditions, measure of treatment effect on the curve amplitude, the plant density at which crop yield maximizes and the curve slope at the right tail which was an indication of the treatment effect on the rate of yield reduction beyond the seeding rate that maximized the crop yield, respectively. Model diagnostics and agreement analysis showed that the modified gamma density function described the functional response of the main crop to seeding rate of the cover crop equally well across a variety of treatment effects. Response curve analysis showed that in both levels of nitrogen, canola yield was more responsive to barley as cover crop when compared to winter wheat. Kanola arazilerinde yabancı otlar ile mücadelede tahılların örtü bitkisi olarak kullanımları ve kullanım yoğunluğu dört parametreli gama yoğunluk fonksiyonu kullanılarak modellenmiştir. 2012/2013 yıllarında ana bitki (kanola), örtü bitkisi (buğday veya arpa) ve yabancı otların birbiri ile yarışının kanola verimi üzerine etkisi çalışılmıştır. Her bitki dört farklı ekim sıklığı (% 0, 25, 50 ve 75) ve iki farklı (75 ve 150 kg ha-1 azot) ile ekilmiştir. Gama yoğunluk fonksiyonu ile kanolanın veriminin örtü bitkisinin ekim sıklığına bağlı olması durumundan yararlanılarak yabancı ot baskılanması hesaplanmıştır. Alfa, kappa, eta ve lambda parametreleri sırasıyla örtü bitkisi olmadığı durumda azotun verime etkisini, eğri üzerinde uygulamanın etkisini, ana ürün veriminin maksimum olduğu bitki yoğunluğunu ve uygulamanın verim kaybına etkisini gösteren eğriyi özetlemektedir. Modelleme sonucunda gama yoğunluk fonksiyonu ana bitkinin ekim sıklığına tepkisini tanımlayabilmiştir. Çalışma sonuçları, tüm azot seviyelerinde kanola veriminin arpaya buğdaydan daha fazla tepki gösterdiğini ortaya çıkarmıştır.

In order to investigate the effect of herbicide and choice of adjuvant on three grass weed species; downy brome (Bromus tectorum), littleseed canarygrass (Phalaris minor) and green foxtail (Setaria viridis); a greenhouse study was conducted in a factorial experiment laid out in randomized complete block design. Treatments included herbicide at five levels (propaquizafop, fluazifop-p-butyl, cycloxydim, sethoxydim and quizalofop-p-ethyl) each applied at two concentrations and either with/without adjuvant (volck or citoweet). The performance of herbicides and adjuvants was evaluated by rating the effect of treatment on an ordinal scale in each experimental unit at 10 and 20 days after planting (DAP). The results showed that herbicide efficiency rating distributions were significantly different between two times (10 and 20 DPA). Application of quizalofop-p-ethyl and propaquizafop were recorded as the best herbicide treatments in controlling the weeds used in this study 10DAP, however the difference between herbicides faded at 20 DAP. Also, no significant effect was found for concentration of herbicides and type of adjuvant. In addition, 30 days after herbicide application, maximum dry weight and leaf area of canola was recorded for cycloxydim, propaquizafop and quizalofop-pethyl, respectively whereas minimum dry weight and leaf area of canola was observed in pots sprayed with sethoxydim and fluazifop-p-butyl respectively.