A model for predicting seedling emergence of chenopodium album in different irrigation systems in sunflower(Helianthus annus L.)

Increasing public awareness and concern about the impacts of herbicides on the environment، development of herbicide-resistant weeds need to reduce the amount of herbicides used in agriculture. There are several models that could be used for predicting weed seedling emergence. However، the ability to predict emergence of given species is different between models. For better prediction of emergence we should be able to select a suitable model. Therefore، seedling emergence from experiment conducted in different irrigation levels (40، 60، 80، 100 percent of crop water requirement and furrow irrigation) was studied to develop a thermal time seedling emergence model for Chenopodium album in sunflower fields. Weed seedling emergence was monitored in plots from late-May through mid-September of growth season. Cumulative seedling emergence for C. album was described against thermal time using Gompertz and Weibull functions. The Gompertz and Weibull models predicted seedling emergence of this species in different irrigation levels with reasonable accuracy. The R2 values of these models were ranged between 2. 2 and 7. 8. This species showed different patterns of emergence and thermal time required for the onset of emergence in different irrigation levels. However، in furrow irrigation، there was a later peak of emergence followed by a lesser emergence early in the season. At thermal time of 549، 90 percent of C. album seeds emerged in the furrow irrigation، suggesting early emergence pattern for this irrigation system، while، in the tape system seeds required 602 - 654 thermal time unit for the same percentage of emergence، which is an evident for later emergence pattern for this system. Late emergence could allow this species to escape weed control practices because most weed management strategies (e. g. cultivation and herbicide applications) are implemented early in the season. Therefore، it should be mentioned and this seedling must be controlled as a part of integrated weed management program to limit the size of the seedbank. Key words: modelling، furrow irrigation، tape irrigation، thermal time، weed control