Document Type : Research Article
Author
Islamic Azad University, Science and Research Branch, Tehran
Abstract
Introduction The presence of broadleaf weeds not only reduces the aesthetic quality of the turfgrass, but more importantly they compete with desired turfgrass for water, nutrients, and light. Weed management after seeding is an important component to successfully establishing a healthy stand of cool season turfgrass. Weed seed germination is a key process because determines both the number of weeds that could potentially emerge and the timing of their appearance in the turfgrass. Temperature is of the most important factor regulating germination of non-dormant seeds in irrigated, annual agroecosystems at the beginning of the growth season where light, nutrients, and moisture are typically not growth limiting. Also prostrate knotweed (Polygonum aviculare L.) and annual sowthistle (Sonchus oleraceus L.) are two annual common broad leaf weeds in cool season turfgrass. Prostrate knotweed is very competitive in infertile and compacted soils and often invades turfgrasses along driveways, sidewalks, and beaten paths across lawns. Annual sowthistle is found in open habitats that include waste areas, turf, and roadsides. The aim of this study was to evaluate different nonlinear regression models to describe response of germination rate to different temperatures in perennial ryegrass (Lolium perenne L.), fescue (Festuca rubra L.), prostrate knotweed and annual sowthistle.
Materials and Methods This experiment was based on completely randomized design with 4 replications at Islamic Azad University in the laboratory of Science Research Branch in 2015. The seeds were treated with different temperatures (2, 5, 10, 15, 20, 25, 30, 35, 40 and 45oC) Twenty five seeds were placed in each petri dish for each species in per replication. Ten milliliters of distilled water were added to each petri dish and the filter papers were regularly moistened to ensure saturation throughout the germination tests. Petri dishes were placed in germinator with 16 hour day, 8 hour night and 60% relative humidity. Seeds were considered germinated when the radicle protruded at least 2 mm from the seed coat. Germinated and rotted seeds were counted and discarded at 24 hour intervals until no germination had occurred over four consecutive days. The germination percentage was obtained by dividing the number of germinated seeds at any time by the total number of seeds germinated multiplied by 100. Data from this experiment were first subjected to analysis of variance and means of treatments were compared using the least significant difference at the 5% level of probability. The following nonlinear regression models were used to quantify the response of the germination rate to temperature and to determine cardinal temperatures.
Results and Discussion The analysis of variance showed that temperature had a significant effect on all seed germination percentage and germination rates. Seed germination percentage and rate increased to a point with increasing the temperature. Germination model based on temperature can be used for the prediction of cardinal temperatures. Cardinal temperatures are required because a portion of the crop model is developed for prediction of the timing of germination. Non-linear regression models have been used to quantitatively describe development rate in many plants. Three regression models (Intersected-lines, Dent-like and Quadratic Polynomial) used to predict germination rate and cardinal temperature. Root mean square of error (RMSE) and R2 adjusted were used to find the appropriate model(s). Intersected-lines model was superior compared to other models in perennial ryegrass, fescue and annual sowthistle and Dent-like model was superior for prostrate knotweed. It was concluded that this model can be used to quantify response of turfgrass and common weeds of turfgrass germination to temperature and to obtain cardinal temperature of germination. Also base, optimum and maximum temperatures were for perennial ryegrass 4.12, 24.66 and 43.27oC; fescue 2.0, 24.86 and 43.48oC ; Prostrate knotweed 2.95, 19.94-22.21 and 44.97oC and annual sowthistle 2.0, 17.77 and 44.86oC, respectively.
Conclusions These results show that fescue germinated earliest among the studied species, because it had the lowest base temperature. In comparison to perennial ryegrass, using turfgrass seed with more fescue seed causes sooner turfgrass establishment and less weed competition. Because of their narrow leaves, young seedlings of prostrate knotweed grow upright and appear at first glance to be grass seedlings. With maturity, most plants grow prostrate, especially with traffic or mowing, so mechanical control of this species in turfgrass is impossible andit could be controlled with pre-emergence herbicide. Pre-emergence herbicides are applied prior to the germination of weeds; thus, predication of timing germination help us in decreasing prostrate knotweed competition with turfgrass and its proper management.
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