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Title:   Author  item
                                            EKELEME, FRIDAY - MICHAEL OKPARA AG UNIV.item
                                            Forcella, Frankitem
                                            Archer, Daviditem
                                            CHIKOYE, DAVID - INTL INSTITUTE OF TROPICA
  Submitted to: North Central Weed Science Society US Proceedings
                                    Publication Type: Abstract Only
                                    Publication Acceptance Date: 12/5/2002
                                    Publication  Date: 12/5/2002
                                    Citation: EKELEME, F., FORCELLA, F., ARCHER, D.W., CHIKOYE, D. WEED SEEDLING EMERGENCE AND MICROCLIMATE IN A TROPICAL ENVIRONMENT. NORTH CENTRAL WEED SCIENCE SOCIETY ABSTRACTS. 2002. v. 57. p. 125.Interpretive Summary:
                                Technical Abstract: Tropic ageratum (Ageratum conyzoides) is an important annual weed in tropical cropping systems. Better and more timely strategies for its control might be developed through a more thorough understanding of its emergence behavior. Seedling emergence of tropic ageratum was monitored periodically and standard weather data were collected daily for each of four years at IITA, Ibadan, and for one year at Umudike. The weather data were used in the SHAW (Soil Heat and Water) model to estimate soil temperature and soil water potential at the 2 cm depth. The estimated variables were converted to soil hydrothermal time (HTT). Cumulative relative emergence (CRE) values for all four years from Ibadan were compared iteratively against HTT using a series of base temperatures and base water potentials. The four sets of data "collapsed" best upon one another when HTT was calculated using a base temperature of 28 deg C and a base water potential of - 0.02 MPa. The aggregate data fit a Weibull function of the form: CRE = 100*(1-e**(0.0054*HTT**1.4268)). This model was used to simulate emergence of tropic ageratum at Umudike. The simulated results compared favorably with observations: r**2 = 0.98, and the coefficient describing the dependence of observed emergence on simulated emergence was near unity (0.97). Both statistics indicate that the model simulated emergence of tropic ageratum dependably.


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