Using thermal and hydrothermal time to model seedling emergence of Avena sterilis ssp ludoviciana in Spain

Historical records on the field emergence of seedlings of Avena sterilis in winter cereal crops were used to develop thermal/hydrothermal models to predict the emergence of this weed as a function of meteorological conditions. When water was not a limiting factor, a Weibull function provided a good description of the relationship between thermal time and seedling emergence. The variability in the rate of seedling emergence observed under these conditions was associated with variation in the differential between measured and base temperatures. When water was limiting in the soil, the rate of seedling emergence was reduced, a different function was required to describe the process. The use of a hydrothermal model enabled the use of a single function to describe the patterns of seedling emergence of the nine site-years considered in the study. Using this model we can conclude that 70% seedling emergence will be reached, under very diverse conditions, within 300 hydrodegree days. The hydrothermal model proposed was validated with independent seedling emergence data, supporting the idea that this model is robust enough to be used as a predictive tool for seedling emergence of A. sterilis in a variety of conditions.