CONICET | Buscador de Institutos y Recursos Humanos

ABSTRACT Root and stem lodging cause significant yield losses in sunflower (Helianthus annuus L.) production in Argentina. Lodging is defined as the permanent displacement of the stem from its vertical position without possibilities of recovering. Few studies have investigated the mechanistic processes of root or stem lodging and no one have attempted to interrelate the complex interactions between climatic and soil variables, husbandry practices and plant characteristics for sunflower lodging. Model of lodging had been developed for wheat and barley and can be used as base for sunflower lodging model. The objectives of this work are to develop a root/stem lodging model for sunflower and to validate it. The root lodging model calculates the root failure wind speed using as main variable the root plate diameter. The thickness of the epidermis+cortex measured in the lower third of the stem was the main variable used as input by the stem lodging model for the calculation of the stem failure wind speed. This model was tested against individual field experiments in which natural root or stem lodging had occurred at different crop development stages under different husbandry practices and it could recreate the differences observed in the field between hybrids and crop population densities in relation to lodging susceptibility. A parametric analysis showed the root plate diameter and epidermis+cortex as the main variables of the model and indicated that sunflower could be more susceptible to root than stem lodging. Key words: Epidermis+cortex failure wind speed model testing root lodging root plate diameter stem lodging