Reconsideracao do conceito da umidade de murchamento permanente

Abstract

Tensions to which soil moisture at the "wilting point" is subjected were deter-mined for five plant species, in soils with high and low moisture conductivity. Instead near of values of 15 atmospheres as usually expected, results varied from 39 atm for Agropyron intermedium to 7 atm for Helianthus annus, with highly significant differences Letween soils, species and environmental conditions of plants

A thesis is developed that the main limiting factor that determines permanent wilting of plants is the rate of moistme movement through the soil to plant roots, and that, instead of the concept of wilting at 15 atm, xerophytic plant species or plants adapted to nevic conditions can resist high tensions of soil moisture, while moistures moves slowly until it reaches the roots. Such plants could have wilting points at low contents of moisture and could absorb and use water beld under tensions considerably above to 15 atmospheres.