Abstract

CABALLERO MEJIA, Bibiana  and  JARAMILLO JARAMILLO, Daniel Francisco. CRITICAL MOISTURE AND WATER REPELLENCY ON ANDISOLS UNDER Cupressus lusitanica AND Quercus humboldtii COVER IN THE PIEDRAS BLANCAS WATERSHED ( MEDELLÍN, COLOMBIA ). Rev.Fac.Nal.Agr.Medellín [online]. 2007, vol.60, n.2, pp. 4001-4024. ISSN 0304-2847.

In two hillside of the Piedras Blancas watershed ( Medellín, Colombia ) was studied the relation humidity - persistence of the water repellency on the surface of the andisols under two vegetable covers: Cupressus lusitanica (cypress) and Quercus humboldtii (oak groves). These were found in three different positions along the side of low hills: upper, middle and lower grounds, as well as in two conditions of humidity: with the humidity acquired when equilibrated with the air during two days (samples originally dried at 105 °C) and with the field humidity. In each place of the hill slope was located a plot of 6 m by 5 m and in this slope, 60 samples of soil were taken in a netting of 1 m by 0,5 m. The persistence of the repellency to water was evaluated with the WDPT method with samples sifted at 1 mm. A high number of samples that were very repellent to water was observed in all working conditions, being greater the frequency in cypress that in oak groves. The water repellency as well as water humidity presented a differential behavior by cover and by position on the hill slope inside of the same cover. A consistent relationship between the humidity content of the samples and the persistence of the water repellency that these presented could not be established. A zone of critical humidity transition could not be defined either so that the repellency to water could be revealed, neither in the two vegetable covers nor in any position of the hill slope.

Keywords : Hydrophobicity of the soil; persistence of the water repellency; WDPT; andisols; critical value of soil humidity; transitional zone of the critical soil humidity.