Este trabajo ha sido realizado dentro de los planes de investigación de la Comisión Asesora de Investigación Científica y Técnica

The present work has two parts. The first one deals about the results obtained in the study of the water evaporation and the water movement in sandy and sandy-clay soil samples. The samples are wetted by imbibition and subjected to drying on four different evaporating demands. The accumulated evaporation of water to the end of periods of 24, 48, 72, 96, 120 and 144 hours is determined using gravimetric controls. The water mobility during the drying process is analysed by the study of the initial and final soil-water profiles. The data obtained show that the evaporation rate is greater in the sandy-clay soil than in the sandy soil, excepting to the end of the process; furthermore, the sandy-clay soil has a more adjustable water mobility.

Um experimento foi realizado em condições de campo, em Piracicaba (SP), visando avali ar a eficiência de diferentes produtos químicos, em aplicação foliar, na taxa transpiratória e no potencial da água de folhas das plantas de seringueira (He Yea brasiliens is cv. RRIM 600) com 1,5 ano de idade. Os tratamentos utilizados foram: polissulfetc, de polietileno (Good-rite peps) 0,04 %, oxietileno docosanol (Oed green) 2%, caulim (silicato de aluminio) 3%, e atrazine 50 ppm, alem do controle. Através do método da pesagem rápida de folhas desta cadas, com balança de torço tipo Jung, verificou-se a perda de água pelas plantas de seringueira foi restringida significativamente pelo anti-transpirante metabólico (atrazine) com relação ao controle, aos formadores de filme e ao refletor. Polissulfeto de polietileno apresentou as menores amplitudes de variações na taxa respiratória. Atrazine também promoveu a manutenção do potencial da água das folhas mais alto (-7,8 bars) com relação ao controle (-14,8 bars), de acordo com determinações efe tuadas através da Câmara de Scholander.<br>This research deals with the effects of chemicals on transpiration and water potential of Hevea brasiliens is cv. RRIM 600 on plants, with 1,5 year old, under field conditions. Rubber plants were sprayed with poliethylen e polys ulfite 0,04%, oxyethylen e docosanol 2%, kaolin 3%, atrazine 50 ppm, and check. A higher efficiency again st water loss was observed for atrazine (10,9 mg water . cm-2 . min-1) in relation to check plants (14,6 mg water . cm . min-1) at the maximum transpiration rate average. Polyethylen e polysulfite presented lower amplitude variation of the transpiration rates during the measurements at the day period. Atrazine promoted the maint enance of a higher water potential (-7,8 bars) compared to check treatment (-14,8 bars).