Plant-water relationship in beans (Phaseolus vulgaris L.).I. Soil-water depletion under different irrigation levels

Juan Tosso T.1

Water content in the soil profile was measured during two growing seasons: in 1976, the soil was un· der the Gloria Pink cv; in 1977, under the Light Red cv., in a saline and in a normal soil. Eight levels of irrigation were established, using the sprinkler line source; however, only four of them are reported here, in order to facilititate the discussion and since adjacent levels of irrigation showed small difference.

Using these values, soil water depletion was calculated and analyzed, in relation to: time, soil depth, level of irrigation, cultivar, and soil salinity. Conelusion were:

- Beans extracted water down to soil depths of 225 cm, and about 20 to 50% came from layers be· low 105 cm. The highest values of soil water depletion occurred in the layers with highest values of field capacity. A relatively low amount of water was extracted from the first 15-45 cm of soil.

- Soil water extraction by roots is a very dynamic process, that varied with: time during the growing season, soil depth, amount of water present, and salt concentration in the soil profile. As the applied water increased, according to the level of irrigation, the total amount and the rate of water extraction from the soil profile increased. When pre-irrigated to shallow depth, the rate of soil water extraction in the upper layer increased. Excess salt in the profile produced a reduction of the soil water depletion, of about 34% in the humid treatment (VIII) and 20% in the dry treatment (without irrigation).

1 Instituto de Investigaciones Agropecuarias (INIA), Casilla 439, Correo 3, Santiago, Chile.