Manuel José Gandarillas I.1, Ramón García L.1 y Hernán Tejeda S.2

The association among wheat grain yield and the number of days the soil moisture tension was equal or greater than 8, 10, 12, or 14 atm. was studied. Wheat yields corresponding to the 192 Kg/ha. of N and 240 Kg/ha. of P2O5 fertilizer treatment in 26 fertilizer experiments were used. The experiments were located within the Aconcagua and Curicó area. Soil moisture tension was estimated by measuring the electricial resistance with blocks buried in the plots at depths of 20, 45 and 75 cm and transforming the readings into soil moisture tension by using a calibration curve. Development of the crop was divided into five stages as follows: 1 = from seeding to tillering; 2 = from tillering to jointing; 3 = from jointing to heading; 4 = from heading to milky grain; and 5 = from milky grain to maturity.
Grain yield presented the highest correlation with the number of days the soil moisture tension was 12 atm. at a depth of 20 cm during the heading to milky grain stage.

1Ings. Agrs. Proyectos Leche-Carne-Lana y Cereales, respectivamente, Estación Experimental La Platina, Instituto de Investigaciones Agropecuarias, Casilla 5427, Santiago, Chile.
2Ing. Agr. MS, Centro de Apoyo Suelos, Estación Experimental Quilamapu, Instituto de Investigaciones Agropecuarias.