The experiment was conducted in a laboratory at the Federal University of Ceara, in Fortaleza, Ceara State, Brazil, from July to September 2002. Constant water table depth drainage tanks were used to study the relationship between the Stress Daily Index (SDI) and sugarbeet yield (cultivar Early Wonder). The experimental design was completely randomized with five treatments in four replications using 48-useful plant plots. Treatments consisted of 0; 120; 180; 240 and 300 cm as the total of excess water (SEW30). The crop flooding susceptibility coefficient (SC) was calculated for the first, second and third development stage. Plants were submitted to a four-day flooding period by raising the water depth up to 0.10 m, at each stage. The root mean diameter (DM) was evaluated as well as the length of the largest leaf (CMF) and the productivity (PT). Only DM presented significant variation as a result of soil water excess, varying from 5.51 without stress to 4.71 when the stress was applied at the last stage. The values of SC obtained for the first, the second and the third development stages were 0.10, 0.16 and 0.28, respectively. The weighted value of SC (0.17) associated with the respective values of SEW (0; 120; 180; 240 and 300 cm) allowed us to calculate values of stress daily index (SDI), for each treatment: 0; 20.4; 30.6; 40.8 and 51.0, respectively. Only the treatment with highest stress level treatment (water table at 5 cm) presented statistical difference (p<0.05). DM varied from 5.51 to 4.00, while CMF was reduced from 43.35 to 26.10, and the productivity dropped from 40.4 to 15.8 t.ha-1. The estimate of SDI that produced the highest value of productivity (41.8 t ha-1) was 12.8 cm, based on quadratic regression (r² = 0.87).
Beta vulgaris L.; stress day index; sum excess water
