THERMAL CONDITIONS FOR CUCUMBER IN THE TAQUARI VALLEY, RS. 1 - LOW LIMITING TEMPERATURE

Abstract

The goal of this study was to determine the probabilities of low air temperature for cucumber in the Taquari valley. Daily data of minimum air temperature from 20 Jan 1963 to 31 Jan 1999 measured in Taquari State of Rio Grande do Sul, Brazil (latitude:29°48'S, longitude:51°49'W and altitude:75m) were used to calculate the probability of temperatures lower or equal than 0°C, 3°C, 4°C, 5°C, 12°C and 15°C. Such values were chosen because 0°C is a reference for frost, and 3°C, 4°C, 5°C are the lethal values for the crop during night time conditions of weak, moderate and strong inversion temperature profile, respectively, and 12°C and 15°C are values used as base temperature for the crop. The minimum number of days with the temperature supra cited was well described by a negative binomial distribution for the majority of the periods (decades = 10 days) used in the computation. Therefore we used this probability distribution to calculate the probabilities. For the periods that were not well described by that distribution, the probabilities were calculated using the Poisson distribution. The probability of lethal temperatures is higher from decade 2 in April to decade 1 in October which varied from 1 to 78% and from decade 2 in September to decade 2 in May in which this probability is lower than 20%. Minimum temperatures lower than 12°C and 15°C may occur ali year long, but the frequency is lower from the beginning of Decernber to the end of March.