Épocas de menor risco de estresse hídrico e térmico para o feijoeiro na região central do Rio Grande do Sul

Abstract

The common bean is the main food of many Brazilians and it is produced in the whole national territory, wich means that this spcies cultivated in variety of meteorological conditions. In spite of its great importance, the national production of this legume fluctuates, because it is, in most of the cases, cultivated with low technology land during times of the year with risks as a complete knowledge of the predominant meteorological conditions during the growing season lacks. The objective of this study was determine the growing seasons with smallest risk for the bean production determining deficiency and surplus of soil water and the probability of its occurrence, for different phases of the developmental cycle of common bean, and the frequency of daily maximum air temperature greater then or equal to 30ºC during the flowering, in Santa Maria - RS. The water balance of the soil was calculated to determine the deficiencies and surpluses of soil water for 29 growing seasons, during the safra and safrinha. Data were collected in a climatological station in Santa Maria, RS from August of 1968 to July of 2004. The different levels of occurrence of surplus and deficiency of soil water were analyzed through the fit of a parametric distribution and related to the levels of occurrence of the surplus and deficiency of water indicators with the occurrence probability to each growing season. The fitted parametric distribution curves used were Gama, Lognormal and Exponential. The tests used to verify the goodness of fit of the parameters and to choose the function that show better adjustment were Anderson-Darling, Cramér-von Mises, Chi-square and Kolmogorov-Smirnov. The empiric frequency was determined to show the growing season in that there is greatest risk of damage caused by elevated air temperature, i. e., the number of days in that the maximum air temperature is greater then or equal to 30ºC in relation to the total number of days of the period between the beginning of the flowering and 20 days after, being considered every year of the database and all the growing seasons. In most cases there was adjustment of at least one of the parametric distribution curve, prevailing the Gama curve. In some cases, it was not possible to adjust any function being used the empiric frequency to analyze the risk of damages. Considering the methodology used in this work, the greatest risk of damage is when water deficiency takes place during the periods from sowing to germination and from the beginning of flowering to 20 days after and when water surplus takes place during the period 20 days after the beginning of the flowering and the physiologic maturity and when elevated air temperature occurs during the period from the beginning of the flowering to 20 days after, the results allowed to conclude that the recommended growing seasons are 15/Ago to 15/Set and 01/Fev to 10/Fev.