Favorable soil temperature to begin the irrigated rice sowing period in the State of Rio Grande do Sul, Brazil

Abstract

The State of Rio Grande do Sul is the main producer of irrigated rice in Brazil, corresponding to about 60 of the na onal rice produc on. In the predominant sowing system (dry seeds in dry soils), the low soil temperatures can be a problem at the beginning of the sowing period. The objec ve of this study was to characterize the bare soil temperature, at 5,0 cm depth, during September and October, aiming to indicate the favorable periods to begin sowing rice in the State of Rio Grande do Sul, Brazil. The daily bare soil temperature average from 30 meteorological sta ons of the State, most of them having between 20 and 40 years of data, were used. From these data, the ten day period averages, of September and October, were calculated. The maps, one for each ten day period, were done using the softwares Idrisi and Surfer. Two classes of soil temperature were used being the rst lower than 20 C and the second equal to or higher than 20 C. The second class was used as reference to indicate the beginning of the sowing period. The results indicate that the favorable soil temperature to begin sowing starts on the second ten day period of September, for only seven locali es (Uruguaiana, Alegrete, S o Borja, Santa Maria, Santa Rosa, Santo Augusto and Taquari), but in the third ten day period of October, it is favorable in the en re State, except in Caxias do Sul.