Soma térmica em arroz de terras baixas irrigado por aspersão

Abstract

The objective of this study was to evaluate thermal time methods and duration of developmental stages of lowland rice irrigated by sprinkling. The experiment was conducted during three growing seasons (2010/2011, 2011/2012 and 2014/2015), and treatments were five irrigation levels (0%, 50%, 100% 150% e 200% of crop evapotranspiration) in the first and third year of experiment and four in the second year (0%, 50%, 100% e 150% of crop evapotranspiration), three lowland rice cultivars (IRGA 417, IRGA 424 e INOV CL – 2010/2011 e 2011/2012; IRGA 428, IRGA 429 e XP 102 CL – 2014/2015), with four replications. Six thermal time methods were tested, two using lower basal temperature, two using the lower basal temperature and the optimum, and two using the lower basal, optimum and higher temperature. To calculate the thermal time the crop development cycle was divided into vegetative, reproductive and grain filling phases. The methods that use three cardinal temperatures had lower coefficient of variation in most developmental phases. Irrigation levels influenced the thermal time and rice cultivars responded differently in each development phase. The higher water availability the lower duration of development cycle, and thermal time is dependent upon the calculation method.