Bioclimatic indices for the coffee crop

Besides degree-days, which considers air temperature, there are several bioclimatic unit systems. However, their use and limitation is little known for coffee crop. Therefore, this study evaluated the performance of four bioclimatic indices to estimate the length of the sub-periods flowering-light green fruit, light green fruit-cherry fruit and flowering-cherry fruit, in coffee crop. The thermal index, accumulation of photosynthetic active radiation, Geslin's heliothermic index and the accumulation of the reference evapotranspiration were evaluated during the agricultural year 2008/2009 for ten coffee cultivars, in Uberlandia-MG, Brazil. The data for each bioclimatic index were analyzed with the classical statistics, determining the mean, the standard error, and the coefficient of variation. This last parameter was the basis for the choice of the bioclimatic index used for the quantification of the length of the sub-periods for each coffee cultivar and for the classification of the cycle as early, medium and late. Geslin's heliothermic index and accumulation of the reference evapotranspiration presented the smallest mean coefficients of variation among the cultivars.