COEFICIENTE DA CULTURA DA CANA-DE-AÇÚCAR NO ESTÁDIO INICIAL DE DESENVOLVIMENTO EM CAMPOS DOS GOYTACAZES, RJ

Abstract

The sugarcane crop coefficient in initial growth stage (Kc_ ini) was adjusted to climate conditions of different planting dates and soil texture in Campos dos Goytacazes, State of Rio de Janeiro, Brazil. The planting dates and growth lengths were defined from varieties characteristics and cropping systems (annual or 18 months) and maturation characteristics (early, medium and late) of sugarcane. The analytic approach proposed in the FAO-56 guideline was used to adjust Kc_ ini. This approach is based in climatic data (rainfall and evapotranspiration) and soil characteristics (texture). The reference evapotranspiration was determined by Hargreaves-Samani method as a function of air temperature and solar radiation at the top of the atmosphere. The climatic series were measured at Brazilian National Weather Institute in Campos dos Goytacazes (-21.75° S; - 41.33° W e 11 m). The soil textures considered were Clay and Sandy Loam. The planting dates for annual growing period were September, October and November, and for 18 months growing period were February, March and April. Kc_ ini adjusted for annual period was 2.5 to 35% higher than the tabulated (0.4) in the FAO-56. The exception was September planting, in Sandy Loam soil, which showed no difference from the tabulated value. The Kc_ ini adjusted for the annual and a half period showed differences of -30 to 2.5% (early), -27.5 to -17.5% (medium) and -22.5 to - 12.5% (late). The Clay soil texture presented higher K c than Sandy Loam texture. The changes in Kc_ ini are results of the planting date, soil texture and varieties characteristics, being recommended theirs adjust.