Cotton zoning based on sowing periods of lower risk in Parana State, Brazil

Cotton is cultivated in the North and West of Parana State, southern Brazil , under conditions of climatic risk variable in space and time. Risks of te mperature below 15 degrees C at the establishment period, daily average tem perature below 20 degrees C at the stage of cotton boil opening, and soil w ater deficit for both plant establishment and flowering periods, were estim ated to identify homogeneous zones with sowing periods of lower climatic ri sk. The time interval with adequate temperature, associated with minimum ri sks of the other factors and yield data from field experiments allowed the identification of seven distinct zones, with best sowing periods ranging fr om September 20 to November 20. Official credit to the farmers is condition ed by the Central Bank of Brazil upon following these recommendation of bes t sowing periods for each municipality.