CORN SOWING DATES AS A FUNCTION OF SOIL-W ATER DEFICITS AT CAMBARA-PR, BRAZIL

The aim of this study was to try the forecast of corn (Zea mays L.) so wing dates, the understanding of the quantitative effect of water defi cits on that crop and crop yield decrease on a basis of a climatic mod el of water deficit forecast. This model was applied at Cambara (lat. 23 degrees 00'S, long. 50 circle 02'WGr, altitude 450 m), PR, Brazil. The model estimates yield decrease, in relation to potential values, a s a function of the sowing dates which determine flowering and grain f illing dates, highly critical times in relation to water deficit. The estimates were done from expected values of water deficit, at the 80% probability level and accumulated degrees-days, using several climatol ogical data. Results show that the first ten days of November are the best corn sowing date under dry or irrigated conditions. Under these s ame conditions, the worst time showed to be August. Estimates of total needs of supplementar irrigation get values of 126 e 226 mm, respecti vely to the corn sowed at the first ten days of November and August.