Estimativa da necessidade de irrigação suplementar para algumas culturas no Estado de Alagoas.

Abstract

The supplimentary irrigation need for the 10 day periods is estimated with the help of probabilistic analyss at therisk levels of 80%, 75%, 60%, 50% and 25%, by fitting an incomplete gamma: distribution function to the spacial averages of precipitation data for each of the mesoregions in the State of Alagoas. The effective precipitation is determined by using the ratio between the potential evapotranspiration and precipitation (PAO, DASTANE,1974) . the analysis of the growing season was performed in accordance with the criteria proposed by FRERE and POPQv (1979).The potential evapotranspiration (ETP) was estimated using the method described by Thornthwaite & Mather (1955), whereas the water needs of the crops were obtained through the crop coefficients recommended by Doorembos S Kassan (1979). The actual evapotranspiration (ETR) was calulated as the product of the crop coefficient and the potential evapotranspiration. The suppÎimentary irrigation need on a 10- day basis (NISD) was obtained by subtracting the effective precipitation (PE) from the actual evapotranspiration obtained from the 10~day, periods (ETRd).Tables of effective precipitation, precipitation totals. and the deptho-F supplimentary irrigation, all - for the periods o f 10-days, were elaborated for the different crops and f or different regions of the State of Alagoas. The masoregion which is more appropriate for planting cottonis " Sertão " with the planting date in the beginning of May, and needs 214.7 mm of irrigation. The mesoregion which is adequate for planting the beans, corn, sweet potato and tomato crops is the " Litoral " region requiring the minimum amount of supplimentary irrigation It was noted that at the 75% probability level, all the crops considered need supplimentary irrigation .