Funções de estimativa do armazenamento de água no solo sob diferentes níveis de capacidade de água disponível

The estimative of soil water storage is essential for representation of soil water relations for Brazil agricultural planning purposes. We had to aim evaluate the performance of five equations used to estimate soil water storage, through simulations of a daily water balance to the cities of Goiânia-GO and Ponta Grossa-PR, considering different amounts of total available water in the soil. For that purpose, were used daily data series of precipitation, reference evapotranspiration, crop coefficient, p fraction and initial soil water storage. It was considered total available water from 20 mm to 320 mm, with an interval of 30 mm. Potential functions of First and Second Order were approximately equal to the Cosine function in a daily water balance simulations, under conditions of supplementary irrigation and non-irrigation over the year. The Exponential function was not adequate in the estimative of soil water storage. Braga function was not adequate when considering additional irrigations in a daily water balance. We recommend the improvement of the functions to estimate soil water storage from replacement of “negative cumulative” function by other parameters, which could better explain the variation of soil water storage available for plants.