Characterization of soil chemical properties was performed according to the methodology described in EMBRAPA [13], and the following parameters were deter- mined: levels of exchangeable P, K, and Na were obtained by Mehlich-1 extracting solution (HCl 0.05 mol L−1 + H2 SO4
0.0125 mol L−1 ) followed by colorimetry and flame photome-
try, respectively; and exchangeable Ca and Mg were obtained by KCl 1 mol L−1 extraction solution followed by atomic absorption spectrometry. To determine the pH and the electrical conductivity of the soil saturation extract (CE), saturated paste was prepared according to the method proposed by APHA [16]. CE was determined by electrometric method and the pH of water by potentiometric method [13]. The data of sunflower fresh and dry matter yield of over-ground plant parts was performed according to the methodology described in BENICASA [17]. The obtained data were subjected to analysis of variance and regression with significance levels of 5% for the