Critical analysis of the field determination of soil hydraulic conductivity functions using the flux-gradient approach - Reichardt, Klaus; Portezan Filho, Otavio; Libardi, Paulo Leonel; Bacchi, Osny Oliveira Santos; Moraes, Sérgio Oliveira; Oliveira, J. C. M. de; Falleiros, M C (Soil & Tillage Research, 1998)