Estimation of moisture at field capacity in soils under 'Cerrado'

The objective of this study was to estimate the soil moisture at field capacity (theta fc) by an equation based on the soil water retention curve (SWRC) and by correlation with physico-hydrical attributes and data from texture and organic matter for very clayey, clayey, loamy, and sandy soils. The study was carried out with 2242 samples from 'Cerrado' soils, which contained information on textural classification, physical attributes and soil water retention. For 745 samples, there was information on the saturated hydraulic conductivity (Ko) and for 472, on clay, silt, sand and organic matter contents. For samples with measured Ko, theta fc was determined based on parameters of the equation of Genuchten (1980), assuming that the drainage rate (tau) is a percentage p of Ko. p values of 0.0025, 0.0050, 0.0100, 0.0150, and 0.0200 were considered. It was observed that theta fc can be estimated by the equation based on SWRC, considering tau as 1% of the Ko value. theta fc can also be estimated as a function of moisture at the inflection point of SWRC and soil porosity for each soil horizon. The soil water tension corresponding to. fc was between 6.5 and 7.5 kPa, for tau equivalent to 1% of the Ko value.