Associação entre a capacidade de campo “in situ” e o ponto de inflexão da curva de retenção de água no solo

Abstract

Field capacity is a soil property of agricultural relevance. Its standard determination is performed in situ. This is considered to be laborious and time-consuming. As a result, alternative methods arise to estimate it, such as the inflection point of the soil water retention curve. The use of a soil water tension for determination of field capacity is contested by the scientific community. Nevertheless, it was adopted by Ferreira and Marcos (1983), who proposed that the water content at the inflection point of the water retention curve in the soil is a good estimator of field capacity obtained in situ. There is no paper that supports or refutes this association based on the classic concept of Veihmeyer and Hendrickson (1931). Therefore, the aim was to test the hypothesis that the water content of the field capacity in situ is represented by the inflection point of the soil water retention curve, regardless of the textural and structural condition of the soil sample from the soil water retention curve and its adjustment model. For this purpose, soil field capacity was assessed for different textural classes in situ. In these areas, undisturbed and disturbed samples of soils were collected to perform laboratory procedures that allowed to confront the water content obtained in situ, at the field capacity condition, with that estimated from the inflection point of the soil water retention curve obtained in the laboratory under various structural conditions of the soil sample, considering two adjustment models - van Genuchten model and cubic polynomial model. Thus, water content data were analyzed in a completely randomized design with five treatments and five replicates and the means compared by Dunnett's test (p = 0.1) considering the field method as a reference. I conclude that the in situ field capacity estimation criterion, clay content of soil sample, soil water retention curve fitting model, and structural condition of soil sample interferes at the association between water content estimated an inflection po