On-line version ISSN 1678-992X
CALBO, Adonai Gimenez. A rapid method for measuring soil water content in the field with a areometer. Sci. agric. (Piracicaba, Braz.) [online]. 2002, vol.59, n.4, pp. 811-814. ISSN 1678-992X. http://dx.doi.org/10.1590/S0103-90162002000400029.
The availability of a rapid method to evaluate the soil water content (U) can be an important tool to determine the moment to irrigate. The soil areometer consists of an elongated hydrostatic balance with a weighing pan, a graduated neck, a float and a pynometric flask. In this work an areometer was adapted to rapidly measure soil water content without the need of drying the soil. The expression U = (MA - MAD)/(MM -MA) was used to calculate the soil water content. In this equation MM is the mass to level the areometer with the pycnometric flask filled with water, MA the mass to level the areometer with a mass MM of soil in the pycnometer, the volume being completed with water, and similarly MAD the mass added to the pan to level the areometer with a mass MM of dried soil in the pycnometric flask. The convenience of this method is that the values MM and MAD are known. Consequently, the decision on irrigation can be made after a measurement that takes, about, ten minutes. The procedure involves only stirring the soil with water for at least 2 minutes to remove the adhered air. The soil water content data obtained with the areometric method were similar to those obtained weighing the soil before and after drying to constant weight, in an oven at 105º C.
Keywords : hydrostatic balance; irrigation moment; pycnometer; soil humidity.