Three laboratory experiments were conducted to calibrate and evaluate filter paper method for the purpose of soil moisture characteristic curve determination. The objective of this study is developing calibration curve of the filter paper under completely controlled isothermal condition to be used in determining soil moisture characteristic curve.
First experiment was carried out to find out the suitable equilibration time between the filter paper and osmotic suction using NaCl salt solutions under isothermal conditions.
Second and third experiments were carried out to show the relationships between suction and moisture content of both filter papers and soil samples, respectively.
The obtained results showed that 5 days was enough time to reach equilibrium. Also, both filter paper calibration curve and soil moisture characteristic curve were developed.
The research recommended using filter paper method in determining soil moisture characteristic curve because it is simple, cheap, reliable, and cover a wide range of water potential comparing with other available methods. The research also lead us to further required studies to validate the method at extremely wet and extremely dry soils and also using a comparison with different methods to ensure its accuracy and reliability.