Glycerol-extraction refractometry for determination of gravimetric water content of soil samples

We developed a simple and rapid method suitable for on-site determination of gravimetric water content of soil samples. The proposed procedure was as follows; i) take 10–20 g of a soil sample in a tared mortar and weigh with a portable electronic balance, ii) add glycerol at a soil:glycerol ratio of 1 to 2 and weigh again, iii) mix the soil and glycerol thoroughly to ‘extract’ soil water into the added glycerol, iv) measure the refractive index of the ‘extract’ passed trough a filter placed on a refractometer, and vi) calculate the water content of the soil sample from a calibration curve relating the refractive index to water content of glycerol and the weights of the soil sample and glycerol. We tested the method on four soils at various moisture levels and found that the water contents from the proposed method were close to those from the standard oven-drying method with slight downward deviations.