GLYCEROL-EXTRACTION REFRACTOMETRY FOR DETERMINATION OF GRAVIMETRIC WATER-CONTENT OF SOIL SAMPLES

We developed a simple and rapid method suitable for on-site determinat ion of gravimetric water content of soil samples. The proposed procedu re 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 so il:glycerol ratio of 1 to 2 and weigh again, iii) mix the soil and gly cerol thoroughly to 'extract' soil water into the added glycerol, iv) measure the refractive index of the 'extract' passed trough a filter p laced on a refractometer, and vi) calculate the water content of the s oil sample from a calibration curve relating the refractive index to w ater content of glycerol and the weights of the soil sample and glycer ol. We tested the method on four soils at various moisture levels and found that the water contents from the proposed method were close to t hose from the standard oven-drying method with slight downward deviati ons.