LABORATORY DETERMINATION OF FIELD BULK DENSITY FOR IMPROVING FERTILIZER RECOMMENDATIONS OF ORGANIC SOILS

Abstract

The objectives of this study were to find ways to improve the accuracy of soil fertilizer recommendations by taking into account the variation in bulk density (BD) of organic soils. To achieve this end, field BD values of 30 organic soils (0.100–0.504 g/mL) were used to evaluate methods of measuring the BD in the laboratory by means of correlation and regression techniques. A simple and rapid procedure using the reconstituted BD of field-moist soils was the most accurate means of determining the average field BD in the laboratory, as indicated by the correlation coefficient obtained between the BD values obtained by this method and those in the field (r = 0.975**). The second most accurate method relied upon the exponential relationship between the water content of soils and their BD (R² = 91.1 %). The least exact method of correcting for BD variations was to scoop a volume of dried (65 °C) and sieved (2-mm) soils, as is done in some soil test laboratories. Although the values obtained by this method were related (r = 0.502**) to the field data, drying caused shrinkage of soils, thereby increasing their BD about twofold. Soil pH (r = 0.716**) and percentage ash contents (r = 0.851**) were also related to the field BD of soils. These tests could be used to estimate the BD of soils when the preferred method cannot be used. Regression equations are provided for relating appropriate test values to the BD of organic soils.