A method to predict bulk density of tilled Ap horizons

Abstract Bulk density of the Ap horizon is dynamic with respect to time and land use and therefore multiple field measurements are necessary to characterize it. Researchers often need a bulk density value to use in models, characterize field conditions, or convert gravimetric to volumetric measurements. A method is described to predict the field bulk density of the Ap horizon by measurement of the bulk density in the laboratory. The bulk density value measured with this method is independent of the use and temporal dynamics of the tillage zone. The method involves four treatments that have application in predicting bulk density values irrespective of the soil condition when sampled were tested. The treatments are: (1) capillary wetting and desorption at 33 kPa suction; (2) capillary wetting, inundation, air drying, rewetting by capillary action, and desorption at 33 kPa suction; (3) Treatment 2 followed by oven drying; (4) standard mechanical compaction at various water contents to obtain the Proctor density. Bulk densities for Treatments 1–3 were similar for soils with coefficient of linear extensibility less than 0.01. Bulk densities for Treatment 3 were similar to interpretive values used by the USDA-SCS and values predicted from Gupta and Larson's (Soil Sci. Soc. Am. J., 43: 758–764, 1979) packing model. Bulk densities for Treatment 2 are similar to field measurements. Comparison of bulk densities for Treatment 2 and field measurements provide an evaluation of soil health.