Effects of Agronomic Management on Soil Bulk Density

Ponciroli, G., S. Halstead, G.P. Robertson, and A. Smucker

Presented at the All Scientist Meeting (1996-07-16 to 1996-07-17 )

Soil bulk density is a measure of the mass of a given volume of soil. It is used to calculate air or water filled porosity, to convert values for soil properties from a gravimetric basis (e.g. µg g soil-1) to a aerial (e.g. mg m-2) or a volumetric (e.g. g cm -3) basis, and to indicate compaction over time or within similar soil types.Bulk density (B.D.) measurements were taken post-plow in 1991 on the LTER main site at depths of 0 – 7.5 cm and 15 – 22.5 cm. This sampling used an undisturbed core technique. In 1996, B.D. was measured pre-plow for all LTER plots to a total depth of 25 cm. The 1996 sampling used an excavation method. A core 80 cm in diameter and approximately 15 cm high was taken using an Elkjamp root corer. The depth of the hole was measured to calculate the volume of excavated soil. A second core was taken from the same hole to a depth of 25 cm. The cores were dried at 105 C for 24 hours and weighed to determine the mass of soil excavated.The 1996 results exhibited a decrease in B.D. from the 1991 sampling for all treatments, except conventional till (T1) and poplar (T5) treatments (Figure 1). The native treatment (T8) had the lowest B.D. of the main site treatments and showed no change in B.D. from the 1991 sampling. The changes in B.D. maybe attributed to cropping system, time of sampling, or sampling technique. A second post-plow sampling in July is currently being processed.

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