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Gamma Radiation Measurements of Bulk Density Changes in a Soil Pedon Following Irrigation¹

ABSTRACT

Bulk density in a soil pedon was measured with a gammaray transmission technique utilizing ¹³⁷Cs and ²⁴¹Am. Both gamma-ray sources could not be used simultaneously for bulk density determinations in a system where the sources were uncollimated and the detector was not shielded. By alternating sources for each scan down the soil profile, it was shown that bulk density decreased in the top 6 cm of soil about 30 minutes after water was ponded on the soil surface. As soon as the water drained from the surface, bulk density values approached preirrigation levels. Changes in height of the soil surface upon irrigation corresponded with changes in bulk density.

¹ Contribution from the Agricultural Research Service, USDA, Phoenix, Ariz.

² Soil Scientist, US Water Conservation Lab., 4331 East Broadway, Phoenix, Arix. 85040.

Received for publication April 30, 1973. Accepted for publication September 27, 1973.