SOIL BURROWING AND MIXING BY A CRAYFISH

Observation of rapid lateral water flow through, rather than over, the surface of a level, clayey, mixed, thermic Typic Albaquult (Bladen se ries) prompted study of the abundant burrows of a crayfish, Procambaru s rogersi rogersi Hobbs. The area was a 20-yr-old experimental plantat ion of slash pine (Pinus elliottii Engelm. var. elliottii), with a wid e range in tree growth, ground vegetation, and O-horizon thickness. Th e objective was to better understand the elaborate macropore system an d its consequences for mixing the surface layers of a very poorly drai ned soil where other burrowing animals were lacking. Excavation of bur rows and burrow casts revealed galleries, 4 to 10 cm in diameter, > 1. 5 m long, chiefly in the upper 30 cm of soil but with vertical shafts to > 1 m in depth. Fifty to 80% of randomly located 0.1-m2 subplots in well-forested plots had from one to five openings through the mineral soil surface into surficial burrows, demonstrating widespread distrib ution of the latter. Bands of rock phosphate broadcast on the surface 20 yr previously provide a marker of cumulative mixing; almost one-hal f of the residual P had been mixed into the 5-to 15-cm depth by crayfi sh activity.