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Effects of Tillage and Fertilization on Persistence of Crude Oil Contamination in an Alaskan Soil¹

ABSTRACT

The persistence of Prudhoe Bay crude oil was evaluated with cereal plantings over a 4-year period on field plots at Palmer, Alaska, oiled at 10 and 20 liters/m² with tillage and fertilization as treatments. Following the field study soil was removed for greenhouse evaluations and analyses.

Tilling aided water infiltration on the oiled plots in the field. Oiled plots without tillage or fertilization produced negligible growth during the first three growing seasons and very poor growth (< 10% coverage) in the fourth year. In the first year, only the 10-liter tilled plots provided tangible growth, about one-tenth that of the unoiled plots. The 20-liter plots required both treatments to produce growth in the second and third years, while either treatment sufficed for the 10-liter plots, with growth still much reduced from the controls. Oil decomposition was sufficiently advanced in the fourth year to permit over 75% coverage on the tilled 10-liter plots, about 50% coverage on the tilled and fertilized 20-liter plots, and about 25 to 40% coverage on the tilled, unfertilized 20-liter and on the fertilized, untilled 10-liter plots. Annual weeds were mostly unsuccessful in invading the oiled plots until the fourth year.

Greenhouse studies with oiled, fertilized soil removed from the field in the fourth year showed that tillage benefited growth of barley and bromegrass in the surface layer but was detrimental to growth in the 10- to 15-cm layer. Laboratory analyses corroborated the greater contamination of the deeper layers from the tilled plots. Field moisture levels were highly negatively correlated with residual oil contents, thus emphasizing the droughty effects of oil contamination. Residual oil contents of 13.5% completely inhibited germination of barley and brome, while levels under 7.5% allowed germination but reduced shoot heights. Decreasing levels of residual oil with increasing depth of tilled soil did not result in significantly greater plant growth. Beneficial degradation of oil may be retarded at depths in the soil, thus prolonging its phytotoxic effects. Tillage is best delayed to allow volatilization and some weathering to occur.

Key Words: cereal plantings • oil extraction • soil hydrophobicity • reclamation

¹ Contribution from Dep. of Agronomy, Alaska Agric. Exp. Stn., Palmer, AL 99645. Published with the approval of the Director as Paper no. J-138, Journal Series, Alaska Agric. Exp. Stn., Univ. of Alaska.

² Professor, Assistant Professor, and Associate Professor, respectively, Dep. of Agronomy, Alaska Agric. Exp. Stn. Dr. Loynachan is currently Assistant Professor, Iowa State Univ., Ames, IA 50011.

Received for publication January 10, 1979.