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Degradation of Structure of Yolo Loam by Compaction¹

ABSTRACT

Field compaction of Yolo loam soil over 6 years resulted in marked changes in several physical characteristics of the soil. The degradation of structure was more than temporary in that air drying, crushing, and sieving of the soil did not remove all evidence of the deliberate compaction. Remolded briquets of crushed and sieved soil from the plots receiving supplemental compactive effort had a modulus of rupture of 3,300 millibars, while briquets of soil from plots receiving only the minimum traffic necessary for cultivation over the 6-year period had a modulus of rupture of 1,200 millibars. The water stability of aggregates by wet sieving was reduced from 9% to 2%. Unconfined compressive and tensile failure tests on remolded samples showed that the soil from compacted plots reconsolidated after wetting and drying into stronger casts. Increased mechanical strength of remolded soil from the compacted plots was demonstrated by compression and penetrability measurements. The changes in strength were taken as evidence of reduction of water stability of soil aggregates by compaction. A residual effect of the compaction was definitely detected.

¹ Joint contribution from the Department of Soils and Plant Nutrition and the Department of Vegetable Crops, University of California, Davis.

² Associate Soil Physicist and Associate Olericulturist, respectively.

Received for publication June 11, 1964. Accepted for publication September 15, 1964.