EFFECTIVENESS OF ORGANIC-MATTER INCORPORATION IN REDUCING SOIL COMPACTIBILITY

Incorporation of organic matter (OM) into soil can reduce its suscepti bility to compaction. However, the significance of incorporated OM for different soil and soil water conditions is not well documented. We i nvestigated the effectiveness of incorporated OM at different soil and soil water conditions and the OM effect on strength and structure rec overy of compacted soils. A sandy soil (sandy Orthod), a silt loam (lo amy Udalf), and a clay soil (clayey Umbrept) were amended with up to 8 0 g kg(-1) of highly and slightly humified peat. The peat-soil mixture s were compacted at different water contents using the standard Procto r procedure. Soil strength was determined with a penetrometer. Structu re recovery was determined by bulk density changes and disintegration of clods through wetting-drying cycles. For the cohesive silt loam and clay soils, OM was most effective at reducing compactibility at water contents lower than those for maximum Proctor compaction. For the san dy soil, OM was most effective at the Proctor-optimum water content. T he slightly humified peat had a greater effect than the highly humifie d. We found that OM is most effective for soils with high compactibili ty. The maximum penetration resistance, P-max of the clay soil was red uced from 0.49 to 0.30 MPa, and that of the sandy soil increased from 0.64 to 1.08 MPa. For the silt loam, 30 g kg(-1) peat content had the highest P-max. After five wetting-drying cycles, bulk densities showed no significant differences among treatments. Clod disintegration was hindered by the OM incorporation. Although soil compactibility was red uced by OM incorporation, OM was more effective as soil compactibilty increased and at water contents lower than or close to the Proctor-opt imum water content. Structure recovery of compacted soils was not impr oved. The penetration resistance after compaction is not consistently related to the incorporated OM.