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Incorporation of organic matter (OM) into soil can reduce its susceptibility to compaction. However, the significance of incorporated OM for different soil and soil water conditions is not well documented. We investigated the effectiveness of incorporated OM at different soil and soil water conditions and the OM effect on strength and structure recovery of compacted soils. A sandy soil (sandy Orthod), a silt loam (loamy Udalf), and a clay soil (clayey Umbrept) were amended with up to 80 g kg -1 of highly and slightly humified peat. The peat-soil mixtures were compacted at different water contents using the standard Proctor procedure. Soil strength was determined with a penetrometer. Structure 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 sandy soil, OM was most effective at the Proctor-optimum water content. The slightly humified peat had a greater effect than the highly humified. We found that OM is most effective for soils with high compactibility. The maximum penetration resistance, P max , of the clay soil was reduced 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 reduced by OM incorporation, OM was more effective as soil compactibilty increased and at water contents lower than or close to the Proctor-optimum water content. Structure recovery of compacted soils was not improved. The penetration resistance after compaction is not consistently related to the incorporated OM. |
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