Reference [11] using a similar compaction effort showed a similar relationship between Cmax and moisture content for a marl soil. Peak surface hardness ranged from 164-248 Cmax with corresponding moisture contents of 5%-25% wt.Peak surface hardness and associated critical
moisture contents seemed related to organic matter content. The former variable showed lower values for higher organic matter levels, with an inverse effect seen for the latter. Reference [10] alluded to the increases in surface hardness with reductions in soil moisture at high compaction.Reference [32] showed no significant differences between sand and sand plus peat treatments for bulk density but significant differences were observed for Peak surface hardness, with the peat treatment showing lower values.Critical moisture contents for Peak surface hardness was similar or slightly lower among the soils compared to peak penetration resistance, but were much lower compared to particle density bulk density. Reference [10] linked changes in soil bulk density to increase surface hardness. However, correlations between these indices showed a strong positive and significant (p < 0.001) relationship between surface hardness and penetration resistance (r2= 0.796), indicating that in this
study bulk density was not an indicator of surface conditions and reversibly, surface hardness was not able to assess bulk soil condition. Reference [25] also found poor relations between cone index and bulk density . Although surface hardness may substitute for penetration resistance, no data exist to facilitate correlation to crop response, in-situ values under traffic or other soil properties. However, the Clegg Impact Tester is practical where the cone penetrometer in limited, such as in sandy, dry or wet soils, or where surface layers interferes with cone insertion. Reference [25] further indicated that in high strength soils (>6 MPa) the ability to maintain uniform insertion speed and force using a hand held penetrometer is greatly diminished.
Reference [11] using a similar compaction effort showed a similar relationship between Cmax and moisture content for a marl soil. Peak surface hardness ranged from 164-248 Cmax with corresponding moisture contents of 5%-25% wt.Peak surface hardness and associated critical
moisture contents seemed related to organic matter content. The former variable showed lower values for higher organic matter levels, with an inverse effect seen for the latter. Reference [10] alluded to the increases in surface hardness with reductions in soil moisture at high compaction.Reference [32] showed no significant differences between sand and sand plus peat treatments for bulk density but significant differences were observed for Peak surface hardness, with the peat treatment showing lower values.Critical moisture contents for Peak surface hardness was similar or slightly lower among the soils compared to peak penetration resistance, but were much lower compared to particle density bulk density. Reference [10] linked changes in soil bulk density to increase surface hardness. However, correlations between these indices showed a strong positive and significant (p < 0.001) relationship between surface hardness and penetration resistance (r2= 0.796), indicating that in this
study bulk density was not an indicator of surface conditions and reversibly, surface hardness was not able to assess bulk soil condition. Reference [25] also found poor relations between cone index and bulk density . Although surface hardness may substitute for penetration resistance, no data exist to facilitate correlation to crop response, in-situ values under traffic or other soil properties. However, the Clegg Impact Tester is practical where the cone penetrometer in limited, such as in sandy, dry or wet soils, or where surface layers interferes with cone insertion. Reference [25] further indicated that in high strength soils (>6 MPa) the ability to maintain uniform insertion speed and force using a hand held penetrometer is greatly diminished.
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