A Study On the Soil Bulk Density As Affected by Compression in Column Test.

A quantitative assessment of soil compaction is required to enhance soil management for crop production and environmental sustainability. The objective is (1) to analyze the relationship of aeration porosity and bulk density and (2) to investigate the relationship of the pressure on the soil column and bulk density in the laboratory prior to practicing field experiment. Two types of soil texture were conducted as follows : coarse one (clay content : 6%) and fine one (clay content : 30%). (1) "Aeration porosity" was calculated by the difference between total porosity (%, v/v) and water content (%, v/v) at 10 kPa water potential with bulk density with non-disturbed soil, using a pressure chamber. Relationship of bulk density (Mg m-3) and aeration porosity (%) is as follows : y = -54.44ln(x) + 36.40 (R2=0.795, p<0.01) in sandy loam, y = -81.23ln(x) + 40.03 (R2=0.869, p<0.01) in clay loam. At 10% aeration porosity, bulk densities were 1.62 Mg m-3 in sandy loam, 1.45 Mg m-3 in clay loam, which means that the critical value of bulk density is 1.62 Mg m-3 (SL) and 1.45Mg m-3 (CL) for at least 10% aeration porosity. (2) Soil compression was operated by using soil compaction equipment with pressure gauge on the disturbed soil and then bulk density was calculated. Experimental soil water content was 4.2, 16.0 and 20.3% (w/w) of sandy loam and 11.6, 15.0, 19.5 and 25.8% (w/w) of clay loam. The increment of bulk density increased with increasing pressure higher in clay loam than in sandy loam. That characteristic increased with increasing soil water content, but the bulk density rarely rose over some state of water content. Therefore, it would be thought to consider the soil water state more in clay loam than in sandy loam as driving an agricultural machinery. Key Words Soil compaction, bulk density, agricultural machinery, aeration porosity