COMPACTIBILITY OF CULTIVATED SPHAGNUM PEAT MATERIAL AND ITS INFLUENCE ON HYDROLOGIC CHARACTERISTICS

Deformation-stress-moisture relationships of cultivated sphagnum peat materials were studied in the laboratory using the Ottawa Texture Measuring System, an apparatus developed by Agriculture Canada. Impact of compaction on hydrologic characteristics was also investigated to determine the maximum stress which may be applied in the field during seed-bed preparation without limiting aeration for crop production. The study revealed that the compactibility of peat is relatively unaffected by moisture content at compactive pressure less-than-or-equal-to 13 kPa. However, under higher compactive pressure, the peat reaction was very similar to that of mineral soils, in which the compactibility increases with increasing moisture content until it reaches a maximum bulk density at saturation. The deformation-stress-moisture content relationships may be expressed by a simple third order polynomial equation. In response to compaction, the saturated hydraulic conductivity of the peat material reduced more than three orders of magnitude as bulk density increased from 0.1 to 0.25 g/cm3. A major increase in moisture retentivity was found in the compacted peat. Changes in hydrologic characteristics are primarily attributed to the reduction in large pores. Based on this information, it is concluded that compactive pressure exceeding 50 kPa may cause adverse effects on soil aeration.