EFFECT OF LOOSENING AND COMPACTING ON SOIL PHYSICAL-PROPERTIES AND SUGAR-BEET YIELD

On lessive soil derived from heavy medium sand deposited on light loam, 3-year field experiments were carried out to determine the effect of differences in soil bulk density caused by chiselling or compaction by tractor wheels or tracks on some soil physical properties and yield of sugar beet roots. Six treatments with different intensities of loosening and compaction were compared. Compared with the soil in control plots, the annually superimposed effect of soil compaction by tractor wheels or tracks resulted in increased bulk density and soil strength. The effect of loosening the plots with a chisel (60 X 60 cm) to abate these effects was only small. The relationship between the yield of sugar beet roots and soil bulk density was curvilinear, while that between sugar beet yield and soil strength was rectilinear. Under the environmental conditions of the experiment, the optimum bulk density was 1.64 g cm-3 in the 0-60-cm layer and 1.51 g cm-3 in the 0-30-cm layer. Optimum average soil strength in these layers was 2.90 and 1.75 MPa, respectively. Significantly negative effects on crop yield were observed when mean soil bulk density was greater-than-or-equal-to 1.70 g cm-3 in the 0-60-cm layer and greater-than-or-equal-to 1.64 g cm-3 in the 0-30-cm layer. The same effects were observed when soil strength was greater-than-or-equal-to 4.65 MPa in the 0-60-cm layer and greater-than-or-equal-to 3.75 MPa in the the 0-30-cm layer.